Nti lCiti lZ Ob t i PNational Critical Zone Observatories Program All Hands meeting ...web.sahra.arizona.edu/education2/czo/abs/CZOprogram_All.pdf · 1:30 PM - 3:00 PM: Biosphere

N ti l C iti l Z Ob t i PNational Critical Zone Observatories ProgramAll Hands meeting, May 8-13, 2011

UA’s Biosphere 2, Tucson, AZ

ABSTRACTSABSTRACTS

Biosphere 2 Campus Map

Poster Abstract Index

Session 1 (Monday AM) Ecosystem Exchange and Hydrologic Partitioning

1. Shanley et al 2. Eissenstat 3. Naithani et al. 4. Lin: Takagi and Lin 5. Gill 6. Hicks et al. 7. Levia: Van Stan et al. 8. Kelly and Goulden 9. Kirchner et al. 10. Son and Tague 11. Biederman et al. 12. Harpold and Brooks 13. Mahmood and Vivoni 14. Mitra et al. 15. Nelson et al. 16. Papuga et al. 17. Rasmussen et al. 18. Loescher & Berukoff

Session 2 (Monday PM) Subsurface Biogeochemistry

1. Gabor 2. Charaska et al 3. Jones and Schaap 4. Lybrand and Rasmussen 5. Stielstra et al. 6. Chorover: Vazquez‐Ortega et al. 7. Aufdenkampe et al. 8. Brereton and McDowell 9. Clark et al. 10. Hall and Silver 11. Goldsmith: Porder et al. 12. Stone et al. 13. Thompson et al. 14. Dere et al 15. Ma et al. 16. Lazareva et al. 17. Pan et al. 18. Rosier et al. 19. Berukoff & Loescher

Session 3 (Wednesday AM) Ground and Surface Water Dynamics .

1. Inamdar et al. 2. Graham and Lin 3. Graham et al. 4. Kuntz et al. 5. Yu et al. 6. Zhang and Lin 7. Bales et al. 8. Broxton et al. 9. Driscoll et al. 10. Heidbuechel and Troch 11. Perdrial et al. 12. Porter et al. 13. Zapata‐Rios et al 14. Karwan et al. 15. Shanley et al 16. Loescher & Berukoff

Session 4 (Wednesday PM) Critical Zone Evolution

1. Brubaker et al. 2. White and Anderson 3. Brocard et al. 4. Khan et al. 5. Leon 6. Litwin and Jerolmack 7. Occhi and Willinbring 8. Phillips and Jerolmack 9. Willenbring 10. Orem and Pelletier 11. Pelletier et al 12. Pelletier et al 13. Yoo et al. 14. Hunsaker 15. Stacy et al. 16. Tucker

National Critical Zone Observatories Program All Hands Meeting May 8-13, 2011

Biosphere 2 University of Arizona

Tucson, Arizona Workshop Schedule Sunday, May 8th 6:00 PM – Icebreaker reception, B2 Café Patio 6:30 PM - Dinner - B2 Café Patio 8:00 PM – Keynote lecture introducing the theme of the workshop - Plenary meeting room (Larry Band, UNC-Chapel Hill) Climate, geomorphic and ecohydrologic controls of nitrogen cycling and export along a continental transect Monday, May 9th 7:00 - 8:00 AM: Breakfast, B2 Cafe Session 1 – Ecosystem Exchange and Hydrologic Partitioning (eddy covariance water and carbon flux measurements, ecosystem production and respiration, snow and rain partitioning, infiltration dynamics, evapotranspiration, ground water recharge) - Plenary meeting room 8:00 AM: Introduction by session convener (Shirley Papuga) 8:05 AM: Keynote lecture (Russ Monson - UA) Surface atmosphere fluxes of H2O and CO2 in the subalpine ecosystem critical zone (25 min + 10 min discussion) 8:40 AM: Mike Goulden et al. (SS-CZO) Relationships between elevation, photosynthesis and evapotranspiration in the Sierra CZO (10 min + 5 min discussion) 8:55 AM: Greg Barron-Gafford et al. (JSC-CZO) Sensitivity of soil CO2 efflux to climatic and topographic factors in a montane drainage system (10 min + 5 min discussion) 9:10 AM: Martha Scholl et al. (LM-CZO) Use of stable isotopes to understand recharge sources and streamflow generation in the Luquillo Mountains, Puerto Rico (10 min + 5 min discussion) 9:25 AM: Poster introductions (brief <2-min, 1 slide overviews of poster content; 18 posters ~ 40 min) 10:05 AM: Coffee break & poster session - B2 Planning Center 11:15 AM: Rapporteur from SoS CZO to summarize poster session and to lead plenary discussion 11:30 AM: Break for lunch - B2 Cafe 1:00 PM – 1:30 PM: X-CZO Data Management (Mark Williams)

1:30 PM - 3:00 PM: Biosphere 2 Tours - Assemble outside B2 Cafe Session 2 – Subsurface Biogeochemistry (vadose/saturated zone mineral weathering processes, root and microbial dynamics, mineral/water and microbe/mineral interfacial processes, carbon sequestration, pedogenic element mass balance, topo-, litho-, chrono- and climo- sequences) - Plenary meeting room 3:00 PM Introduction by session convener (Craig Rasmussen) 3:05 PM: Keynote lecture (Libby Hausrath - UNLV) Biogeochemical weathering of serpentine minerals from bedrock to soil (25 min + 10 min discussion) 3:40 PM: Chunmei Chen et al. (CR-CZO) Elucidating the interaction between organic matter and mineral components along a pasture hillslope: Importance of iron-redox coupling processes (10 min + 5 min discussion) 3:55 PM: Lixin Jin et al (SSH-CZO) Water chemistry reflects hydrological controls on weathering in Susquehanna/Shale Hills CZO (Central Pennsylvania, USA) (10 min + 5 min discussion) 4:10 PM: Eve-Lyn Hinckley (BC-CZO) et al. Integrated study of critical zone architecture, near‐surface hydrology, and biogeochemistry to understand the fate of N in montane catchments (10 min + 5 min discussion) 4:25 PM: Poster introductions (brief <2-min, 1 slide overviews of poster content; 18 posters ~ 40 min) 5:05 PM: Coffee break & poster session - B2 Planning Center 6:15 PM: Rapporteur from CRB CZO to summarize poster session and to lead plenary discussion 6:30 PM: Dinner - B2 Exhibit Hall; Jemez Basin Virtual Tour (Paul Brooks) Guest: Joaquin Ruiz, Dean - College of Science Tuesday, May 10th 6:30 - 7:15 AM: Breakfast, B2 Cafe Tour of Santa Catalina Mountains CZO Buses leave Biosphere 2 at 7:30 am - Soldier Canyon - Mt. Bigelow eddy covariance tower - Marshall Gulch catchment experiments 7:00 PM: Dinner - B2 Exhibit Hall Concurrent: PI’s/Steering Committee to meet with CUAHSI Wednesday, May 11th 7:00 - 8:30 AM: Breakfast, B2 cafe 7:45 Wireless Sensor Demonstration - B2 Lawn (Steve Glaser) Session 3 – Ground and Surface Water Dynamics (hillslope and ground water hydrology, deep subsurface fluid flow, stream water response, hydrograph separation, end-member-mixing, catchment biogeochemistry, sediment transport) - Plenary meeting room

8:30 AM: Introduction by session convener (Jen McIntosh) 8:35 AM: Keynote lecture (Kip Solomon, U. Utah) Groundwater Surface Water Interactions: Historical Context and the Transit Time Distribution as a Unifying Theoretical Framework (25 min + 10 min discussion) 9:10 AM: Marek Zreda et al. COSMOS project. (10 min + 5 min discussion) 9:25 AM: Louis Kaplan et al. (CR-CZO). In-situ measurements of stream water organic carbon, nitrate, and suspended solids with a UV-VIS diode array spectrophotometer probe (10 min + 5 min discussion) 9:40 AM: Peter Hartsough et al. (SS-CZO). Soil moisture and tree water status dynamics in mixed-conifer forest, Southern Sierra CZO, CA (10 min + 5 min discussion) 9:45 AM: Poster introductions (brief <2-min, 1 slide overviews of poster content; 18 posters ~ 40 min) 10:25 AM: Coffee break & poster session - B2 Planning Center 11:45 AM: Rapporteur from SSh CZO to summarize poster session and to lead plenary discussion 12:00 AM: Break for lunch - B2 Cafe 1:30 PM – 2:30 PM: Cross-CZO Breakout Group Discussions / Preparation for the Thursday Workshop. Form 6-7 X-CZO/X-disciplinary subgroups (ca.15 people each): Begin developing an initial set of research questions that helps to design a road map for cross-CZO collaboration. Specifically, we want these to motivate research to address the broader overarching question of the workshop: How can the cross CZO network (human resources, infrastructure, models) be deployed to develop a unified theory of the critical zone that links long-term landscape evolution and critical zone architecture (geomorphology) to its short-term (hydrologic, biogeochemical) dynamics? The questions developed in this initial set of breakout groups should be brought as starting material for the Thursday workshop. Concurrent: Steering Committee to meet with NSF and PIs. 2:30 PM – 3:00 PM: Reporting back of subgroups (5 min each) Session 4 – Critical Zone Evolution (geophysical characterizations of subsurface structure, landscape evolution over geologic time scales, valley density development, surficial erosion, soil production functions, flow path development, geomorphology) - Plenary meeting room 3:00 PM Introduction by session convener (Jon Pelletier) 3:05 PM: Keynote lecture (Oliver Chadwick, UCSB) Climate/Weathering Control on Hillslope Morphology in Tectonically Quiescent Regions (25 min + 10 min discussion) 3:40 PM: Douglas Jerolmack (LM-CZO) Controls and feedbacks of particle size and mobility: Bringing down mountains one grain at a time (10 min + 5 min discussion)

3:55 PM: Nicole West et al. (SSH-CZO) Spatial variability of soil residence time within the Susquehanna Shale Hills Critical Zone Observatory, PA: Insights from multiple isotopic systems (10 min + 5 min discussion) 4:10 PM: Bob Anderson et al. (BC-CZO) Of damage zones, reactors and conveyor belts: a geomorphologist’s view of the long-term evolution of the critical zone (10 min + 5 min discussion) 4:25 PM: Poster introductions (brief <2-min, 1 slide overviews of poster content; 18 posters ~ 40 min) 5:05 PM: Coffee break & poster session - B2 Planning Center 6:15 PM: Rapporteur from BC CZO to summarize poster session and to lead plenary discussion 6:30 PM: Dinner - B2 Exhibit Hall; Landscape Evolution Observatory Experiment (Steve DeLong) 8:30 PM: Closing lecture: Ron Amundson (UCB) What have we learned? Thursday, May 12th 7:00 - 8:00 AM: Breakfast, B2 cafe Workshop to develop (i) questions, (ii) hypotheses, (iii) approaches, and (iv) methods for X-CZO network pursuit (open to all) Concurrent Data Management Group breakout session. 6:30 PM: Dinner, B2 Café patio Friday, May 13th 6:00 - 8:00 AM: Continental Breakfast, B2 Café - grab and go items - very simple

NSF Workshop: Towards a Unifying Theory of Critical Zone Structure, Function and Evolution

National Critical Zone Observatories Program

All Hands Meeting Field Trip - Tuesday, May 10, 2011 Biosphere 2 - Mt. Lemmon

Field Trip Schedule Tour of Santa Catalina Mountains CZO 6:45 Quick Breakfast 7:30 Buses depart from Biosphere 2 8:30 Rest stop at Tanque Verde & Catalina Highway (30 min) 9:00 depart 9:20 Geomorphic & Ecologic overview - Soldier Canyon pull-off (60 +25 min) 10:45 depart -- Lunch on the bus or after first stop

Bus A Bus B 11:30 Mt. Bigelow eddy covariance tower (120 min on site) 1:30 depart

11:45 Marshall Gulch catchment experiments (120 min on site) 1:45 depart

Bus - wait at Summerhaven for other bus

2:00 Marshall Gulch catchment experiments (120 min on site) 4:00 depart

2:10 Mt. Bigelow eddy covariance tower (120 min on site) 4:10 depart

6:30 Arrive at Biosphere 2 7:00 Dinner

Agenda for Thursday of All Hands Meeting May 2011: Workshop to develop (i) questions, (ii) hypotheses, (iii) approaches, and (iv) methods

for X-CZO network pursuit May 12, 2011

One goal of Critical Zone science is to develop a better understanding of the couplings among physical, chemical and biological processes in the surface Earth. To do that requires an ability to work collaboratively across disciplines, scales, and datasets. This is something that is being pursued by each CZO site. However, to the extent that we are collecting comparable data streams across the expanded “parameter space” of the CZO network, cross-site data can be queried for emergent patterns that may or may not be discernable at the CZO site scale. Therefore, the objective of the All Hands Thursday Workshop is to develop a set of questions, hypotheses, and research approaches/methods for possible network pursuit by the CZO teams that will:

(i) make synergistic use of existing commonalities across the CZO data sets, and/or (ii) give rise to novel X-CZO collaborations.

Specifically: How can the cross CZO network (human resources, infrastructure, models) be deployed to develop unified theory of the critical zone that links long-term landscape evolution and CZ architecture to its short-term (hydrologic, biogeochemical) response? The workshop effort should ideally result in cross-site paper(s), follow on proposal(s), etc. Agenda for the Thursday Workshop Session: A. Breakout Groups 1 (QUESTIONS): Continuation of breakout groups that were initiated on Wednesday. Develop a set of X-CZO questions that can likely be addressed through cross site comparisons. (8:00-10:00 am). B. Full Group 1 (QUESTIONS): Present the research questions to the full group. Full group should identify a manageable set (5-10 depending on total number of participants) by merging and prioritizing to give a sufficient cross section of disciplines and time scales. Identify new breakout groups to meet after lunch that self-organize around the questions identified. (Note, breakout group composition doesn’t need to be same group composition as breakout 1 and hopefully won’t be.) (10:00-noon) C. Lunch (noon-1:00) D. Breakout Groups 2 (HYPOTHESES/APPROACH): Break out into groups focusing on the questions identified. Develop no more than three hypotheses to be tested under that question. Consider a research approach that will enable testing. What do we need information on? Evaluate extent to which needed data are already being acquired across CZOs, how they are being acquired, etc. What are commonalities and differences in how we are collecting the requisite data? What new data do we need? Is it possible to get it? What new infrastructure is required? (1:00-3:00 pm) E. Full Group 2 (HYPOTHESES/APPROACH): Report back on hypotheses and approach developed. Discuss in larger group. Identify follow-on activities and potential collaboration. (3:00-5:30 pm) F. Dinner (6:30 pm)

CZO All Hands Meeting, Biosphere 2, May 2011

Sunday Night Keynote: Sun. May 8, 8:00 pm

Climate, geomorphic and ecohydrologic controls of nitrogen cycling and export along a continental transect

L.E. Band

UNC‐Chapel Hill

Forest watersheds respond to geomorphic and climate dynamics through the transient adjustment of space/time patterns of carbon, water and nutrient cycling. This is manifested in the distribution of canopy foliar and root carbon, soil water patterns and the release of excess moisture and nutrients as runoff and nitrogen concentration regimes. We investigate the integrated dynamics of forest watershed response to disturbance, hydroclimate and geomorphology in a transect of intensively studied forest catchments from central Ontario through the southern Appalachians. The transect ranges from a snow‐dominated climate, through sites with itinerant or negligible snow, and with a range of geomorphic conditions. Characteristic regimes in the timing and magnitude of streamwater nitrogen concentrations and loads are found along the transect, resulting from seasonal and interannual hydroclimate variability and geomorphic characteristics of the catchments. We use a combination of detailed field measurements, with a spatially distributed ecohydrologic model to investigate controls of nitrogen regime as a function of short term water, carbon and nutrient cycling within the catchments, and transient, long term forest growth and aggradation. We also infer the impact of climate change on catchment hydrology and biogeochemistry along the transect and the mechanisms by which more northern, snow dominated catchments may begin to evolve to more closely resemble warmer, snow‐free catchments.


Session 1 Keynote: Mon. May 9, 8:05 am

Surface atmosphere fluxes of H2O and CO2 in the subalpine ecosystem critical zone

Russell Monson

Institute of the Environment, The University of Arizona

The net exchange of H2O between ecosystems and the atmosphere is typically observed using approaches incapable of direct partitioning between soil and vegetation fluxes. Our understanding of the exchange of water between ecosystems in the critical zones between rock and air, however, require that we know something about the differential influences of plants and soils as conduits for water transfer. Methods that have been developed to accomplish the partitioning include: (1) stable isotope methods, which carry uncertainties associated with assumptions about steady state in the isotopic balance within the system, determination of fractionation processes at the sites of soil evaporation and regression approaches to estimate atmospheric mixing processes, and (2) the assimilation of flux data from eddy covariance towers into ecosystem process models that use previous knowledge about plant and soil processes to partition the various fluxes. In the first part of my lecture, I will discuss both of these approaches within the context of predicting ET fluxes from natural ecosystems, with an emphasis on the subalpine ecosystem of Colorado. In the second part of my lecture, I will focus on recent studies of the pine beetle infection in Western North America and our studies of soil carbon cycling in the Rocky Mountain subalpine forest ecosystem. Massive disturbances to forests have the potential to disrupt critical zone processes. I will focus on carbon cycle processes assessed across chronosequences of beetle disturbance. Our observations have shown that soil carbon cycling is in fact disturbed significantly with regard to the partitioning of soil respiration between autotrophic and heterotrophic processes. However, overall carbon fluxes from the critical zone to the atmosphere are not disturbed to the same extent. In the final part of my lecture, I will present a case of control over forest carbon sequestration and winter versus summer hydrological inputs to the subalpine forest ecosystem in Colorado. Our observations using the stable isotopes of water show that winter snowpack, rather than summer rain, exerts the principal control over coupling between the carbon and water cycles in this ecosystem, and this control is highly susceptible to future changes in winter climate.


Session 1: Mon. May 9, 8:40 am

Relationships between elevation, photosynthesis and evapotranspiration in the Sierra CZO

Michael Goulden1, Greg Winston1, Anne Kelly1, Matt Meadows2, Roger Bales2

1Department of Earth System Science, University of California, Irvine

2School of Engineering, University of California, Merced

We are operating four eddy covariance flux towers along an elevation gradient (a climosequence) in the Sierra CZO to understand the relationships between climate, plant biogeography, plant production, evaptranspiration, and water balance. Flux towers are located in Oak/Pine woodland (1320' elevation, annual mean T 14.4oC, mean precip 510 mm), Ponderosa Pine forest (3900' elevation, T 10.9oC, precip 870 mm), Midmontane forest (6600' elevation, T 8.9oC, precip 1010 mm), Subalpine forest (8900' elevation, T 4.1oC, precip 1080 mm).

Key findings include: (1) Drought stress decreases and winter cold stress increases with elevation. The midmontane forest occupies a climatological sweet spot where neither drought nor cold curtail photosynthesis. (2) The year‐round growing season at the midmontane sites causes large GPP and Et. The subalpine forest is dormant in winter, resulting in much reduced GPP and Et and increased water yield. (3) This shift in winter activity reflects a basic difference in plant physiology. Midmontane trees have high rates of winter photosynthesis at T > 6oC; subalpine trees are dormant throughout winter, even when T > 6oC. (4) Climate warming should increase winter photosynthesis and Et in midmontane, since there will be more days above 6oC. Climate warming may have little effect on winter photosynthesis and Et in Subalpine. (5) A key question is whether and how quickly midmontane species will expand into the current subalpine belt. Upslope migration would markedly increase winter Et at these elevations and decrease water yield.



Sensitivity of soil CO2 efflux to climatic and topographic factors in a montane drainage system

Greg Barron‐Gafford

Dept. of Ecology and Evolutionary Biology, The University of Arizona, Tucson, AZ Background/Question/Methods Carbon budget analyses suggest montane ecosystems as a potentially large, but highly uncertain, portion of the North American carbon sink. While eddy covariance measurements of net ecosystem exchange of CO2 provide insight into the carbon‐sink potential of montane ecosystems, compartmentalization of ecosystem respiration (Reco) into aboveground and belowground soil (Rsoil) fluxes is often difficult. This is particularly true in areas of non‐homogenous topography and variable soil microclimate, such as those found in complex terrain. Understanding the relative contribution of Rsoil to Reco and the spatio‐temporal responses of Rsoil to varying temperatures and moistures will inform predictions of Rsoil in future climate scenarios. This study was conducted along a pair of converging drainages within a montane mixed‐conifer forest located below an eddy covariance tower in the Santa Catalina Mountains of southern Arizona. Rsoil was quantified at fixed points along transects running perpendicular to each drainage such that the influence of upslope accumulated area and distance from the drainage could be interpreted. Measurements were made across these spatially distributed points nearly bi‐weekly from prior to the monsoon until snow accumulated and again after periods of snow melt. Soil moisture, soil temperature, air temperature, and litter‐layer thickness were quantified along with soil respiration and evaporation. Results/Conclusions We were able to quantify the relative influence of topographic and environmental drivers of seasonal and cumulative patterns of Rsoil. Rsoil was significantly influenced by the onset of our summer monsoon in that average Rsoil stimulated by 118%. While additional rains increased soil moisture by 58%, average Rsoil remained unchanged. Rates decreased throughout the post‐monsoon following patterns of decline in available water. With regard to topography, aspect influenced patterns of Rsoil though distance to drainage did not. The influence of aspect was seasonally important, in that it was a major driver in the early monsoon but less so under moist summer conditions. Together, these results illustrate the influence of Rsoil to water pulse events at the initiation of the monsoon season, to topography under wet conditions, and to low soil temperatures during melt. Further spatial analysis will allow us to calculate the influence of upslope accumulated area, which is a measure of the concentrating water resources due to topography, on point measures of Rsoil. In so doing, we will link the influence of hydrologic forces to ecologically relevant processes in this complex terrain setting.



