GEOC 31 |
| Anne C. Sigleo, COAS, COAS, US EPA & OSU, 2111 SE Marine Science Drive, Newport, OR 97365 |
| Rivers draining watersheds of the Coast Range in the northwestern United States frequently contain high concentrations of dissolved nitrate, particularly after high flow events (up to 180 microM nitrate-N). The nitrate source appears to originate from the fixation of atmospheric nitrogen by Red Alder (Alnus spp.) which forms a symbiotic relationship with the actinomycete Frankia spp. The three likely sinks for the dissolved nitrate include sediment sorption, photosynthetic (algal) uptake and denitrification. Elevated 15N:14N ratios in phytoplankton in several regions of the Yaquina estuary suggested that active denitrification was occurring during the summer months, forcing late summer plankton to utilize residual, isotopically heavy nitrate. To verify this hypothesis, potential denitrification activity was measured in surface sediments of the Yaquina Estuary during the summer, fall and winter of 2003. Sediment cores from selected sites indicated significant denitrification activity. Nutrient data from the water column at the stations studied indicated that as denitrification activity increased, the dominant species of nitrogen changed from nitrate to ammonium. The results indicate that the system shifts from a dominantly autotrophic system in spring to a more heterotrophic system in late summer and early fall. |
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Multi-Tracer Studies in Geochemistry: When the Sum is Greater Than the Parts
8:10 AM-11:30 AM, Monday, March 29, 2004 Marriott -- Marquis NW, Oral
Division of Geochemistry |