Vulnerability of Shallow Groundwater and Drinking-Water Wells to Nitrate in the United States

Abstract

Two nonlinear models were developed at the national scale to (1) predict contamination of shallow ground water (typically < 5 m deep) by nitrate from nonpoint sources and (2) to predict ambient nitrate concentration in deeper supplies used for drinking. The new models have several advantages over previous national-scale approaches. First, they predict nitrate concentration (rather than probability of occurrence), which can be directly compared with water-quality criteria. Second, the models share a mechanistic structure that segregates nitrogen (N) sources and physical factors that enhance or restrict nitrate transport and accumulation in ground water. Finally, data were spatially averaged to minimize small-scale variability so that the large-scale influences of N loading, climate, and aquifer characteristics could more readily be identified. Results indicate that areas with high N application, high water input, well-drained soils, fractured rocks or those with high effective porosity, and lack of attenuation processes have the highest predicted nitrate concentration. The shallow groundwater model (mean square error or MSE = 2.96) yielded a coefficient of determination (R(2)) of 0.801, indicating that much of the variation in nitrate concentration is explained by the model. Moderate to severe nitrate contamination is predicted to occur in the High Plains, northern Midwest, and selected other areas. The drinking-water model performed comparably (MSE = 2.00, R(2) = 0.767) and predicts that the number of users on private wells and residing in moderately contaminated areas (>5 to < or =10 mg/L nitrate) decreases by 12% when simulation depth increases from 10 to 50 m.

Applying a statewide geospatial leaching tool for assessing soil vulnerability ratings for agrochemicals across the contiguous United States

“…Groundwater in the United States (US) was found to be vulnerable to a mixture of various contaminants, such as nitrate, pesticides, and volatile organic compounds (VOCs) (Nolan and Hitt, 2006;Squillace et al, 2002). Soil and groundwater contamination occurred from intensive human activities in both urban and agricultural areas, e.g., industrial discharges, landfills, hazardous waste dumps, septic tanks, and fertilizer applications (USEPA, 1997;Zogorski et al, 2006).…”

Design and methods of the Midwest Stream Quality Assessment (MSQA), 2013

“…The high inputs of agricultural chemicals required in RC agriculture are commonly associated with some of the highest concentrations of nutrients (Dubrovsky and others, 2010) and pesticides (Gilliom and others, 2006) in streams in the country. For sites in permeable areas with strong surface connections to groundwater, shallow groundwater also has some of the highest nitrate concentrations nationally (Nolan and Hitt, 2006). Some of the largest loadings of nutrients to the Gulf of Mexico and Lake Erie (not shown) (Robertson and others, 2009;Robertson and Saad, 2011) are derived from the Corn Belt region.…”

Economic Feasibility of Irrigated Agricultural Land Use Buffers to Reduce Groundwater Nitrate in Rural Drinking Water Sources

“…Only 50% of N applied to agricultural soils is taken up by crops [13]; an additional ~25% is emitted to the atmosphere, ~2%-5% accumulates in the soil, and the remaining ~20% is discharged into aquatic systems [9]. While other factors contribute to groundwater nitrate concentrations [8,14,15], the proportion of the total area covered by cropland, pasture, and well-drained soil (which tends to be favored for agricultural production) are often prominent determinants of risk of nitrate leaching to groundwater [16][17][18], report a positive relationship between the amount of residual soil mineral N at harvest and the concentration of upper groundwater NO3 concentrations.…”