Arctic hyporheic proposal - Project text for circulation

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Will climate change affect hyporheic processes in arctic streams? An assessment of interactions among geomorphology, hydrology, and biogeochemistry in Arctic stream networks PROJECT SUMMARY

The goal of this project is to assess how geomorphology and seasonal changes in the thawed region of soil and sediment around the open channel (i.e.; the thaw bulb) control hydraulic and biogeochemical dynamics in the hyporheic zone of Arctic streams. Our premise is that a) stream geomorphology sets a physical template that controls the seasonal development of the sub-stream active layer (or thaw bulb) around Arctic streams, b) the thaw bulb extent controls the potential for development of the hyporheic zone, and c) the hyporheic zone substantially contributes to C, N and P processing in streams. We expect that climate change in the Arctic has the potential to significantly alter the thaw bulb and hyporheic dynamics through its influences directly on precipitation, runoff, average annual temperature, and thaw season duration, and indirectly on stream geomorphology. To address this central hypothesis we propose four objectives:

1. Select and characterize stream reaches that represent the range of geomorphologic conditions in

rivers of the North Slope.

2. Monitor the sub-stream thaw bulb size through the thaw season using ground penetrating radar and subsurface temperature measurement in several stream cross-sections within each reach.

3. Conduct repeated hyporheic exchange studies (stream solute addition experiments) through the thaw season in each reach to determine hyporheic hydraulic characteristics.

4. Conduct repeated measures of nutrient (N and P) concentrations and turnover time in the hyporheic zone through the thaw season in each reach to determine biogeochemical characteristics.

These objectives will be addressed through a combination of field monitoring (thermistor arrays, hyporheic sampling), field experiments (solute additions), and modeling (groundwater transport and transient storage) efforts.

This proposed activity is important because there is virtually no reported literature on the structure and functions of the hyporheic zone in Arctic systems. Considerable research in temperate regions suggests that hyporheic zones are critical components of stream ecosystems. A significant portion of the primary production in streams may be supported by nutrients regenerated from hyporheic processes. This regeneration is dependent on organic matter inputs (both autochthonous and allochthonous). Thus hyporheic processing is also important in understanding how streams modify carbon, nitrogen, and phosphorous transport across landscapes. Research which quantifies these important functions in Arctic streams is non-existent.

Research on this subject is important as a direct input to our understanding of the ecological functions of Arctic streams. However, this research has broader implications for climate change research in the Arctic and the concept of Unaami, as defined in the Arctic Systems Science (ARCSS) program’s Study of Environmental Arctic Change (SEARCH) initiative. Given that rivers are the conduits that link land to the ocean, then processes within streams that modify material transport must be important to understanding how runoff from land affects oceans. Furthermore, if climate change affects the rate or extent of in-stream processing, then there may be important impacts on the transport of materials from land to the ocean, which this research would begin to address. Therefore, these studies are essential to provide data and knowledge that will be of use to other scientists, policy makers, resources managers, and ultimately to community stakeholders.

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Will climate change affect hyporheic processes in arctic streams? An assessment of interactions among geomorphology, hydrology, and biogeochemistry in Arctic stream networks INTRODUCTION

Channel geomorphology exerts important controls on hydraulic and biogeochemical processes in the hyporheic zone (Harvey and Bencala 1993, Hill et al. 1998, Kasahara and Wondzell 2003). In arctic regions, climatic conditions control development of in-stream ice and permafrost, which have strong influences on channel geomorphology (McNamara 2000). Thus, there is an implicit link through channel form between climatic conditions in the arctic and hyporheic processes. Furthermore, in arctic tundra regions most lower-order streams freeze solid to permafrost during the winter (exceptions include spring-fed streams and deep pools). The North Slope of Alaska is underlain by thick and continuous permafrost which extends under the rivers and streams. This frozen zone extends to the surface during the winter and thaws to a depth of up to 1 meter in terrestrial soils by late summer. The result is that the stream begins its active season (at snowmelt) with virtually no hyporheic zone. As the thaw season progresses, the active layer beneath streams begins to grow. Climate, therefore, exerts controls on hyporheic processes in arctic environments in two ways. First, it sets the physical template through its control on channel geomorphology (i.e. hydraulic geometry, riffle/pool sequences). Second, it controls the actual existence and extent of a hyporheic zone as the stream sediments thaw.

McNamara et al. (1997) showed that the seasonal expansion of the active layer on hillslopes has important controls on hillslope hydrology and suggested that the changing hydrologic response through a thaw season may serve as an analog to the hydrologic changes we might see in a changing climate. We expect that the same might be true for in-stream processes. That is, as the depth of thaw increases under a stream we might see important changes in hyporheic functions, and that the relationship between thaw depth and hyporheic processes operates within the geomorphologic template established by in-stream ice and permafrost. Because biogeochemical regeneration in hyporheic zones is likely to be an important source of nutrients in Arctic streams (Edwardson 1997, Edwardson et al. in press), the seasonal expansion of the hyporheic zone and hyporheic processing should have important impacts on the structure and function of Arctic streams. Finally, climate change in the Arctic is likely to cause important changes to precipitation patterns and runoff, and so, may cause important changes to the geomorphology of Arctic streams and the depth of permafrost thaw around them. Thus, improved knowledge about this poorly understood component of Arctic streams will provide essential information about the likely impacts of climate change on fluvial transport and fate of solutes from Arctic landscapes to the ocean.

The goal of this project is to assess how geomorphology and seasonal changes in the thawed region of soil and sediment around open stream channels control hydraulic and biogeochemical dynamics in the hyporheic zone of Arctic streams. These interactions and their relationship to Arctic System Science are shown in Fig. 1 (next page). Our premise is that a) stream geomorphology sets a physical template that controls the seasonal development of the sub-stream active layer (or thaw bulb) around Arctic streams, b) the sub-stream active layer extent controls the potential for development of the hyporheic zone, and c) the hyporheic zone substantially contributes to C, N and P processing in streams. We expect that climate change in the Arctic has the potential to significantly alter hyporheic dynamics through its influences directly on precipitation, runoff, average annual temperature, and thaw season duration, and indirectly on stream geomorphology. We plan to collect the data necessary to test this latter hypothesis and develop an initial assessment of how important these impacts might be. If warranted, we would refine and extend this analysis through a regional modeling approach, in a future project. We assert that it is essential to study these interactions to better understand the possible impacts of climate change in the Arctic on material processing and transport from land to the ocean.

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This project depends on the collaborative interactions among experts in three disciplines relevant to Arctic System Science. These disciplines include geomorphology (McNamara), hydrology (Gooseff), and biogeochemistry (Bowden). This project will also be able to leverage knowledge and activities associated with closely-related Arctic research programs in which two of the PIs (Bowden and McNamara) are already involved.

The following section (Results from Prior NSF Support) explains what we know now, followed by what we propose to do next (Hypothesis, Objectives, and Methods). The strategic context for this proposed work relative to key planning documents for Arctic research is explained in a final section on the Intellectual Merit and Broader Impacts of this research.

