Wednesday, May 28, 2008 - 3:30 PM
465

Nitrate retention in a Wisconsin sand plains stream: The influence of groundwater discharge

Robert S. Stelzer1, Damion Drover1, Maureen Muldoon2, and Susan L. Eggert3. (1) Biology and Microbiology, University of Wisconsin-Oshkosh, 800 Algoma blvd, Oshkosh, WI 54901, (2) Geology, University of Wisconsin-Oshkosh, 800 Algoma blvd, Oshkosh, WI 54901, (3) USDA Forest Service North Central Research Station, 1831 Hwy 169 East, Grand Rapids, MN 55744

Humans are rapidly modifying the global nitrogen cycle by increasing quantities of available forms of nitrogen. Many streams in the Central Sand Plains of Wisconsin receive large, spatially variable fluxes of nitrate in ground water.  Our main objective was to determine the capacity of a sand plains stream, Emmons Creek, to retain nitrate, while accounting for focused discharge of ground water.  We quantified nitrate inputs and outputs in a gaining 700-m reach of Emmons Creek and used a mass balance model to estimate nitrate retention.  Water samples were collected weekly from surface water at upstream and downstream stations and biweekly from 23 instream minipiezometers.  Chloride was used to establish water balance. Groundwater nitrate concentrations were weighted by specific discharge.  Nitrate concentrations in the surface water were lower in summer than in winter while nitrate concentrations in ground water did not show seasonal variation.  Nitrate retention ranged from 110 mg NO3-N m-2 d-1 in the winter to 550 mg NO3-N m-2 d-1 in the summer.  These values represented < 5 and 20 % of inputs to the reach during winter and summer.  Our results suggest that instream nitrate retention can be substantial during the growing season in these high-N ecosystems.


Web Page: nitrate retention, mass balance, ground water

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