VADOSE ZONE
INTERACTION WITH
HYPORHEIC ZONE
NITROGEN CYCLING
Doug Higbee
BAE 558 – Fluid Mechanics of Porous Materials
May 8, 2009
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
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.
Introduction
Introduction
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
Introduction

Riparian Ecosystem
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Vegetative growth
Rich soil deposits
Water availability
Benthic organisms
Wildlife habitat
Water quality
Stream biota
 ESA (i.e., bull trout)
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
Introduction
Nitrogen Cycle

Benefits of Nitrogen
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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.
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 (NH4-)
 Nitrite (NO2-)
 Nitrate (NO3-)
Nitrogen Cycle

Nitrification: Conversion of ammonia to
nitrates
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Primarily by soil bacteria
Also by bacteria in hyporheic zone
Aerobic environment
nitrosomonas
nitrobacter
Nitrogen Cycle
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Denitrification: reduction of nitrates to
nitrogen gas (N2)
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Anaerobic environment
Deeper regions of the hyporheic zone
Pseudomonas
Clostridium
Nitrogen Cycle
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Boundary – surface water/ground water
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Oxygenated surface water
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Extents
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Field methods
◦ Does not necessarily extend to outer riparian zone
◦ Benthic habitat extending below vegetated area
◦ Can extend hundreds of meters from the stream bank,
and greater.
◦ Depending on fluvial geomorphology and surrounding
topography
◦ Shallow wells
 Monitor water chemistry and gradients
◦ Tracer injection
 Monitor with time domain reflectometry or groundpenetrating radar
Hyporheic Zone Delineation
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Monitoring Wells
◦ Dissolved Oxygen (DO)
◦ Dissolved Organic Carbon (DOC)
◦ Groundwater gradient determination
Hyporheic Zone Delineation
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Tracer Injection
Hyporheic Zone Delineation
Tracer Injection
 Monitoring with
Ground-Penetrating
Radar
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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
Hyporheic Zone Delineation
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Tracer Injection
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Piezometers
◦ 20cm depth
◦ 40cm depth
Hyporheic Zone Delineation
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Tracer Injection
Hyporheic Zone Deliniation
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Tracer Injection
Hyporheic Zone Delineation
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Tracer Injection
Hyporheic Zone Delineation
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Potentiometric surface maps
◦ Ground water
elevation
◦ Horizontal
direction
of ground
water flow
◦ Useful for
Qualitative flux
analysis
◦ Not useful for
quantifying
flux
Hyporheic Zone Delineation
Flow/flux determination
• Fluvial geomorphology
• Typically for Saturated Flow
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Directional
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Darcy’s Law: q=K(dh/dx)
Hyporheic – parallel to stream flow
Vadose/regional groundwater – perpendicular
to stream flow
Residence Time
Hyporheic Zone Fluid Mechanics
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Fluvial Geomorphology
Hyporheic Zone Fluid Mechanics
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Stream structures and sinuosity
Hyporheic Zone Fluid Mechanics
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Degree of saturation
◦ Hyporheic saturated flow/non-saturated flow
Hyporheic Zone Fluid Mechanics
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Residence Time
◦ Average linear velocity
 V=(K/n)(dh/dl)
◦ Hyporheic zone deliniation
 Operational definition,
◦ open to interpretation
 Hours -> Days -> Weeks
Hyporheic Zone Fluid Mechanics
Hydrologic
Cycles
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◦ surface water
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level fluctuation
flux gradients
 Dynamic
groundwater
surface water
interaction
Watershed Hydrology and the
Hyporheic Zone
Ephemeral Streams
Watershed Hydrology and the
Hyporheic Zone
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Ephemeral Streams
Watershed Hydrology and the
Hyporheic Zone
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Riparian zone hydraulic recharge
◦ Vadose zone
 Seasonal recharge (longer)
◦ Hyporheic zone
 Flood frequency (shorter)
Watershed Hydrology and 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 NH4
Nitrogen Cycling in the
Hyporheic Zone
Basic diagram of the
nitrogen cycle.
Nitrogen
Cycling in the Hyporheic Zone

Dissolved Oxygen (DO) rich environment
enables nitrification (aerobic conditions)
◦ Continuous mixing of surface water and
groundwater
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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
Nitrogen Cycling in the
Hyporheic Zone
Reduced mineral phases also contribute to
denitrification (Mn2+, Fe2+, S2-)
 Clay particles can also be a significant
source for denitrification
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◦ pH controls this process
◦ Sorption-desorption
Nitrogen Cycling in the
Hyporheic Zone
Nitrogen Cycling in the
Hyporheic Zone
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.”
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◦
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.
Conclusion