Hill, A. R.. York University, email@example.com
Devito, K. R.. University of Alberta, firstname.lastname@example.org
Sanmugadas, K. York University, email@example.com
DENITRIFICATION IN STREAM RIPARIAN ZONES: INFLUENCE OF INTERACTIONS BETWEEN HYDROLOGICAL FLOW PATHS AND SUPPLIES OF NITRATE AND CARBON.
Groundwater hydrology and chemistry were examined along transects across a 200m wide stream riparian forest zone which received large groundwater nitrate inputs from an agricultural sand plain in southern Ontario, Canada. Nitrate-rich (10-30 mg N/L) groundwater flowed along a subsurface horizontal path towards the stream in sands at depths of 2-4m below riparian organic soils. A large decline in groundwater nitrate concentrations to < 0.1 mg N/L was observed in a zone 20-40m from the stream bank. Analysis of N isotopes suggested that denitrification was the major mechanism of nitrate removal. Short-term injections of acetylene into piezometers which produced large increases in nitrous oxide, delimited a narrow zone of denitrification activity at depths of 1-3 m. In this zone, gradients of lower DO and higher DOC concentrations occurred at the interface between sands and buried channel bed deposits. Co-injection of either glucose or nitrate with acetylene into piezometers indicated that groundwater denitrification was limited by nitrate near the stream, whereas carbon limitation was important towards the riparian zone perimeter. These results suggest that subsurface denitrification in riparian zones is frequently restricted to
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