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Communication at the NABS Annual meeting, Keystone, 2000
(396) NITRATE MOVEMENT AND TRANSFORMATION WITHIN THE UPPER MISSISSIPPI RIVER - FLOODPLAIN SYSTEM.
L.A. Bartsch, D.M. Soballe, W.B. Richardson, E.A. Strauss, and D.M. Wasley. Upper Midwest Environmental Sciences Center, U.S. Geological Survey, 2630 Fanta Reed Rd., La Crosse, WI 54603.
Nitrogen from the Mississippi River has been linked to ecological declines in the Gulf of Mexico. The potential for the riparian areas, floodplain and backwaters of the Upper Mississippi River (above the Missouri River confluence) to process nitrogen is not well understood. Further, nitrogen effects on biota in these areas are unquantified. To examine overall system processing of nitrogen, we performed a large-scale mass-balance analysis which indicated that the Upper Mississippi River and floodplain removes (on average) less than 15% of the total nitrogen input from the tributaries. To better understand small-scale nitrogen dynamics, we combined limnological data from stratified random sampling (1993-99) with detailed morphometry, output from a detailed flow model, and GIS technology to examine seasonal relationships among nitrogen (nitrate) concentrations, water movement, and biological transformation. We found the lowest nitrate concentrations (<0.25 mg/1) in fall (September-October), and the highest concentrations (>2 mg/1) during spring flooding (April-May). Consistent with biological transformation of nitrogen transported into off-channel areas from the main channel, we found that nitrate concentrations were generally lower in off-channel areas than in the main channel and decreased with increasing isolation (distance or time-of- travel) from main channel sources. This patterned varied dramatically with season.
Presented at 1:00 PM on Wednesday, May 31, 2000 in Nutrient Dynamics
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