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A Landscape Model to Predict Total Nitrogen Levels in Surface Waters of the Willamette and Central Valleys Ecoregion of the Western United States
Daniel T. Heggem 1, Anne C. Neale 1, Robert K. Hall 2, and K. Bruce Jones 1
1 USEPA ORD Environmental Sciences Division, Landscape Ecology Branch, Las Vegas, NV 89119
2 USEPA Region 9, WTR2, 75 Hawthorne St., San Francisco, CA 94105
Excess nutrients are a leading cause of impairment to streams, rivers, lakes and the coastal ecosystems. Excessive nutrient loadings result in increased primary productivity of plant and algal communities leading to eutrophication and other impacts to aquatic resources. Nitrogen is an essential macronutrient for primary production of plant communities and, when out of balance, is a direct contributor to water body impairment. As a part of the Western Environmental Monitoring and Assessment Program (EMAP), we are developing a landscape indicator to predict nitrogen loading to western aquatic systems. The key to this work is to establish a quantitative relationship between landscape pattern metrics and nitrogen loading in streams. A number of recent studies have shown strong relationships between surface water quality and landscape characteristics. In this study, a simple nutrient export simulation model based on land-cover composition is used to estimate total loads of nitrogen to the stream using EMAP surface water nitrogen data collected in Oregon in 1997 and 1998. A regression model is developed using the landscape metric of nitrogen loading and relating that metric to the surface water nitrogen data. This paper describes this model and then applies it to the Willamette and Central Valley nutrient ecoregions. This model will be a valuable tool for land use managers in determining nutrient conditions in surface waters and for identifying and reporting impaired water bodies.
Keywords: Nutrient modeling, nitrogen modeling, modeling, nitrogen, landscapes