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Thursday, June 7, 2007 - 9:00 AM
352
Tracing the Fate of 15N Enriched Lake-derived Seston in Four Outlet Streams in Arctic Alaska
Lisa Bare and Anne E. Hershey. Biology, UNC - Greensboro, 312 Eberhart, Greenboro, NC 27402
During the summers of 2005 and 2006, we enriched four lakes near Toolik Lake, arctic Alaska, with 15N-NH4+. Sampling of the lake outlet streams was conducted to determine the fate of lake-derived seston. Each outlet exhibited different physical characteristics: wetland-dominated with a low gradient; wetland-influence at outlet followed by a high gradient; heterogeneous channel with areas of subsurface flow; and a beaded stream characterized by a series of pools connected by narrow channels. Seston δ15N values obtained prior to 2006 enrichment show elevated δ15N when compared to that of an arctic reference stream, suggesting that the outlets retained 15N over fall, winter, and spring from the previous season. Preliminary analysis of longitudinal patterns of seston δ15N among outlets suggests that the beaded stream had greatest retention while lowest retention was exhibited by the outlet with a high gradient. These data suggest that physical characteristics of an outlet influence its ability to retain seston. Seston C:N in the high gradient stream increased with distance from the lake, indicating an increase in importance of terrestrial organic matter. The beaded stream seston showed no longitudinal pattern, with relatively low C:N throughout the reach, which likely reflects phytoplankton input from the pools.