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., The influence of riparian-hyporheic zone on the bydrological responses in an intermittent stream. Hydrology and Earth System Sciences, Volume 6(3), pp

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

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)

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., 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