HR: 15:15h
AN: B33A-06    [Abstracts]
TI: Tracing Water and Nitrogen Sources to Identify Controls on Stream Nitrogen Variation.
AU: * Sebestyen, S D
EM: sds@nature.berkeley.edu
AF: University of California, 140 Mulford Hall ESPM 3114, Berkeley, CA 94720-3114, United States
AU: Boyer, E W
EM: boyer@nature.berkeley.edu
AF: University of California, 140 Mulford Hall ESPM 3114, Berkeley, CA 94720-3114, United States
AU: Shanley, J B
EM: jshanley@usgs.gov
AF: US Geological Survey, PO Box 628, Montpelier, VT 05602, United States
AU: Kendall, C
EM: ckendall@usgs.gov
AF: US Geological Survey, 345 Middlefield Road Bldg 15, McKelvey Building, Menlo Park, CA 94025, United States
AB: Our work explores ecological and hydrological processes that control the variation of key nitrogen species in streams of an upland catchment in northeastern Vermont, USA. Using high-frequency sampling over event and seasonal timescales along with chemical and isotopic tracers of water and nitrogen sources, we show how anthropogenic nutrient enrichment directly affected the forms and concentrations of nitrogen in streams draining a northern hardwood forest. Although flushing of nitrate from nitrified sources in soils is an important control on stream nitrogen variation during storm flow, atmospheric sources contributed up to 50 percent of the stream nitrate during specific runoff events. This atmospheric nitrate was delivered to the stream along preferential flowpaths effectively bypassing biogeochemical processes that typically retain nitrogen in the landscape. Furthermore, we investigated coupled biogeochemical transformations and hydrological transport processes to shed light on seasonal controls on the timing and magnitude of stream nitrogen fluxes. For example, stream nitrogen responses to autumn leaf fall showed that interactions of the water, carbon, and nitrogen cycles affected fluxes of nitrate and dissolved organic nitrogen in stream water. Overall, our high-frequency hydrochemical data provided key insights to open the blackbox of landscape processes that influence stream nutrient variation over time.
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 1803 Anthropogenic effects (4802, 4902)
DE: 1806 Chemistry of fresh water
DE: 1860 Streamflow
DE: 1879 Watershed
SC: Biogeosciences [B]
MN: 2007 Joint Assembly