Use of stable isotopes to understand recharge sources and streamflow generation in the Luquillo Mountains, Puerto Rico

Scholl, M.A.1, Shanley, J.B.2, Scatena, F.N.3 and McDowell, W.H.4

1,2U.S. Geological Survey, Reston, VA and Montpelier, VT

3University of Pennsylvania, Philadelphia, PA 4University of New Hampshire, Durham, NH

At the Luquillo Critical Zone Observatory (CZO), stable isotopes of water (rain and cloud water, throughfall, streamflow, shallow groundwater) were used to understand the climate patterns that contribute to the water supply and to investigate streamflow generation processes. The CZO includes two watersheds of contrasting geology, the Rio Mameyes (35 km2) in volcaniclastic bedrock and the Rio Icacos/ Rio Blanco (32 km2) in granodiorite. Rainfall samples

were collected at weekly and monthly intervals and analyzed for δ2H and δ18O composition. The isotopic values were correlated with local and mesoscale weather patterns and cloud height to assign isotopic signatures to different sources of recharge to the watersheds. Throughfall samples were collected and compared with rainfall collected at the same time. There was no evidence of significant evaporative fractionation during the throughfall process. Monthly samples from streams showed that fluctuations in stream isotopic composition matched those in rain, but with a much smaller amplitude. This suggests a shallow flowpath component with approximately monthly residence time, combining with a deeper groundwater baseflow component. The shallow groundwater system in the R. Icacos basin was sampled twice, in January and May of 2010. Groundwater isotopic composition varied with well position on the hillslope, and the range of values indicated that both recent infiltration and older groundwater were sampled. Hydrograph separation experiments that are planned for the field season will yield more details with mixing model interpretations from both stable isotopes and solute chemistry. The precipitation and groundwater samples will establish the isotopic composition of end member water sources for streamflow. These will be used to understand seasonal sources of streamflow, and to build conceptual models of the effects of climate variation on streamflow generation.

Monday AM Posters: 1.1

CZO All‐hands meeting ‐ Session 1: Ecosystem Exchange and Hydrologic Partitioning

High mercury wet deposition at a “clean air” site in Puerto Rico

James B. Shanley1, Mark A. Engle2, Martha Scholl2, David P. Krabbenhoft3, Robert Brunette4, Mark L. Olson3

1 USGS, Montpelier, VT

2 USGS, Reston, VA 3 USGS, Middleton, WI

4 Frontier Geosciences, Seattle, WA Atmospheric mercury deposition measurements are few in tropical latitudes. Here we report two years (April 2005 to March 2007) of wet Hg deposition at a tropical wet forest in the Luquillo Mountains, northeastern Puerto Rico, USA. Despite receiving unpolluted air off the Atlantic Ocean from northeasterly trade winds, the site averaged 27.9 µg m‐2 yr‐1 wet Hg deposition, or about 30% more than Florida and the Gulf Coast, the highest deposition areas within the USA. These high Hg deposition rates are driven in part by high rainfall, which averaged 2855 mm yr‐1. The volume‐weighted mean Hg concentration was 9.8 ng L‐1, and was highest during the summer and lowest during the winter dry season. Rainout of Hg (decreasing concentration with increasing rainfall depth) was minimal. Low reactive gaseous mercury (RGM) concentrations (<10 pg m‐3) at ground level did not support high Hg in rain; rather, we contend that high convective cloud tops scavenge RGM from above the mixing layer. In the tropics, elevated photooxidation rates of Hg0 from the global pool likely maintain upper tropospheric RGM. The high wet Hg deposition at this “clean air” site suggests that high Hg deposition may occur in the tropics worldwide.



Tree transpiration at the Shale Hills Critical Zone Observatory

David Eissenstat1, Frederick Meinzer2, David Woodruff2 and Tom Adams1.

1Penn State University, Department of Horticulture 2USDA Forest Service‐Pacific Northwest Research Station

The Shale Hills CZO had relatively high tree species diversity. Different canopy tree species potentially utilize water in very different ways. When estimating land surface transpiration, does the tree species matter? We estimated tree transpiration by looking at stem sap flux in tree species exhibiting three types of sap wood: coniferous that have no vessels and only tracheid, ring‐porous in tree species with large vessels formed in the spring and smaller vessels formed in the summer, and diffuse porous where tree species have only moderately‐sized vessels and they don’t shift in diameter over the growing season. We found that ring‐porous species like oaks had higher sap flux that either diffuse porous and conifer species, which is consistent with their more limited sap‐wood cross‐sectional area on a tree. We also found that in general, sap flux seasonal patterns closely tracked soil water potential to a depth of 15 cm, especially in June and July. However, the oaks were more capable of maintaining positive sap flux during periods of low soil water potential and quickly resuming maximum water flux with soil rewetting into late August and September. The other species (coniferous and diffuse‐porous wood types) exhibited inelasticity in sap flux recovery by the end of August. Collectively these data suggest that different tree species may have distinctly different patterns of water use in this region.



Spatial and Temporal Dynamics of Vegetation and Hydrological Properties at Shale Hills Critical Zone Observatory in Central Pennsylvania

Kusum J. Naithani1,2,3, Katie Gaines3,4, Doug Baldwin5, Henry Lin5, David Eissenstat3,4

1Department of Meteorology, The Pennsylvania State University, University Park, PA 16802. 2Department of Geography, The Pennsylvania State University, University Park, PA 16802.

3Intercollege Graduate Degree Program in Ecology, The Pennsylvania State University, University Park, PA 16802.

4Department of Horticulture, The Pennsylvania State University, University Park, PA 16802. 5Department of Crop and Soil Sciences, The Pennsylvania State University, University Park, PA 16802.

Understanding the interaction of vegetation and hydrology and determining the changes in this relationship across spatial and temporal domains is critical for modeling landscape hydrology. Trees release water into the atmosphere via stomatal pores in exchange for carbon dioxide and play an important role in landscape hydrology. Our objective was to investigate the coupled spatial and temporal dynamics of vegetation and hydrological properties in a forested catchment covering 7900 m2 area in central Pennsylvania at the Shale Hills Critical Zone Observatory. During 2010, we measured leaf area index (LAI) and canopy closure to characterize vegetation properties and measured soil water content, soil water tension and water table depth to characterize hydrological properties at a spatial grid of 70 sampling points across an entire watershed at 15‐day intervals. We used geostatistical techniques to quantify spatial structure (semi‐variograms) and visualize spatial patterns (Kriging) of vegetation and hydrological properties and their relationship to each other. Our results show an exponential increase (90‐600 m) in spatial range from leaf onset (April) to leaf maturity (July) and subsequent decline (600‐100 m) in spatial range from leaf maturity (July) to leaf senescence (October). Soil water content (at all measured depths) decreased from leaf onset to maturity and subsequently increased from leaf maturity to senescence. Results from this study suggest that the landscape canopy area and soil water become more homogenized and coupled from leaf onset to maturity (increasing spatial dependence and decreasing water content) and the landscape becomes more heterogeneous and uncoupled from leaf maturity to senescence (decreasing spatial dependence and increasing water content). Our results provide insight into tight coupling between vegetation and hydrology across space and time; incorporating these spatial and temporal feedbacks in hydrological models will improve current and future landscape modeling of temperate forests.



Changing Controls of Soil Moisture Spatial Organization in the Shale Hills Catchment

Ken Takagi and Henry Lin

The Pennsylvania State University, University Park, PA 16802

Modeling hydrological processes often requires the identification of dominant controls on soil moisture organization under different climatic conditions at various soil depths. In this study, we utilized a four‐year database consisting of soil moisture measurements at 106 locations from the surface down to 1.1‐m depth within the Shale Hills CZO. Our objectives were to 1) compare the spatial organization of soil moisture within different soil‐landform units and its temporal persistence at different depths under varying catchment wetness conditions and 2) investigate correlation strength between soil moisture content and 11 soil‐terrain attributes and the temporal change of such correlation. Our results showed that the catchment’s near‐surface (< 0.3‐m) soil moisture organization exhibited clear seasonal trends: during the winter through early summer, areas of high soil moisture were concentrated within convergent landforms; while during the summer through early fall, soil moisture was more uniformly distributed throughout the catchment. This indicates that under dry conditions soil moisture removal (primarily through evapotranspiration) had a significant influence on the organization of near‐surface soil moisture, while topography was an important control on soil moisture organization under wet conditions. Subsurface (> 0.3‐m down to 1.1‐m) soil moisture organization, however, exhibited increasing temporal persistence with increasing depth, and subsoil moisture above the catchment‐wide average was concentrated within convergent landforms under both wet and dry conditions. Deep soil profiles in convergent landforms provide a store of soil moisture that persisted throughout year, indicating that soil moisture organization within the subsurface is influenced by both surface topography and soil depth. Topographic wetness index (TWI), slope, depth to bedrock, and percent (by weight) clay and rock fragment were significant (p < 0.05) factors influencing soil moisture on at least 80% of 91 measurement days analyzed for all soil depths. Intermediate depths (0.3 to 0.7‐m) exhibited the highest coefficient of determination (R2) in linear regression for TWI and upslope contributing area, suggesting that lateral subsurface flow may be an important driver of soil moisture dynamics at these depths in this catchment. Mean R2 values for slope and depth to bedrock increased with increasing soil depth, confirming the importance of deep soil moisture storage on subsoil moisture organization. We conclude that the controls on this catchment’s soil moisture spatial organization at the near‐surface (< 0.3‐m) fluctuates seasonally between evapotranspiration and topography; that at intermediate depths (0.3‐ to 0.7‐m) the soil moisture organization is controlled significantly by lateral subsurface flow; and that the organization at deeper depths (> 0.7‐m) becomes more temporally persistent and is primarily a function of both topography and soil depth.



Introducing the Principles and Processes of Earth’s Critical Zone to Teachers, Informal Educators and Students

Susan Gill

Stroud Water Research Center, Avondale, PA

Humans occupy a dynamic, ever‐changing environment at the surface of the Earth called the Critical Zone. This zone, stretching from the base of the soil to the top of the vegetative canopy, is where humans come into direct contact with, and have an impact on Earth systems. Understanding the principles and processes that form this environment is vital to understanding the planet and human impacts on the environment. The Stroud Water Research Center is building on research of the Christina Basin Critical Zone Observatory as a way to communicate Earth system science to teachers, students, informal educators and citizen scientists. These projects create place‐based educational experiences for participants that introduce them to both natural processes and human impacts that shape the environment within Earth’s Critical Zone. By linking processes that act at the local scale to conditions that occur at the global scale, these projects provide participants with a means to comprehend the integrated and complex nature of Earth system science.

We currently have two NSF‐funded projects and one foundation‐funded project that are based on the CZO activities. These projects incorporate sensor building, deployment and data harvesting; data visualization; and, hydrologic modeling.



A Wireless Environmental Sensor Network Based on Open‐Source Electronics

for the Christina River Basin CZO

Steven Hicks 1, Anthony Aufdenkampe 1, Olesya Lazareva 2, David Montgomery 1, Louis Kaplan 1, Denis Newbold 1, Delphis Levia 2, Donald L Sparks 2

1Stroud Water Research Center. http://www.stroudcenter.org

2University of Delaware, Delaware Environmental Institute (DENIN). http://denin.udel.edu/ All‐Christina River Basin CZO. http://www.udel.edu/czo/

The search for biogeochemical “hot spots” and “hot moments” that control ecosystem‐level processes requires a rethinking of how we observe the environment. Massive multi‐sensor/measurement arrays are required to realize 2D, 3D or 4D maps of environmental properties with sufficient spatial and temporal resolution to find and understand hot spots and hot moments. To date, the cost of the data logging and communication infrastructure has been a major limitation to large‐scale sensor deployment, especially in near‐real‐time (NRT) wireless networks. For example, a 16‐channel datalogger with radio communications from Campbell Scientific costs $2500 or more.

The recent explosion of open‐source electronics platforms offers an opportunity for environmental observatories to deploy sensors at massive scales by reducing data logging and communications costs by more than an order of magnitude. Leading the open‐source electronics revolution is the Arduino project (http://arduino.cc/), designed to make the process of using electronics in multidisciplinary projects more accessible to hobbyists and professionals alike. An active community of more than 100,000 users have developed and shared hundreds of practical applications that receive input from a variety of sensors and use embedded logic to control lights, motors, and other actuators. Likewise, more than a dozen companies build low‐cost Arduino‐based and Arduino‐compatible boards that snap together in a modular framework that enables nearly any application without the need for a soldering iron or electrical engineering degree.

Based on these open‐source technologies and products, we are beginning to deploy a 16‐channel, 18‐bit, solar‐powered datalogger with self‐meshing wireless communications for $162. Thus, we can deploy 155 wireless sensor nodes for the same hardware cost as 10 nodes based on products from Campbell Scientific. Resources can thus be prioritized to sensor hardware rather than to data acquisition and communication hardware.

Here we will describe and demonstrate our Arduino‐based data system, and show real‐world results for analog‐to‐digital conversion, data transmission rates and distances.



Reducing Error Associated with Compression Derived Measurements of Whole‐Tree Rainfall Interception within the

Christina River Basin Critical Zone Observatory

John Van Stan1, Delphis Levia2, Matthew Jarvis3, Jan Friesen4

1 Department of Geography, University of Delaware, Newark, DE 19716, USA 2 Departments of Geography & Plant and Soil Sciences, University of Delaware,

Newark, DE 19716, USA; 3 Independent scholar, Newark, DE 19713, USA

4 Department Computational Hydrosystems, Helmholtz Centre for Environmental Research, 04318 Leipzig, Germany

Strain sensors have been employed to quantify whole‐tree canopy interception at the intra‐storm scale. Imprecise sensor placement, however, can lead to significant measurement error. We developed an instrumental procedure using the LaserBarkTM automated tree measurement system to minimize such measurement error by optimizing the installation location of strain sensors. The derived method approximates the location of neutral bending axes, and then a follow‐up routine instructs the LaserBarkTM to optically indicate exact positioning for strain sensors over the bending axes. Our method is designed to remove noise and error engendered by wind throw, off‐center loading within unevenly‐distributed canopies, and human error that can decrease rainfall interception measurements. Based on our US‐Germany collaboration, the Christina River Basin Critical Zone Observatory will be among the first sites in the USA to install mechanical displacement sensors for the quantification of whole‐tree rainfall interception.



Mechanisms to escape limitations of winter cold and summer drought on primary productivity in Sierra mixed conifer forest

Anne E. Kelly, ML Goulden

Department of Earth System Science, University of California, Irvine

The forests of the Sierra Nevada are strikingly large. John Muir describes, "Here... are the grandest forest‐trees, the Sequoia, king of conifers, the noble Sugar and Yellow Pines, Douglas Spruce, Libocedrus, and the Silver Firs, each a giant of its kind, assembled together in one and the same forest, surpassing all other coniferous forests in the world, both in the number of its species and in the size and beauty of its trees." The climatology of these forests predicts a cold steppe or open woodland and not a dense forest of gigantic trees. The growing season is predicted to be only a few months, with drought limitation in summer and cold limitation in winter. The Miami model predicts an aboveground NPP of 3 tC ha‐1 yr‐1. Why are these forests so big? There are three possible mechanisms for allowing such a large forest in a winter cold‐ and summer drought‐limited environment: 1) the forest growth rate is extraordinarily fast during a short growing season, 2) the forest growth rate is moderate during a short growing season, but large biomass has built up over many years, or 3) the forest growth rate is moderate and the growing season is not limited by winter cold or summer drought. The goal of this project is to understand how the large‐stature Sierra mixed conifer forest exists in a climate with cold winters and dry summers.



Seeing the Snow Through the Trees: Accumulation in forested catchments as determined from snow depth sensor and LiDAR measurements

P. B. Kirchner1, R. C. Bales1, K. N. Musselman2 J. Flanagan1, Q. Guo1

1 University of California, Merced Sierra Nevada Research Institute, PO Box 2039 2500 lake Rd., Merced, Ca 95344

2 Department of Civil and Environmental Engineering, University of California, Los Angeles, 5731 Boelter Hall, Box 951593, Los Angeles, CA 90095‐1593

The relationship between forest cover, snow depth and snow density is central to determining snow water equivalence in forested catchments. Most modeling, research and forecasting are based on a limited number of measurements made in non representative areas of the mountainous west. Thus the problem of understanding snow distribution at large spatial extents and frequent time steps has not been solved. Snow accumulation in forested environments is a result of the multiple feedbacks between precipitation, topography, and vegetation. Here we present and analysis of snow accumulation from the Wolverton Basin, Southern Sierra Critical Zone Observatory. Continuous snow depth measurements collected from 26 stratified locations over the 2008‐2010 water years are compared to canopy gap fraction as determined by hemispherical photographs. Canopy gap fraction and snow accumulation are found to be highly correlated, R2=0.6 to 0.9 dependant on time interval and area of integration. Snow depths measured at point locations are also compared with snow depth data computed from snow on and snow off 1m digital elevation models, derived from the 2010 CZO LiDAR over‐flights. Additional analysis of canopy density derived from 30m Landsat products and the 1m LiDar product is also presented. Canopy density and elevation are found to be the most significant factor in determining snow depth at peak accumulation and provide a robust physically based approach to estimating accumulation in areas with forest snow cover.



Importance of sub‐watershed spatial heterogeneity in ecohydrological modelling using multi‐scale and multi‐criteria data in the context of climate

variation and change

Kyongho Son, Christina Tague

Bren School of Environmental Science and Management, University of California, Santa Barbara One of the goals of the Southern Sierra Critical Zone Observatory (SSCZO) is to strategically combine field data and spatial models to improve our ability to predict how ecohydrologic variables (snow, soil moisture, ET, photosynthesis and streamflow) will respond to a warming climate. While there have been a variety of modeling studies in the Sierra that have examined how these variables respond to warming, most studies have been done at relatively coarse spatial scales (120m grids). Further calibration and validation of these models often relies solely on streamflow data. The SSCZO provides an opportunity to assess how well models of coupled eco‐hydrologic processes captures plot‐hillslope scale patterns of ecohydrologic variables, and then to test whether including this level of spatial heterogeneity in a modeling study is important for accurately estimating aggregate watershed responses to climate variability and change. In the Sierra CZO, we have applied Regional Hydro‐Ecologic Simulation System (RHESSys), a physically based spatially distributed model of coupled carbon, nutrient cycling and hydrology. We initially implement the model at a 30m spatial resolution and calibrate subsurface drainage parameters using measured streamflow. We also compare model predictions with several existing CZO data sets including co‐located snow depth, soil moisture sensor, sapflow and flux tower data. Initial comparisons highlight the importance of microclimate variation and point to inadequacies in current approaches used to upscale point meteorology measurements (or downscale gridded estimates) for ecohydrologic modeling. We then use this baseline model to develop a strategy for further data collection that is explicitly directed at evaluating the model’s ability to capture spatial heterogeneity in eco‐hydrologic processes including soil moisture and transpiration. We present our initial results from this model‐driven data collection and show how it can be used to a) identify weakness in model parameterization and b) develop strategies for improving model estimates. We interpret model results in the context of climate variability and change and show how accounting for both local vegetation‐driven heterogeneity in snow accumulation and melt and related processes and hillslope scale topographic‐driven heterogeneity can be important in estimating aggregate watershed responses



Hydrologic partitioning of precipitation in headwater catchments

in the Jemez River Basin CZO, New Mexico

Joel Biederman1, Krystine Nelson2, Courtney Porter1, Zulia Sanchez Mejia2, Xavier Zapata‐Rios1, Adrian Harpold1, Julia Perdrial3, Paul Brooks1, Jennifer McIntosh1

1Hydrology and Water Resources, University of Arizona 2School of Natural Resources, University of Arizona

3Soil, Water, and Environmental Sciences, University of Arizona The amount of precipitation that is partitioned into evapotranspiration (ET, including vapor fluxes), infiltration and direct runoff can have profound effects on ecosystem function, subsurface biogeochemical processes, surface water dynamics, and landscape evolution. This study aims to determine the partitioning of water in 5 headwater catchments around Redondo Peak in the Jemez Mountains in northern New Mexico, by calculating water yields for 3 water years (2008‐2010). The amount of precipitation (from 5 met stations) and ET (from 3 eddy flux towers) will be distributed across the catchments, and compared to stream discharge at 7 flumes. Combining these results with stable isotopes of water, we can estimate source water contributions to stream flow from snowmelt, summer monsoons, and groundwater. We expect water yields and source water contributions to vary between catchments as a function of different catchment characteristics, such as EEMT gradients, soil depths, and slope/aspect/areas. In addition, we might expect differences in water yields and source water contributions within catchments as a function of seasonality (e.g. winter versus summer).



Investigating the controls on snow water inputs to a small mixed‐conifer catchment in the Valles Caldera National Preserve, NM

Harpold, A.A and P.D. Brooks

Dept. of Hydrology and Water Resources, The University of Arizona, Tucson, AZ

Sublimation of snow reduces the amount of water and controls the timing of snow water inputs available for runoff and ecological services in dry, southern latitude forests. The effects of sublimation on snow water inputs however, remain difficult to quantify at the catchment‐scale. Here we use multiple LiDAR datasets on a 1 by 1 m resolution from the Valles Caldera National Preserve to develop snow depth maps for a 16 ha catchment. The LiDAR datasets are used to develop a distribution of vegetation heights and model incident short‐wave radiation under three scenarios: 1. Bare earth, 2. Bare earth with remote shading, and 3. Vegetation with remote shading. The snow water equilvalent (SWE) was relatively equal in the east and west facing hillslopes of the catchment despite large differences in vegetation and short‐wave radiation due to shading from vegetation. The three radiation scenarios were also related to the snow water inputs on a pixel by pixel basis and suggested that the incident short‐wave radiation can only capture snow water inputs on both the east and west facing hillslopes at locations of moderate to higher solar forcing. At lower solar forcing, generally closer to vegetation and shaded, other factors such as long‐wave radiation and/or scattering of short‐wave radiation may be important. Overall our results suggest that shading from vegetation reduces snowpack sublimation and increases snow water inputs while vegetation also intercepts snow and causes sublimation from the canopy. The co‐evolution of vegetation and snow water inputs represents an important control on critical zone development in seasonally snow covered areas by spatially regulating the magnitude and timing of snow water inputs to the soil and vegetation. This study effectively demonstrates the utility of LiDAR investigations for estimating snow water inputs at the catchment‐scale and highlights the potential for extending this research at this and other CZO sites.



