| Institution: | (1) Centro de Investigación Científica y de Educación Superior de Ensenada (CICESE), Departamento de Ecología, Baja California, Ensenada, Mexico;(2) Boyce Thompson Institute, Cornell University, 14850 Ithaca, NY, USA;(3) Kansas Geological Survey, University of Kansas, 66047 Lawrence, KS, USA;(4) National Institute of Water and Atmospheric Research (NIWA), M.R. Scarsbrook, P.O. Box 11-115, Hamilton, New Zealand;(5) National Institute of Water and Atmospheric Research (NIWA), M.A. Weatherhead, P.O. Box 8602, Christchurch, Riccarton, New Zealand;(6) Institute of Applied Environmental Research, Stockholm University, SE-10691 Stockholm, Sweden;(7) Department of Systems Ecology, Stockholm University, SE-10691 Stockholm, Sweden;(8) Present address: Department of Physical Geography, Stockholm University, SE-10691 Stockholm, Sweden;(9) P.O. Box 434844, San Diego, CA 92143-4844, USA |
| Abstract: | We have used a total of 496 sample sites to calibrate a simple regression model for calculating dissolved inorganic nutrient
fluxes via runoff to the ocean. The regression uses the logarithms of runoff and human population as the independent variables
and estimates the logarithms of dissolved inorganic nitrogen and phosphorus loading with R2 values near 0.8. This predictive capability is about the same as has been derived for total nutrient loading with process-based
models requiring more detailed information on independent variables. We conclude that population and runoff are robust proxies
for the more detailed application, landscape modification, and in-stream processing estimated by more process-based models.
The regression model has then been applied to a demonstration data set of 1353 river catchments draining to the sea from the
North American continent south of the Canadian border. The geographic extents of these basins were extracted from a 1-km digital
elevation model for North America, and both runoff and population were estimated for each basin. Most of the basins (72% of
the total) are smaller than 103 km2, and both runoff and population density are higher and more variable among small basins than among larger ones.While total
load to the ocean can probably be adequately estimated from large systems only, analysis of the geographic distribution of
nutrient loading requires consideration of the small basins, which can exhibit significant hydrologic and demographic heterogeneity
between systems over their range even within the same geographic region. High-resolution regional and local analysis is necessary
for environmental assessment and management. |
