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Thursday, May 29, 2008 - 2:15 PM
573
Stream network position affects epilithic nitrogen to phosphorus ratio and nutrient uptake in a northern California watershed
Jill R. Welter1, Shawna S. Handschug1, John Schade2, and Carrie A. Booth3. (1) Biology Department, College of St. Catherine, 2004 Randolph Avenue, St. Paul, MN 55105, (2) Biology Department, St. Olaf College, Northfield, MN 55057, (3) Ecology, Evolution and Behavior, University of Minnesota, 1987 Upper Buford Circle, St. Paul, MN 55108
In the South Fork Eel River watershed, changes in light and source of organic matter in the drainage network influence food webs, but impacts on nutrient uptake are unclear. We compared uptake of DIN and PO4 by biofilms in 5 streams ranging in drainage area from 0.58-140 km2. Uptake was measured by incubating rocks collected from each site in re-circulating chambers. DIN and PO4 were added to chambers and uptake was estimated by change in nutrient concentration over time. Biofilms were analyzed for organic matter, chlorophyll a, and % carbon, nitrogen and phosphorus. DIN uptake was higher than PO4 uptake in all streams. DIN uptake showed little variation among sites, while PO4 uptake increased with drainage area, with the largest stream 4-fold higher than the smallest. The difference between DIN and PO4 uptake decreased with increasing drainage area, suggesting a shift from N towards P limitation. DIN uptake was not related to any explanatory variables. PO4 uptake was positively related to chl a and to biofilm N:P, both of which increased with drainage area. These results suggest decreasing severity of N limitation with increasing drainage area, leading to an increase in PO4 uptake as it becomes scarce relative to DIN.
Web Page: epilithon, nutrient uptake, drainage network