HR: 13:30h
AN: B53A-01    [Abstracts]
TI: Seasonal and event-scale controls on dissolved organic carbon and nitrate flushing from catchments
AU: * Sebestyen, S D
EM: sdsebest@syr.edu
AF: State University of New York College of Environmental Science and Forestry, 211 Marshall Hall 1 Forestry Dr, Syracuse, NY 13210 United States
AU: Boyer, E W
EM: boyer@nature.berkeley.edu
AF: University of California, Berkeley, Hilgard Hall, Berkeley, CA 94720 United States
AU: Shanley, J B
EM: jshanley@usgs.gov
AF: US Geological Survey, 87 State St Room 324, Montpelier, VT 05602 United States
AU: Doctor, D H
EM: dhdoctor@usgs.gov
AF: US Geological Survey, 345 Middlefield Rd, Menlo Park, CA 94025 United States
AB: To explore terrestrial and aquatic linkages controlling nutrient dynamics in forested catchments, we collected high-frequency samples from 2002 to 2004 at the Sleepers River Research Watershed in northeastern Vermont USA. We measured DOC (dissolved organic carbon), SUVA (specific UV absorbance), nitrate, and major ion concentrations over a wide range of flow conditions. In addition, weekly samples since 1991 provide a longer term record of stream nutrient fluxes. During events, DOC concentrations increased with flow consistent with the flushing of a large reservoir of mobile organic carbon from forest soils. Higher concentrations of DOC and SUVA in the growing versus dormant season illustrated seasonal variation in sources, characteristics (i.e. reactivity), availability, and controls on the flushing response of organic matter from the landscape to streams. In contrast, stream nitrate concentrations increased with flow but only when catchments "wetted-up" after baseflow periods. Growing season stream nitrate responses were dependent on short-term antecedent moisture conditions indicating rapid depletion of the soil nitrate reservoir when source areas became hydrologically connected to streams. While the different response patterns emphasized variable source and biogeochemical controls in relation to flow patterns, coupled carbon and nitrogen biogeochemical processes were also important controls on stream nutrient fluxes. In particular, leaf fall was a critical time when reactive DOC from freshly decomposing litter fueled in-stream consumption of nitrate leading to sharp declines of stream nitrate concentrations. Our measurements highlight the importance of "hot spots" and "hot moments" of biogeochemical and hydrological processes that control stream responses. Furthermore, our work illustrates how carbon, nitrogen, and water cycles are coupled in catchments, and provides a conceptual model for future work aimed at modeling forest stream hydrochemistry at the catchment scale.
DE: 1806 Chemistry of fresh water
DE: 1860 Runoff and streamflow
DE: 1871 Surface water quality
SC: Biogeosciences [B]
MN: 2005 Joint Assembly