VADOSE ZONE INTERACTION WITH HYPORHEIC ZONE NITROGEN CYCLING
Doug Higbee BAE 558 Fluid Mechanics of Porous Materials May 8,
2009
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Introduction The Hyporheic Zone is that part of the ground
water/surface water continuum containing water originating both
from the neighboring aquifer and from the river channel. Butturini,
A., Bernal, S., Sabater,. S., and Sabater, F., 2002. The influence
of riparian-hyporheic zone on the bydrological responses in an
intermittent stream. Hydrology and Earth System Sciences, Volume
6(3), pp 515-525.
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Introduction
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Introduction
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Introduction Geologic Compartments of the Riparian Zone Vadose
Zone: portion that lies above the annual water table, characterized
by variable saturation Hyporheic Zone: portion that lies below
annual water table, characterized by saturated flow
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Introduction Riparian Ecosystem Vegetative growth Rich soil
deposits Water availability Benthic organisms Wildlife habitat
Water quality Stream biota ESA (i.e., bull trout)
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Introduction Presentation Content Nitrogen cycle Delineation of
the hyporheic zone Fluid mechanics of the hyporheic zone Watershed
hydrology and the hyporheic zone Nitrogen cycling in the hyporheic
zone
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Nitrogen Cycle
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Benefits of Nitrogen Essential element for all plants and
animals Creation of proteins Amino acids (DNA & RNA) Plant
respiration All nitrogen obtained by animals can be traced back to
the eating of plants at some stage of the food chain.
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Nitrogen Cycle Nitrogen Fixation Necessary to free up nitrogen
from gas form for use by organisms. Fixation through: Lightning
Nitrogen fixing bacteria Through the process of mineralization
(ammonification) nitrogen is also converted from organic nitrogen
to: Ammonium (NH 4 -) Nitrite (NO 2 -) Nitrate (NO 3 -)
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Nitrogen Cycle Nitrification: Conversion of ammonia to nitrates
Primarily by soil bacteria Also by bacteria in hyporheic zone
Aerobic environment nitrosomonas nitrobacter
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Nitrogen Cycle Denitrification: reduction of nitrates to
nitrogen gas (N 2 ) Anaerobic environment Deeper regions of the
hyporheic zone Pseudomonas Clostridium
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Hyporheic Zone Delineation Boundary surface water/ground water
Does not necessarily extend to outer riparian zone Oxygenated
surface water Benthic habitat extending below vegetated area
Extents Can extend hundreds of meters from the stream bank, and
greater. Depending on fluvial geomorphology and surrounding
topography Field methods Shallow wells Monitor water chemistry and
gradients Tracer injection Monitor with time domain reflectometry
or ground- penetrating radar
Hyporheic Zone Delineation Tracer Injection Monitoring with
Ground-Penetrating Radar John Bradford (Boise State University)
Michael Gooseff (Penn State University) Jim McNamara (Boise State
University) http://water.engr.psu.edu/gooseff/gpr_hz_proj.html
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Hyporheic Zone Delineation Tracer Injection Piezometers 20cm
depth 40cm depth
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Hyporheic Zone Deliniation Tracer Injection
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Hyporheic Zone Delineation Tracer Injection
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Hyporheic Zone Delineation Tracer Injection
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Hyporheic Zone Delineation Potentiometric surface maps Ground
water elevation Horizontal direction of ground water flow Useful
for Qualitative flux analysis Not useful for quantifying flux
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Hyporheic Zone Fluid Mechanics Flow/flux determination Fluvial
geomorphology Typically for Saturated Flow o Darcys Law: q=K(dh/dx)
Directional o Hyporheic parallel to stream flow o Vadose/regional
groundwater perpendicular to stream flow Residence Time
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Hyporheic Zone Fluid Mechanics Fluvial Geomorphology
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Hyporheic Zone Fluid Mechanics Stream structures and
sinuosity
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Hyporheic Zone Fluid Mechanics Degree of saturation Hyporheic
saturated flow/non-saturated flow
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Hyporheic Zone Fluid Mechanics Residence Time Average linear
velocity V=(K/n)(dh/dl) Hyporheic zone deliniation Operational
definition, open to interpretation Hours -> Days ->
Weeks
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Watershed Hydrology and the Hyporheic Zone Hydrologic Cycles
surface water level fluctuation flux gradients Dynamic groundwater
surface water interaction
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Watershed Hydrology and the Hyporheic Zone Ephemeral
Streams
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Watershed Hydrology and the Hyporheic Zone Ephemeral
Streams
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Watershed Hydrology and the Hyporheic Zone Riparian zone
hydraulic recharge Vadose zone Seasonal recharge (longer) Hyporheic
zone Flood frequency (shorter)
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Nitrogen Cycling in the Hyporheic Zone Nitrogen cycle in the
hyporheic zone is directly affected by hydraulics and watershed
hydrology Degree of Saturation affects transport Hydraulics affect
residence time Hyporheic exchange- Hyporheic zones can be a source
or sink of NH 4
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Nitrogen Cycling in the Hyporheic Zone Basic diagram of the
nitrogen cycle.
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Nitrogen Cycling in the Hyporheic Zone Dissolved Oxygen (DO)
rich environment enables nitrification (aerobic conditions)
Continuous mixing of surface water and groundwater Dissolved
Organic Carbon (DOC) rich environment enables denitrification
(anaerobic conditions) Flood deposits - colloidal DOC transported
through porous media Typically the most common source of
electrons
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Nitrogen Cycling in the Hyporheic Zone Reduced mineral phases
also contribute to denitrification (Mn 2+, Fe 2+, S 2- ) Clay
particles can also be a significant source for denitrification pH
controls this process Sorption-desorption
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Nitrogen Cycling in the Hyporheic Zone
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Conclusion The hyporheic zone can potentially play a
significant role in the removal of nitrogen from streams and
rivers. Understanding the factors that influence gradients and
hydraulics is essential for analysis. Calculations of nitrogen load
from regional ground water to a river that do not account for
hyporheic zone chemical and biological transformations, could
result in significant errors. Hinkle, S.R., Duff, J.H., Triska,
F.J., Laenen, A., Gates, E.B., Bencala, K.E., Wentz, D.A., and
Silva, S.R., 2001. Linking hyporheic flow and nitrogen cycling near
the Willamette River a large river in Oregon, USA, Journal of
Hydrology, Volume 244, Issues 3-4, pp 157-180.