VADOSE ZONE INTERACTION WITH HYPORHEIC ZONE NITROGEN CYCLING

VADOSE ZONE INTERACTION WITH HYPORHEIC ZONE NITROGEN CYCLINGDoug HigbeeBAE 558 Fluid Mechanics of Porous MaterialsMay 8, 2009

IntroductionThe 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

IntroductionGeologic Compartments of the Riparian ZoneVadose Zone: portion that lies above the annual water table, characterized by variable saturationHyporheic Zone: portion that lies below annual water table, characterized by saturated flow

IntroductionRiparian EcosystemVegetative growthRich soil depositsWater availabilityBenthic organismsWildlife habitatWater qualityStream biotaESA (i.e., bull trout)

IntroductionPresentation ContentNitrogen cycleDelineation of the hyporheic zoneFluid mechanics of the hyporheic zoneWatershed hydrology and the hyporheic zoneNitrogen cycling in the hyporheic zone

Nitrogen Cycle

Nitrogen CycleBenefits of NitrogenEssential element for all plants and animalsCreation of proteinsAmino 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 CycleNitrogen FixationNecessary to free up nitrogen from gas form for use by organisms. Fixation through:LightningNitrogen fixing bacteria

Through the process of mineralization (ammonification) nitrogen is also converted from organic nitrogen to:Ammonium (NH4-)Nitrite (NO2-)Nitrate (NO3-)

Nitrogen CycleNitrification: Conversion of ammonia to nitratesPrimarily by soil bacteriaAlso by bacteria in hyporheic zone Aerobic environmentnitrosomonasnitrobacter

Nitrogen CycleDenitrification: reduction of nitrates to nitrogen gas (N2)Anaerobic environmentDeeper regions of the hyporheic zonePseudomonasClostridium

Hyporheic Zone DelineationBoundary surface water/ground waterDoes not necessarily extend to outer riparian zoneOxygenated surface water Benthic habitat extending below vegetated areaExtentsCan extend hundreds of meters from the stream bank, and greater. Depending on fluvial geomorphology and surrounding topography

Field methodsShallow wells Monitor water chemistry and gradientsTracer injectionMonitor with time domain reflectometry or ground-penetrating radar

Hyporheic Zone DelineationMonitoring WellsDissolved Oxygen (DO)Dissolved Organic Carbon (DOC)Groundwater gradient determination

Hyporheic Zone DelineationTracer Injection

Hyporheic Zone DelineationTracer InjectionMonitoring withGround-PenetratingRadar

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 DelineationTracer Injection

Piezometers20cm depth40cm depth

Hyporheic Zone DeliniationTracer Injection

Hyporheic Zone DelineationTracer Injection

Hyporheic Zone DelineationTracer Injection

Hyporheic Zone DelineationPotentiometric surface mapsGround water elevationHorizontal direction of ground water flowUseful for Qualitative flux analysisNot useful for quantifying flux

Hyporheic Zone Fluid MechanicsFlow/flux determinationFluvial geomorphologyTypically for Saturated FlowDarcys Law: q=K(dh/dx)DirectionalHyporheic parallel to stream flowVadose/regional groundwater perpendicular to stream flowResidence Time

Hyporheic Zone Fluid MechanicsFluvial Geomorphology

Hyporheic Zone Fluid MechanicsStream structures and sinuosity

Hyporheic Zone Fluid MechanicsDegree of saturationHyporheic saturated flow/non-saturated flow

Hyporheic Zone Fluid MechanicsResidence TimeAverage linear velocityV=(K/n)(dh/dl)Hyporheic zone deliniation Operational definition, open to interpretationHours -> Days -> Weeks

Watershed Hydrology and the Hyporheic ZoneHydrologicCyclessurface waterlevel fluctuation flux gradientsDynamicgroundwatersurface waterinteraction

Watershed Hydrology and the Hyporheic ZoneEphemeral Streams

Watershed Hydrology and the Hyporheic ZoneEphemeral Streams

Watershed Hydrology and the Hyporheic ZoneRiparian zone hydraulic recharge

Vadose zoneSeasonal recharge (longer)

Hyporheic zoneFlood frequency (shorter)

Nitrogen Cycling in the Hyporheic ZoneNitrogen cycle in the hyporheic zone is directly affected by hydraulics and watershed hydrologyDegree of Saturation affects transportHydraulics affect residence timeHyporheic 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 ZoneDissolved Oxygen (DO) rich environment enables nitrification (aerobic conditions)Continuous mixing of surface water and groundwaterDissolved Organic Carbon (DOC) rich environment enables denitrification (anaerobic conditions)Flood deposits - colloidal DOC transported through porous mediaTypically the most common source of electrons

Nitrogen Cycling in the Hyporheic ZoneReduced mineral phases also contribute to denitrification (Mn2+, Fe2+, S2-)Clay particles can also be a significant source for denitrificationpH controls this processSorption-desorption

Nitrogen Cycling in the Hyporheic Zone

ConclusionThe 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.

Chart178211

ATMOSPHERIC GASES78%21%1%

Sheet1ATMOSPHERIC GASESNitrogen78Oxygen21trace gases1To resize chart data range, drag lower right corner of range.