USGS Washington Water Science Center
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The Issue: Links between nitrate application to the land surface and measured nitrate concentrations in groundwater or surface water are poorly understood in the Yakima River basin due to the variety of potential nitrate sources. Fertilizer-intensive irrigated agriculture has been prevalent in the basin for decades, and since 1994 the growth of dairy operations has resulted in numerous liquid-manure processing reservoirs and a variety of associated crops farmed for nutrient-management purposes. These nitrate loadings are then attenuated at an unknown rate by biological uptake in plants and subsequent denitrification or immobilization by subsurface microbial communities. Residual nitrate concentrations have contaminated drinking-water wells, where they can have human health implications, and they have discharged to surface waters, where they may disrupt ecosystem function.
How the USGS will help: A recently completed regional groundwater-flow model for the Yakima River basin will be enhanced to allow the model to be used to examine the sources, migration, and fate of nitrate in groundwater in the Yakima River basin. The addition of contaminant-transport capabilities will be tested against observed nitrate measurements, and the resulting model will be evaluated to assess whether it may appropriately be used to test potential future nitrate-management scenarios.