PI PRODUCTIVITY AND RESULTS FROM PRIOR NSF SUPPORT (indicated by ‘*’ in the literature cited) Bowden Awards: NSF, "Ecosystem reactions to disturbance: arctic streams and lakes." $102,667, March 1988-Feb 1991. Co-principal investigator. Subcontract for 1 month per year.NSF, "Ecosystem reactions to disturbance: arctic streams and lakes." $125,000, March 1991-Feb 1994. Co-principal investigator. Co-principal investigator. Subcontract for 1 month per year. NSF-Office of Polar Programs, “Controls of structure and function of aquatic ecosystems in the arctic”, NSF OPP-9400722, $124,500, 1994-1997. Co-principal investigator. Subcontract for 1 month per year. NSF-Ecosystems, “Nitrogen uptake, retention and cycling in stream ecosystems: An intersite N-15 tracer experiment.”, $141,649, 1996-1999. Co-principal investigator on a multi-site group project, 1 month/year. NSF-Office of Polar Programs, “Key connections in arctic aquatic landscapes”, NSF-OPP-9615949, $158,303, 1997-2000. Co-principal investigator. Subcontract for 1 month per year. NSF-Office of Polar Programs, Aquatic Ecosystem Responses to Changes in the Environment of an Arctic Drainage Basin. $260,000, July 1, 2000 to May 31, 2005. Co-principal investigator. Subcontract for 1 month per year.

Figure 1. A flow chart representation of this proposal and its context in the larger study of Arctic System Science. The objectives are explained in the Proposed Research section, below.

Climate

Permafrost (Thaw bulb)

Stream geomorphology

Hyporheic extent

Arctic LTER & OPP (Streams)ARCSS/Monitoring

Hyporheic function (biogeochemistry)

Objective 1

Stream ecosystem structure & function

Landscape processes

Coastal processes

Arctic System Science

Natural Influences

Human Influences

GeologyTopographyVegetationGlacial history

This proposal

Objective 2

Objective 3

Objective 4

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Peer-reviewed Publications: Bowden et al. (1992 and 1994), Finlay and Bowden 1994, Harvey et al. (1997 and 1998), Hershey et al. (1997), Hobbie et al. (1995 and 1999), The Stream Bryophyte Group (Bowden, organizer and lead author)(1999), Arscott et al. (1998 and 2000), Wollheim et al. (1999 and 2001), Peterson et al. (2001), Edwardson et al. (in press), Slavik et al. (in review) Graduate Student Theses: Arscott (MS 1998), Edwardson (MS 1999) Research Experience for Undergraduates: 8 students, each with a formal report. Professional Presentations: numerous (20+) Sample and Data Archives: numerous datasets contributed to and maintained on the Arctic LTER web site (http://ecosystems.mbl.edu/ARC/) Gooseff Awards: Supported as a Ph.D. student and Post-doctoral researcher by the following: NSF-Office of Polar Programs “McMurdo Dry Valleys: A Cold Desert Ecosystem” NSF OPP-9813061 from 1998- 2000, NSF Office of Polar Programs “The Role of Natural Legacy on Ecosystem Structure and Function in a Polar Desert: The McMurdo Dry Valley LTER Program” NSF-OPP-0096250 from 2000-2001, and NSF Hydrologic Sciences, “Interactions Between Streams and Groundwater Along the River Continuum: Scaling up to a Stream Network” NSF EAS-9909564 from 2001-2002. Peer-reviewed Publications: Gooseff et al. (2002, 2003), Maurice et al. (2002), Gooseff et al. (in press a,

b), Scott et al. (in press) Research Experience for Undergraduates: N/A Professional Presentations: 12 Sample and Data Archives: contributed to hydrologic and water chemistry data collection for McMurdo Dry Valleys LTER (http://huey.colorado.edu) and Andrews LTER (http://www.fsl.orst.edu/lter/). McNamara Awards: NSF 9214927, Hydrologic Linkages with Arctic Freshwater and Terrestrial Systems, 9/1992-2/1995, $953,536 NSF 9814984, Temporal Variation of Hydrology in the Alaskan Arctic, November 15, 1998-October 20, 2003, $959,954, BSU component $250,000. Peer-reviewed Publications: Hinzman et al. (2000), Kane et al. (1999, 2000), McNamara (1999, 2000, 2002) McNamara et al. (1997, 1998, 1999), McNamara and Stieglitz (2001), Taylor et al. (2002), Yang et al. (2000). Professional Presentations: 18 Sample and Data Archives: contributed to hydrologic and meteorological data collection archived at the National Snow and Ice Data Center (http://nsidc.org/data/ggd232.html) WHAT WE KNOW NOW (with Results from Previous NSF-Funded Research in bold)

General background: Frozen water – both surface and subsurface (permafrost) – has profound influences on the structure and function of Arctic tundra streams and the aquatic communities that live in them. With notable exceptions (e.g. springs, see Craig and McCart 1975, and Slavik et al. in review) Arctic tundra streams in the upper reaches of watersheds in the North Slope of Alaska freeze solid during the winter, although open water may persist in some higher-order, deeper reaches. The typical progression of the spring thaw in these streams creates both cap ice (i.e.; surface layers of ice that are undercut by flowing water) and bed ice (i.e.; submerged ice on stream bottom that is eroded by overflow). Cap and bed ice remain in place for a substantial portion of the spring thaw and strongly influence local runoff and discharge patterns, which in turn, strongly influence stream geomorphology (McNamara et al. 1999, McNamara 2000).

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Furthermore, the foothills region of the North Slope of Alaska is underlain by thick and nearly continuous permafrost at depths of less than 1 m from the surface. While it has long been known that a zone of thawed soil/sediment begins to form around a stream channel as the summer flow season progresses, very little is known about the hydrology or the biogeochemistry of the hyporheic zone that develops within this thaw bulb. Substantial evidence from temperate streams (Duff and Triska 1990, Triska et al. 1990, Wondzell and Swanson 1996a, Mulholland et al. 1997, Dahm et al. 1998, Hill et al. 1998, Baker et al. 1999, Chapra and Runkel 1999) suggests that the hyporheic zone can be an important – perhaps critical – source of organic matter turnover and nutrient regeneration. The first studies on hyporheic dynamics in polar regions have only recently been published (Edwardson 1997, Runkel et al. 1998, McKnight et al. 1999, Gooseff 2001, Gooseff et al. 2002, Maurice et al. 2002, Edwardson et al. in press, Gooseff et al. in press a). We initially assumed that hyporheic processing in steams in these extreme environments would be rather limited by low temperatures, either directly (through physical control by permafrost) or indirectly (through limitation on biochemical processes; e.g. mineralization of organic matter). However, results from research published in these recent papers suggests that biogeochemical processing in hyporheic zones is important in Arctic and Antarctic streams as well as temperate streams (at least during the flowing season). Virtually nothing is known about this important interaction in Arctic landscapes, nor how climate change may affect this interaction and the transport of solutes to coastal zones.

Influences of climate change on Arctic stream geomorphology: Polar regions are particularly sensitive to climate change. Recent studies suggest that the hydrologic regime of polar watersheds is already responding to climate change (Stone et al. 2002), resulting in warmer soil and active layer temperatures (Zhang et al. 1997). Modeling exercises suggest that increased air temperatures will increase active layer depths across the Arctic tundra landscape (Hinzman and Kane 1992, Kane et al. 1992).

The effects of global warming on Arctic hydrology and geomorphology are poorly known. Watershed morphology in Arctic regions is strongly controlled by permafrost, ice, and snow. Because watershed morphology and hydrologic response are tightly coupled, changes in watershed morphology due to thawing permafrost will undoubtedly cause changes in the hydrologic response, in addition to the direct hydrologic changes in a new climate. For example, McNamara et al. (1997 and 1998) showed that permafrost, snow, and ice strongly control the timing, magnitude, and sources of streamflow during rainstorms and snowmelt in the Kuparuk River basin. In addition, McNamara et al. (1999) analyzed channel networks obtained from a digital elevation model and field mapping in the Imnaviat Creek watershed to show that permafrost has restricted the erosional development of the basin. ‘Immature’ channel networks are directly responsible for many of these hydrologic observations. McNamara et al. (2000) showed that channel ice exerts different controls on channel morphology depending on watershed size. In headwater basins anchor ice acts as an erosion inhibitor and the channels are undeveloped. In large basins cap ice acts as a scouring agent and the channels are enlarged. Results of this fundamental field work are currently being used to simulate geomorphic and subsequent hydrologic changes in Arctic tundra river basins caused by a warming climate.