Breakdown of hydrologic spatial patterns upon model coarsening at hillslope scales

Taufique H. Mahmood and Enrique R. Vivoni

School of Earth and Space Exploration, Arizona State University, Tempe, AZ, 85287 Model resolution is an important characteristic for simulating reliable hydrologic patterns at the hillslope scale. However, there is little knowledge on the threshold resolution beyond which the fidelity of simulated spatial patterns are no longer reliable. In this study, we use a distributed hydrologic model, known as the TIN‐based Real‐time Integrated Basin Simulator (tRIBS), to investigate the effects of coarsening on the breakdown of hydrologic patterns in a ponderosa pine hillslope. Our results indicate a prominent curvature control at the finer resolution and strong vegetation control at coarser resolutions on the distributed soil moisture pattern. Coarsening eliminates many small scale topographic features causing a steady decline of curvature control on the soil moisture distribution. Using a flatness index, we find that coarsening enhances the homogeneity of soil moisture and runoff patterns. We also observed a threshold model resolution of about 10% of original topographic field at which large change in model response occur. Our findings point the differential impacts of coarsening on vegetation and curvature controls and the breakdown of model response for severely‐aggregated hillslope representations.



Toward an improved understanding of the role of transpiration in critical zone dynamics

Bhaskar Mitra1, Shirley A. Papuga1,2, Michelle L. Cavanaugh3, Joseph R. McConnell4, Nate Abramson2, Greg A. Barron‐Gafford5, Erik P. Hamerlynck3, Peter Troch2, Paul Brooks2

1. School of Natural Resources and Environment, University of Arizona, Tucson, AZ 85721 2. Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721

3. Southwest Watershed Research Center, USDA‐ARS, Tucson, AZ 85719 4. Division of Hydrologic Sciences, Desert Research Institute, Reno NV 89512

5. B2 Earthscience, University of Arizona, Tucson, Arizona, USA As a vertical water flux, plant transpiration plays a significant role in modulating the soil water balance which in turn influences the subsurface biogeochemical and landscape evolution processes in the critical zone. Within the subalpine mixed conifer ecosystems in the Jemez River Basin – Santa Catalina Mountains Critical Zone Observatory (JRB‐SCM CZO), multiple sets of sap flux sensors are proposed or have been established within the footprints of eddy covariance towers (one in JRB and one in SCM), and at three sites located within small order drainage basins (one in JRB and two in SCM). We propose a data‐synthesis from these different sites to address the following critical zone questions:

1. What is the role of slope, altitude, forest stand dynamics and plant‐physiology in the magnitude and seasonal dynamics of transpiration at these different sites? 2. Can we identify a primary driver or drivers of transpiration across these sites? 3. Can we determine the primary water source used for plant transpiration, and how this varies within the CZO? To address these questions, we seek to establish an effective robust method of up‐scaling from tree to plot level to landscape level transpiration in this complex terrain. We anticipate that this synthesis using a “bottom‐up” reductionist approach will help in understanding the role plant transpiration play in critical zone dynamics.



Influence of snow cover duration on soil respiration and evaporation efflux in mixed‐conifer ecosystems

Krystine Nelson1, Shirley A. Papuga1, Grace John2, Rebecca Minor3, Greg A. Barron‐Gafford3

1 School of Natural Resources and Environment, University of Arizona, Tucson, AZ 85721

2 Biology, University of Dayton, Dayton, OH 45469 3 Biosphere 2, Earthscience, University of Arizona, Tucson, AZ 85721

Ecosystem respiration is becoming an increasingly important topic in the area of climate change. Of the different components of ecosystem‐scale respiration, soil respiration – the efflux of CO2 leaving from the soil to the atmosphere – is perhaps the least well understood. Since a significant portion of the world’s terrestrial carbon stores are found within soils, it is important to study how the CO2 flux might change with a changing climate. Subalpine mixed conifer ecosystems are sensitive to a warming climate and are dependent on snow fall, which is expected to decrease in coming years. Thus, this study looks at soil respiration within these ecosystems and explores how the changing snow accumulation and duration of snow cover will affect CO2 fluxes out of the soil. Our study takes place within a mixed conifer ecosystem within the Santa Catalina Mountains where we have three understory time‐lapse digital cameras located within the footprint of an eddy covariance tower. Using the cameras, we identified locations with short and long snow duration. Then, within the field of view of each camera, we placed 6 soil collars (3 in short snow duration; 3 in long snow duration). Since July 2010, soil respiration and evaporation data have been collected regularly from these collars. In this preliminary analysis, we show three main results: (1) short and long snow season fluxes differ from one another throughout the year, usually with short snow season sites showing higher respiration values than long snow sites, (2) both short and long snow season CO2 fluxes have a strong relationship with soil temperature, and (3) both short and long snow season CO2 fluxes have a poor relationship with soil moisture.



Using time‐lapse digital photography to monitor changes in the critical zone

Shirley A. Papuga, Krystine Nelson, Bhaskar Mitra

School of Natural Resources and Environment, University of Arizona, Tucson, AZ 85721

Within the critical zone (CZ), important interconnected physical, chemical, and biological processes influence the mass and energy exchange that governs everything from biomass production to water storage. However, many of these processes operate on different temporal and spatial scales, and little is known about how these processes interact. We have begun to link these processes by analyzing time‐lapse digital images. These images have the potential to quantitatively link processes across different disciplines, such as snow hydrology and ecology. In December 2009 and March 2010, we co‐located time‐lapse enabled digital cameras and eddy covariance towers within the Santa Catalina Mountain and Jemez River Basins of the University of Arizona CZ Observatory, respectively. We mounted an overstory camera at the top of each of the eddy covariance towers and three understory cameras at heights of 1 m within the footprints of the towers. All cameras record images hourly. Here we describe our methodology for processing these hourly images and show preliminary results from our image analysis.



Scaling water partitioning, standing biomass, and effective energy and mass transfer in the SCM‐CZO

And

Thermodynamic constraint on critical zone effective energy and mass transfer

Craig Rasmussen

Dept. of Soil Water and Environmental Science, The University of Arizona

Understanding the partitioning of water, energy and carbon to primary production and effective precipitation is central to quantifying the limits on critical zone evolution. Recent work

suggests quantifying energetic transfers to the critical zone in the form of effective precipitation and primary production provides a first order approximation of critical zone

process and structural organization. However, explicit linkage of this effective energy and mass transfer (EEMT; W m‐2) to critical zone state variables and well defined physical limits remains

to be developed. The objective of this work was to place EEMT in the context of thermodynamic state variables of temperature and vapor pressure deficit, with explicit

definition of EEMT physical limits using a global climate dataset. The data demonstrated three physical limits for EEMT: i) an absolute vapor pressure deficit threshold of 1,200 Pa above which

EEMT is zero; ii) a temperature dependent vapor pressure deficit limit that scales with temperature following the slope of the saturated vapor pressure function up to a temperature

of 292 K; and iii) a minimum precipitation threshold required from EEMT production at temperatures greater than 292 K. Within these limits, EEMT scales directly with precipitation, with increasing conversion of the precipitation to EEMT with increasing temperature. The

thermodynamic based state‐space approach defined here provides a simplified framework with well‐defined physical limits for calculating EEMT directly from the mass flux precipitation and

the state variables of temperature and vapor pressure deficit, and provides a scale‐independent means for scaling EEMT from regional to pedon scales.



Fundamental Instrument Unit: Challenges for consistent, long‐term measurements

and

NEON’s Airborne Observation Package (AOP) system

Hank Loescher

NEON


Session 2 Keynote: Mon. May 9, 3:05 PM

Biogeochemical weathering of serpentine minerals from bedrock to soil

Elisabeth M. Hausrath1, Amanda A. Olsen2, Julie L. Baumeister1, Valerie Tu1, Eileen Yardley2

1Department of Geoscience, University of Nevada, Las Vegas, 4505 S Maryland Parkway, Las Vegas, NV

2 Department of Earth Sciences, University of Maine, 5790 Bryand Global Sciences Center, Orono, Maine, 04469

The chemistry of serpentinite rocks strongly controls the chemistry of the soils that form on them. These soils, termed serpentine soils, host unique biota that are significantly different from biota on different rock types in the same regions. The vegetation adapted to serpentine soils and the effect of such soils on the biota present has been extensively studied. However, fewer studies have examined the effect of these biological populations on weathering of serpentinites and formation of serpentine soils. Here we explore the effect of chemical weathering and biological interactions on serpentine minerals from bedrock to soil surface, analyzing both rock and soil profiles from the field, and laboratory experiments with and without organic acids. We are measuring rates of dissolution of serpentine minerals in the field and laboratory. We are also characterizing mobility of trace elements from serpentine minerals dissolved with and without organic acids in the laboratory, and from profiles within soils and the weathered rock beneath the soil surface.


Session 2: Mon. May 9, 3:40 pm

Elucidating the Interaction between Organic Matter and Mineral Components along a Pasture Hillslope: Importance of Iron‐Redox Coupling Processes

Chunmei Chen1*, Peter Leinweber2, A. Aufdenkampe3, D. L. Sparks1

1 University of Delaware, Delaware Environmental Institute, Newark, Delaware;

2 Institute for Land Use, University of Rostock, Rostock, Germany; 3 Stroud Water Research Center, Avondale, Pennsylvania

The association of organic matter (OM) with minerals is recognized as a major process for stabilizing organic matter and makes it to be less prone to microbial degradation. However, the specific mineral phases or the mechanisms responsible for the mineral stabilization of OM remain unclear. A number of studies have emphasized the importance of Fe oxides for carbon (C) sequestration due to their high surface area. Iron is susceptible to redox variability along a landscape gradient. Iron (III) oxides predominate at the top of upland hillslopes where soil is well‐drained, whereas they are subject to reductive dissolution at the base of hillslopes where soil is sometimes poorly drained. Dissolution of Fe minerals governs the amount, form and transport of sequestered C. Therefore it is important to understand C stabilization and sequestration impacted by Fe cycling under various redox environments. In this study, we focused on a pasture hillslope transect within the Christina River Basin Critical Zone Observatory (CRB‐CZO). Soil samples were collected from the A and B horizons at the top and the base of the hillsope. Soil clay fractions were obtained by centrifugation after ultrasonic dispersion. Pyrolysis Field Ionization Mass Spectrometry (Py‐FIMS) was used to identify organic matter composition in the clay fractions and bulk soils. The results show that C content is less at the base of the hillslope compared to the top of the hillslope, especially in the B‐horizon, which corresponds to the lower Fe oxide content and mineral specific surface area at the base of the hillslope. Py‐FIMS analysis also shows that in the A horizon, there is no significant difference in the composition of organic matter between the top and the bottom of the hillslope, while in the B‐horizon, samples from the base of the hillslope are enriched in phenols and lignin monomers as well as alkyl‐aromatics but depleted in lignin dimers and lipids compared to the top of the hillslope. Thermograms show that in the B‐horizon, carbohydrates, phenols and lignin monomers, lipids, sterols and peptides in the samples from the base of the hillslope were released at higher temperatures than the same classes from the samples from the top of the hillslope. This indicaties that OM is retained more tightly and thus has a higher thermal stability at base of the hillslope. These results indicate that reduction of Fe oxides under poorly drained conditions result in a loss of labile C and therefore selective accumulation of more stable C. To elucidate the specific mineral‐OM binding mechanisms, scanning transmission X‐ray microscopy‐C near edge X‐ray absorption fine structure spectroscopy (STXM‐CNEXAFS) was applied to map the major mineral elemental (Si, Al, Ca, Fe, K) composition and to determine the spatial distribution of carbon and carbon functional groups. This information is also critical to enhance our understanding of stabilization of OM on mineral surfaces. This study highlights the importance of Fe‐redox coupling processes in affecting the carbon cycle at soil/sediment‐water interfaces.



Water chemistry reflects hydrological controls on weathering in Susquehanna/Shale Hills Critical Zone Observatory (Central Pennsylvania, USA)

Lixin Jin*1, Danielle M. Andrews2, George H. Holmes3, Christopher J. Duffy3, Henry Lin2 and Susan L. Brantley1

1Center for Environmental Kinetics Analysis, Earth and Environmental Systems Institute,

Pennsylvania State University, University Park, PA 16802 2Department of Crop and Soil Sciences, Pennsylvania State University, University Park, PA 16802

3Department of Civil Engineering, Pennsylvania State University, University Park, PA 16802 *Corresponding author; current address: Department of Geological Sciences,

University of Texas at El Paso ([email protected])

In catchment studies, it has been observed that water chemistry and discharge vary independently. In such studies, controls on water chemistry are difficult to discern because only outlet chemistry is measured for first‐order streams. We address the conundrum of independent controls on chemistry and discharge by comparing chemistry of rainfall, soil porewaters, and streamwater at the Susquehanna/Shale Hills Critical Zone Observatory . Soil water solutes are predominantly contributed by clay dissolution kinetics. As such, solute concentrations are primarily controlled by the residence time of water in soil. Translocation and deposition of secondary clays have created B‐horizons that channelize flow laterally, limiting the extent of vertical flow along a steep planar hillslope. Consistent with soil moisture monitoring data, water flows out of the hillslope predominantly along lateral pathways defined by the A/B and B/C soil horizons . The lateral fluxes must be fed by subvertical pathways, here called macropores. Porewater chemistry is consistently more dilute at these interfaces and more concentrated in the intervening layers (the A and B horizons respectively) where mineral‐water contact time is much longer. The amplitude of seasonal variations in O and H isotopes decreases in the order, precipitation>> soil water > stream > groundwater, consistent with progressively older water as rainfall infiltrates the soil and eventually recharges to ground water. Interestingly, Mg concentrations increase with the residence time of the water due to increasing contact time with minerals (clay and ankerite). Stream water is a mixture of groundwater and shallow soil water where the relative proportions change seasonally. The discharge of the first‐order stream responds closely to precipitation, documenting the rapid release of both old groundwater and relatively young soil water during storms.



Integrated Study of Critical Zone Architecture, Near‐surface Hydrology, and Biogeochemistry to Understand the Fate of N in Montane Catchments

Eve‐Lyn S. Hinckley1, Rebecca T. Barnes2, Mark W. Williams 1,3,

and Suzanne P. Anderson 1,3

1Institute of Arctic and Alpine Research, 1560 30th St, Boulder, CO, 80309 2Department of Earth Science, Rice University, 6100 S. Main, Houston, TX, 77005

3Department of Geography, University of Colorado, Boulder, CO, 80309 Over a decade of research in the alpine zone of the Colorado Front Range has shown that nitrogen (N) deposition originating from low elevation, developed areas has changed ecosystem stoichiometry, microbial transformation rates, and aquatic community structure. Markedly less research has occurred in the montane zone, which sits at the current snow line and may be vulnerable both to climate change impacts on precipitation and temperature, as well as increased N loading. We conducted 15N‐nitrate and lithium bromide (LiBr) tracer studies during spring snowmelt – the major hydrologic event in this system – to determine the fate and transport of N in a forested montane catchment that is part of the Boulder Creek Critical Zone Observatory. At the onset of snowmelt, we applied the tracers to instrumented plots along a hillslope cross‐section, including crest, midslope, and toeslope positions, as well as north‐ and south‐facing aspects. Integrating hydrological theory with measurements of N species and tracers in soil, soil water, microbial biomass, and vegetation provided a means of determining residence time, export pathways, and biological uptake of deposited N. Tracers broke through immediately to 0.3 m depth on the north‐facing slope, where the seasonal snowpack was melting, and transported completely out of soil waters within 40 days. Additionally, 5% of the applied 15N was recovered in vegetation. On the south‐facing slope, which does not develop a snowpack, tracers were transported to depth only during spring storms, and approximately 22% of the 15N was recovered in vegetation. Tracer persisted in soil waters through the 54‐day observation period. These results suggest that N residence time is longer on the south‐ than the north‐facing slope, due to sporadic melt water transport, and biota that are adapted to respond rapidly to N availability in the spring. Our results lend insights that are important for understanding catchment‐scale timing of N transport to streams and the role of mid‐elevation forests in metabolizing deposited N within the larger landscape context, from alpine to plains.

Monday PM Posters: 2.1

CZO All‐hands Meeting ‐ Session 2: Subsurface Biogeochemistry

An analysis of the chemical character of dissolved organic matter and soluble soil organic matter within the same catchment

Rachel S Gabor, Diane M McKnight

Boulder Creek CZO

Trends of increasing dissolved organic matter (DOM) concentrations have been reported in many parts of the world. To better understand how organic matter is transported throughout and used within watersheds, it is important to measure not only how much there is, but to also its chemical character. In this study, spectroscopic techniques were used to analyze the DOM from Boulder Creek in Colorado, as well as the soluble organic matter in soil from a smaller catchment within the watershed. Samples from the creek were taken at regular intervals for several years and the DOM quantity and quality was analyzed to determine both seasonal impacts and the affect of Barker Dam halfway up the watershed. Observed trends followed similar patterns to that seen in other alpine ecosystems, with a peak in microbial DOM just before snowmelt, followed by increasing terrestrial input. However, the storage in the reservoir made the signal less clear below the dam. Soil organic matter samples were taken with an aim to observing both spatial and temporal patterns. A large number of both surface and deep samples were taken in one time snapshot, and surface samples were taken from the same plots over several months beginning during snowmelt and reaching the end of the growing season. Surface samples displayed a stronger correlation with DOM in the stream than samples taken at depth, indicating much of the DOM comes from overland flow. However, strong microbial signals from samples at depth indicated the possibility that microbes may be using OM as an electron acceptor during bedrock weathering processes. Little variation was shown temporally in surface samples, although there was some seen in the riparian zone during snowmelt.



Controls of Effective Energy and Mass Transfer (EEMT) on soil carbon and nitrogen pools and dissolved losses in the Jemez River Basin

Emily Charaska1, Kathleen Lohse12, Clare Stielstra3, Paul Brooks3, and Jon Chorover4

1Department of Geosciences, Idaho State University, Pocatello, ID 83209,

2Department of Biological Sciences, Idaho State University, Pocatello, ID 83209, 3Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721,

4Department of Soil Water and Environmental Sciences, University of Arizona, Tucson, AZ 85721 Dissolved carbon and nitrogen in soils can be a source of energy and nutrients to streams and other downstream ecosystems. A critical control on carbon and associated elemental fluxes is energy input, yet the relationship between energy input and carbon dynamics and storage is poorly understood. The overarching hypothesis of Jemez River Basin –Santa Catalina Mountain Critical Zone Observatory (JRB‐SCM CZO) is that variation in effective energy and mass transfer (EEMT), which is mass and energy balance described by the terms effective net primary production and effective precipitation, controls critical zone structure and function. To address how variability in energy input and related mass fluxes influences carbon and nitrogen pools and dissolved losses, we posed two hypotheses. First, the variability in EEMT will determine the quantity of soil carbon and nitrogen in the soil surface (0‐30 cm), which can do work on the subsurface through energy and mass transfer of dissolved forms. Second, differences in vegetation will affect the quantity and quality of carbon and nitrogen input and mass transfer via dissolved forms. We collected soils at twenty‐seven sites around Redondo Peak in the Valles Caldera, NM that varied in aspect and EEMT. Specifically, soils were collected to 30 cm depth from riparian and two hillslope positions from each of the 7 catchments with flumes around Redondo. From these soils, we obtained bulk density, gravimetric soil moisture, soil organic matter, exchangeable dissolved organic carbon and other elemental losses, and exchangeable nitrogen for organic surface and mineral soils. Water‐extractable carbon and other elements were determined by adding 40 g of 2mm sieved soil to 200 ml water, shaking them for 1 hour, and filtering them through 0.7 um filters for dissolved organic carbon (DOC) and nutrients and through 0.45 um nylon filters for metals. Exchangeable nitrogen was determined by 2N potassium chloride (KCl) extraction. Solid carbon and nitrogen were dried at 60 degree C, ground, and packed for mass and isotope analysis at Idaho State University. Dissolved carbon and nitrogen were analyzed on a Shimadzu TOC/TN, nutrients on a Smart Chem discrete analyzer, anions on a DIONEX ion chromatograph, and base cations and trace metals on a ICP MS. EEMT was weakly correlated with both solid soil and dissolved organic carbon and total nitrogen. The EEMT data is available in 10 meter pixels, which may be too coarse to show a strong correlation between exchange‐able carbon and nitrogen. Variance in soil carbon and nitrogen pools with respect to vegetation type was not observed. Anomalously high fluxes of DOC were observed in Lower and Upper Jaramillo and Upper Redondo mineral soils. Across sites, dissolved organic carbon losses, ammonium, nitrate and other weathering product were linked to carbon to nitrogen ratios; higher DOC and other elemental losses were observed below a C:N ratio of 22:1. DOC and total dissolved nitrogen (TDN) were also significantly correlated to sulfate. Preliminary results suggest that EEMT and vegetation type are not strong controls of dissolved fluxes of DOC and other elements; rather coupled carbon and nitrogen mineralization dynamics may drive transfer of energy and nutrients to the subsurface and streams.



TDR‐EC: A Rapid Subsurface Characterization of Particle Size & Hydrologic Properties

Christopher A. Jones1, and Marcel Schaap2

1Department of Hydrology and Water Resources University of Arizona 2Soil, Water, and Environmental Sciences, University of Arizona

Time‐domain reflectometry (TDR) is a geophysical tool used in the field and laboratory to collect data on soil moisture, bulk soil electric conductivity (EC) and salinity. To understand temporal and spatial soil dynamics in a zero order basin (ZOB), we employ this tool in a number of ways. A 700 meter transect in the Valles Caldera National Preserve was surveyed using TDR with the intention of characterizing the spatial distribution of soil properties. Data was collected a few weeks after the snowmelt, when the relationship between soil texture and moisture content is strongest, and we assumed to be at field capacity. Clay and sand fractions in the soil correlate with bulk soil EC, which provides us with an estimate of soil type. Using a pedo‐transfer function, we can then approximate saturated hydraulic conductivity and other hydraulic properties. How bulk soil EC and particle size relate was further examined by performing the same survey in two ZOBs of different parent material. Temporal characterization is achieved with the use of data from soil pits instrumented at several depths with sensors recording, water content, EC, temperature, and matric potential at 10 minute intervals. Preliminary results from HYDRUS 1‐D will guide us in determining whether or not a 2 or 3‐D model is necessary to characterize subsurface dynamics.



