HR: 09:10h
AN: H21F-05    [Abstracts]
TI: The Influence of Watershed Properties on the Large-Scale Transport of Nitrogen
AU: * Alexander, R B
EM: ralex@usgs.gov
AF: U.S. Geological Survey, 12201 Sunrise Valley Drive 413 National Center, Reston, VA 20192 United States
AU: Smith, R A
EM: rsmith1@usgs.gov
AF: U.S. Geological Survey, 12201 Sunrise Valley Drive 413 National Center, Reston, VA 20192 United States
AU: Schwarz, G E
EM: gschwarz@usgs.gov
AF: U.S. Geological Survey, 12201 Sunrise Valley Drive 413 National Center, Reston, VA 20192 United States
AU: Boyer, E W
EM: boyer@nature.Berkeley.EDU
AF: University of California Dept. of Environmental Science, Policy, and Management, 137 Mulford Hall #3114, Berkeley, CA 94720 United States
AU: Scott, D T
EM: dscott4@unlnotes.unl.edu
AF: University of Nebraska Dept. of Geosciences, 214 Bessey Hall, Lincoln, NE 68588 United States
AU: Harvey, J W
EM: jwharvey@usgs.gov
AF: U.S. Geological Survey, 12201 Sunrise Valley Drive 430 National Center, Reston, VA 20192 United States
AB: Considerable advances have been made in understanding the hydrological and biogeochemical processes that control nitrogen cycling and transport in soils, ground waters, and the riparian and hyporheic areas of streams. This includes expanded knowledge of the dynamic coupling of these processes and their influence on flow paths and residence times of nitrogen through landscapes. Much of the progress reflects improved understanding at small spatial scales. Less progress has been made in 'scaling-up' these processes to assess their large-scale effects on the downstream transport of nitrogen. Modeling techniques are viewed as essential scaling tools, but questions have emerged about how accurately complex mechanistic models describe the large-scale effects of processes on nitrogen cycling and transport. One area of increased modeling research emphasizes the use of less complex model structures to identify the principle controls at catchment and watershed scales. Here, we illustrate the use of spatially referenced, statistical models to identify major terrestrial and aquatic properties that influence nitrogen transport across a range of stream and watershed sizes. We use the Spatially Referenced Regression on Watershed Attributes (SPARROW) model of mean-annual total nitrogen loads, applied to major streams of the conterminous United States. The SPARROW model relates in-stream measurements of total nitrogen loads to geographic data on nitrogen sources and properties of the landscape that influence transport. The model employs mechanistic components and mass balance constraints within a formal parameter-estimation structure to empirically quantify the sources, attenuation rates, and transport of nitrogen through terrestrial and aquatic ecosystems. We identified the influence of topography, soils, climate, reservoirs, and in-stream and riparian properties on the long-term and long-distance transport of nitrogen. Nitrogen transport is best described by nonlinear interactions with these properties; the interactions only partially scale with catchment size. Progress in evaluating and scaling-up these relations is currently limited to watershed properties with well defined spatial attributes. We discuss the types of experimental and spatial data needed to further advance the use of models to describe nitrogen transport across broad temporal and spatial scales.
DE: 0469 Nitrogen cycling
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 1847 Modeling
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: Fall Meeting 2005