Hyporheic Dynamics in Polar Streams: There are few reports in the literature on hyporheic dynamics in polar streams. Recently several papers have been published on stream/hyporheic systems in Antarctica. Antarctic stream systems are ephemeral (10-12 week flowing period) and are relatively simple, both physically and biologically, compared to temperate streams. They have a saturated near-stream active layer (thaw bulb) that extends downward <1 m to permafrost and laterally several meters toward dry soils. There are no hillslope processes contributing to Antarctic stream hydrology. Runkel et al. (1998) found evidence of large hyporheic zones and rapid hyporheic exchange in a small Dry Valley stream, and attributed these characteristics to the highly porous, unconsolidated streambed substrate. Studies of chemical weathering in Antarctic streams suggest that hyporheic exchange controls stream chemistry to a large degree, because of the simplified hydrology (Gooseff et al. 2002, Maurice et al. 2002). McKnight et al. (1999, in press) and Gooseff (2001) have shown that hyporheic processes are important to Antarctic stream N cycling, providing a location of nitrate reduction.

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Literature on hyporheic dynamics in Arctic streams is virtually non-existent. Arctic streambeds experience the same active layer dynamic (thaw through the summer), but also interact with local tundra hillslope inputs. Results from field studies reported by Edwardson (1997) and Edwardson et al. (in press) are consistent with results from previous studies on the controls of hyporheic exchange in temperate mountain streams, which suggest that geomorphic profiles of stream channels (longitudinal more so than lateral) provide the necessary hydraulic gradients to drive hyporheic exchange through the streambed (Harvey and Bencala 1993, Kasahara and Wondzell 2003). However, we are unaware of any literature on the effects of changing active layer depth on hyporheic zone dynamics in Arctic streams. Edwardson (1997) and Edwardson et al. (in press) showed that biogeochemical processing, in the field, was important and could potentially supply from 14 to162% of the benthic N uptake requirements in the Kuparuk River. Bowden (unpublished data) used hyporheic microcosms to demonstrate that there is a stoichiometric relationship between oxygen consumption and respiration in hyporheic sediments and to explore how key environmental driving variables (N concentration, C source, temperature, oxygen level) affect N and P dynamics in hyporheic sediments. Finally, there is tantalizing evidence from our long term nutrient data and from Peterson et al. (1992) for the Kuparuk River that nitrate fluxes through the Kuparuk River actually increase over the season, despite increasing biotic demand, possibly (we suspect) as a consequence of the increasing influence of the hyporheic zone.

Hyporheic Processes and Climate Change in the Arctic: This background leads us to believe that hyporheic processes are important in the Arctic, not just physically, but biogeochemically and ecologically. The distribution and extent of thawed soils and sediments in the Arctic region is the result of a delicate balance between energy gains and losses across the landscape. There is growing evidence that climate may change radically in the Arctic in the near future and a few reports have addressed the possible consequences of these changes on aquatic ecosystems (e.g. Rouse et al. 1995, Hodkinson et al. 1999, Hobbie et al. 1999, Arctic Climate Impact Assessment, in preparation at http://www.acia.uaf.edu/). Notably, however, none of these reports considers how a future warmed climate might change sub-stream active layer depths and hyporheic extent or functions. As streams are the primary conduits of water and materials from land to the coast, stream – and hyporheic – processes may have significant influences on the fluxes of nutrients through whole Arctic systems. PROPOSED RESEARCH

We propose one central hypothesis with four associated objectives that will explore the relationships between channel geomorphology, thaw bulb extent, hyporheic functions and biogeochemical dynamics in Arctic streams (Fig. 1, above). Research results generated from this exploration will provide a foundation for assessing the probable consequences of climate change on geomorphology and biogeochemistry in Arctic tundra streams. Central Hypothesis

As the extent of the sub-stream thaw bulb increases through a summer, the physical dimensions of the hyporheic zone also increases, as does the potential for biogeochemical processing in the hyporheic zone. The interactions between thaw depth and hyporheic functions operate within a structure dictated by channel geomorphology. Specific Objectives

1. Select and characterize stream reaches that represent the range of geomorphologic conditions in rivers of the North Slope.

2. Monitor the sub-stream thaw bulb size through the thaw season using ground penetrating radar and subsurface temperature measurement in several stream cross-sections within each reach.

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3. Conduct repeated hyporheic exchange studies (stream solute addition experiments) through the thaw season in each reach to determine hyporheic hydraulic characteristics.

4. Conduct repeated measures of nutrient (N and P) concentrations and turnover time in the hyporheic zone through the thaw season in each reach to determine biogeochemical characteristics.

Methods

Objective 1: Site Selection and Geomorphologic characterization

We have tentatively selected 6 sites that represent three different winter ice conditions, the logic being that the winter ice condition has important controls on channel geomorphology. Ice conditions include 1) cap-ice with no open surface water, 2) bed-ice reach with no open surface water, and 3) spring-fed stream that remains ice-free in the winter. Each site will be described and classified according to the system described in Montgomery and Buffington (1997) to determine potential reach-scale geomorphologic controls on hyporheic extent (i.e. riffle/pool sequence, bends versus straight reaches). These sites include:

Kuparuk at Pipeline: The Kuparuk River at the Trans-Alaska Pipeline crossing is a fourth order stream (blue-line network on a USGS 1:63360 map) that has been the site of numerous hydrologic, geomorphologic, and biologic studies since 1980. It is a riffle/pool reach that freezes solid with bed ice each winter.

Kuparuk Headwaters: The Kuparuk headwater site is located approximately 10 km upstream from the pipeline site at the confluence of two second-order streams. Both tributaries and the main stream below the confluence freeze to bed ice. One tributary is fed by a series of lakes and has a plane-bed morphology and the other originates as small channels in the foothills of the Brooks Range and has a step-pool morphology. The main stream below the confluence has a plane-bed morphology.

Kuparuk Headwater Spring: A spring located midway between the pipeline and headwaters sites freezes solid most winters, but opens well before the mainstem so that the streambed is exposed to high snowmelt flows.

Toolik Inlet: The Toolik Inlet is a small stream that flows into Toolik Lake. It is fed by a series of lakes and has a plane-bed morphology.

Kuparuk Icing: A permanent icefield located approximately 25 km downstream of the pipeline is fed by localized groundwater springs. The channel remains open all winter most winters.

Toolik River: The Toolik River site is selected because a previous study revealed that unfrozen water exists through the winter under cap ice.

Objective 2: Monitor depth of thaw in each reach The depth of thaw in the stream bed will be monitored using ground penetrating radar (GPR) and in-situ thermistor profiles in several cross-sections within each reach to capture the influence of sub-reach geomorphologic variability.

GPR Investigations: In GPR studies, the transmitting antenna generates an oscillating electric field that propagates through the subsurface and is reflected at boundaries separating materials with differing electric properties (electric permittivity, magnetic permeability, and conductivity). The reflected wavefield is recorded and used to produce a reflector map that is an image of electric impedance contrasts in the subsurface. The reflector map is similar to a cross section of the subsurface. Radar is primarily sensitive to contrasts in electric permittivity, and there is a large permittivity contrast between ice and water (~4:80). A number of models have been developed to describe the relationship between the material filling the pore space and electric permittivity (Greaves et al. 1996). Although there are some variations, each of these models indicate that replacing water in the pore space with ice yields a significant decrease in electric permittivity, or equivalently an increase in radar velocity. Field observations have verified this effect (Hinkel et al., 2001). For example, Arcone et al. (1998) found that electric permittivity decreased

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by a factor of 4 or more at the saturated sediment/permafrost boundary at Ft. Wainwright, Alaska. They were able to map strong reflections associated with this contact both above and below the permafrost layer. A strong sensitivity to water, and the fact that GPR can provide high resolution sub-surface geophysical information, suggests that radar is optimal for mapping the saturated sediment/permafrost boundary. We have conducted preliminary modeling that demonstrates the excellent potential for GPR to measure the depth of thaw (Fig. 2).

The resolving power of the GPR system will limit the thickness of a thaw depth that we can measure accurately. The wavelength (λ) of the signal controls the resolution with a shorter wavelength signal capable of resolving finer features. Wavelength and frequency are inversely related so that higher frequencies correlate with greater resolving power. However, higher frequencies are attenuated more strongly, so there is always a trade off between resolution and depth of penetration. Lateral resolution is a function of depth and is given by /2zλ , where z is depth. In the migrated domain, the depth dependence is eliminated and the lateral resolution is approximately λ/2. The often quoted λ/4 vertical resolution limit (Yilmaz 2001) means that objects closer than this distance cannot be identified as two separate objects. This will be the lower limit of our ability to accurately measure the thickness of the thaw bulb, but in practice we are typically limited to values somewhat higher than this. The wavelength of the signal decreases with velocity so that low velocities lead to higher resolution potential. Because the thaw bulb is comprised of water saturated sediments, the velocity is very low and we have maximal resolution potential. Preliminary modeling suggests that we can expect to measure the sub-stream thaw depths as thin as 10 cm with 200 Mhz antennas, 5 cm with 450 Mhz antennas, or 2.5 cm with 900 Mhz antennas. For the proposed application of measuring the thaw bulb beneath a river bed, we have an added complication. Water strongly attenuates the radar signal, and the rate of attenuation increases as the

Figure 2. Finite-difference simulation showing the response of a 200 Mhz GPR signal to thaw-bulb thicknesses of 0.4 m and 1 m. There is a strong reflection from both the water bottom (WBR) and the permafrost boundary (PMR). The large impedance contrasts at the water bottom and permafrost boundaries generate high-amplitude multiple returns (WBM, IBM) that must be considered in processing and interpretation.



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dissolved solid concentration (and electrical conductivity) increases. In spite of this limitation, several authors have demonstrated that GPR can be effective for providing high-resolution sub-bottom images in fresh water bodies where the water has relatively low conductivity (Haeni et al. 1999). The electrical conductivity of the water streams and rivers in the tundra foothills of the North Slope depends in part on the geology of the land that the streams drain. On older landscapes the conductivity is low (~30 μS/cm). Streams draining the younger landscapes may have electrical conductivities of ~120 μS/cm. These levels should not prohibit effective sub-streambed imaging with radar. An unknown is what frequency will be capable of reaching the target depth, which as previously mentioned, will limit our resolution potential. We have GPR system capability ranging from 25 - 900 Mhz and anticipate that peak antenna frequencies in the range of 200 - 900 Mhz will provide adequate penetration.

We will conduct an initial set of experiments with a range of antenna frequencies to determine the optimal acquisition hardware and geometry for the monitoring surveys. Data will be acquired with the antennas placed in the bottom of a small non-metallic boat that is tethered on either side of the river. A string odometer system will be used to trigger the GPR at regular intervals as the boat is pulled across the channel. Once we have determined optimal acquisition parameters, a profile will be acquired every 1-2 weeks at each site to monitor the change in thaw bulb extent through time. Additionally, we will acquire an expanding spread profile at each location to measure the radar velocity in the water saturated sediment and permafrost. We will apply this information in an appropriate mix model (Greaves et al. 1996) to estimate porosity.

Thermistor profiles: We will confirm that our interpretations of the GPR output are consistent with the actual extent of the sub-stream thaw bulb depth with a series of nested thermistor arrays to monitor sub-stream temperature. We will establish a minimum of two cross-sections consisting of four vertical temperature profiles in each reach. More nested thermistors will be used if necessary, to capture responses to the geomorphic variability of a particular site. Thermistors will be soldered to 2-conductor wire in a waterproof casing. Each profile will consist of approximately six depths in the bed. Actual depths will be determined at the time of installation. All thermistors in a reach will be monitored with a CSI CR10X logger with a 32 channel multiplexer. Installing thermistors in the stream sediments in a design that will withstand the breakup period will be challenging. We will install thermistors at the road-accessible Kuparuk at Pipeline and Toolik Inlet sites in early Winter 2003 after the stream and sediments are frozen. A gas-powered jack hammer will be used drill access holes in the ice, and a gas powered auger will be used to drill access holes for the thermistors. Cables will be directed underground from the thermistors to dataloggers on the floodplain. We have successfully used this installation method in the past. These will be the only two sites with thermistors during the first field season. During the early Fall 2004 when the depth of thaw is at a maximum we will install thermistors in other sites using conventional techniques taking care to route cables in a manner to protect against them breakup in the Spring. We acknowledge that we will not be able to install thermistors in the deep-water Toolik River site with the resources available on this project. We believe we will have sufficient data from other sites, however, to verify relationships between GPR images and a water/ice interface detected by thermistor profiles.

Objective 3: Hyporheic hydraulics

Background: The thaw bulb extent under an Arctic tundra stream may or may not coincide with the extent of the hyporheic zone. The sub-stream thaw bulb is a zone in which water is in its liquid state (i.e.; great than 0oC). However, that water may or may not exchange readily with water in the open channel. The hyporheic zone is a saturated zone adjacent to or beneath a stream in which stream water has recently entered and will eventually leave. (Note: For the purposes of this proposal we will include parafluvial zones within the general definition of hyporheic zones.) As a rule of thumb, at least 10% of the water in the hyporheic zone is made up of stream water (sensu Triska et al. 1989). Thus, the hyporheic zone is a subset of the saturated near-stream active layer, but is not necessarily identical (in size) to it. Stated differently, the extent of the saturated near-stream active layer sets the potential for the development of the hyporheic zone. Other factors (e.g.; substrate characteristics, stream slope, hillslope hydrology, and geomorphology) determine how much of this potential is fulfilled. With this in mind, we

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Figure 3. Example of groundwater flow model and particle tracking model results for a 2nd-order stream in the H.J. Andrews Experimental Forest. Hyporheic upwelling and downwelling lengths are denoted by LUPand LDN respectively. Red flow paths return to the stream (hyporheic), blue flow paths do not.

Nested hyporheic flow paths

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Figure 3. Example of groundwater flow model and particle tracking model results for a 2nd-order stream in the H.J. Andrews Experimental Forest. Hyporheic upwelling and downwelling lengths are denoted by LUPand LDN respectively. Red flow paths return to the stream (hyporheic), blue flow paths do not.


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propose that the growth of this sub-stream thaw bulb through the Arctic summer directly influences the extent of near-stream sediments within which hyporheic exchange occurs. While there is an extensive body of literature on hydrologic active layer dynamics (e.g. Hinzman et al. 1991, Woo and Winter 1993, Woo and Xia 1996, Nelson et al. 1998, Woo 2000, Metcalfe and Buttle 2001), we unaware of any studies on sub-stream thaw bulb dynamics in Arctic settings, though we are aware of one study on sub-stream thaw bulb dynamics, in Antarctic streams (Conovitz, 2000).