Primary mineral compositions of granitic rocks from the Santa Catalina Mountains, Arizona

Rebecca Lybrand and Craig Rasmussen

Department of Soil, Water and Environmental Science, The University of Arizona, Tucson, AZ 85721

Quantifying chemical weathering and mineral transformation is critical to understanding the interactive effects of physical erosion, climate, soil genesis, and chemical weathering processes on soil and landscape evolution. The main objective of this research was to quantify the elemental compositions of primary minerals from granitic rocks collected along an environmental gradient in southern Arizona. The research was conducted within the Santa Catalina Mountain Critical Zone Observatory (SCM‐CZO). There are climate‐associated shifts in vegetation across the gradient with significant ranges in mean annual precipitation (>50 cm yr‐1) and mean annual temperature (>10°C). Granitic rock samples were sampled from five distinct ecosystems ranging from desert scrub to mixed conifer. Electron microprobe analyses were used to determine the elemental compositions of primary minerals from representative rock samples. Specifically, silica, magnesium and iron percentages were used to characterize changes in mica type and composition among samples. Calcium, sodium and potassium measurements were used to differentiate end members of the feldspar continuum in rocks collected across the gradient. Mica type at the low elevation sites was predominately biotite; muscovite was dominant at the high elevation locations. The low elevation biotite contained an average of ~17% Si, ~8% Mg and ~12% Fe compared to the high elevation muscovite, which was composed of ~21% Si, ~0.5% Mg and ~4% Fe. Orthoclase and calcium/sodium‐rich plagioclase feldspars were the prominent feldspar end members at the low elevation sites while orthoclase and more sodium‐rich plagioclase were the dominant feldspars in rocks collected from high elevation sites. The elemental composition of several primary minerals changed across the SCM‐CZO environmental gradient, reflecting differences in rock composition and age of pluton intrusion. These data were combined with quantitative x‐ray diffraction (QXRD) and x‐ray fluorescence (XRF) data to better quantify primary and secondary mineralogical components in soils. These data are useful for constraining weathering processes related to initial mineralogical conditions in rocks and for formulating a better understanding of soil genesis processes in semiarid landscapes.



Monitoring Carbon Fluxes from Shallow Surface Soils in the Critical Zone

Clare M. Stielstra1, Paul D. Brooks1, and Jon Chorover2

1 Department of Hydrology and Water Resources, University of Arizona, Tucson, AZ 2Department of Soil, Water and Environmental Science, University of Arizona, Tucson, AZ

The critical zone (CZ) is the earth’s porous near‐surface layer, characterized by the integrated processes that occur from bedrock to the atmospheric boundary layer where water, atmosphere, ecosystems, and soils interact on a geomorphic and geologic template. We hypothesize that CZ systems organize and evolve in response to open system fluxes of energy and mass, including meteoric inputs of radiation, water, and carbon, which can be quantified at point to watershed scales. The goal of this study is to link above‐ground and below‐ground carbon processes by quantifying carbon fluxes from near surface soils as CO2 and dissolved organic carbon (DOC) across soil type, vegetation type and season. To do this we measure the amount of DOC present in surface soils, and install ion exchange resins at the A/B soil horizon interface to capture DOC leachate mobilized during snowmelt and summer rainfall. DOC leachate is then compared with DOC in stream water to infer the extent of subsurface processing that could include mineralization and/or stabilization in deeper soil horizons. Throughout the summer rain and spring snowmelt seasons we monitor soil respiration of CO2. The results of this study allow us to evaluate the variability of carbon fluxes with vegetation and soil type within a shallow soil carbon pool and help constrain the contributions of soil organic carbon to net carbon balance in CZO catchments with seasonal precipitation regimes.



Fractionation of DOM during Reactive Transport: Testing a Zonal Model of Organo‐Mineral Interactions

Angélica Vázquez‐Ortega, Selene Hernández‐Ruíz, Mary Kay Amistadi, Craig Rasmussen, and Jon Chorover

Soil, Water and Environmental Science, University of Arizona, Tucson, Arizona

Background: Sorptive retention of dissolved organic matter (DOM) at mineral surfaces is a key control on carbon flux through the critical zone. Improved understanding of the sorption process depends on better resolving the nature of organo‐mineral interfaces, including the impacts of mineral and DOM type. The goal of this study is to test a hypothetical “zonal” model of organo‐mineral interactions. The model assumes that the molecular structure of humic substances consists of small and chemically diverse organic molecules linked by hydrophobic, cation‐bridging, and hydrogen bond interactions which are capable of self‐organizing (pseudo‐micellar) behavior in aqueous solution and, therefore, at the mineral‐water interface. The zonal model postulates the distribution of sorbed DOM among three distinct zones: (i) mineral contact zone, intermediate hydrophobic zone, and peripheral kinetic zone. The hydrophobic zone is mainly characterized by hydrophobic interactions and moderate DOM exchange rate. Finally, the kinetic zone is characterized by cation bridging and hydrogen bonding interactions, further accumulation of OM, and a high DOM exchange rate. Al and Fe oxy‐hydroxide minerals have been implicated as particularly reactive surfaces in DOM stabilization.

Experimental: DOM solutions were extracted from organic horizons in (i) grass and (ii) mixed conifer forest vegetation types within the JRB. The extracted solutions were filtered and then used to sequentially irrigate glass chromatography columns packed with quartz sand (QS), Al‐hydroxide‐coated quartz sand (Al‐QS), and Fe‐hydroxide‐coated quartz sand (Fe‐QS). The reason for using two distinct sources of DOM was to investigate how oxy‐hydroxide mineral surfaces influence DOM uptake and fractionation from solution, and how these processes changed with progressive coating of mineral surfaces with DOM. To investigate the mobilization and fractionation of DOM during reactive transport, effluent solutions were characterized for DOC concentration, molar absorptivity, and fluorescence excitation‐emission spectroscopy.

Results: During the initial irrigation of fresh mineral media with grassland DOM (Phz 1), the magnitude of DOM sorption followed this trend Al‐QS > Fe‐QS > QS. An increase in pH, suggests ligand exchange as a possible mechanism for DOM adsorption to the hydroxylated mineral surfaces. Low molar absorptivity values were observed in effluent solutions of early pore volumes, indicating preferential surface retention of aromatic moieties. Compounds traditionally characterized by excitation‐emission matrix (EEM) spectroscopy as being more highly humified were favorably adsorbed onto the Al‐QS and Fe‐QS surfaces. Humification indices (HIX) were also correlated with DOM aromaticity. HIX results suggest that the presence of Al‐QS and Fe‐QS surfaces affect the preferential uptake of high molar mass constituents of DOM solutions during reactive transport. For Al‐QS and Fe‐QS treatments, regional fluorescence integration (RFI) ratios were low during the initial irrigation for region III and V, consistent with adsorption of humic and fulvic acid‐like compounds. At the end of phase 1, columns were dried for a period of seven days (Phz 2). Introduction of mixed conifer DOM (Phz 3) to grassland OM coated surfaces revealed competitive desorption of grassland‐derived OM from the organo‐mineral interface. Initial effluent solutions exhibit high DOC, low pH and intermediate molar absorptivity values. During all treatments, high HIX values were observed in effluent solutions suggesting the displacement and mobilization of grassland DOM via forest DOM displacement. Fluorescence emission and RFI ratios suggest that fulvic and humic acid‐like compounds are eluted from the organo‐mineral interface, providing some evidence for kinetic DOM exchange reactions.



Is mineral motion the ultimate control on critical zone carbon sequestration?

Anthony Aufdenkampe1, Kyungsoo Yoo2, Rolf Aalto3, Chunmei Chen4, Denis Newbold1, Diana Karwan1

1Stroud Water Research Center. http://www.stroudcenter.org

2Univ. of Minnesota, Dept. of Soil, Water and Climate. http://www.swac.umn.edu/ 3Univ. of Exeter, Geography. http://geography.exeter.ac.uk/

4Univ. of Delaware, College of Agriculture & Natural Resources. http://ag.udel.edu/ All ‐ Christina River Basin CZO. http://www.udel.edu/czo/

In the last decade, modeling and mechanistic studies of organic carbon (OC) turnover in soils and sediments have converged on one key finding – that organic matter (OM) complexation to fine minerals is a critical factor to stabilizing and sequestering carbon. However, OC production and mineral production are typically spatially separated. Biological primary production primarily occurs where there is light – above the soil surface or in the low‐turbidity euphotic zone of lakes and oceans. Mineral surface area (SA) is produced in the sapprolite, or bedrock‐soil interface, where primary minerals are chemically weathered to secondary silicate clays and Fe and Al hydroxides. This physical separation between fresh OC and fine minerals results in rapid turnover of most photosynthesized carbon in soil litter layers, and most fresh clay minerals remain carbon‐free due to limited contact. Likewise, OC mobilized into river corridors is in significant excess of the system’s capacity to stabilize it, with most OC being rapidly metabolized and returned to the atmosphere as CO2. We therefore hypothesize that the rate at which fresh minerals are delivered to and mix with fresh OC determines the rate of carbon preservation at a watershed scale. Although many studies have examined the role of erosion in carbon balances, none consider that fresh carbon and fresh minerals interact. Our hypothesis – that the rate of mixing fresh carbon with fresh minerals is a primary control on watershed‐scale carbon sequestration – is central to our Christina River Basin Critical Zone Observatory (CRB‐CZO) project in Pennsylvania and Delaware, entitled: “Spatial and temporal integration of carbon and mineral fluxes: a whole watershed approach to quantifying anthropogenic modification of critical zone carbon sequestration.” Here we present recent data from the CRB‐CZO that support our overall hypothesis.



Riparian nitrogen dynamics in a tropical rainforest catchment

R. L. Brereton and W. H. McDowell

Department of Natural Resources and the Environment, University of New Hampshire

In a first‐order catchment in the Luquillo CZO, riparian processes exert strong controls on N dynamics and cause decreased N flux from groundwater into streams. Previous studies in the upper Rio Icacos catchment have found upslope groundwater with 0.6‐0.8 mg N/L and stream water with 0.2 mg N/L, indicating significant N removal before groundwater reaches the stream. In upslope wells, NO3‐N dominates, while NH4 dominates in riparian wells. The mechanisms causing this pattern in N dynamics and ultimate N removal are not yet understood. We propose to explore several competing hypotheses explaining the observed pattern: 1) Denitrification accounts for the drawdown of NO3 from upslope to riparian wells. 2) Mineralization of DON accounts for the high riparian NH4 concentrations. 3) Dissimilatory nitrate reduction to ammonium (DNRA) converts upslope NO3 to NH4. 4) Coupled nitrification‐denitrification in the hyporheic zone accounts for the removal of NH4 across the riparian‐stream margin. Preliminary data from Hydrolab sondes and microelectrodes show high variability in oxygen and redox conditions over small temporal (days) and spatial (microns) scales, suggesting that competing redox processes can occur nearly simultaneously and in adjacent microenvironments. Characterization of 15N signatures of NO3, NH4, and DON in the various wells will allow us to differentiate N sources and N cycling pathways. We will also examine the spatial variation in weathering products across the riparian zone, as several of the solutes produced by weathering are redox‐sensitive and can play a role in altering the redox conditions that affect N transformations.



Controls on Soil Organic Carbon Storage in the Luquillo Critical Zone

Clark, J.D., Scatena F.N., Johnson A.H., Hao X, Leon M.

Department of Earth and Environmental Science, University of Pennsylvania

Luquillo Mountain soils were sampled in 216 quantitative soil pits from 24 sites during the summer of 2010 and winter of 2011. The 24 sites span an elevational and climatic gradient (342 ‐ 810 m) for the two main geologies (granodiorite and volcaniclastic rocks) and three major forest types (Palo Colorado, Tabonuco, and Palm). At each site, soil samples were collected by catena position (ridge, slope and valley) in triplicate. Differences were observed between bedrock types for bulk density and C concentration but not for C content. Soils derived from granodiorite have a higher bulk density but a lower C concentration than soils derived from volcaniclastic sandstone. Valley soils generally contain more C and N than slopes or ridges but these differences do not appear to be significant across forest types but are significant within a forest type. Multivariate regression tree analysis is being used to determine factors that best described the variability soils across the Luquillo Critical Zone Observatory. Initial results show that at the scale of the entire Luquillo Mountain, bedrock and climatic variables.



When wet gets wetter: soil moisture and decreased redox potential suppress greenhouse gas fluxes from a humid tropical forest soil

Steven J. Hall and Whendee L. Silver

University of California‐Berkeley, Department of Environmental Science, Policy, and Management

Climate change is likely to perturb rainfall patterns in the humid tropics, with uncertain consequences for biogeochemical processes that control soil greenhouse gas fluxes. We tested the hypothesis that increasingly intense rainfall events could affect greenhouse gas fluxes from an upland tropical forest soil by altering redox potential, using a field water addition experiment. We predicted that increased soil moisture would decrease soil‐atmosphere fluxes of carbon dioxide (CO2) and nitrous oxide (N2O) as oxygen became depleted and soils became increasingly reduced, while methane (CH4) fluxes would increase after more energetically favorable electron acceptors were depleted. At our Puerto Rican field site, we measured soil‐atmosphere fluxes of CO2, N2O, and CH4 from 18 replicate plots every 48 hours over a period of 25 days. We measured soil moisture and soil oxygen concentrations continuously and measured a broader suite of redox‐active species (nitrate, manganese (II), iron (II), and sulfate) in soil extractions every eight days. A subset of plots received daily water additions over 24 days, or fluctuating water addition over eight‐day intervals.

Our watering treatments generated dramatic variation in soil moisture among plots, which ranged between 30 – 60 % by volume over the course of the experiment. As predicted, fluxes of CO2 and N2O displayed a strongly significant negative relationship with soil moisture and soil oxygen concentrations after controlling for repeated sampling and temporal correlation using a mixed‐effects model. Concentrations of redox‐active species generally co‐varied according to thermodynamic predictions; oxygen, nitrate, and sulfate tended to decline while reduced iron and manganese increased with soil moisture, with an apparent non‐linear threshold response at > 55 % soil moisture. The first principal component of the correlation matrix of redox‐active species explained 50% of the total variance among these constituents. Using this principle component as an integrative multivariate measure of soil redox yielded significant relationships with CO2 and N2O fluxes, providing support for our hypothesis that redox potential provides an important influence on soil greenhouse gas fluxes. Several plots were consistent weak sources of CH4, but fluxes showed no relationships with moisture or redox. In sum, our data suggest that tropical wet forests could respond to increased rainfall with decreased global warming potential from fluxes of CO2 and N2O, in accordance with predicted thermodynamic constraints. Furthermore, large pools of alternative electron acceptors (especially iron) appear sufficient to constrain CH4 fluxes even over prolonged periods of elevated soil moisture.



The influence of rock type, forest community, and topographic position on soil phosphorus in the Luquillo Mountains of Puerto Rico

Stephen Porder, Steven Goldsmith, Susanna Mage

University of Pennsylvania

Soil phosphorus (P) availability is assumed to influence primary production and decomposition in many tropical forests, but the underlying controls of soil phosphorus status in these hyperdiverse ecosystems is still poorly understood. We explored the influence of parent material, forest community composition, and topographic position on total soil P concentrations and the loss of P relative to bedrock at the Luquillo LTER and CZO in Puerto Rico. We sampled soils six replicates of each combination of two parent materials (granodiorite and volcaniclastics), two forest types (Tabonuco and Colorado) and three topographic positions (ridge, midslope, valley). We also collected five samples of unweathered parent material for analysis of parent material composition.

Volcanclastic parent material had significantly higher P (535ppm) than did granodiorite (385ppm), leading us to hypothesize that soils atop these two parent materials would differ in their P status. As expected, total P differed significantly (p<0.0001) and by a factor of 2 between volcaniclastic‐derived and granodiorite‐derived soils. While valleys tended to have higher P concentrations than ridges, the increase was significant only at 0‐20cm depth, not from 0‐50cm. Nevertheless, these trends support the hypothesis that erosion can provide rejuvenation of rock‐derived material in tropical landscapes with highly weathered soils.

Depletion of soil P relative to parent material (τP) was calculated by indexing to niobium (Nb),

which was assumed to be immobile. τP did not differ between parent materials, which indicates that loss of P from these soils proceeds at a similar rate despite differences in mineralogy, other P‐binding elements such as iron and aluminum, and soil texture. However topographic

position had a significant (p<0.05) effect on τP,, valleys had less depletion than ridges, with slopes showing intermediate depletion. Colorado forests showed significantly (p<0.01) more P depletion than Tabonuco Forests, although forest type is correlated with elevation (and rainfall) and thus we cannot attribute this difference to forest community alone.



The role of microbial enzymes in mediating nutrient cycling in a montane tropical forest

Maddie Stone, Alain Plante, Art Johnson


Soil microbes produce extracellular enzymes that degrade a variety of carbon (C)‐containing polymers in soil organic matter. These enzymes are key regulators of the terrestrial C cycle and influence other major nutrient cycles such as nitrogen (N) and phosphorus (P). However, environmental factors that regulate soil enzyme activity are poorly understood, and tropical studies are particularly scarce.

We are investigating how microbial enzyme activity varies across dominant vegetation types at the Luquillo Critical Zone Observatory (LCZO) in Puerto Rico. Soils for this study were collected in the summer of 2010 from three catenas in neighboring Tabonuco and Colorado forests with similar soil properties and abiotic characteristics. This study focuses on two enzymes important for the C cycle (β‐glucosidase and polyphenol oxidase), one N‐releasing enzyme (leucine aminopeptidase), and one P‐releasing enzyme (acid phosphatase).

Maximal rates of acid‐phosphatase, β‐glucosidase and leucine aminopeptidase activity (Vmax) are being measured using fluorimetric assay techniques that have been widely applied to soils. A colorimetric technique is being used to assess maximal potential polyphenol oxidase activity under non substrate‐limiting conditions. We expect to find higher β‐glucosidase and polyphenol oxidase activities on catena ridges and valleys relative to slopes, reflecting the general trend of decreasing soil C content with increasing landscape slope. We also predict that β‐glucosidase and polyphenol oxidase activity will be higher in the Colorado forest relative to the Tabunuco forest, due to higher C:N ratios and thus greater microbial C‐limitation. Finally, we expect to see no significant differences in leucine aminopeptidase or acid phosphatase activity across catena positions or forest types since we have no evidence of significant changes in N or P availability across these sites.

Focusing on common C‐, N‐ and P‐releasing enzymes will improve our understanding of how nutrient availability differs between these forests. This knowledge will be useful in characterizing how decomposition and nutrient cycling change across the LCZO landscape. Ultimately we intend to develop a more complete picture of how microbial processes drive nutrient cycling in the critical zone, and how such processes are influenced by parent material, topography, climate and biology.



Redox cycling and Fe atom exchange at the Bisley Site in Luquillo Exp. Forest

Aaron Thompson1, Brian Ginn1, Viktor Tishchenko1, Christof Meile2, Michelle Scherer3, Jared Wilmoth1 and Tim Pasakamis3

1 Department of Crop and Soil Sciences, University of Georgia 2 Department of Marine Sciences, University of Georgia

3 Department of Civil and Environmental Engineering, University of Iowa

A quantitative understanding of the coupled cycling of Fe, C, and P in soil systems is necessary to understand broader ecological system performance. This is especially apparent in soils exposed to frequent shifts in redox status, which can substantially alter Fe cycling in the system. We examined the influence of dynamic redox conditions on soils collected from the Bisley Site of the Luquillo National Forest Critical Zone Observatory in Puerto Rico. We present three novel aspects of Fe cycling in these soils: (1) We paired selective chemical extractions with Mössbauer (MBS) characterization of the Fe solid phase material. We’ve found ca. 80% of the Fe is present in nanocrystalline forms (best approximated by nano‐goethite) with MBS quadrapole splitting values of ca. ‐0.14 mm s‐1 at 13 degrees Kelvin. The balance of the FeIII resides in silicate phases (~14%), with solid phase FeII split evenly between silicates (~3%) and an Fe‐rich mineral best approximated by illmenite (~3%). (2) We conducted eight‐week incubations of triplicate Bisley soil slurries subjected to oxic/anoxic oscillations at three frequencies, with and without phosphate additions: 3‐d anoxic/0.5 d oxic; 6‐d anoxic/1 d oxic; and 12‐d anoxic/2‐d oxic. HCl‐extractable FeII was reduced to less than 30 mmol kg‐1 during all oxic cycles and increased to >140 mmol kg‐1 during the later reducing cycles. Fe reduction rates were directly related to oscillation frequency; they were more rapid in the 3‐d oscillation treatments than the 6 and 12 d treatments. The net trajectory of Fe reduction increased similarly over the eight‐week experiment across all frequencies. (3) Finally, we have conducted the first Fe‐atom exchange experiments with soils or sediments by reacting isotopically labeled Fe2+(aq) (

57Fe enriched) in Bisley soil slurries. After 30‐days of reaction under sterile conditions, ~15% of the solid‐phase Fe atoms were exchanged with aqueous Fe atoms.



Shale weathering across a continental‐scale climate gradient

Ashlee Dere, Tim White and Susan L. Brantley

Pennsylvania State University

Both ecosystems and humans are dependent on soil for nutrient and water cycling as well as food, making the loss of soil a major issue facing humanity. However, the rate at which soil forms (replacing what is lost) is not well understood. To investigate rates of soil formation in various climates, a latitudinal climosequence of forested sites has been established in North America and Wales. All sites are underlain by an organic‐poor, iron‐rich (Silurian‐age) shale, providing a constant parent material from which soil is forming.

The climosequence is bounded by a cold/wet end member in Wales and a warm/wet end member in Puerto Rico; in between, temperature and rainfall increase as sites extend south through New York, Pennsylvania, Virginia, Tennessee and Alabama. Soil sampling and geochemical analyses, which provide a snapshot of shale weathering with depth, were completed similarly at all sites to allow direct comparisons and eventual modeling of the shale weathering processes. In addition, instrumentation deployed at each site gathers basic meteorology and soil moisture and temperature measurements providing present‐day climate data for each soil. Initial results show soil depth increases as a function of temperature but is not correlated with precipitation. Chemical depletion profiles of Mg, which approximate chlorite and illite dissolution, show deeper weathering fronts at warmer sites. Similarly, Na, a proxy for feldspar dissolution, shows greater depletion in warmer climates. Overall, data collected from soils across the transect will promote a better understanding of how climate changes and human activities impact soil formation rates.



