U.S. Department of Agriculture: Agricultural Research Service, Lincoln, Nebraska


Document Type


Date of this Version

April 2007


Published in Soil Science 2007;172:313-332.


The loss of agricultural chemicals in runoff from agricultural land is a major cause of poor surface water quality in the United State. Scientists (Natural Resources Conservation Service) developed a technique using climatic, hydrologic, and soil survey information to estimate the impact of agricultural watersheds on natural water resources. The objective of this study was to apply this technique on the Wagon Train (WT) watershed to predict loss of alkaline earth elements (calcium [Ca], magnesium [Mg], barium [Ba], and strontium [Sr]) by runoff from soils and to estimate elements loading into WT reservoir. The predicted losses of Ca, Mg, Ba, and Sr by runoff were 67.5, 19.9, 0.17, and 0.05 kg ha-1 yr-1, respectively. These data give a total annual loss of 262.1 and 77.1 Mg of Ca and Mg, respectively, for the entire watershed and could be considered as the annual loading for WT reservoir. The total annual loss was 668 kg for Ba and 186 kg for Sr and could represent the annual loading for the reservoir. The predicted Ca, Mg, and Ba concentrations in runoff were in good agreement with those observed in water samples collected weekly from the main stream in the watershed. However, the predicted Sr concentration in runoff was much less than that observed in the stream water. Subsurface seepage into the stream might contribute to the high Sr concentration observed in the stream water. We concluded that the technique could provide a reasonable estimation of Ca, Mg, and Ba losses in runoff from agricultural watersheds and loading into surface water bodies.