We propose to use several different methods to monitor the influence of transient storage and hyporheic exchange on stream solute transport.

Monitoring water isotope distributions: Previous studies of stable isotopes of water (D and 18O) at the watershed scale in nearby Imnaviat Creek watershed have suggested that streamflow is generally all new water during snow melt, but mostly old water during summer rain storms, and that fractionated snowmelt and active layer soil waters have similar depleted signatures (Cooper et al. 1993, McNamara et al. 1997). We intend to analyze a smaller spatial scale by sampling stream water and hyporheic waters within our reference stream reaches to determine long (weeks to months) time scale hyporheic exchange throughout the summer, similar to the technique of Gooseff et al. (in press, a). We expect that sub-surface waters will have a distinctly different isotopic signature than stream waters. Inputs of snowmelt and rain through the summer will provide altered isotopic stream signals which we intend to capture in hyporheic isotope samples. Samples will be acquired from the same samplers used in the Hyporheic Regeneration studies (Objective 4, below).

Repeated Solute Addition Experiments: Solute injection experiments are commonly used to characterize hyporheic exchange. A conservative tracer (e.g. bromide) is introduced at a point in the stream and measured over time at a number of downstream points. This data set can be used as the input to solute transport models to discern the influences of transport processes (advection, dispersion) including transient storage within the hyporheic zone (Harvey et al. 1996, Harvey and Wagner 2000). Alternative models based on a single mass transfer coefficient (Bencala and Walters 1983, Runkel 1998) or a distribution of transfer coefficients (Haggerty and Reeves 2002, Haggerty et al. 2002) exist for modeling stream solute transport. This method provides reach-scale estimates of hyporheic exchange, but does not provide details about specific flow paths.

We will also run up to 5 conservative solute addition experiments on each experimental reach identified in Objective 1 throughout the summer to quantify distinct changes in the tailing behavior of the solute breakthrough curves downstream. For these experiments our preference is to use Rhodamine WT dye (RWT) because it can be detected over a very wide range of concentration and during long-term slug addition experiments, late-time concentrations will clearly be low. However, we recognize that RWT is not an ideal conservative tracer. Thus we intend to derive RWT sorption isotherms using streambed substrate and use additions of a conservative salt tracer (e.g. Br) in place of RWT, should we find that RWT strongly sorbs in the tundra stream field settings.

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Figure 4. Results of an RWT slug tracer experiment in a 2nd order stream in HJ Andrews Experimental Forest.Figure 4. Results of an RWT slug tracer experiment in a 2nd order stream in HJ Andrews Experimental Forest.

Groundwater flow and particle tracking models: These alternative models identify hyporheic flow paths based on hydraulic head gradients generated by fluvial geomorphology and stream water elevations (Wondzell and Swanson 1996b, Kasahara and Wondzell 2003). An example application is shown in Fig. 3 (previous page) for a 2nd-order stream reach in the H.J. Andrews Experimental Forest. Spatial survey data were collected for the reach to create a digital elevation model (DEM) of the streambed as well as the stream water surface. The DEMs were used as input to a groundwater flow model (MODFLOW) to provide a physical template through which hyporheic exchange is simulated. The groundwater flow model was run to steady state. A particle tracking model uses the information from the groundwater model to provide information that can be used to determine hyporheic flow path lengths and travel times, and hyporheic exchange upwelling and downwelling lengths (Fig. 3).

In the first field season we propose to collect the stream survey data necessary to parameterize and run these models for each stream reach identified in Objective 1. This information will be useful for our other modeling efforts as well. We will relate the information about hyporheic upwelling and downwelling lengths to the geomorphic characteristics of the selected stream reaches. Residence Time Distribution models: Gooseff et al. (in press, b) have shown that a single mass transfer coefficient model often does not adequately fit the observed distribution of stream RWT concentrations late in slug addition tracer experiments (Fig. 4). Rather, stream storage characteristics are better portrayed with a distribution of residence times. A solute transport model (STAMMT-L) has been developed (Haggerty and Reeves 2002) which represents exchange with a user-specified residence time distribution (RTD) applied to a general one-dimensional advection-dispersion transport equation:

tC

xC

DxC

vtC S

tot ∂∂

−∂∂

+∂∂

−=∂∂

β2

2

(Eq. 1) where, v is the mean advection velocity (equivalent to discharge divided by cross sectional area of the stream, Q/A (m s-1)), βtot is the ratio of storage to stream volumes, t is time, x is distance downstream, C is the stream solute concentration (concentration units), CS is the hyporheic zone solute concentration (concentration units), and D is dispersion (m2 s-1). In the general RTD model, the storage zone concentrations are defined as:

∫ ∂−∂

=∂∂ tS dg

ttC

tC

0

* )()( τττ (Eq. 2)

where, τ is a lag time (s). The function g*(t) is a general probability density that a tracer molecule entering the hyporheic zone at t = 0 will still be in the hyporheic zone at time t. This function can be defined with a distribution of residence times, corresponding to a particular RTD type. For instance, previous work by Haggerty et al. (2002) and Gooseff et al. (in press, b) suggests that stream RWT concentration breakthrough curves behave as power-laws at late time in stream tracer experiments. For a power-law RTD, g*(t) takes on the form

∫ −−−− −

−=

max

min

22

min2

max

*

)()2(

)(ω

ω

ω ωωωω

dek

tg tkkk (Eq. 3)

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where, ω is a first order mass-transfer rate coefficient (s-1), and k is the power-law coefficient, which is given by the slope of late time concentration tail. Application of this model is presented in Figure 4.

Particle travel times from groundwater flow modeling (described above) can be used to derive a distribution function similar to the g*(t) function from the solute transport modeling. For each particle that returns to the stream within the reach (defining the flow path as hyporheic) a flow weighted probability (f(T)) is generated as:

∑=

− −= n

i

Si

Si

ii

Q

Qff

1

1)T()T( for all i > 1 (Eq. 4)

where, SiQ is the vertical component of the flow in the starting cell of particle i. For each particle, a

corresponding travel time from release at t = 0 to emergence into the stream is noted as Ti. Also, f(T0) = 1. This derivation is similar to that of Elliott and Brooks (1997), in which they term a function similar to the f(t) function a distribution of residence times (or RTD). The final probability density function is computed as

∫=

end

start

t

tdttf

tftg)(

)()(* (Eq. 5).

The g*(t) functions from the solute transport and groundwater flow model approaches can then be compared to elicit characteristics of hyporheic exchange based on reach-scale transport processes defined by an explicit physical template.

We intend to use this combined solute transport/groundwater and particle tracking modeling approach to characterize differences in RTDs as the saturated near-stream active layer and hyporheic zone grow through the summer. Surveys of our selected stream reaches (Objective 1) will provide groundwater flow modeling data. Ground penetrating radar measurements and streambed temperature data (Objective 2) will provide potential depths of hyporheic zone extent as an additional constraint for the groundwater flow and particle tracking modeling. Additional long term exchange data from stream and hyporheic water isotopic analyses will provide comparisons with solute and groundwater model g*(t) results. We hypothesize that as the summer progresses there will be a general shift in the shape of the g*(t) curve toward functions that indicate increased hyporheic retention. Objective 4: Hyporheic regeneration Background: The extent of the hyporheic zone is defined by points at which sub-surface waters under and adjacent to a stream contain at least 10% of stream water that has recently been in the open channel and will eventually return to the open channel (Triska et al. 1989). The exchange of stream water into and out of stream-bed sediments has been shown to be an important component of stream water residence times in temperate catchments (Bencala 2000, Haggerty et al. 2002). This exchange of stream water with hyporheic water is driven by hydraulic head gradients, which to a large degree are dictated by stream channel geomorphology (Harvey and Bencala 1993, Kasahara and Wondzell 2003). Hyporheic exchange lengthens contact time with more extensive sediment surface areas which promotes nutrient cycling in temperate streams (Grimm and Fisher 1984, Duff and Triska 1990, Jones et al. 1995, Dahm et al. 1998, Hill et al. 1998). Limited evidence suggests that similar processes occur in polar streams (McKnight et al. 1999, Gooseff 2001, McKnight et al. in press, Edwardson 1997, Edwardson and Bowden in press).