North versus south: Implications from U‐series isotopes about regolith formation at the Susquehanna Shale Hills Critical Zone Observatory

Lin Ma1,2,3*, Francois Chabaux2, Lixin Jin1,3, and Susan Brantley1

1 Earth and Environmental Systems Institute, Pennsylvania State University,

University Park, Pennsylvania 16802, USA. 2 Laboratoire d'Hydrologie et de Geochimie de Strasbourg, EOST,

University of Strasbourg and CNRS, Strasbourg, France. 3 Department of Geological Sciences, University of Texas at El Paso, El Paso, TX 79968, USA.

* Corresponding author (email: [email protected]; phone: +1 (915) 747‐5218; fax: +1 (915) 747‐5073)

To investigate the role of topography on regolith formation, we measured U‐series isotopes on six regolith profiles developed on two slopes with contrasting aspect (north vs. south) at the Shale Hills catchment in central Pennsylvania. The regolith samples from the catchment display significant U‐series disequilibrium resulting from shale weathering processes. Furthermore, regolith production and shale weathering differ systematically between the two slopes: the regolith profiles on the sun‐facing slope are characterized by faster regolith production rates, shorter duration of chemical weathering, and lower extents of chemical depletion compared to the non‐sun‐facing slope. Aspect most likely exerts an important control on regolith formation at Shale Hills because it induces different microclimatic conditions that affect slope stability and erosion, setting different residence times for the weathering materials. Such an effect of aspect would be even more important at Shale Hills during the peri‐glacial period ~15 kyrs ago given that the two slopes were most likely under more significantly different microclimatic conditions. We also calculate changes in landform geometry and regolith thickness over time with a geomorphologic mass transport model for the Shale Hills catchment. The simulation results show that the current landscape and regolith thickness along the planar transect are not in a geomorphologic steady state. The landscape system is probably still responding to the last peri‐glacial perturbation that occurred at the catchment about 15 kyr ago. Only after ~200 kyr in the model simulation, does the geometry of the land surface approaches steady state. This study highlights the importance of both topographic and climate effects in influencing hill slope evolution and chemical weathering over the 104 ‐105 year timeframe. U‐series isotopes hence have great potential to serve as a geochronologic tool to quantify regolith formation rates and durations of chemical weathering.



Role of Fe‐ and Mn‐ Redox Coupling on the Carbon Cycle in a Mixed Land Use Watershed

O. Lazareva1*, D. L. Sparks1, A. Aufdenkampe2, K. Yoo3, S. Hicks2, J. Kan2

1 University of Delaware Environmental Institute, Newark, Delaware, 2 Stroud Water Research Center, Avondale, Pennsylvania, 3 University of Minnesota, St. Paul, Minnesota

A multitude of scientific publications have emphasized the importance of an organic carbon (C) ‐mineral complexation mechanism as a crucial factor in C stabilization and sequestration. Carbon‐mineral complexation is strongly controlled by mineral surface area, mineralogy, pH, redox, polyvalent cations, ionic strength, and the chemical composition of organic matter. These factors vary spatially as a function of geomorphologic, hydrologic, and microbiological processes. Soil horizons and sediments with abundant Fe and Mn oxides/hydroxides have high mineral surface area and thus a high capacity to complex C, reducing its susceptibility to microbial degradation. Additionally, both sediment and hydrological fluxes transport these minerals in both solid and dissolved phases (Fe can be hydrologically transported in its reduced state and then oxidized to iron oxides with high mineral surface area).

At the Christina River Basin‐Critical Zone Observatory (CRB‐CZO), we investigate how Fe‐ and Mn‐ redox coupling affects the C cycle under varying redox conditions across a wide range of landscape positions and uses, such as floodplain forest, upland forest and agriculture.

The proposed research questions include the following: (1) How do redox conditions in soils affect the transport of mineral surface area via the dissolved phase? (2) How deep and fast does oxygen penetrate through soils

under different land use types and landscape positions? (3) Does oxygen diffusion back into riparian soil/sediments facilitate complexation between C and newly‐precipitated Fe and Mn oxides in the pore water? (4) How do soil properties, such as composition, mineralogy, mineral surface area, as well as redox state, vary depending on different types of land use and topographic position? and (5) How do microbial communities within soils and pore and stream water respond to redox gradients and seasons, and what groups of bacteria interact extensively with the C cycling under these redox fluctuations?

This presentation will demonstrate some preliminary data from a number of state‐of‐the‐art in‐situ monitoring sensors, such as pressure transducers (stream/groundwater), soil moisture/temperature probes, gas probes (O2, CO2), and DO/temperature sensors, that have been installed within the White Clay Creek Watershed. In addition, we are conducting an extensive field sampling and analysis of soil cores, soil pore waters, stream water, and groundwater. The water samples are being analyzed for pH, temperature, DO, Fe2+ , conductivity, turbidity, TDS, DOC, TOC, NO3, C, N, major anions, major cations, and metals. Soils samples will be examined for total chemical composition, C%, C isotopes, and mineral surface area. Selected samples will be analyzed by XRD, SEM, EPR, Mossbauer Spectroscopy, and molecular analysis on microbial communities. Bench‐scale leaching experiments with in‐tact soil cores and X‐ray computed tomography are also planned along with geochemical reactive transport modeling using the field and laboratory data.



Controls of landuse and landscape position on dissolved organic carbon (DOC) and mineral complexation

W. Pan, S. Inamdar, D. Sparks, A. Aufdenkampe, and K. Yoo

Christina River CZO, Univ. of Delaware Recently, increasing evidence from studies indicates that sorptive protection of organic matter may be of particular importance to carbon stabilized and sequestered in soils. Since sorption is defined as the transfer of a solute from solution to a solid phase, a significant fraction of OM need to be passed through dissolved phase prior to sorption. This gives rise to the investigation of DOM sorption not only in the river system but also in soils. Our previous study indicates that both DOC quantity and quality (aromatic or humic nature) play a vital role in regulating C sorption. Land use influence the quantity and quality of organic matter introduced to soil as well as microbial DOM production and cycling. Meanwhile, research shows that DOM in well‐aerated upland locations is lower in concentration and is less humic/aromatic compared to that in the valley bottom wetland. Likewise, land use and landscape positions interact and shape DOC characteristics in the catchment and thus influence the carbon‐mineral complexation at the different locations in the watershed. While lots of previous laboratory studies have investigated DOC sorption on the minerals, very few in‐situ studies have been done to look at water‐ scale variation of redox potential and its impact on DOC‐mineral‐complexation. Here, we propose an overall hypothesis that DOC sorption on mineral surface is a function of landscape position and landuse. We will test this hypothesis with both laboratory and in‐situ approach. Sorption experiment will be carried out with DOC samples collected at the various landscape positions. The DOC characteristic and sorption isotherm will be compared under different redox conditions (oxygen rich vs. oxygen poor). Proposed fieldwork will be performed in the two first‐order watersheds – one forested and the other agricultural, both associated with Christina River Basin Critical Zone Observatory. Bags containing soils with known mineral surface area will be buried at various landscape positions. Real‐time sensors will be installed at those locations for redox potential, soil moisture and soil temperature. Zero‐tension and suction lysimeters will be installed at each sample location to collect DOC solution. After retrieved from field, bags will be examined for C‐content. Mineral surface area will be determined using N2 adsorption BET method. The contents of amorphous, crystalline, and organically‐complexed iron oxide pools will be determined by combining chemical extractions with ICP measurements. Humic and non‐humic DOC constituents will be characterized using innovative new spectrofluorometric methods. OM functional group will be determined through XAFS technique. We believe that the result from this study will further our understanding of the controls of landuse and landscape on DOC sorption/ stabilization and shed light on the spatial pattern of DOC‐complexation at watershed scale.



Soil Organic Matter Dynamics: Assessment of Abiotic and Biotic Factors Controlling Soil Organic Matter Complexation and Stabilization

with Mineral Surfaces

C. Rosier1, K. Yoo2 and A. Aufdenkampe3

1 Delaware Biotechnology Institute, University of Delaware, Newark, DE 2 University of Minnesota, Twin Cities, MN,

3 Stroud Water Research Center, Avondale, PA Approximately 2400 petagrams (Pg‐1015 g) of carbon are stored in the Earth’s soil as soil organic matter (SOM), representing two times the amount of carbon stored in the Earth’s vegetation and atmosphere combined. The dynamic nature of SOM significantly influences several essential ecosystem services including nutrient cycling, mitigation of soil erosion, and storage of atmospheric CO2. Studies suggest that SOM dynamics are complex, requiring understanding of both biological and chemical interactions between organic compounds and mineral soil constituents. However, studies aimed at investigating specific abiotic and biotic interactions that facilitate the complexation of SOM to mineral surfaces are mostly non‐existent. The aim of the current study is to determine the degree to which iron oxide concentrations and biological processing complex and stabilize SOM to mineral surfaces. We hypothesize that macro‐scale biological processing (i.e. mixing) in conjunction with increased iron oxide concentrations will significantly affect the complexation potential of organic matter to mineral surfaces. In order to address this hypothesis, we will conduct a series of laboratory soil incubation experiments using carbon amended B horizon soils with low and high iron oxide concentrations in the presence and absence of biological processing. The experimental design of our study will allow us to track the possible fate of soil carbon: (i) CO2 mineralization (modified Li‐COR), (ii) particulate organic matter (density fractionization), mineral surface complexed carbon (N2 adsorption BET method) and (iii) organism biomass. Additionally we will use Fourier transform infrared spectroscopy (FTIR) to determine iron oxide and microbial mediated changes to mineral surfaces. Results from our study will provide important insight into understanding the affect of soil chemistry and biology on SOM mineral complexation and stabilization. This knowledge will greatly improve our ability to model and predict SOM storage potential.



The NEON Cyberinfrastructure: Enabling continental‐scale ecological science

And

Data Products from NEON: Insights across ecoclimatic domains

Steve Berukoff

NEON


Session 3 Keynote: Wed. May 11, 8:35 am

Groundwater Surface Water Interactions: Historical Context and the Transit Time Distribution as a Unifying Theoretical Framework

D. Kip Solomon

University of Utah

Historically groundwater and surface systems were considered to be separate, especially from a water resources and legal point of view. Research regarding the interaction between groundwater and surface water has escalated in the past decade revealing complexities that also seem to grow exponentially with each new study. This presentation will explore the possibility of the transit time distribution (TTD) being the foundation of the CZO goal of “developing a unifying theoretical framework”. Rates of biogeochemical reactions, solute transport, and water resources, all depend on transit time, which might serve as a normalization factor. Experimental approaches to evaluating transit times include stream tracer tests, periodicity in stable isotopes, and groundwater dating, all of which are related to different absolute time scales. Many challenges remain unresolved for the direct measurement of the TTD, including the non‐linearity in the tracer concentration‐transit time transfer function. Modeling approaches include discharge (lumped parameter) models and stratigraphic models, both of which can be non‐unique singly, but may lead to relatively constrained results when used jointly. Some of the opportunities and challenges associated with developing a meaningful TTD will be illustrated using field results from Red Butte Canyon, Utah, the LaSelva Biological Reserve, Costa Rica, and the Southern Vienna Basin, Austria.


Session 3: Wed. May 11, 9:25 am

In Situ Measurements of Stream Water Organic Carbon, Nitrate, and Suspended Solids with a Submersible UV‐VIS Diode Array Spectrometer Probe

Louis A. Kaplan, Steven Hicks, Christine McLaughlin, J. Denis Newbold,

Anthony K. Aufdenkampe

Stroud Water Research Center Rapid in situ measurements of solutes and particles in stream water hold enormous potential to transform our understanding of biogeochemical dynamics in aquatic systems. We have deployed two UV‐VIS spectrophotometers (scan spectroanalysers) that collect absorbance values every 2 minutes to measure turbidity‐compensated spectra for dissolved species and suspended solids in White Clay Creek, a 3rd ‐ order stream within the Christina River Basin. One spectrophotometer is constructed with a quartz optical window and 35 mm path length and takes readings at 214 wavelengths with 2.5 nm resolution from 200 to 732.5 nm, and the other is constructed with a sapphire optical window and 5 mm path length and takes readings at 218 wavelengths with 2.5 nm resolution between 200 and 742.5 nm. With all in situ devices biofouling is a common problem and both instruments are equipped with cleaning valves that provide blasts of compressed air for automated removal of biofouling. The cleaning can be manually augmented with a brush. Fouling by metal oxides is not typically encountered or considered, but in this headwater stream with its proximity to groundwater sources and different redox conditions manganese oxide fouling poses a problem. Over a three week period that included 4 storms and several non‐storm days with diel patterns of fluctuating stream discharge associated with snow‐melt, both instruments were able to capture the dynamics of solute and suspended solid transport. However, the quartz window outperformed the sapphire window in resisting metal oxide fouling presumably because of the differences between the affinities of the Albased sapphire versus the Si‐based quartz for manganese. A comparison of the accuracy of the in situ measurements against laboratory‐based measurements showed reasonable agreement. We are working to improve this agreement and extend the in situ detection to other analytes by adjusting the calibration of the spectrophotometers with laboratory‐based data.


Session 3: Wed. May 11, 9:40 am

Soil Moisture and Tree Water Status Dynamics in Mixed‐Conifer Forest Southern Sierra Critical Zone Observatory, CA

Hartsough1, P., A. Malazian1, M. Meadows2, T. Kamai1, M. Kandelous1, E. Eumont1, K.

Roudneva1, R.C. Bales2, J.W. Hopmans 1

1Department of Land, Air and Water Resources, UC Davis 2Sierra Nevada Research Institute, UC Merced

As part of an effort to understand root‐water interactions in multi‐dimensional soil/vegetation systems, we instrumented a mature white fir (Abies concolor) and the surrounding root zone, to better characterize the water dynamics for a single tree. Recently a second tree, a Ponderosa pine (Pinus ponderosa) was instrumented, along a drier, exposed slope. The trees are located in a mixed‐conifer forest at an elevation of ~2000m in the Southern Sierra Critical Zone Observatory. The additional deployment of more than 250 sensors to measure temperature, volumetric water content, matric potential, and snow depth in the general area near these two trees complements trunk sap‐flow and canopy stem‐water‐potential measurements. We show the results of a multi‐year deployment of soil moisture sensors as critical integrators of hydrologic/ biotic interactions in a forested catchment. Uncertainty exists in the depth from which tree roots extract soil water, specifically related to the presence of underlying saprolite/ bedrock, and the role of deep moisture storage. To better characterize processes in the subsurface, we excavated the root system of a mature (> 60 years old) white fir, using compressed air to remove the soil surrounding the tree roots. This method left the roots intact and enabled quantification of root density with depth in addition to in situ root architecture. The roots were imaged using a Terrestrial LiDAR system to build a 3‐D model of root size and density relative to presence of soil horizons. LiDAR images allowed us to also determine tree root volume. The results from this experiment will be used in a computer modeling study to test assumptions about tree root water extraction.

Wednesday AM Posters: 3.1

CZO All‐hands Meeting ‐ Session 3: Ground and Surface Water Dynamics

Fluorescence characteristics and sources of dissolved organic matter for stream water during storm events and baseflow

Shreeram Inamdar1, Shatrughan Singh1, Delphis Levia1 and Myron Mitchell2

1 University of Delaware, Newark, DE 19716

2 SUNY‐ESF, Syracuse, NY 13210 The concentration and quality of dissolved organic matter (DOM) and their sources were studied for stream water during storm events and baseflow in a forested headwater (12 ha) catchment in the mid‐Atlantic, Piedmont region of the USA. A total of 27 storm events were evaluated over a three‐year period (2008‐ 10). DOM constituents were characterized using a suite of indices derived from UV absorbance and PARAFAC modeling of fluorescence excitation emission indices (EEMs). In addition to stream water, watershed sources that were analyzed include: rainfall, throughfall, litter leachate, soil water, seeps, hyporheic water, and riparian and deep groundwaters. Runoff sources and hydrologic flow paths for stream water during storm events and baseflow were identified using an end‐member mixing model (EMMA) and stable isotope data. DOM constituents and their sources differed dramatically between baseflow and storm‐event conditions. The aromatic and humic DOM constituents in stream water increased significantly during storm events and were attributed to the contributions from surficial sources such as throughfall, litter leachate and soil water. Groundwater sources (seeps, riparian and hyporheic groundwaters) contributed to a large fraction of the DOM constituents during baseflow and were responsible for the high % protein‐like fluorescence observed in baseflow. EMMA‐derived hydrologic flow paths were critical for explaining the within‐event patterns of DOM moieties. Summer events produced the highest concentrations for humic and aromatic DOM while the corresponding response for winter events was muted.



The hydropedograph: a toolbox for analyzing soil moisture time series data

Chris B Graham and Henry Lin

Department of Crop and Soil Science, Pennsylvania State University

Soil moisture content and matric potential have been measured at increasingly fine temporal resolution through in situ real‐time sensors. Methods for analyzing high frequency soil moisture time series have lagged behind those of stream hydrology, where hydrograph separation, recession analysis and other methods have allowed for meaningful analytical comparison between sites. Here we begin an effort to develop tools for analyzing soil moisture time series data in a consistent manner using a toolbox developed in Matlab. The hydropedograph toolbox includes modules that analyze temporal and spatial trends in soil moisture data, identify and classify preferential flow, develop moisture release curve and related parameters (based on collocated matric potential data), identify and quantify hydraulic redistribution from vegetation, quantify soil physical properties, and determine statistical properties of soil moisture time series. Here we present the hydropedograph toolbox and demonstrate its utility with data from the Shale Hills CZO. This toolbox will be beneficial to cross‐CZO studies.

Figure: Sample output from Module 1 of the hydropedograph toolbox.



Modeling Shale Hills catchment soil hydrology using distributed soil‐terrain properties

Chris B Graham, Henry Lin, Doug Baldwin

Department of Crop and Soil Science, Pennsylvania State University

Using the spatially dense network of long‐term soil moisture monitoring and physical surveys of the Shale Hills CZO, we have developed detailed maps of a number of soil properties, such as soil moisture, soil texture, soil thickness, and soil water retention parameters. Most catchment models assume some (if not all) of these parameters are constant across a catchment, or that mapped soil units can be described with discrete bulk parameters. Field measurements of soil moisture patterns, however, clearly demonstrate the influence of soil‐terrain physical heterogeneities on system response. Here we develop a low dimensional hydrological model of the Shale Hills catchment, and demonstrate the importance of spatially distributed soil parameters on soil moisture storage, stream discharge, lateral subsurface flow and deep percolation.

Figure: Soil moisture distribution from preliminary runs of modeled Shale Hills Catchment



Laboratory, Field and Modeling Analysis of Solute Transport Behavior at the Shale Hills Critical Zone Observatory

Brad W. Kuntz1, Shira Rubin2, Brian Berkowitz2, Kamini Singha1, Laura Toran3

1 Penn State University; 2 Weizmann Institute of Science; 3 Temple University

We collected and analyzed breakthrough curve (BTC) data to identify the parameters controlling transport from a series of undisturbed fully saturated soil cores and a field test at the Shale Hills Critical Zone Observatory in central Pennsylvania. The soil cores were collected in a continuous hole extending across the soil profile vertically at one location to quantify how solute transport behavior changes with physical and chemical weathering. Additionally, we performed a field scale doublet tracer test to determine transport behavior within the weathered shale bedrock. Hydraulic conductivity and porosity are as low as 1e‐15 m/s and 0.035, respectively, in the shale bedrock and range as high as 1e‐5 m/s and 0.45, respectively, in the shallow soils. Bromide BTCs demonstrated significant anomalous tailing in soil cores and shale bedrock, which do not fit classical advection‐dispersion model equations. To quantify the behavior, numerical simulation of solute transport was carried out with both a mobile‐immobile (MIM) model and a continuous‐time random walk (CTRW) approach. MIM 1D modeling results on the soil cores yielded low mass transfer rates (<1/d) coupled with large immobile domains (immobile to mobile porosity ratios of 1.5‐2) and revealed that solutes were transported within only 30‐40% of the total pore space. MIM modeling results also suggested that immobile porosity is a combination of soil texture, fracture spacing, and porosity development on shale fragments. Similarly, the field scale doublet tracer test between boreholes indicated fractures are controlling transport and the surrounding shale matrix has a large potential to store and retard solute movement. CTRW modeling in 1D yielded a parameter set indicative of a transport regime that is consistently non‐Fickian across the vertical length of the soil profile, identified solute tracer velocities are up to 50 times greater than the average fluid velocity, predicted that anomalous transport behavior could extend for significant periods of time, and identified the need to incorporate a continuum of mass transfer rates to accurately predict and describe the observed tailing behavior. These modeling results confirmed the important role of preferential flow paths, fractures, and mass transfer between more‐ and less‐mobile fluid domains, and established the need to incorporate a mass transfer process that utilizes a distribution of mass transfer rates.



Simulation of hyporheic exchange flow by a physically‐based model at the

Susquehanna/Shale Hills Observatory (SSHO)

Xuan Yu, Christopher Duffy, Gopal Bhatt

Civil & Environmental Engineering, The Pennsylvania State University Diel variations in shallow groundwater table and stream discharge have been recognized by ecologists and hydrologists as a result of evapotranspiration (ET) from riparian vegetation. To better understanding the detailed processes of ET‐caused diel fluctuations in groundwater table and streamflow, researchers are formalizing models to explain the groundwater elevation and discharge. In this study, we use a physical based model ‐‐‐ the Penn State Integrated Hydrologic Modeling System (PIHM) to understand the process of the ecosystem exchange. The model captured hyporheic exchange flow between stream and the hyporheic zone and diel variation of groundwater table. The observed diel signal in discharge was not well predicted in the model, likely due to errors in estimated bed roughness parameters. Since the diel signals in groundwater table and discharge rate are cause by diel weather data fluctuation, we test impacts of different temporal resolution weather data on hyporheic exchange flow by the model. Using hourly weather data in the model for hyporheic exchange proved to be insufficient to capture both the groundwater level and streamflow diel response. The spatial and temporal pattern of gaining and losing reaches at the SSHO were found to be complex, although insufficient observations were available to test the validity of the models. The initial modeling results suggest that 10‐15 minute weather, soil water and groundwater data distributed along the channel are necessary to resolve diel relationships in the hyporeic zone at the SSHO. Improved simulation of hyporheic exchange flow should be constrained by high‐resolution observation of hydrologic variables and further calibration of the model. This experiment is currently being installed at the SSHO.



