HR: 09:45h
AN: NB21D-06 INVITED     [Abstracts]
TI: Atmosphere-soil drivers and internal stream cycling of DON in forested watersheds
AU: * Brookshire, E J
EM: ebrooksh@vt.edu
AF: Department of Biology, Virginia Tech, Blacksburg, VA 24061
AU: Valett, H M
EM: mvalett@vt.edu
AF: Department of Biology, Virginia Tech, Blacksburg, VA 24061
AU: Thomas, S A
EM: sat43@cornell.edu
AF: Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853
AU: Webster, J R
EM: jwebster@vt.edu
AF: Department of Biology, Virginia Tech, Blacksburg, VA 24061
AB: Dissolved organic nitrogen (DON) often dominates N loss from unpolluted watersheds but is not thought to vary with N inputs, capital, or demand. Here we show results from a multi-year survey of soils and streams in forested mountain watersheds spanning a wide atmospheric N deposition gradient (5 to 45 kg N ha ^-1yr^-1) in the Appalachian Mts., USA. Stream DON and dissolved inorganic N (DIN) concentrations increased significantly and non-linearly with higher atmospheric deposition, shifting abruptly at a threshold deposition of ~ 9 kg N ha ^-1yr^-1). Dissolved organic matter (DOM) C: N ratios declined with increased deposition, suggesting a shift in DOM quality. Soil C: N ratios showed steep declines with N deposition (from ~ 30 to 17). As a result, DON and DIN losses were negatively associated with soil C: N ratios. Temporal patterns in DON were not seasonal but rather related to antecedent precipitation. Yet, previous experiments showed rapid stream cycling of added monomeric DOM, suggesting an important role for labile DON in stream metabolism. Such forms, while low in abundance, may influence internal N demand in streams. At the landscape scale, atmospheric deposition, soil chemistry and hydrologic conditions are key drivers of watershed DON losses.
DE: 0400 Biogeosciences
DE: 1615 Biogeochemical processes (4805)
DE: 9901 NABS Student Award - Basic Research
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly