vadose zone interaction with hyporheic zone nitrogen cycling

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VADOSE ZONE
INTERACTION WITH
HYPORHEIC ZONE
NITROGEN CYCLING

Doug Higbee

BAE 558


Fluid Mechanics of Porous Materials

May 8, 2009

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.

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


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


Nitrogen Cycle

Nitrogen Cycle


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.



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
-
)




Nitrogen Cycle


Nitrification: Conversion of ammonia to
nitrates


Primarily by soil bacteria


Also by bacteria in hyporheic zone


Aerobic environment



nitrosomonas


nitrobacter

Nitrogen Cycle


Denitrification: reduction of nitrates to
nitrogen gas (N
2
)


Anaerobic environment


Deeper regions of the hyporheic zone


Pseudomonas


Clostridium

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


Monitoring Wells


Dissolved Oxygen (DO)


Dissolved Organic Carbon (DOC)


Groundwater gradient determination


Hyporheic Zone Delineation


Tracer Injection

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


Hyporheic Zone Delineation


Tracer Injection



Piezometers


20cm depth


40cm depth

Hyporheic

Zone
Deliniation


Tracer Injection

Hyporheic Zone Delineation


Tracer Injection

Hyporheic

Zone Delineation


Tracer Injection

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


Hyporheic

Zone Fluid Mechanics


Flow/flux determination


Fluvial geomorphology


Typically for Saturated Flow

o
Darcy’s Law: q=K(dh/dx)


Directional

o
Hyporheic


parallel to stream flow

o
Vadose/regional groundwater


perpendicular
to stream flow


Residence Time

Hyporheic

Zone Fluid Mechanics


Fluvial Geomorphology


Hyporheic

Zone Fluid Mechanics


Stream structures and sinuosity


Hyporheic

Zone Fluid Mechanics


Degree of saturation


Hyporheic saturated flow/non
-
saturated flow


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

Watershed Hydrology and the
Hyporheic

Zone


Hydrologic

Cycles



surface water



level fluctuation



flux gradients


Dynamic

groundwater

surface water

interaction

Watershed Hydrology and the
Hyporheic Zone

Ephemeral Streams

Watershed Hydrology and the
Hyporheic Zone


Ephemeral Streams

Watershed Hydrology and the
Hyporheic

Zone


Riparian zone hydraulic recharge



Vadose zone


Seasonal recharge (longer)



Hyporheic zone


Flood frequency (shorter)


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

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


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 (Mn
2+
, Fe
2+
, S
2
-
)


Clay particles can also be a significant
source for denitrification


pH controls this process


Sorption
-
desorption

Nitrogen Cycling in the

Hyporheic

Zone


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.