Evidence of Subsurface Lateral Flow in the Shale Hills CZO As Revealed by Real‐Time Soil Moisture Monitoring

Jun Zhang and Henry Lin

Dept. of Crop and Soil Science, Pennsylvania State Univ., University Park, PA

Subsurface lateral flow has been observed to contribute substantially to hillslope and catchment runoff. Understanding the occurrence and intensity of subsurface lateral flow is fundamental to conceptualize subsurface water flow and contaminant transport. In this study, we monitored real‐time soil moisture dynamics in different locations and at different depths along a concave hillslope in the Shale Hills CZO to investigate the significance of subsurface lateral flow. By comparing the storage increase at each horizon and total storage increase at each site with rainfall, we identified both strong and weak evidence of subsurface lateral flow. The results indicated a threshold behavior between the rainfall and total storage increase and this threshold value increased from wet season of 3.1‐5.0 mm to dry season of 5.5 ‐7.9 mm, suggesting the effect of initial soil condition on the lateral flow. The results also indicated that the shoulder slope site and the valley floor site had higher frequency of strong subsurface lateral flow occurrence (12.3% and 11.5%, respectively) than other sites along the same hillslope. This was likely due to the steep slope and relative deep soil in the shoulder slope site and large contributing area in the valley floor site. In addition, we found that the layers where subsurface lateral flow most likely to occur varied among different hillslope sites, which were linked to different soil types and hillslope locations. This study provided an improved understanding of the spatial and temporal pattern of subsurface lateral flow in the forested catchment and can improve process‐based hydrological modeling in the Critical Zone.



Soil moisture response to snowmelt and rainfall in a Sierra Nevada mixed‐conifer forest

Roger Balesa, Jan Hopmansb, Anthony O’Geenb, Matthew Meadowsa, Peter Hartsoughb,

Peter Kirchnera, Carolyn T. Hunsakerc, Dylan Beaudetted

aSierra Nevada Research Institute, UC Merced; bDept. Land, Air and Water Resources, UC Davis;

cUSFS Pacific Southwest Research Station, Fresno, CA; dSoils and Biogeochemistry Graduate Group, UC Davis

Co‐located, continuous snow‐depth and soil‐moisture measurements were deployed at two elevations in the rain‐snow transition region of a mixed‐conifer forest in the Southern Sierra Nevada. At each elevation sensors were placed in the open, under the canopy, and at the drip edge on both north‐ and south‐facing slopes. Snow sensors were placed at 27 locations, with soil moisture and temperature sensors placed at depths of 10, 30, 60 and 90 cm beneath the snow sensor; in some locations depth of placement was limited by boulders or bedrock. Soils are weakly developed (Inceptisols and Entisols) formed from decomposed granite with properties that change with elevation. The soil‐bedrock interface is hard in upper reaches of the basin (> 2000 m) where glaciers have scoured the parent material approximately 18,000 yrs ago. Below an elevation of 2000 m soils have a paralithic contact (weathered saprolite) that can extend beyond a depth of 1.5‐m facilitating pathways for deep percolation. Soils are wet and not frozen in winter, and dry out in weeks following spring snowmelt and rain. Based on data from two snowmelt seasons, it was found that soils dry out following snowmelt at relatively uniform rates; however the timing of drying at a given site may be offset by up to four weeks owing to heterogeneity in snowmelt at different elevations and aspects. Spring and summer rainfall mainly affected sites in the open, with drying after a rain event being faster than following snowmelt. The drying responses of soil moisture at depths of 30 and 60 cm were similar and generally systematic; with drying responses at 10 cm affected by the groundcover and litter layer. Responses at both 60 and 90 cm showed evidence of low‐porosity saprolite and short circuiting at some locations. Water loss rates of 0.5‐1.0 cm d‐1 during the winter and snowmelt season reflect a combination of evapotranspiration and deep drainage, as stream baseflow remain relatively low. We speculate that much of the deep drainage is stored locally in the deeper regolith during period of high precipitation, being available for tree transpiration during summer and fall months when shallow soil‐water storage is limiting.



Topographic Influences on Mountain Hydrology under Different Climatic Conditions

Patrick D. Broxton, Peter A. Troch, Paul D. Brooks

Department of Hydrology and Water Resources, University of Arizona

Climate change has the potential to greatly influence hydrologic systems in hydroclimatically sensitive regions, such as in mountainous areas in the southwestern United States. Furthermore, different portions of the landscape have different responses to such changes because of variations in the way in which water gets partitioned. In this study, we use a distributed energy balance snow model coupled and a distributed root zone water balance model along with spatial and hydrometeorologic data from the Valles Caldera, New Mexico, USA to try to infer how changes in temperature and precipitation might influence the region’s water budget. We pay particular attention to different responses on adjacent landscape units with different elevations and slope characteristics (aspect and gradient). Our modeling results suggest that the higher elevations in the Valles Caldera experience energy limited conditions, while lower elevations experience water limited conditions. These efforts are not only helping us to understand the topographic controls on the water balance of the Valles Caldera, but they provide insight about how energy and water limited ecosystems may respond differently to a changing climate.



Geochemical Modeling of Snowmelt in Alpine and Subalpine Catchments in the Southwestern USA

Jessica M. Driscoll1, Thomas Meixner1, Noah P. Molotch2, James O. Sickman3, Mark W.

Williams2, Jennifer C. McIntosh1, Paul D. Brooks1

1University of Arizona, Department of Hydrology and Water Resources; 2Colorado University at Boulder, INSTAAR; 3University of California at Riverside, Department of Environmental Sciences Snowmelt from alpine catchments provides 70‐80% of water resources to the American Southwest. Climate change threatens to alter the timing and duration of snowmelt in high elevation catchments. Variation in snowmelt dynamics threatens the quantity and the quality of these water resources. Modeling of these systems provides a robust theoretical framework to process the information extracted from the sparse physical measurement available in these sites due to their remote nature. A suite of hydrogeochemcial models will be applied to three catchments in the Southwest (see map) for relatively wet and dry snow years for each catchment. The spatial distribution of these catchments provides both continental and coastal snowmelt regimes, and by applying our geochemical models on both wet and dry snowmelt years we can determine how hydrochemical connectivity might vary as snowpack properties vary in response to climate change. The study areas chosen for this study are all felsic igneous geologic terrains; two intrusive and one extrusive. The geochemical models to be applied to these sites are a) inverse geochemical reaction path model (RPM) via PHREEQC, a model developed by the United States Geologic Survey (Parkhurst et al., 1991) and b) the alpine hydrochemical model (AHM) developed at the University of Arizona (Wolford et al., 1992). These models, run for both wet and dry snowmelt scenarios, will both have inputs of hydrochemistry samples of snowpack, precipitation and spatially distributed surface waters within the catchment from selected snowmelt seasons. In addition, the RPM will also use the available mineralogy and mineral weathering reactions and the AHM will also use land surface properties and the results of a spatially‐distributed snowmelt model. These models will be used to address our research questions: How does geochemical connectivity change between wet and dry years and with geography? Which mineral weathering connections are dominant during each of the modeled scenarios? What conclusions can be made from the geochemical modeling results about the hydrologic structure of a watershed? Preliminary RPM results for Green Lakes Valley show increases in connectivity early during the snowmelt season for the wet year and late in the season during the dry year, while dominant weathering reactions are consistent at this site across the years. The independently derived snowmelt model shows that the periods of increased surface water connectivity are concurrent with increased spatially‐distributed melt. Further modeling efforts will provide measurement of change in water quality of these water resources in alpine ecosystems due to climate change.



The Catchment Master Time Distributions: New tools to describe hydrologic catchment response

Ingo Heidbuechel, Peter A. Troch

Department of Hydrology and Water Resources, University of Arizona

Most biological and geochemical processes in a catchment are coupled to water fluxes. Carbon production and mineral weathering, for example, are strongly dependent on water availability. Since they form also the basis of soil genesis, they in turn influence hydraulic properties and water storage. This cycle of mutual dependence and control is an inherent feature of a dynamic system that defines how a catchment reacts when it is forced by precipitation events. Because of this close interdependence between water fluxes and biological and geochemical processes, tracking variations in catchment water transit times produces valuable information that can help to understand and quantify many of the dynamic processes that are emerging, taking place or ceasing within a catchment.

Theoretically, there are two aspects of catchment‐scale hydrologic response that need to be considered. First, the pressure wave response deriving from an impulse of precipitation and secondly the particle wave response from the same impulse. The pressure wave response is generally faster than the particle wave because the water molecules do not need to transit through the whole catchment in order to create a physical response in the stream, such as a quick flooding event. The particle wave on the other side moves slower but defines the stream chemistry and governs the release of pollutants or weathering solutes. In order to determine the variable mean reaction time (mRT) of the pressure wave the amount of discharge at the outlet can be deconvolved into a sequence of impulse responses derived from the application of a specific (linear or non‐linear) impulse response function (IRF) to every single precipitation input amount. In doing so, each IRF can be considered an independent reaction time distribution (RTD) resulting from individual precipitation events. We track variable mRT by moving a window over the time series and fitting the best mRT for each of the windows. Since the exact shape of each individual RTD is unknown (as it depends on both internal and external catchment properties), we start out by tracking only one important descriptor of the RTD, its mRT, while leaving other parameters constant. The MRTD is created by superimposing all individual (input‐weighted) RTDs. Once the variable RTD is known, we can turn to the particle wave and its characteristic time scales, the mean transit time (mTT). The mTT is often considered to be stationary and no generally applicable method exists that allows for the tracking of temporal variations of mTT, especially in catchments with large temporal variability in terrestrial water storage. We present a novel method to estimate varying mTT from stable isotope measurements. The approach is based on the principle that water leaving the catchment is a mixture of water with different transit times that entered the catchment at different locations. Therefore its final isotopic composition can be described by means of an IRF that lags and disperses the input impulse in time (creating slow and quick components). Time series of δ2H in precipitation and stream water were recorded over a period of three years in a small semi‐arid catchment in the Santa Catalina Mountains near Tucson, AZ (USA). The isotopic signature of the streamflow within a moving window is reproduced with an advection‐dispersion IRF that uses the δ2H time series of precipitation as input. The model is calibrated for each time step by adjusting the mTT of the IRF. The resulting time series of mTTs defines a specific TTD for each time step of the modeling period. With this information, a characteristic master transit time distribution (MTTD) is produced.



Sources and cycling of dissolved carbon in stream waters: insights from semi‐arid, seasonally snow‐covered CZO catchments in the Valles Caldera, NM

Julia Perdrial1, Paul Brooks2, Jon Chorover1, Adrian Harpold2, Ingo Heidbuechel2, Jennifer

McIntosh2, James Ray3, Xavier Zapata‐Rios2

1University of Arizona, Soil, Water, and Environmental Science, Tucson, AZ, 2University of Arizona, Hydrology and Water Resources, Tucson, AZ, 3University of Puget Sound, Department of Geology, Tacoma, WA

Seasonally snow‐covered mountain catchments are an area of active carbon (C) cycling and stream water carbon is a direct result of cycling but also different water and C sources. While melt waters dominate during snowmelt, groundwater dominates during most of the rest of the year. To study C sources and cycling, five flumed streams at catchment outlets located around Redondo peak in the Jemez River Basin (JRB) CZO were sampled 10 times over the water year 2010 and analyzed for total dissolved organic and inorganic carbon (DOC and DIC), DOC quality and stable isotopes of DIC. For all catchments, stream water DOC showed a flushing pattern with highest concentrations during peak snowmelt and low concentration during dry season. SUVA 254 confirms the more aromatic character of organic matter (OM) indicating mobilized organic soil constituents of lignin based precursors. DIC in contrast shows a dilution pattern during snowmelt and highest concentrations in the dry season, which may indicate that DIC is dominantly derived from groundwater inputs. Carbon isotope analysis of DIC (δ13C‐DIC) shows a general trend of progressively increasing values since snow melt suggesting longer residence times consistent with increasing amounts of ground water input. Additionally, two distinct end member patterns are discernable where one is characterized by a linear increase in δ13C‐DIC values with no response to snowmelt or dry season (SE side of Redondo peak). The other end member pattern reveals pronounced intra annual variation in δ13C‐DIC values for the diametrically opposed catchment at the NW side of Redondo. Dominant features in this latter case are the very enriched values during the dry season (maxima of ‐2.3‰) which may indicate a delayed release of old ground water that is being pushed out during snowmelt induced recharge. Preliminary results of OM PARAFAC quantification additionally suggests that stream water OM is not only soil derived but also a function of dominant water sources. While a component with fluorescence in Region II follows the flushing pattern (soil derived) another component with fluorescence in region I follows the δ13C‐DIC evolution, consistent with dominantly GW origin.



Determining solute inputs to soil and stream waters in a seasonally snow‐covered mountain catchment in northern New Mexico: multi‐tracer approach

Courtney Porter, J. McIntosh, T. Meixner, J. Chorover, C. Rasmussen, P. Brooks, and J. Perdrial

Department of Hydrology and Water Resources, The University of Arizona

The critical zone is the environment near the Earth’s surface in which biological, chemical, and physical processes interact and contribute to the evolution and structure of life on Earth. Mineral dissolution is an important process in the critical zone that supplies essential nutrients, such as Ca, to the biotic foundation of ecosystems. These nutrients improve tree growth and freeze tolerance, while preventing forest dieback, drought, and disease. Stream and soil waters play an important role in the availability and supply of these elements to the ecosystem. This study aims to determine the influence of mineral weathering on stream and soil water composition in a seasonally snow‐covered headwater catchment in the Jemez Mountains in northern New Mexico by using a multi‐tracer approach including major cations, strontium isotopes, rare earth elements, and trace metals. Likely inputs of solutes to stream waters include snowmelt, atmospheric wet and dry deposition, and groundwater and soil waters influenced by mineral weathering. Preliminary results show that groundwater dominates the stream water composition in La Jara Creek from June‐March, following the snowmelt period. An increase in base cation concentrations is observed compared to snowmelt discharge, suggesting contributions from mineral weathering along subsurface flowpaths. Stream waters are enriched in Ca, relative to Na, Mg, and Sr, which may be indicative of plagioclase or calcite weathering.



Sources of Streamflow in Small Semi‐Arid Catchments during Snowmelt and Summer Monsoons

Xavier Zapata‐Rios, Jennifer McIntosh, Peter Troch, Adrian Harpold, Paul Brooks, Julia Perdrial

Department of Hydrology and Water Resources, The University of Arizona, Tucson, AZ

Snowmelt is the most important contributor of water in the semiarid mountain catchments of the western U.S. Recent research has shown that western mountain snow packs are declining, precipitation is shifting to more rain instead of snow, and the major pulses of snowmelt and peak streamflow are occurring earlier. In this context of changing amounts, timing and forms of precipitation there is a need for better understanding of hydrological processes in semi‐arid regions. The availability of water and variability of water chemistry in the landscape could be better understood by studying the mechanisms of streamflow generation. Therefore this study aims to identify the different water sources contributing to streamflow generation in several mountain catchments around Redondo Peak located in the Jemez Mountains, NM during the year 2010. In addition to data gathered in the region from previous research, monthly isotopic and chemistry data from surface water and springs have been collected since September 2009 as part of the Critical Zone Observatory (CZO). Seasonal differences in water sources are quantified using stable water isotopes and solutes applying end member mixing models.



Characterization and Source Determination of Stream Suspended Particulate Material in White Clay Creek, USA

Diana Karwan, Rolf Aalto, James Pizzuto, Anthony Aufdenkampe, Denis Newbold, Jinjun Kan

The University of Pennsylvania

The material exported from a watershed reflects its origin and the processes it undergoes during downhill and downstream transport. Due to its nature as a complex mixture of material, the composition of suspended particulate material (SPM) integrates the physical, biological, and chemical processes effecting watershed material. In this study, we integrate sediment fingerprint analyses common in geomorphological studies of mineral SPM with biological and ecological characterizations of particulate organic carbon. Through this combination, we produce quantifiable budgets of particulate organic carbon and mineral material, as well as integrate our calculations of carbon and mineral cycling in a complex, human‐influenced watershed. More specifically, we (1) quantify the composition and sources of SPM in the White Clay Creek Watershed, (2) examine longitudinal trends in SPM composition and source in first to fourth reaches of the White Clay Creek, and (3) quantify the differences in composition and source with hydrologic variations produced by storms and seasonality. SPM is isolated from the streamwater using a continuous flow centrifuge and analyzed for several components, including particle size, mineral surface area, total mineral elemental composition, fallout radio isotope activity for common erosion tracers (7Be, 210Pb, 137Cs), organic carbon and nitrogen content with stable isotope (13C, 15N) abundance, organic matter lability and pigment content, microbial community analysis, and Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy. Potential sources are collected from the watershed landscape in surface material samples and cores down to approximately 2 m depth stratified by land cover and hillslope position. Exposed streambank surfaces as well as other likely sources of erosion (e.g. road material, gully and ditch walls, recreational trails, etc.) are also collected. All potential sources will be analyzed for the same chemical fingerprints as SPM and fingerprint data will be used in an end member analysis to evaluate SPM source. Through a combination of sediment fingerprint analyses common in geomorphological studies of mineral sediment with biological and ecological characterizations of particulate organic carbon, we will be able to integrate our calculations of carbon and mineral cycling in a complex, human‐influenced watershed. This interdisciplinary project will be conducted as one of many studies in the Christina River Basin Critical Zone Observatory (CZO) and will directly contribute to the overall research focus of this CZO: to quantify the net carbon sink or source due to mineral production, weathering, erosion and deposition as materials are transported and transformed across geophysical boundaries within a dynamic watershed.



Long‐Term Patterns and Short‐Term Dynamics of Stream Solutes and Suspended Sediment in a Rapidly Weathering Tropical Watershed

James B. Shanley, U.S. Geological Survey, Montpelier, VT 05601, [email protected]

William H. McDowell, University of New Hampshire, Durham, NH 03824,

[email protected]

Robert F. Stallard, U.S. Geological Survey, Boulder, CO 80303, [email protected]

The 326‐ha Rio Icacos watershed in the tropical wet forest of the Luquillo Mountains, northeastern Puerto Rico, is underlain by granodiorite bedrock with weathering rates among the highest in the world. We pooled stream chemistry and suspended sediment datasets from three discrete periods: 1983‐87; 1991‐97; and 2000‐08. During this period three major hurricanes crossed the site; Hugo in 1989, Hortense in 1996, and Georges in 1998. This mountainous landscape is also subject to frequent disturbance by landslides. Stream major ion chemistry reflects sea salt inputs (Na, Cl, SO4), and high weathering rates of the granodiorite (Ca, Mg, Si, alkalinity). During rainfall, stream composition shifts toward that of precipitation, diluting 90% or more in the largest storms, but maintains a biogeochemical watershed signal marked by elevated K and DOC concentration. DOC exhibits an unusual ”boomerang” pattern, initially increasing with flow but then decreasing at the highest flows as it becomes depleted, and/or vigorous overland flow minimizes contact with watershed surfaces. The relations of total suspended sediment and most solute concentrations with stream discharge were stable through time, suggesting minimal long‐term effects from repeated hurricane disturbance. The exception was nitrate, which increased from near 5 µeq L‐1 during the 1983‐87 period to greater than 12 µeq L‐1 and remained elevated for up to several years following hurricanes. The combined datasets provide insight about important hydrologic pathways, a long‐term perspective to assess response to hurricanes, and a framework to evaluate future climate change in tropical ecosystems.


Session 4: Wed. May 11, 3:40 pm

Controls and feedbacks of particle size and mobility: bringing down mountains one grain at a time

Douglas Jerolmack

Luquillo CZO Researchers have long posited a link between precipitation and landscape denudation, however the relationship is not straight forward. Recent global compilations of data seem to suggest that climatic variability enhances denudation rates over geologic timescales, but a reasonable mechanism has not been advanced. A major effort of our LCZO work is to determine how high intensity, short duration precipitation events move sediment and drive landscape denudation. Do large storms produce pulses of sediment that migrate through watersheds, or does sediment storage and transport within streams “buffer” these inputs? Is sediment mobility enhanced in a stormy environment, or does channel slope and geometry adjust to accommodate these large floods such that there is little net effect on denudation? To address these questions, we are tracking the movement of hundreds of individual cobbles and boulders in two watersheds using Radio Frequency Identifiers (RFIDs). Precipitation and stream gages provide high‐resolution hydrologic data about storm events, while stream channel morphology and grain size distributions provide necessary data for characterizing hydraulic conditions. Tracking the migration of tagged “radio rocks” through several years of floods will allow us to determine (1) the conditions for initiation of grain motion in these coarse‐grained streams, (2) annual rates of bedload transport and (3) dispersion of grains as a result of hydrodynamic and granular impulses. By directly studying how flood signals drive sediment movement, we can begin to address how climate signals propagate through landscapes and influence their evolution. A major variable determining mobility of sediment is grain size. The dominant view in geomorphology is that grain‐size selective transport is the principal driver of downstream fining observed along river profiles. Abrasion and fracturing of grains can occur due to energetic collisions during fluvial transport; many studies assume however, without justification, that these effects are secondary in terms of controlling grain size distribution. This view implies that the grain size population of a given river is inherited from hillslopes due to chemical and physical weathering there. We are undertaking a combined field, laboratory and theoretical approach to understand how sediment lithology, grain shape and collision energy control the rates of abrasion and the size of particles produced during bed load transport. Field studies are using imaging techniques to rapidly collect data on grain size distributions and shapes along streams draining two very different lithologies: volcaniclastics and granodiorites. Experiments are exploring the kinetic energy exchange, rock deformation and damage resulting from binary collisions of river rocks, and will be used to inform a refined model of abrasion that will be used to interpret field data. The relationships between grain mobility and abrasion present the possibility for a fascinating but little explored feedback: the frequency and magnitude of bed load transport should strongly control abrasion rate, while continued abrasion changes the mobility of particles by altering grain size and shape. Exploring this feedback will allow a better understanding of the ultimate controls on landscape denudation and the rate of evolution of the critical zone.



