|YEN, HAW - Texas Agrilife Research|
|GAMBONE, MARILYN - Texas Agrilife Research|
Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2014
Publication Date: 4/23/2015
Citation: White, M.J., Harmel, R.D., Yen, H., Arnold, J.G., Gambone, M., Haney, R.L. 2015. Development of sediment and nutrient export coefficients for U.S. ecoregions. Journal of the American Water Resources Association. 51(3):758-775.
Interpretive Summary: In the U.S., many waterways are polluted with excessive nutrients and sediment. Export coefficients are a simple method to quantify the sources of pollutants in a watershed and develop a plan to reduce that pollution. Unfortunately there are not enough small watershed monitoring data to support the use of this method in many areas. In this research we seek to improve the accuracy of these nutrient export estimation methods by developing a national database of localized export coefficients by land use for each ecoregion in the U.S. This research allows a watershed planner to rapidly estimate the pollutant load for any small watershed in the U.S.
Technical Abstract: Water quality impairment due to excessive nutrients and sediment is a major problem in the U.S. The first step in the mitigation of impairment in any given water body is to determine pollutant sources and amount. The sheer number of impaired waters and limited resources makes simplistic load estimation methods such as export coefficient methods attractive. Unfortunately export coefficients are typically based on small watershed monitoring data which are very limited and/or often based on data collected from distant watersheds with drastically different land use and hydrologic conditions. In this research we seek to improve the accuracy of these nutrient export estimation methods by developing a national database of localized export coefficients by land use for each ecoregion in the U.S. A stochastic sampling methodology loosely based on the Monte-Carlo technique was used to construct a database of 45 million SWAT simulations. These simulations consider a variety of climate, topography, soils, weather, land use, management, and conservation implementation. Extensive effort was invested in successfully validating the SWAT model simulations with edge-of-field monitoring data. Simulated nutrient export coefficients compared favorably with previously published studies. The distribution of predicted export coefficients, exhibited considerable overlap with observed distributions derived from literature summaries. These export coefficients may be used to rapidly estimate nutrient loading for any small catchment in the U.S. provided the location, area, and land use distribution are known.