HR: 09:00h
AN: H51G-05    [Abstracts]
TI: Tracing Nitrogen Sources in Forested Catchments Under Varying Flow Conditions: Seasonal and Event Scale Patterns
AU: * Sebestyen, S D
EM: sdsebest@syr.edu
AF: State University of NY College of Environmental Science & Forestry, 211 Marshall Hall 1 Forestry Dr, Syracuse, NY 13210 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: Boyer, E W
EM: ewboyer@syr.edu
AF: University of CA Berkeley, Environmental Science, Policy, and Management Hilgard Hall, Berkeley, CA 94720 United States
AU: Kendall, C
EM: ckendall@usgs.gov
AF: US Geological Survey, 345 Middlefield Rd MS 434, Menlo Park, CA 94025 United States
AB: Our ability to assess how stream nutrient concentrations respond to biogeochemical transformations and stream flow dynamics is often limited by datasets that do not include all flow conditions that occur over event, monthly, seasonal, and yearly time scales. At the Sleepers River Research Watershed in northeastern Vermont, USA, nitrate, DOC (dissolved organic carbon), and major ion concentrations were measured on samples collected over a wide range of flow conditions from summer 2002 through summer 2004. Nutrient flushing occurred at the W-9 catchment and high-frequency sampling revealed critical insights into seasonal and event-scale controls on nutrient concentrations. In this seasonally snow-covered catchment, the earliest stage of snowmelt introduced nitrogen directly to the stream from the snowpack. As snowmelt progressed, the source of stream nitrate shifted to flushing of soil nitrate along shallow subsurface flow paths. In the growing season, nitrogen flushing to streams varied with antecedent moisture conditions. More nitrogen was available to flush to streams when antecedent moisture was lowest, and mobile nitrogen stores in the landscape regenerated under baseflow conditions on times scales as short as 7 days. Leaf fall was another critical time when coupled hydrological and biogeochemical processes controlled nutrient fluxes. With the input of labile organic carbon from freshly decomposing leaves, nitrate concentrations declined sharply in response to in-stream immobilization or denitrification. These high-resolution hydrochemical data from multiple flow regimes are identifying "hot spots" and "hot moments" of biogeochemical and hydrological processes that control nutrient fluxes in streams.
DE: 1806 Chemistry of fresh water
DE: 1860 Runoff and streamflow
DE: 1871 Surface water quality
DE: 1040 Isotopic composition/chemistry
DE: 1615 Biogeochemical processes (4805)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting