HR: 14:00h
AN: NB13B-03    [Abstracts]
TI: Longitudinal Patterns of Metabolic Nutrients in a Large Midwestern River
AU: * Popp, A S
EM: aspopp@wisc.edu
AF: University of Wisconsin-Madison, Center for Limnology 680 N. Park St., Madison, WI 53706 United States
AU: Stanley, E H
EM: ehstanley@wisc.edu
AF: University of Wisconsin-Madison, Center for Limnology 680 N. Park St., Madison, WI 53706 United States
AB: Small streams can be more efficient at processing nutrients per unit length than large rivers, which are assumed to transport nutrients downstream without substantial transformation or retention. However, recent studies have suggested that processing in large channels may be substantial. Two longitudinal surveys were taken over a 36-mile section of the Wisconsin River to assess the degree of large-river nutrient processing. Samples were analyzed for DOC, specific UV absorbance (SUVA), chl-a, NH₄, NO₃, and SRP. NH₄ flux decreased logarithmically from 15g/s to 5g/s over 36 miles of river (R²=0.62, p<.01) and nitrate flux increased linearly from 30g/s to 65g/s over the same distance (R²=0.75, p<.01). NH₄ reduction is likely due to biological uptake and nitrification. DOC quality did not change with distance (R²=0.12, p=0.13), although overall DOC flux increased downstream (R²=0.99, p<.01), as did SRP flux (R²=0.45, p<.01). If the DOC increase were due to autochthonous (algal) sources, a change in DOC quality (SUVA) would be expected; however, no such change was observed. Therefore, there must be alternate sources of DOC along the study reach. We found evidence of significant in-channel carbon and nitrogen transformation in the Wisconsin River, indicating that large rivers may transform substantial quantities of nutrients.
DE: 0400 Biogeosciences
DE: 1806 Chemistry of fresh water
DE: 1860 Runoff and streamflow
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly