HR: 11:50h
AN: H51G-06    [PDF]
TI: Estimates of Nitrogen Removal in U.S. Streams and Reservoirs from the SPARROW Watershed Model
AU: * Alexander, R B
EM: ralex@usgs.gov
AF: US Geological Survey, 413 National Center 12201 Sunrise Valley Drive, Reston, VA 20192 United States
AU: Smith, R A
EM: rsmith1@usgs.gov
AF: US Geological Survey, 413 National Center 12201 Sunrise Valley Drive, Reston, VA 20192 United States
AU: Schwarz, G E
EM: gschwarz@usgs.gov
AF: US Geological Survey, 413 National Center 12201 Sunrise Valley Drive, Reston, VA 20192 United States
AU: Nolan, J V
EM: jnolan@usgs.gov
AF: US Geological Survey, 413 National Center 12201 Sunrise Valley Drive, Reston, VA 20192 United States
AU: Boyer, E W
EM: ewboyer@syr.edu
AF: State University of New York, College ot Environmental Science and Forestry 1 Forestry Drive, Syracuse, NY 13210 United States
AB: Greater understanding is needed of the biotic and abiotic processes that remove nitrogen (N) from streams and reservoirs to quantify transport to downstream coastal waters where eutrophication is a major concern. Recent studies have improved estimates of N removal rates (e.g., denitrification, biological uptake) over small spatial scales in low-order streams. However, limited knowledge of the factors that explain the large variation in literature removal rates has made it difficult to accurately predict N transport through the range of stream and reservoir sizes that link sources to downstream waters. Spatially referenced watershed models (SPARROW) have been used to statistically estimate long-term mean-annual rates of total nitrogen removal in streams and reservoirs over large spatial scales. These rates are estimated as a function of physical and hydraulic properties (channel depth, water travel time) that influence the contact and exchange of water with benthic sediment. We recently refined our SPARROW model structure with expanded descriptions of climatic, topographic, and other surficial features of terrestrial and aquatic landscapes. We find that the net rates of N removal decline from about 0.3 day-1 of water travel time in streams with depths less than 0.5 meters to negligible quantities in large rivers (greater than 4 meters). These rates are generally consistent with those of earlier regional and national SPARROW models and with measured rates from the literature (adjusted for water travel time) over the reported range of stream depths. A settling velocity of approximately 8 meters year-1 is estimated for lakes and reservoirs and agrees well with literature rates for lakes where denitrification is the predominant removal process. We applied these removal rates within the SPARROW stream and reservoir network to estimate the regional-scale N transport and delivery to U.S. coastal waters.
UR: http://water.usgs.gov/nawqa/sparrow
DE: 1803 Anthropogenic effects
DE: 1806 Chemistry of fresh water
DE: 1848 Networks
DE: 1857 Reservoirs (surface)
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: 2003 Fall Meeting