In particular, Edwardson (1997), Edwardson et al. (in press) have shown that biogeochemical processing in the hyporheic zones of Arctic tundra streams in the Toolik Lake and Kuparuk River region is extensive and important. In recent experiments, we have demonstrated that these biogeochemical processes are rapid and responsive to key environmental variables (e.g.; temperature, nutrient loading and type, dissolved organic carbon level) (Bowden unpublished data).

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This objective (4) links Objective 3 (Hyporheic hydraulics) to these previous observations. We expect that as the hyporheic zone grows during the thawed season, biogeochemical regeneration from the hyporheic zone will increase as well. Hyporheic samplers: We will install hyporheic samplers based on a design modified from Edwardson (1997). This samplers will be installed at the same times and places that the thermistors are installed in Objective 2. Thus, the samplers will be deployed at several nested depths and at several locations within riffles, habitats where we have confirmed that biogeochemical cycling and regeneration are particularly strong. Our experience is that some samplers will fall in areas that are thawed but have very low hydraulic conductivity and thus, do not fall in the hyporheic zone, per se. Thus, we can control for samplers that are in the thawed bulb but not the hyporheic zone.

These hyporheic samplers can be used for several different purposes that are of central importance to address our proposed hypothesis. First, the samplers will be used to acquire the sub-stream water samples that will be used for isotopic analyses relevant estimation of residence time in Objective 3. Second, we can use these samplers to determine vertical hydraulic gradients and estimate hydraulic conductivity in the vicinity of the installed units. Both of these metrics will be useful for our modeling efforts, described in Objective 3. Third, water will be extracted from these samplers during conservative tracer runs to evaluate the timing and extent of conservative tracer penetration into the hyporheic zone within the selected study reaches. Finally, and most importantly, we will measure nutrients (NH4

+, NO3-,

and PO43-) in the same samples, to assess whether and to what degree nutrients accumulate or are taken up

in transit through the hyporheic zone. These assessments will be done at several times over the season. This information on nutrient content will be combined with information about water flux from the groundwater transport and particle tracking models, to determine nutrient fluxes through the hyporheic zone in the different geomorphic reaches identified in Objective 1. RESPONSIBILITIES AND TIMELINE FOR PROPOSED PROJECT ACTIVITIES Bowden will be responsible for overall management and administration of the project and will mentor one graduate student (to be named) who will focus biogeochemical dynamics in the hyporheic zone (Objective 4). Gooseff will be responsible for the solute injection experiments, isotope analyses, and hyporheic modeling described in Objective 3 and will mentor one graduate student (to be named) who will focus on this aspect of the project. McNamara will be responsible for the installation of the samplers and thermistors and with Branford will manage the GPR effort. McNamara will mentor one graduate student (to be named) who will focus on interpretation of the GPR and thermistor data (Objective 2). The entire team will participate in the characterization work outlined in Objective 1, although McNamara will manage this effort. We expect to employ 3 undergraduate students (one from each institution) to assist with field work at the Toolik Field Station. These same students (and/or others) will assist with data reduction during the off-season.

The time line for this proposed research is as follows:

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Task/Activity J J A S O N D J F MA MJ J A S O N D J F MA MJ J A S O N D J F MA MJ J A S O NReconnaissancePlanningFabrication, hyporheic samplers/thermistorsInstallation, hyporheic samplers/thermistors (1)Data acquistion, thermistors (2)Stream GPR surveysIntensive reach charaterizationHyporheic sampling (isotopes, nutrients) (3)Solute injection experimentsModelling and synthesis (4)Papers and/or presentationsNotes:1 - Winter installation by drilling frozen permafrost is preferred. A summer installation (see Edwardson 1997) is planned as a backup.2 - Gray indicates time of early winter installtion is successful.3 - Gray indicates possible backup sampling season, if needed.4 - Includes NSF automatic, no-cost extension period as backup.

Award PeriodPostFY1 (2003/2004) FY1 (2004/2005) FY1 (2005/2006)Pre

STRATEGIC CONTEXT FOR THIS RESEARCH: INTELLECTUAL MERIT AND BROADER IMPACTS This research falls within the mission the Office of Polar Programs which includes, in part, support for interdisciplinary research that provides a better understanding of earth and biological sciences in the Arctic (Arctic Research Opportunities, NSF 00-96). This proposed research is directly relevant to the mission of the Arctic Systems Science (ARCSS) program, especially the Study of Environmental Arctic Change (SEARCH) and the Arctic Freshwater Cycle initiative within SEARCH. Quoting from this latter solicitation (NSF 02-071):

“Land-based systems, including continental water, glaciers, and terrestrial ecosystem elements, figure prominently in [recent changes to high-latitude ocean dynamics], yet are incompletely understood due to the complexity of land-based hydrologic processes and the absence of coordinated observations and process modeling. Changes in precipitation, evaporation, snowmelt, permafrost and freeze-thaw dynamics, vegetation, and biogeochemistry are linked directly to changes in the pan-Arctic freshwater budget.”

The research we have proposed here seeks to more completely understand these complexities – or ‘Unaami’ (i.e.; inter-related, pan-Arctic, decadal change) as defined in the draft SEARCH Implementation Strategy (January 2003). We seek to address these complexities under both current conditions and (eventually) conditions that may prevail in a future changed climate. This research directly addresses several aspects of Question 5 in the SEARCH Implementation Strategy, specifically: “5) How does Unaami interact with biogeochemical cycles? 5a) How are key biogeochemical (e.g., C, N, P, S, greenhouse gasses, and contaminants cycles) coupled with Unaami?” and especially…“5c) Is Unaami affecting fluxes of dissolved and particular matter from land to sea (e.g., coastal erosion) that, in turn, influences ecosystem dynamics?”

Our proposed efforts are relevant to the development of the Distributed Terrestrial Observatories strategy (DTO, Section 4.1.4 in the SEARCH Draft Implementation Strategy), especially items a) Climate, Weather, Snow and Permafrost, d) Runoff and Runoff Chemistry, and h) Soil, Stream, and Lake Chemistry and Aquatic Productivity. It is also relevant to the ‘Linkages and Global Coupling’ strategy (LGC, Section 4.2.2), especially item i) Feedbacks Within the Arctic System: Land Surface-Atmosphere. This proposed research will take advantage of existing infrastructures and knowledge bases identified as priority resources for DTO’s (Section 5.1.6), in particular, the Toolik Lake LTER and Kuparuk River watershed monitoring networks to which both Bowden and McNamara currently contribute.

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This research is also consistent with previous, comprehensive assessments of hydrologic research needs in the Arctic. These were most recently reviewed and enumerated in the ARCUS workshop publication entitled The Hydrologic Cycle and its Role in Arctic and Global Environmental Change: A Rationale and Strategy for Synthesis Study (CHAMP) (Vörösmarty et al. 2001). The focus on this comprehensive report was largely on the physical hydrology of land-atmosphere-ocean systems in the Arctic. However, one of the Key Unresolved Scientific Questions (of four enumerated) from this report was “What are the direct impacts of Arctic hydrology changes on nutrient biogeochemistry and ecosystem structure and function?” The workshop participants recommended that: “Interdisciplinary synthesis studies linking hydrologic processes with other dependent biogeochemical and biogeophysical process should be fostered.”

In a summary section entitled Current Gaps in Understanding the Pan-Arctic Hydrological Cycle, this workshop group identified the following key questions, which the research proposed here is designed to address:

• “What is the timing and magnitude of sediment, carbon, and nutrient loads from hillslopes to large rivers and what is the effective constituent discharge of ice-affected rivers?

• How will sediment and other constituent discharges change as permafrost distribution responds to climate warming?

• What are the controls on the transfer of nutrients and organic matter from soils to [and through] streams across the pan-Arctic?”

Clearly, results from the research proposed here are necessary to provide a foundation for

predicting the consequences of a changing climate in the Arctic on overall stream structure and function. In addition, better understanding of the hydrological and biogeochemical dynamics in Arctic landscapes and streams is important in its own right as input to models that we are currently developing as a part of the Arctic LTER and OPP (Streams and Lakes) research programs (see Results from Previous Research). Indeed, this project will both benefit from and contribute to these efforts. The purpose of the research proposed here is to provide this foundation and to develop initial hypotheses about the possible influences of expected climate change scenarios. In subsequent research, we will propose to test these hypotheses through simulation modeling, based on the foundation developed here.

There is virtually no reported literature on the structure and functions of the hyporheic zone in Arctic systems. Considerable research in temperate regions suggests that hyporheic zones are critical components of stream ecosystems. A significant portion of the primary production in streams may be supported by nutrients regenerated from hyporheic processes. This regeneration must be dependent on organic matter inputs (both autochthonous and allochthonous). And so hyporheic processing is also important in understanding how streams modify C transport across landscapes. Research which quantifies these important functions in Arctic streams is non-existent.

Research on this subject is important as a direct input to our understanding of the ecological functions of Arctic streams. However, this research has broader implications for climate change research, as discussed above. Given that rivers are the conduits that link land to the ocean, then processes within streams that modify material transport must be important to understand how runoff from land affects oceans. Furthermore, if climate change affects the rate or extent of in-stream processing, then there may be important impacts on the transport of materials from land to the ocean, which this research would begin to address. These studies are essential therefore, to provide data and knowledge that will be of use to other scientists, policy makers, and resources managers.

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INTEGRATION OF RESEARCH AND EDUCATION This project will directly engage 3 graduate students and 3 or more undergraduate students in research that is part of a much larger integrated program of research centered at the Toolik Field Station (TFS) in Alaska. Through their work at TFS these students will be exposed to wide range of some of the best Arctic research scientist in the world and will interact with a diverse community of other students and technicians. Specific opportunities for sharing and learning include the weekly ‘Toolik Talk’ seminar series held during the summer at TFS and the annual Arctic LTER/OPP cooperators meeting held in Woods Hole, Massachusetts to which all students are invited. INTEGRATING DIVERSITY INTO NSF PROGRAMS, PROJECTS, AND ACTIVITIES

We intent to solicit applications from underrepresented minorities for the graduate and undergraduate research opportunities associated with this project. It would be difficult to accommodate persons with some – especially physical – disabilities in the field work at TFS. However, this is not exclusively the case and undergraduates with disabilities will be encouraged to assist with data reduction and other support activities at the home institutions for the PIs. LOGISTICS SUPPORT NEEDS

This research will be based out of the University of Alaska’s Toolik Field Station (TFS) on the North Slope of Alaska. In the first winter of this award period be propose to install equipment at the two accessible stream reaches. We anticipate that this effort will take up to two total weeks and, for safety reasons, should include a crew of up to 3 persons. Thus, there will be a need for up to 42 person days in the early winter of 2004. Transport needs can be satisfied with ordinary trucks and snowmobiles. During the spring to autumn field seasons of 2004-2006 there will be three PIs, three graduate students and up to three undergraduates who will utilize the TFS facilities. Bowden and McNamara already participate in projects that are funded from the TFS facility. Thus, there can be some economies of scale in their person-day needs and we request only an additional two weeks for each (14 person days total). Gooseff requests on month of logistics support (28 person days). For each of the three graduate students and the three undergraduates, we request 56 days (8 weeks) of person-day support. To efficiently cover the very early and very late field season periods it is likely that these days will not be scheduled contiguously. Instead, these persons (or subsets of them) will shuttle to and from the TFS from Fairbanks. To save costs we request support to rent a truck that can be used to shuttle project personnel between Fairbanks and TFS as well as to do field work from the TFS. In total we request support for 392 person days at TFS each year. Some additional laboratory space will be required. However, we again expect some economy of scale in the close connections between this proposed work and the existing work being done by Bowden and McNamara. We believe that we can work within the existing space allocations we have to accomplish this research.

Four for the six selected stream reaches are located at sites that are too difficult to access by foot in a single day. To complete the stream reach characterizations (Objective 1), the regular GPR surveys and thermistor datalogger maintenance (Objective 2), the solute addition experiments (Objective 3), and the hyporheic sampling (Objective 4), we will require helicopter support. We anticipate up to 4 visits and each of these 4 remote sites, each year. On each visit at team of up to 6 persons would shuttle to a particular reach, with equipment. While these sites are difficult to access by foot with the equipment we need to take, they are easily accessible by helicopter. We anticipate two rapid, roundtrip shuttles to bring personnel and equipment to a reach on one day, followed by a similar retrieval the following day. These trips would require about 1h of helicopter time total on each day. For 4 sites, visited 4 times, on 2 successive days, with 2 roundtrips per day, we will require 64 total short-haul trips per season or a total of 32 h of helicopter time.

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LITERATURE CITED (PI’s papers and Graduate Student theses supported by NSF funds noted with *) Arcone SA, DE Lawson, AJ Delaney, JC Strasser, and JD Strasser. 1998. Ground-penetrating

radar reflection profiling of groundwater and bedrock in an area of discontinuous permafrost: Geophysics, 63:1573-1584.

*Arscott DB. 1997. Comparison of epilithic algal and bryophyte metabolism in an arctic tundra stream, Alaska. University of New Hampshire. MS.

*Arscott DB, WB Bowden, and JC Finlay. 2000. Effects of desiccation and temperature/irradiance on the metabolism of 2 Arctic stream bryophyte taxa. Journal of the North American Benthological Society 19(2):263-273.

*Arscott DB, WB Bowden, and JC Finlay. 1998. Comparison of epilithic algal and bryophyte metabolism in an arctic tundra stream, Alaska. Journal of the North American Benthological Society 17(2): 210-227.

Baker MA, CN Dahm, and HM Valett. 1999. Acetate retention and metabolism in the hyporheic zone of a mountain stream. Limnology and Oceanography 44: 1530-1539.

Bencala KE. 2000. Hyporheic zone hydrological processes. Hydrological Processes 14:2797-2798.

Bencala KE, and RA Walters. 1983. Simulation of solute transport in a mountain pool-and-riffle stream: a transient storage model. Water Resources Research 19:718-724.

*Bowden WB, BJ Peterson, J Finlay, and J Tucker. 1992. Epilithic oxygen production and consumption in a fertilized arctic stream. Hydrobiologia 240:121-131.

*Bowden WB, JC Finlay, and PE Maloney. 1994. Long-term effects of PO4 fertilization on the distribution of bryophytes in an arctic stream. Freshwater Biology 32:445-454.