Spatial variability of soil residence time within the Susquehanna Shale Hills Critical Zone Observatory, PA: Insights from multiple isotopic systems

Nicole West1, Eric Kirby1, Paul Bierman2, Rudy Slingerland1, Lin Ma3, Lixin Jin3, Susan Brantley1

1Penn State University; 2University of Vermont; 3University of Texas – El Paso

The degree to which the present‐day state and functioning of regolith is influenced by the history of changes in climate and land‐use is a first‐order question at the center of our efforts to understand critical zone dynamics at the Susquehanna Shale Hills Critical Zone Observatory (SSHO). The SSHO is located in the temperate climate zone of central Pennsylvania in a first‐order watershed developed on a Fe‐rich, organic‐poor, Silurian shale. Two perturbations to the landscape have occurred at SSHO in the geologically recent past: significant periglacial activity during the maximal extent of the Laurentide ice sheet (sustained until ~19‐21 ka) and deforestation during mid‐19th Century charcoal production for iron smelters. The SSHO watershed is oriented approximately east‐west, and contains a subtle fill terrace that stands ~1m above the incised channel. Hillslopes on either side of the axial stream exhibit a pronounced asymmetry, with steeper north‐facing slopes (~20°) than south‐facing slopes (~15°).

To quantify soil residence times and corresponding rates of regolith production and erosion on the north‐ and south‐facing slopes at SSHO, we compared measurements of meteoric 10Be, U‐series decay chain isotopes, and bulk soil chemistry in 44 samples of soil and bedrock collected as a function of depth at three locations along each hillslope, representing the ridge top (RT), mid‐slope (MS) and valley floor (VF). Meteoric 10Be inventories and U‐series disequilibrium suggest that thinner soils near the ridge tops and along the south‐facing slope have residence times on the order of 10 ka. In contrast, 10Be inventories and U‐series disequilibrium measured in thicker soils on the north‐facing slope of the watershed reflect longer residence times, on the order of 30 ka. In general, U‐series inventories imply greater regolith production rates on the south‐facing slope (~40‐50 m/My) than along the lower sections of the north‐facing slope (~18 m/My). To characterize the nature of the valley fill deposits we collected and logged 18 soil cores across the valley floor. Cores to the south of the present channel contained layers of coarse, poorly‐sorted, sub‐angular gravels intercalated with layers of moderately well‐sorted, fine sands and coarse silts. The grain sizes and stratified nature of these deposits suggest that they were transported from upslope, during either sheet‐wash or periglacial activity. In contrast, regolith on the hillslopes above the valley floor consists of massive, unstratified and clay‐rich sediment, suggesting that this material has largely formed in place.

The observed asymmetry in hillslope gradient, soil depth and soil production rates suggests two alternative working hypotheses. Greater rates of soil production rates on the south‐facing slope could be sustained if downslope transport maintains thin soils. This hypothesis would require higher regolith fluxes, perhaps associated with variations in soil moisture and vegetation type, that lead to different rates of regolith transport by tree‐throw events. Alternatively, these differences may reflect a legacy of vigorous soil transport during periglacial conditions in the late Pleistocene. Enhanced efficiency of freeze‐thaw and frost‐shattering might be anticipated on slopes with greater insolation, whereas permanently frozen ground in the shadowed north‐facing slopes may promote retention of hillslope colluvium. Although we cannot, at this point, distinguish between these hypotheses, we suggest that it is likely that the soils and the geomorphology of the SSHO retain a memory of past climatic conditions.



Of damage zones, reactors and conveyor belts: a geomorphologist’s view of the long‐term evolution of the critical zone

Robert S. Anderson1,2, Suzanne P. Anderson 1,3, and Greg Tucker 2,4

1 INSTAAR, CU Boulder; 2 Department of Geological Sciences, CU Boulder

3 Department of Geography, CU Boulder; 4 CIRES, CU Boulder

Models of landscape evolution require rules for the rate of detachment of rock into the mobile regolith layer, for the rate of mobile regolith transport, and for channel incision or aggradation rates that serve as boundary conditions for the hillslopes. The fundamental distinction is made between mobile regolith and immobile regolith (or saprolite), but the evolution of material within these two components of the critical zone is typically ignored. The current rules are therefore insufficient to address issues of critical zone evolution, in which the chemical, mechanical, and hydrologic properties of the rock and the regolith matter. These properties evolve as rock is weathered into saprolite during exhumation, and continues to evolve on the conveyor belt of mobile regolith as it moves downslope. One goal of the geomorphic component of the CZ effort is to produce models that honor specific processes involved in the evolution of rock throughout its transit through the CZ that will both serve as better rules for landscape evolution, and provide context for ecological and hydrological components of the CZ community.

We argue that one may envision the sub‐regolith CZ as a process zone in which the rock is progressively damaged as it is exhumed. In general, the rate of damage is most intense nearest the saprolite‐mobile regolith interface, meaning that the history of rock damage during exhumation performs a crescendo to the moment of rock release into the mobile regolith. In some instances, the likelihood of release of the rock into the mobile regolith depends upon the accumulated damage, the more damaged rock being more likely to be released. We illustrate this process using two examples, one in which damage accumulates due to frost cracking, in the other due to tree roots. These allow discussion of an important ratio of time scales: the time required for a rock to pass through the damage process zone (L/e), and the time scale over which climate oscillates, �. Here L is a length scale characterizing the damage zone, and e is the exhumation rate that governs the rate of passage of rock through the damage zone. In most cases in temperate and alpine settings relevant to the present CZOs, the ratio of timescales is such that a rock parcel will experience the full spectrum of Quaternary climates, which in turn requires that we both address climate change and the expected patterns of damage rates associated with all Quaternary climates. In our numerical models, we use the natural experiment afforded by the Boulder Creek CZO Gordon Gulch catchment, in which strong contrasts in CZ development occur on north‐facing and south‐facing slopes that likely reflect differences in both the thermal state and the tree cover of the landscape.

Wednesday PM Posters: 4.1

CZO All‐hands Meeting ‐ Session 4: Critical Zone Evolution

LiDAR imagery improves classification of forested landforms in the Shale Hills/Susquehanna Critical Zone Observatory region of Pennsylvania

Kristen Brubaker, Elizabeth Boyer, Katie Gaines

Pennsylvania State University

Technology is changing the way scientists see the landscape, with new data providing accuracy never before available. Scientists in many fields are looking for concise, effective methods to predict vegetation by classifying landscapes based on digital elevation model‐derived terrain metrics such as slope, aspect, curvature and topographic indices. With newly available LiDAR‐derived elevation data, the accuracy and resolution of is greatly improved but scale is so dramatically different that new approaches should be used to classify topographic features. By identifying LiDAR‐derived patterns of curvature, major gradients impacting vegetation in a catchment including water accumulation, soil characteristics and nutrient availability can be summarized into compact metrics. We applied this approach in the Ridge and Valley region of central Pennsylvania, in the broader basin encompassing the Shale Hills Critical Zone Observatory. By classifying the watershed into four dominant recurring landforms using patterns of lidar‐derived curvature data, dominant vegetation communities and forest structures were successfully predicted and confirmed using multivariate statistical methods. These landform classifications can be used to improve our understanding of forest communities and structures and their occurrence across gradients of physiologic factors.



Bedrock Geologic Characterization of the Susquehanna Shale Hills Critical Zone Observatory

Tim White and Chuck Anderson

Earth and Environmental Systems Institute, The Pennsylvania State University

Bedrock provides parent material from which sediment is eroded and soils are derived, porous media in which groundwater is transmitted and stored, and the substrate host and nutrient source for all terrestrial life. Bedrock weathering mediates long‐term atmospheric CO2 composition and the global carbon cycle. Therefore knowledge of bedrock lithology and structure can greatly influence conceptual models of Critical Zone development. Shale landscapes in the central Appalachian Mountain region are typically mantled by colluvial sediment and soil, forested, and devoid of good natural exposures of bedrock ‐ the Susquehanna‐Shale Hills Critical Zone Observatory (SSHO) is no exception. Based on observations from quadrangle‐scale maps and somewhat limited soil probes, the sedimentary bedrock in the observatory was historically characterized as gently dipping shale. Here we describe the methods for characterizing bedrock stratigraphy and structure at SSHO and demonstrate that the basin is actually underlain by steeply dipping, folded, fractured and cleaved shale with lesser amounts of sandstone and perhaps limestone. The orientation of these features exerts a foundational role in Critical Zone architecture and influences our evolving model of Critical Zone processes in the basin.



Landscape transience in Puerto Rico: from emergence to the modern relief

Gilles Brocard, Jane Willenbring, Fred Scatena

Earth and Environmental Science Department, University of Pennsylvania

Puerto Rico has been located on the front line of plate tectonic activity at the boundary of the Carribean plate from inception to present day.. It first emerged as a Jurassic intraoceanic volcanic arc, and grew through the accretion of successive Cretaceous and Paleogene volcanic arcs, various parts of which are now scattered about the island: accretionary prism mélanges, forearc sediments, volcanic vents and magmatic chambers. The arc comprising Puerto Rico, Cuba and Hispaniola arrived into the Caribbean realm at the start of the Tertiary. In the Paleogene ‐ 40 Ma ago, it collided with an western outlier of the Bahamas platform. This resulted in vigorous folding, faulting, uplift and erosion of the arc. Continuation of the eastward drift of the Caribbean plate sheared away its remnants and entrained them with parts of the fragmented Bahamas platform along the northern, left‐lateral strike‐slip boundary of the Caribbean plate. From then on, the area that encompasses Puerto Rico and the Virgin Islands has behaved somewhat rigidly, sandwiched between two highly deformable belts in the Puerto Rico trench to the north, and the Muertos trench to the south. This block has been bobbing along and spinning above the subducted Atlantic oceanic crust. By the end of Oligocene (23 Ma), the block had been reduced to only a reef platform with few emerged islands, and it probably resembled the modern Bahamas reefs throughout most of the Miocene. The platform experienced a sudden, extremely rapid tilting during the Early Pliocene (5 Ma). Its northern ledge sunk to ‐4500 m, while its southern ledge uplifted by more than 1000 m, creating the high relief of the modern Puerto Rico Island and Virgin Islands.

We posit that the landscape we see today in the CZO is neither the result of progressive decay of the relief created at that time, nor the product of a long‐term equilibrium between rock uplift and erosion. Various landforms, surficial deposits, river profiles and caves hold the marks of successive episodes of uplift, dissection and landscape flattening. In this study, we describe this evolution using a digital elevation model of the island. We map long‐known, widespread planation surfaces of uncertain origin (marine or continental) and use them to distinguish uplift due to local dislocations along fault zones from more regional, probably mantle‐driven isostatic and dynamic uplift pulses. The following step consists of constraining these milestones along the temporal evolution. We will use in situ produced 10Be and 26Al in quartz to date the burial of sediments into caves and littoral plains, and to determine catchment‐wide paleo‐erosion rates. We will use detrital 10Be in modern streams to evaluate to which extent the current landscape transience affects the variations in erosion rates within the Luquillo CZO, concurrently to the variability attributable to the variations in bedrock type (volcanics, hornfelds, granodiorite). We present here the areal extent of some major planation surfaces, and the location of targeted caves and river sampling sites, both at the island scale and within the CZO.



Utility of δ13C and C/N values in organic material in the reconstruction of former sea levels and paleoenvironment in the tropics, Luquillo CZO, Puerto Rico

Nicole S. KHAN1*, Christopher H. VANE2, Benjamin P. HORTON1

1Department of Earth and Environmental Science, University of Pennsylvania, PA 19104, USA, 2British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham, NG12 5GG, UK

*[email protected]

Reliable, quantitative proxies of past sea‐level and paleoenvironmental change are crucial in integrating geologic and historical records into predictive models in order to better understand the response of coastal systems to marine inundation. Microfossils are used to reconstruct Holocene sea level because of their potential for providing high‐resolution archives; however, these biological proxies are somewhat limited due to spatial restrictions and poor preservation in the sedimentary record of temperate and more notably tropical environments. In this study, we aim to overcome the confines of existent indicators by adapting the use of stable carbon isotopes and carbon to nitrogen ratios in organic material – a technique routinely used for paleoenvironmental reconstructions in lacustrine environments – to a tropical coastal setting.

We sampled dominant vegetation and surface sediment (top 1 cm) along modern transects taken through tidal flat, low, red‐dominated mangrove and high, black‐dominated mangrove zones at three sites on the northeastern and southeastern coasts of Puerto Rico, respectively. We find that tidal flat (δ13C = ‐18.5 ± 0.8; C/N = 10.1 ± 3.4), Rhizophora‐dominated lower mangrove (δ13C = ‐22.7 ± 0.5‰; C/N = 19.1 ± 1.1) and Avicennia‐dominated upper mangrove (δ13C = ‐25.2 ± 0.8‰; C/N = 16.2 ± 2.3) zones are distinguishable on the basis of δ13C and C/N and that these values exhibit a relationship to elevation within the tidal frame. Additionally, a 2.5 m core obtained from one of the sites demonstrates changes in δ13C and C/N representative of a shift from terrestrial (δ13C > 25‰; C/N > 19) to marine (δ13C < 25‰; C/N < 19) conditions. The transition occurs over 11 cm at approximately 1.3 m depth and is in agreement with the change in lithology from brown mangrove peat to grey organic‐rich clay.

Our preliminary analysis suggests that together δ13C and C/N hold potential as sea‐level indicator in the tropics because they have a relationship to tidal elevation that is identifiable in the sedimentary record. Thus, this work provides alternative means for filling gaps in data associated with other proxies, as well as attempts the first quantitative reconstruction of Late Holocene relative sea‐level change for the threatened, low‐lying island of Puerto Rico.



Real time rainfall‐induced landslide risk assessment system for the Luquillo Mountains of Puerto Rico

Miguel Leon


Rainfall‐induced landslides are a major natural hazard in Northeastern Puerto Rico. Recent population growth and urban development are pressing human populations further into landslide prone regions which results in an increased risk for loss of life, injury and property damage or loss. An established method for mitigating losses due to landslides is the institution of landslide warning systems that provide residents the time to evacuate or implement other mitigations. These warnings can be distributed through an interactive web based GIS, which allows the general public to receive real time warnings and view areas of increased risk. Previous research in Puerto Rico on rainfall intensity thresholds for triggering landslides and landscape susceptibility maps can be leveraged to facilitate the creation of a landslide warning system. This project developed a real time warning system by combining these rainfall‐intensity thresholds and susceptibility maps with real‐time precipitation and forecasting data from National Weather Service Doppler radar. A prototype landslide warning system for the Luquillo Critical Zone Observatory is described here.



Effects of grain properties on abrasion of river sediments

K.L. Litwin and D.J. Jerolmack

University of Pennsylvania, Department of Earth and Environmental Science The process of abrasion is defined by the production of fine sediments and sand that occurs by saltation of gravel, where particle‐to‐particle collisions supply the energy required to break apart grains. Although previous work has shown that lithology, grain shape, and energy of collision are contributing factors that control abrasion rates of river‐bed material, little is known regarding the relationship between these factors and diminution rates. Without such knowledge, it is not possible to determine the importance of in‐stream abrasion for determining grain sizes of river sediments, relative t o the better‐studied processes of chemical weathering and sorting by transport. In this project, we are investigating the controls on abrasion rates and the products of the abrasion process. The Luquillo Critical Zone Observatory (LCZO) in Puerto Rico is an ideal setting to study sediment abrasion because of the two different lithologies, granodiorite and volcanoclastic, that comprise the channel sediments in the two otherwise similar study watersheds. The volcanoclastic watershed produces a wide range of river‐bed grain sizes, whose distribution changes gradually downstream. Streams draining granodiorite lithologies are rich in sand and boulders but are lacking in intermediate grain sizes. We expect to see a transition from the abrasion‐dominated, steep mountain streams that have no sediment storage capacity to selective sorting‐dominated steams of the alluvial plain that have high sediment storage capacity.

We are measuring size, shape, and lithology of channel sediments in both watersheds to determine their downstream evolution, and to compare to hillslope sediments produced by chemical weathering. We are able to complete grain size measurements over large areas in a short amount of time by using an autocorrelation image analysis method. We characterize grain shape with standardized shape parameters, as well as Fourier analysis, where peaks in low frequencies correspond to large‐scale shape features and peaks in the high frequencies correspond to small‐scale shape features. We are also tracking the transport of grains using radio‐tracer particles, in order to determine the mobility and collision energy of gravels that are transported by floods. Additionally, laboratory experiments are being conducted at the University of Pennsylvania that link the mechanics of granular collisions to parameters such as grain size and shape distributions that can be measured in the field. Furthermore, these experiments investigate how abrasion scales from the energetic binary collision of grains to river systems comprised of multiple grains. The results of this research will enable us to isolate the effects of in‐stream abrasion on the downstream fining of grains in a river, and to understand the specific control that bedrock lithology exerts on this process.



Determining suspended sediment sources using meteoric Beryllium‐10 in Rio Icacos and Rio Mameyes, Puerto Rico

Marcie Occhi and Dr. Jane Willenbring


It is generally accepted that feedback mechanisms exists between climate, tectonics and erosion. However, in recent years it has been found that long‐term global erosion rates are not correlated with climate (von Blanckenburg, 2005) while a better correlation exists between global short‐term sediment fluxes and climate (Ludwig and Probst, 1998). This project is primarily focused on understanding how precipitation signals are transmitted through the geomorphic systems. Specifically, we are trying to show how modern storm events affect short‐term erosion in two watersheds within the Luquillo experimental forest, Rio Icacos and Rio Mameyes in terms of total suspended loads and the sources of that sediment. Estimates of 150 m/Ma long‐term erosion rate from Brown et al. (1995) were determined in the Rio Icacos watershed (mainly granodiorite bedrock) using in‐situ cosmogenic Beryllium‐10 (Be‐10) in river sediments. This erosion rate is generally regarded as low considering the magnitude of precipitation and warm temperatures that dominate the area. Because Rio Mameyes is underlain by volcanoclastics, there is little to no quartz in the bedload, which precludes the measurement of in‐situ Be‐10‐derived erosion rates.

In order to understand how precipitation events affect erosion, we propose a sampling strategy involving the collection of suspended sediment samples from two sites along the main stem for each watershed to be measured for meteoric Be‐10 adsorbed to sediments. Samples will be collected from each site during a storm event, with multiple samples being taken over the course of a single storm hydrograph. Precipitation samples above and below canopy cover will also be collected and analyzed for meteoric Be‐10 in order to estimate Be‐10 fluxes due to precipitation and potential contamination from dust. Sampling sites will also rely on data from established USGS stream flow gauges for flow parameters. In order to characterize the provenance of suspended sediments involved in transport, meteoric Be‐10 concentrations will be determined for various size fractions of sediment and different source areas in an attempt to understand which portions of the landscape are actively eroding during storm events.

In addition, we will using the novel Be‐7/Be‐10 ratio to determine if high levels of Hg documented by Shanley et al. (2008) in stream flow during the storm hydrograph are derived from an atmospheric or terrestrial source and how mercury is routed through organic matter. This isotopic ratio also discriminates between different atmospheric sources to better understand the location of a potential pool of Hg‐contaminated atmosphere.



Determining bedload transport from tracer particle dispersion

Colin B. Phillips and Douglas J. Jerolmack

University of Pennsylvania, Department of Earth and Environmental Science The Luquillo Critical Zone Observatory (LCZO), located in the humid tropical region of North East Puerto Rico, is characterized by rapid weathering rates and frequent high intensity precipitation. Ultimately the rate of landscape denudation is limited by the rate at which material is removed from the system. Bed load transport over short timescales is determined by transport mechanics: channel hydraulics, bed configuration, and the intensity of flow events. Over long timescales, the rate of bed load transport represents the supply of coarse‐grained sediment supplied by hill slopes. Linking the mechanics of (event‐scale) bed load transport to landscape denudation is critical for determining how climate, land use, and tectonics sculpt landscapes.

Multiple methods exist to quantify bed load transport, however many of them are either disruptive to the stream bed or provide limited accuracy. Use of bedload traps requires significant modification of the channel which could influence bedload transport rates, and transport rates measured from these traps are heavily dependent on sampling time. Due to intense short‐duration rainfall events, high‐discharge floods occur frequently allowing the use of tracer particles as a means to quantify bedload transport. Tracer particles provide information of transport distances of individual particles for each flood, and also which particles remained immobile. Sediment‐mobilizing events occur multiples times per year in Luquillo mountain streams, tracer particles may be used to monitor bed load transport following individual floods in a minimally invasive manner. Tracer particles were installed using passive integrated transponder radio frequency identification tags (PIT RFID) in the two primary rivers draining the LCZO, the Rio Mameyes and Rio Blanco, as well as two smaller tributaries in the Rio Mameyes catchment. We installed 150 tracer particles in each large river, and are tracking the motion of each particle following individual floods (when surveying allows) or a series of floods. Initial tracking of sediment particles indicates that the bed typically experiences fractional transport, in which only a portion of the bed is in motion for a flood, with slight size‐selective transport occurring.

Coupling transport distances with USGS stream discharge gaging stations located near all sites allows for a determination of the shear stresses required to mobilize those particles. Our approach will allow calculation of a sediment transport rate for a characteristic storm event, and also an estimation of the bed material flux leaving the catchment on annual timescales. Future laboratory experiments will examine transport distances of particles under varying hydrographs, in order to extract more information about transport mechanics from field tracer data.



Is soil produced from the bottom or top? Yes.

