Annual Precipitation and Effects of Runoff Nutrient From Agricultural Watersheds on Water Quality

Declining surface water quality from agricultural nonpoint sources is of great concern across the Great Plains. Trends in the earth climate create abrupt changes in domestic weather (i.e., precipitation) that can alter the impact of the nonpoint sources on water quality. A 2-year (dry 2009 and wet 2010) study was conducted to assess the impact of soil C, N, and S losses by runoff on water quality of Salt Creek in the Roca watershed, Nebraska. Average dissolved nutrient concentrations in runoff were 95.4 and 94.9% of the total for the dry and wet years, respectively. The remaining nutrients in runoff were associated with sediment. Nutrient concentrations during the dry year were generally greater than those during the wet year. Average concentrations for 2009 were 63.2, 1.87, and 53.5 mg/L for C, N, and S, respectively, whereas concentrations for 2010 were 54.0, 3.0, and 16.6 mg/L, respectively. Total soil nutrient losses were greater for the wet year than those for the dry year. The dry year nutrient losses were 607, 19,978, and 441,569 metric tons for C, N, and S, respectively, whereas losses for the wet year were 1,997, 138,380, and 608,172 metric tons, respectively. These losses could be considered as the annual nutrient loadings for Salt Creek. Concentrations of C, N, and S measured in Salt Creek during the study were not expected to have any adverse effect on human/animal health or aquatic life. We concluded that greater precipitation during the wet year increased the impact on water quality and soil fertility in the Roca watershed.