Tuesday, June 5, 2007
433

Nitrate Retention Capacity in Streams of the Wisconsin Sand Plains

Robert S. Stelzer1, David G. Flagel1, Susan L. Eggert2, and Maureen A. Muldoon3. (1) Biology and Microbiology, University of Wisconsin Oshkosh, 800 Algoma Blvd, Oshkosh, WI 54901, (2) USDA Forest Service North Central Research Station, 1831 Hwy 169 East, Grand Rapids, MN 55744, (3) Geology, University of Wisconsin Oshkosh, 800 Algoma Blvd, Oshkosh, WI 54901

Streams in the Central Sand Plains of Wisconsin have nitrate concentrations among the highest for surface water in the upper Midwestern United States, primarily due to irrigated row-crop agriculture.  Because agricultural streams contribute disproportionately to continental-scale nutrient export it is particularly important to better understand the ability of such streams to process nutrients.  We used a mass balance approach to assess nitrate retention capacity in two Central Sand Plains’ streams.  Water samples for nutrients were collected biweekly from surface water at upstream and downstream stations and from groundwater in riparian wells and minipiezometers with the aim of intercepting short and long groundwater flowpaths, respectively. Chloride was used to establish water balance.  Groundwater nitrate concentrations ranged from undetectable to 30 mg NO3-N/L while surface water concentrations ranged from 1.5 to 4 mg NO3-N/L.  Nitrate concentrations in surface water tended to be lower during the growing season than during winter.  Preliminary results suggest that net nitrate retention in these sand plain streams is negligible during the winter and higher during the growing season. 


Web Page: www.uwosh.edu/faculty_staff/stelzer

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