Chapra SC, and RL Runkel. 1999. Modeling impact of storage zones on stream dissolved oxygen. Journal of Environmental Engineering 125: 415-419.

Conovitz PA. 2000. Active layer dynamics and hyporheic zone storage in three streams in the McMurdo Dry Valleys, Antarctica. Masters Thesis, Department of Natural Resources, Colorado State University, Fort Collins CO, 168 p.

Cooper LW, C Solis, DL Kane, and LD Hinzman. 1993. Application of Oxygen-18 tracer techniques to Arctic hydrological processes. Arctic and Alpine Research, 25:247-255.

Craig PC and PJ McCart. 1975. Classification of stream types in Beaufort Sea drainages between Prudhoe Bay, Alaska, and the MacKenzie Delta, N.W.T., Canada. Arctic and Alpine Research, 7(2):183-198.

Dahm CN, NB Grimm, P Marmonier, HM Valett, and P Vervier. 1998. Nutrient dynamics at the interface between surface waters and groundwaters. Freshwater Biology 40:427-451.

Duff JH, Triska FJ. 1990. Denitrification in sediments from the hyporheic zone adjacent to a small forested stream. Canadian Journal of Fisheries and Aquatic Sciences 47: 1140-1147.

*Edwardson KJ. 1997. Characterizations of hyporheic influences on the hydrology and biogeochemistry of arctic tundra streams. University of New Hampshire. MS.

*Edwardson KJ, WB Bowden, C Dahm, and J Morrice. Transient storage and hyporheic transport in arctic tundra streams. Advances in Water Resources (In press).

Elliott AH, and NH Brooks. 1997. Transfer of nonsorbing solutes to a streambed with bed forms: Theory. Water Resources Research 33:123-136.

*Finlay JC and WB Bowden. 1994. Controls on production of bryophytes in an arctic tundra stream. Freshwater Biology 32:455-466.

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*Gooseff MN. 2001. Modeling hyporheic exchange influences on biogeochemical processes in Dry Valley streams, Antarctica. Ph.D. Dissertation, Civil, Environmtental, and Architectural Engineering. University of Colorado. Boulder, CO 137 p.

*Gooseff MN, McKnight DM, Lyons WB, Blum AE. 2002. Weathering reactions and hyporheic exchange controls on stream water chemistry in a glacial meltwater stream in the McMurdo Dry Valleys. Water Resources Research 38: 1279, doi:10.1029/2001WR000834, 2002

*Gooseff MN, DM McKnight, RL Runkel, and BH Vaughn. Determining long-time scale hyporheic zone flow paths in Antarctic streams. Hydrological Processes (in press, a)

*Gooseff MN, SM Wondzell, R Haggerty, JK Anderson. Comparing transient storage modeling and residence time distribution (RTD) analysis in geomorphically varied reaches in the Lookout Creek basin, Oregon, USA. Advances in Water Resources (in press, b).

*Gooseff MN, JE Barrett, P Doran, AG Fountain, WB Lyons, AN Parsons, DL Porazinska, RA Virginia, and DH Wall. 2003. Snow patch influence on soil biogeochemical processes and invertebrate distribution in the McMurdo Dry Valleys, Antarctica. Arctic, Antarctic, and Alpine Research, 35:92-100.

Greaves RJ, DP Lesmas, JM Lee, and MN Toksoz. 1996. Velocity variation and water content estimated from multi-offset, ground-penetrating radar. Geophysics, 61:683-695.

Grimm NB, and SG Fisher. 1984. Exchange between interstitial and surface water: implications for stream metabolism and nutrient cycling. Hydrobiologia 111:219-228.

Haeni FP, CJ Powers, EA White, and R Versteeg. 1999. Continuous seismic-reflection and ground-penetrating radar methods for subsurface mapping in water-covered glaciated areas, GSA 1999 Annual Mtg.: Denver, CO, Geol. Soc. Amer., p. 142.

Haggerty R, and PC Reeves. 2002. STAMMT-L Version 1.0 User's Manual. ERMS #520308, Sandia National Laboratories, Albuquerque, New Mexico.

Haggerty R, SM Wondzell, and MA Johnson. 2002. Power-law residence time distribution in the hyporheic zone of a 2nd-order mountain stream. Geophysical Research Letters 29:10.1029/2002GL014743.

*Harvey CJ, BJ Peterson, WB Bowden, AE Hershey, MC Miller, LA Deegan, and JC Finlay. 1998. Biological responses of Oksrukuyik Creek, a tundra stream, to fertilization. Journal of the North American Benthological Society 17(2): 190-209.

*Harvey CJ, BJ Peterson, WB Bowden, LA Deegan, JC Finlay, AE Hershey, and MC Miller. 1997. Organic matter dynamics in the Kuparuk River, a tundra river in Alaska, USA. Journal of the North American Benthological Society 16:18-23.

Harvey JW, and KE Bencala. 1993. The effect of streambed topography on surface-subsurface water exchange in mountain catchments. Water Resources Research 29: 89-98.

Harvey JW, and BJ Wagner. 2000. Quantifying hydrologic interactions between streams and their subsurface hyporheic zones. In JB Jones and PJ Mulholland, editors. Streams and Ground Waters. Academic Press, San Diego, CA.

*Hershey A, WB Bowden, L Deegan, JE Hobbie, BJ Peterson, G Kipput, G Kling, M Lock, M Miller, R Vestal. 1997. The Kuparuk River: a long-term study of biological and chemical processes in an arctic river. In: A. Milner and M. Oswood (eds.). Freshwaters of Alaska. Ecological Synthesis. Ecological Studies Series, Volume 119. Springer-Verlag. New York.

Hill AR, Labadia CF, Sanmugadas K. 1998. Hyporheic zone hydrology and nitrogen dynamics in relation to the streambed topography of a N-rich stream. Biogeochemistry 42: 285-310.

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Hinkel KM, JA Doolittle, JG Bockheim, FE Nelson, R Paetzold, JM Kimble, and R Travis. 2001. Detection of subsurface permafrost features with ground-penetrating radar, Barrow, Alaska. Permafrost and Periglacial Processes, 12: 179-190.

*Hinzman LD, M Nolan, A Carr, DL Kane, CS Benson, M Sturm, GE Liston, JP McNamara, and D Yang. 2000. Estimating snowpack distribution over a large arctic watershed. Proceedings of American Water Resources Spring Specialty Conference: Water Resources in Extreme Environments. Anchorage, Alaska, May 1-3, 2000.

Hinzman LD, and DL Kane. 1992. Potential response of an arctic watershed during a period of global warming. Journal of Geophysical Research-Atmospheres, 97 (D3):2811-2820.

Hinzman LD, DL Kane, RE Gieck, and KR Everett. 1991. Hydrologic and thermal properties of the active layer in the Alaskan Arctic. Cold Regions Science and Technology, 19:95-110.

*Hobbie JE, LA Deegan, BJ Peterson, EB Rastetter, GR Shaver, GW Kling, WJ O'Brien, FST Chapin, MC Miller, GW Kipphut, WB Bowden, AE Hershey and ME McDonald. 1995. Long-term measurements at the Arctic LTER site, pp. 391-409. In T M Powell and JH Steele (eds.), Ecological Time Series. Chapman and Hall, New York.

*Hobbie JE, BJ Peterson, N Bettez, LA Deegan, WJ O'Brien, GW Kling, GW Kipphut, WB Bowden, and AE Hershey. 1999. Impact of global change on the biogeochemistry and ecology of an Arctic freshwater system. Polar Research 18 (2):207-214

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Arctic hyporheic proposal - Project text for circulation