New insights from coupled in situ 10Be and adsorbed 10Be/9Be

Jane Willenbring


Soil is formed not only by weathering of underlying bedrock but also by the incorporation of dust, transported soil and organic matter near the surface of the soil. In this way, the total amount of soil represents the balance between these soil formation mechanisms and organic matter degradation, physical erosion and chemical weathering which all act to deplete the soil of mass. Although the very presence of soil in a landscape position attests to faster net soil formation processes than the denudation processes, long‐term rates of soil production and weathering are also increasingly determined by measurements of recalcitrant element abundances and terrestrial in situ cosmogenic nuclides like Beryllium‐10 (10Beinsitu) and are beginning to be measured by the fallout cosmogenic nuclide Beryllium‐10 (10Bemeteoric) that is adsorbed to soil grains through interaction with rain. The quasi‐immobile elements tend to be more concentrated in dust and in more weathered material relative to parent bedrock. Both 10Beinsitu and

10Bemeteoric concentrations in surface material record the long journey through the upper meters of the weathering zone. 10Bemeteoric concentrations may be used to track the movement of the fine‐grained fraction. However, since coarse‐grained sand is almost the exclusive carrier of the 10Beinsitu clock, this system does not accurately record the potentially large mass loss that is fine grained (dust) or organic matter added to the top of the soil column. This mass added to the surface shields the grains from penetrating radiation but the more significant effect is that the average sand particle can spend a longer amount of time in the soil column just below the surface.

In this poster, I present an analysis of the impact of neglecting the fine‐grained, top‐down component of soil production on the amount of time required to reach steady state as well as on rates of weathering, 10Beinsitu‐derived soil production, and basin‐wide denudation. Regions with bedrock weathering rates less than 100 mm/ky near dust plumes and vigorous organic matter growth are most susceptible to underestimation of the physical erosion rates and mass flux – like those in the Luquillo CZO. I will also compare compiled, coupled measurements of 10Beinsitu and

10Bemeteoric concentrations to explore whether this effect could explain discrepancies between rates in the same sites. Understanding what is measured by adsorbed 10Be is especially valuable in light of the promising first results from a new weathering proxy, adsorbed 9Be.



Controls on valley density in Valles Caldera, NM

Caitlin A. Orem, Jon Pelletier

Department of Geosciences, University of Arizona

The density of valleys spatially quantifies stream systems and defines the transition from hillslopes to stream channels in erosional landscapes. As such, valley density defines a fundamental spatial scale of landscapes that influences hydrological and biological systems within the critical zone. Potential controlling factors of valley density include landscape age, soil thickness and permeability, climate, slope, geology, and groundwater flow pathways. In this study, valley density is calculated for the stream systems within the Valles Caldera and other locations nearby with similar climate.

The Valles Caldera is an extinct caldera located in the Jemez Mountains, New Mexico. Within the caldera are Redondo Dome, the main resurgent dome, and many smaller domes from post‐resurgence rhyolitic eruptions. The streams of Redondo Dome receive most of their water from subsurface flow. The dearth of overland flow and abundance of subsurface flow on Redondo Dome is likely related to soil thickness and permeability that affect the hydrologic partitioning of rainfall. The low amount of surface flow inhibits hillslope erosion by slope wash and the creation of channels, while the high amount of subsurface flow enables colluvial transport and the filling of channels.

Valley density was calculated using two methods. For the first method, the length to the nearest stream, or hillslope length, (L) was calculated for each pixel within the region, allowing “valley density” to be approximated for each point. All L values were averaged to generate Lm, the average hillslope length of the region. Valley density (D) was calculated using the “length to

stream” method following the relationship Lm≈1/2D. This method was checked using the

traditional method of calculating valley (drainage) density, D=ΣL/A, where ΣL is the summation of the channel lengths, and A is the area of the catchment or region analyzed. By using both methods, the integrity of the approximation of D by L was tested for this landscape. Calculated valley densities were then compared to soil characteristics as well as other possible controls.

The results of this study document the importance of soils and geology in controlling channel density and identify a positive feedback. Thick, permeable soils on Redondo Dome promote a low ratio of surface‐to‐subsurface flow that inhibits slope wash and promotes colluvial transport, leading to low valley densities relative to adjacent locations. Low valley densities result in less fluvial transport, which suppresses the removal of soil and the formation of channels in a positive feedback as the landscape evolves.



Calibration and testing of upland hillslope evolution models in a dated landscape: Banco Bonito, New Mexico, USA

Jon D. Pelletier1,2.*, Luke A. McGuire2, Jeanine L. Ash1, Todd M. Engelder1, Loren E. Hill1, Kenneth W. Leroy1, Caitlin A. Orem1,2, W. Steven Rosenthal2, Mark A. Trees1, Craig Rasmussen3, Jon Chorover3

1Department of Geosciences, University of Arizona, 1040 East Fourth Street, Tucson, Arizona 85721–0077, USA 2Program in Applied Mathematics, University of Arizona,

617 N. Santa Rita Avenue, Tucson, Arizona 85721–0089, USA 3Department of Soil, Water, and Environmental Science, University of Arizona,

1177 East Fourth Street, Tucson, Arizona 85721–0038, USA *E‐mail: [email protected].

The production of regolith from bedrock and its colluvial transport from hillslopes to channels are the rate‐limiting steps for the erosion of upland (regolith over bedrock) landscapes. Understanding the coevolution of topography and regolith in hillslopes is, therefore, critical to understanding upland landscape evolution. In this study, we constrain the rates of regolith production and colluvial transport over geologic time scales using an integrated approach that includes field measurements of regolith thickness, geochemical analyses of soil, bedrock, and regional dust samples, numerical modeling of regolith production and transport, and quantitative analyses of airborne Light Detection and Ranging (LiDAR) Digital Elevation Models (DEMs). Our study site, Banco Bonito, is a late Pleistocene (40 ± 5 ka) rhyolite flow in the semi‐arid Valles Caldera region of northern New Mexico. Within this flow, many topographically‐closed basins exist as a result of compressional folding and explosion pitting during eruption. The landscape has evolved from an initial state of no soil cover at 40 ± 5 ka to its modern state, which has regolith ranging from 0 to 3+ m, with local thickness values controlled primarily by topographic position. Our models constrain the rate of potential weathering or bare‐bedrock recession in the study area to be in the range of 0.02 to 0.12 m kyr‐1 and the rate of colluvial transport per unit slope gradient to be in the range of 0.2 to 2.7 m2 kyr‐1, with higher values in areas with more above‐ground biomass. Immobile chemical element concentrations in the bedrock, soil, and regional dust constrain the eolian dust content of the soil to be in the range of 0‐13%. Eolian deposition is, therefore, present in the study area but secondary to bedrock weathering as a mechanism of regolith production. Uncertainty in the inferred model parameters is the result of uncertainty in the topography shortly following eruption, the presence of two protoliths (obsidian and tuff) in the study area, and the presence of small‐scale spatial and temporal variability in regolith production and transport processes. We conclude that a depth‐dependent colluvial transport model better predicts the observed spatial distribution of regolith thickness compared to a model that has no depth dependence. This study adds to the database of estimates for rates of regolith production and transport in the western United States and shows how dated, topographically‐closed landscapes can be used to improve our understanding of the coevolution of landscapes and regolith.



Coevolution of topography, hydrology, soil development, and vegetation in the sky islands of the southwestern United States

Jon D. Pelletier*, Craig Rasmussen, Dave Breshears, Paul Brooks, Jon Chorover, Travis Huxman, Kathleen Lohse, Tom Meixner, Jennifer McIntosh, Shirley Papuga, Marcel Schaap, Tyson Swetnam

The University of Arizona

The sky islands of the southwestern U.S. offer a unique opportunity to study the coevolution of landscape processes in areas of similar rock type and tectonic history but a wide range of climates. In this study we compile high‐resolution, spatially‐distributed data for the available energy to drive rock weathering and other landscape processes, i.e. the Effective Energy and Mass Transfer (EEMT) variable of Rasmussen et al. (2005), together with data for LiDAR‐derived above‐ground biomass, soil thickness and water storage potential, and hillslope relief and valley density in the Santa Catalina and Pinaleno Mountains, two predominantly granitic ranges in southern Arizona. Strong correlations exist among these variables such that warm, dry, low elevation portions of these ranges are characterized by low biomass, thin soils, low water‐storage potential, steep slopes, and a high valley density. Cooler, wetter, higher‐elevation portions of these ranges have systematically higher biomass, thicker soils, higher water‐storage potential, gentler slopes, and lower valley densities. Moreover, all of these variables have a nonlinear dependence on climate/elevation. These correlations partly reflect the underlying role of climate in controlling rates of pedologic, hydrologic, ecologic, and geomorphic processes, but they also reflect coevolutionary positive feedback mechanisms among these processes that tend to amplify differences in rates set by climate and rock type. For example, the thicker soils of higher water storage potential that form at higher elevations in these ranges tend to increase the carrying capacity for vegetation, thereby decreasing runoff ratios and increasing rates of colluvial transport that drive watersheds towards a state with still thicker soils, less‐steep slopes and lower valley densities. Thicker soils and lower‐relief, less‐fluvially‐dissected slopes, in turn, promote higher biomass and greater infiltration and evapotranspiration in a positive feedback. We hypothesize that the observed nonlinearity in the elevation gradients of pedologic, hydrologic, ecologic, and geomorphic variables in these ranges partly reflects these feedback mechanisms. To test this hypothesis, we developed a landscape evolution model that couples soil development, the partitioning of rainfall into runoff, infiltration, and evapotranspiration, vegetative carrying capacity, and geomorphic processes (colluvial and fluvial transport) over geologic time scales. Numerical model experiments can be run for a range of input data for climate and rock type. Across a climate gradient similar to that of the sky islands of the southwestern U.S., the model self‐organizes into states similar to those observed in the Catalina and Pinaleno ranges, i.e. lower biomass, soil thickness, water storage potential, and higher relief and valley density at lower elevations. The model also exhibits similar nonlinear relationships among landscape variables across the elevation/climate gradient, lending support to the hypothesis that positive feedback mechanisms contribute to the observed nonlinearity.



Short‐Term and Long‐Term Weathering and Soil Production: Responses to Land Use Changes

Kyungsoo Yoo1, Anthony Aufdenkampe2,

Shreeram Inamdar3, Delphis Levia3, Holly Michael3, Paul Imhoff3, Rolf Aalto4

1 University of Minnesota, Twin Cities, Minnesota, 2 Stroud Water Research Center, Avondale, Pennsylvania,

3 University of Delaware, Newark, Delaware, 4 University of Exeter, UK.

Cristina River Basin (CRB) CZO focuses on the interactions between organic matter and minerals in a mixed land use watershed in Pennsylvania and Delaware with an explicit goal of scaling up this mineral‐grain scale interaction to an entire Cristina River Basin. This abstract focuses on weathering and soil production in upland landscapes. At mineral grain scales, the interaction between organic matter and minerals is significantly affected by the species and surface characteristics of minerals in soils and sediments which are controlled by chemical weathering processes. At soil profile scales, in addition to chemical weathering of minerals, minerals’ vertical translocation (eg., mixing and soil production) within a soil profile may play a critical role in determining their chance of physically interacting with organic matter because organic matter abundances are highly sensitive to soil depths. Lastly, at hillslopes and watershed scales, in addition to minerals’ chemical weathering and vertical translocation, erosion of minerals may deprive organic matter of its interaction with minerals, while deposition of minerals provide increased interactions of the minerals with organic matter. We propose that land management practices – such as tillage and soil clearing for suburban developments – interfere with all of the above processes: minerals’ weathering, vertical translocation, and erosion. Specifically, we focus on soil profile to hillslope scale rates of chemical weathering, soil mixing and production, and physical erosion under different land use regimes: forest, tilled cash crop agriculture, and soil cleared land‐fill sites. Approaches include elemental and mineralogical analyses (mass losses and mineral transportation via chemical weathering), short‐lived isotopes such as 210Pb and 137Cs (soil mixing rates and short‐term erosion and deposition rates), and insitu and meteoric 10Be (long‐term soil production and denudation rates). Lysimeter‐based elemental leaching rates will be also collected for short‐term chemical weathering rates. In‐situ soil (O2) and redox measurements will further help understanding the formation and dissolution of iron oxides that explains significant fraction of mineral surface area. Lastly, we will investigate whether the differences in land use regimes may affect the geochemical equilibrium between soil solution chemistry and mineral species. Within CRB‐CZO, this work aims at providing (1) the processes and history involved in the generation of mineral surface area that interact with organic matter and (2) the flux of mineral surface area from upland to fluvial systems.



Sediment Load Variability, Sediment Sources, and Erosion Rates for Forest Headwater Streams in the Southern Sierra Nevada, California

Carolyn Hunsaker, research ecologist, Pacific Southwest Research Station

USDA Forest Service, Fresno, CA, ([email protected])

The ability to quantify best management practices for forests requires quantification of the variability of stream sediment loads for managed and unmanaged forest conditions and their associated sediment sources. Both mechanical thinning and prescribed fire can be used to restore forests in the Sierra Nevada to pre‐fire‐suppression conditions. Although restoration is a positive activity, there are some concerns about short‐term negative effects from soil erosion and sedimentation on stream organisms. Prior to the Kings River Experimental Watershed (KREW), little was known about sediment erosion rates in the southern Sierra Nevada. Five years of research on sediment yield, suspended sediment, and sediment sources on the eight streams in KREW establishes the variability of sediment conditions in the headwaters of the southern Sierra Nevada. These watersheds are conifer‐dominated forest with meadows and granite rock outcrops. Soils originate from granite bedrock and tend to be coarse in texture. A comparison of sediment loads and sources is made among the four watersheds that receive precipitation as both rain and snow and the four watersheds that are snow dominated. Reasons for differences will be discussed. A unique feature is that one of the watersheds has no disturbance from roads or logging and thus serves as an excellent source of data for natural sediment loads under different precipitation conditions. Interestingly this undisturbed watershed does not have the lowest sediment load. The other seven watersheds have had forest management activities on them, and one of these consistently has the highest sediment load which averages eight‐times as much sediment as the others. One of the watersheds, with forest management in the rain and snow zone, produced 1.8, 15.2, and 18.7 kg/ha/yr for water years 2004, 2005, and 2006, respectively. The increase in sediment accumulation correlates with an increase in yearly precipitation: 14.5 cm in 2004, 27.3 cm in 2005, and 31.1 cm in 2006. The snow‐dominated and undisturbed watershed produces similar, and sometimes higher, sediment loads for these same years.

Each stream has a sediment basin that is emptied each fall to measure the annual sediment load from the watershed. The proportion of organic matter and the particle size distribution of the sediment are also measured. Several measurements in the watershed will allow us to estimate the proportion of the sediment load that comes from various sources such as stream banks. Sediment fences provide measurements of the annual erosion from roads and undisturbed upland areas in the watersheds. Turbidity sensors in the streams provide continuous measurements of the suspended sediment moving through the streams; for several of the streams good relationships between turbidity and suspended sediment samples have been developed. KREW also has an intensive upland soil characterization effort.

The Critical Zone Observatory Program provides a collaborative opportunity to broaden the usefulness of the Forest Service sediment data. New collaborative work includes looking at black carbon in both upland soils and sediment, long‐term soil erosion rates, and soil development mechanisms.



Chemical characteristics of sediment eroded from Sierra Nevada headstream catchments

Erin Stacy1, Asmeret Asefaw Berhe, Stephen C. Hart, Dale Johnson, Carolyn Hunsaker

1Sierra Nevada Research Institute, UC Merced

Lateral distribution of soil and associated soil organic matter (SOM) impose significant controls on the dynamics of SOM within the eroding watershed and overall carbon (C) sequestration potential of the terrestrial biosphere. Typically, more than 70% of the sediment transported from eroding slopes is deposited within the same or adjacent watersheds (Stallard 1998). It is likely that the less than 30% of sediment and associated SOM that is transported from the source watershed is enriched in finer soil particles, light fraction or particulate SOM and pyrogenic black carbon (BC). The quality of this eroded material also has important implications for downstream ecosystem SOM dynamics and forest management because it may contribute to elevated dissolved organic matter levels in downstream waters thus increasing the financial cost of water treatment. Furthermore, in some ecosystems deposition and burial of SOM creates a net carbon sink because lost SOM is replaced upslope through primary productivity, and decomposition rates are slower in depositional sites (Berhe et al. 2008). The stability of eroded SOM, including its molecular architecture and associations with soil minerals, influence complex post‐deposition decomposition dynamics that involve microbial activity and abiotic factors. Because this matter is transported, it is important that we consider these decomposition dynamics within and outside of the watershed.

In this study, we aim to determine the chemical composition of material being transported from eight first‐order watersheds, four in the Southern Sierra Critical Zone Observatory, and four watersheds from a higher elevation that receive a larger fraction of precipitation as snow, but are still in the mixed‐conifer zone and of comparable size (all part of the Kings River Experimental Watershed Project). We aim to determine how the biochemical composition and stability of SOM, and mineralogy of the trapped in sediment basins at the base of each watershed (i.e., material leaving the watersheds) relates to the composition of the upslope soil in the watershed. Specifically, how does the rate of decomposition of trapped sediments compared to the source locations upslope? Previous work indicates that the dry weight of sediment transported by the streams may vary by more than two orders of magnitude between years and between watersheds (when normalized to kg/ha; Eagan et al. 2004). Preliminary results suggest that the carbon to nitrogen (C:N) mass ratio of the sediment is less variable between years and watersheds, and is similar to the C:N ratio of surface soils from upslope positions. High concentrations of particulate organic matter in the sediment would explain higher C concentrations in the sediments than in mineral soils. Enzymatic activity in sediments from the 2010 water year were higher than average activity in soils. Further work will include a more intense sampling design of upslope soils as well as sediments being actively eroded to clarify the relationship between the biochemical composition of upslope soils and eroded sediments. Fourier‐Transform Infrared Spectroscopy and 13C‐Nuclear Magnetic Resonance analyses are also planned to compare the biochemical composition of SOM between eroded and residual material.



Critical Zones and Decaying Mountains: A Simple Model for Post‐Orogenic Landscape Evolution of a Range and its Adjacent Basin

Gregory E. Tucker1, Peter van der Beek2, Abby Langston1, Robert S. Anderson3, Suzanne P.

Anderson4

1 CIRES and Department of Geological Sciences, University of Colorado, Boulder 2 Institut des Sciences de la Terre, Université Joseph Fourier, Grenoble, France

3 Instaar and Department of Geological Sciences, University of Colorado, Boulder 4 Instaar and Department of Geography, University of Colorado, Boulder

The Southern Rocky Mountains have a puzzling landscape history. Although thrust tectonics ended some forty million years ago, geomorphic and sedimentary evidence indicates a surprisingly dynamic pattern of landscape evolution since that time. In particular, basins along the east flank of the Southern Rockies record widespread fluvial sedimentation during the mid to late Miocene period (the Ogallala group) followed by regional incision during the Pliocene and Pleistocene. The Rockies are not alone in this regard: a number of other tectonically quiet mountain ranges show unexpectedly rich post‐orogenic history. In order to explore the possible drivers of post‐orogenic erosion and sedimentation, we formulate and explore a simple mass balance model of coupled range and basin landscape evolution. The main purpose of the model is to clarify the type of changes in climate, lithology, or regional (``epeirogenic’’) tectonics that can account for switches between net erosion to net sedimentation in a post‐orogenic basin, and increases or decreases in relief in the adjacent mountain range.

The model is essentially a box model of rock and sediment mass. The range loses mass through erosion; the basin gains mass via sediment derived from the range and loses it through fluvial transport beyond the basin margin. The mean elevation of both the range block and basin sediment surface depends on their thicknesses and on flexural isostasy. Sediment fluxes from range to basin and from basin to boundary are assumed to depend on mean relief. This set of assumptions leads to a pair of ordinary differential equations that describe the time evolution of thickness and height for a range and basin pair. This simple mass balance framework demonstrates that in order for deposition to occur in an otherwise decaying basin, either sediment flux from the range must increase, or the sediment transport efficiency in the basin must decrease, or both. Similarly, a shift from basin deposition to erosion requires either a reduction in sediment flux from the range or an increase in sediment output from the basin. Such changes can, in principle, be driven by changes in climate, by epeirogeny, or by changes in the lithology of the eroding range, provided that the impact of these changes is substantially different between the range and the basin. Because the critical zone governs the generation of both runoff and sediment, it can strongly influence the sediment mass balance and transport efficiency of the evolving system. We use the mass‐balance model to explore different scenarios for the long‐term geomorphic evolution of the Boulder Creek Critical Zone Observatory in the Colorado Front Range. We also compare the implications of the simple mass‐balance model with a more detailed 2D numerical model of landscape evolution in a range‐basin pair.


Closing Keynote: Wed. May 11, 8:30 pm

What Have We Learned?

Ronald Amundson

Dept. of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720

For now we see through a glass, darkly 1Corinthians

The concept of the Critical Zone is largely consistent with the concept of the Biosphere, the envelope of our isolated planet that sustains the only known life in the Universe. The long‐term ability of this envelope to coarsely oscillate between largely habitable extremes is clearly a powerful concept, one that has sometimes led to unfortunate debates about theoretical issues. The complexity of the Earth’s Biosphere has been revealed through the history of the Biosphere 2, where an attempt to create even a simple inhabitable isolated system proved to be fraught with challenges. There is no pre‐ordained reason to study natural systems, though one compelling reason may be our own preservation. The growing series of CZO and CZEN sites are geared toward developing multi‐faceted perspectives about the properties and some of the key processes of these systems. However, why do we chose the processes we do, how are they inter‐connected with other biological and abiotic processes, and what does it all mean to larger complex systems that operate at global scales, and across decades and centuries. The somewhat obvious, yet profound, message of Biosphere 2 is that we simply don’t know how this all works. Twenty first century scientists are, to use Plato’s striking analogy, somewhat like prisoners trying to decipher nature through the shadows cast on a cave wall. If we chose the argument of planetary sustainability as a valid research goal for Observatory‐based programs, then the varied specific research projects within and among sites must be integrated and connected in conjunction with sophisticated modeling. Just as hypothesis at the individual project scale drive measurements and experiments, the models at regional to global scales must help drive the types of measurements needed at numerous locations to understand an array of biotic/abiotic feedbacks, determine or probe the resistance of the biosphere and its components to perturbations, and assess its ultimate resilience in this most critical of times.

Documents

Nti lCiti lZ Ob t i PNational Critical Zone Observatories Program All Hands meeting ...web.sahra.arizona.edu/education2/czo/abs/CZOprogram_All.pdf · 1:30 PM - 3:00 PM: Biosphere