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Title: Annual precipitation and effects of runoff-nutrient from agricultural watersheds on water quality

Author
item ELRASHIDI, MOUSTAFA - Natural Resources Conservation Service (NRCS, USDA)
item SEYBOLD, CATHY - Natural Resources Conservation Service (NRCS, USDA)
item Delgado, Jorge

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2014
Publication Date: 2/24/2014
Citation: Elrashidi, M., Seybold, C., Delgado, J.A. 2014. Annual precipitation and effects of runoff-nutrient from agricultural watersheds on water quality. Soil Science. 178:679-688.

Interpretive Summary: Increasing nutrient enrichment of surface water bodies and subsequent decline in water quality is an issue that is gaining greater recognition across the Great Plains region. Of particular concern is the quality of surface waters in the Platte river basin in Nebraska. The goal of this 2-year project was to study the effect of annual precipitation on the nutrient enrichment in surface runoff entering natural water systems in the Platte river basin, Nebraska. The data confirmed that most of nutrient losses from cultivated soils by runoff were associated with dissolved forms in water. The majority of dissolved chemical species in Salt Creek water were HCO3-, NO3-, HPO4-2, and SO4-2 for C, N, P, and S, respectively. In general, the dissolved concentrations and species of C, N, and S measured in Salt Creek during the 2-year study were not expected to contribute to any problem related to human/animals health or aquatic life. With respect to the effect on aquatic life in surface fresh waters, the concentration of dissolved P measured in Salt Creek could cause eutrophication and resulting in excessive algae and aquatic plant growth, depletion of oxygen, and death of fish and other aquatic life. The dissolved P concentration in the Salt Creek exceeded the USEPA recommended limit of 100 µg/L in the flowing water. Changes in the mean annual precipitation can affect the quantity of C, P, N, and S loss from soils, both in sediment-bound and dissolved forms. The higher mean annual precipitation resulted in greater quantities of soil nutrient loss and higher concentrations in water bodies. Climate change that results in increases in the mean annual precipitation may require enhanced adaptation management to protect water quality. In conclusion, the study has provided a good and cost effective laboratory/field method to investigate the impact of runoff from agricultural watersheds on water quality.

Technical Abstract: Declining surface water quality from agricultural nonpoint sources is of great concern across the Platte river basin in Nebraska. Recent changes in the earth climate create abrupt changes in domestic weather (i.e., precipitation, temperature, etc.) which can alter the impact of these nonpoint sources on water quality. A 2-year (dry 2009 and wet 2010 year) study was conducted to assess the impact of soil carbon (C), nitrogen (N), phosphorus (P), and sulfur (S) losses by runoff on water quality of Salt Creek in Roca watershed, Nebraska. Both dissolved and sediment-bound forms of nutrients in runoff were investigated weekly. Average dissolved nutrient concentrations in runoff were 91.8 and 90.3% of the total for the dry and wet year, respectively. The remaining nutrients in runoff were associated with sediment. Nutrient concentrations during the dry year were generally greater than the wet year. Average concentrations for 2009 were 63.2, 1.87, 0.46, and 53.5 mg/L for C, N, P, and S, respectively while concentrations for 2010 were 54.0, 3.0, 0.45, and 16.6 mg/L, respectively. Total soil nutrient losses were greater for the wet year than the dry year. The dry year nutrient losses were 607, 19,978, 5,062, and 441,569 metric tons for C, N, P, and S, respectively while losses for the wet year were 1,997, 138,380, 22,615, 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. However, dissolved P concentrations in Salt Creek could cause eutrophication and exceeded the USEPA recommended limit of 100 µg/L for flowing water. We concluded that greater precipitation during the wet year increased the impact of runoff-nutrient from Roca watershed soils on the water quality in Salt Creek.