Probability of Nitrate Contamination of Recently Recharged Groundwaters in the Conterminous United States

Abstract

A new logistic regression (LR) model was used to predict the probability of nitrate contamination exceeding 4 mg/L in predominantly shallow, recently recharged groundwaters of the United States. The new model contains variables representing (1) N fertilizer loading (p < 0.001), (2) percent cropland-pasture (p < 0.001), (3) natural log of human population density (p < 0.001), (4) percent welldrained soils (p < 0.001), (5) depth to the seasonally high water table (p < 0.001), and (6) presence or absence of unconsolidated sand and gravel aquifers (p ) 0.002). Observed and average predicted probabilities associated with deciles of risk are well correlated (r 2 ) 0.875), indicating that the LR model fits the data well. The likelihood of nitrate contamination is greater in areas with high N loading and well-drained surficial soils over unconsolidated sand and gravels. The LR model correctly predicted the status of nitrate contamination in 75% of wells in a validation data set. Considering all wells used in both calibration and validation, observed median nitrate concentration increased from 0.24 to 8.30 mg/L as the mapped probability of nitrate exceeding 4 mg/L increased from e0.17 to >0.83.

Reduced nitrate leaching and enhanced denitrifier activity and efficiency in organically fertilized soils

“…For example, 9% of U.S. domestic wells sampled during 1993-2000 had nitrate concentrations exceeding the U.S. Environmental Protection Agency's (EPA) maximum contaminant level of 10 mg⅐liter Ϫ1 as N (8). In the Yakima River Basin of Washington State, where this study was conducted, 13% of the samples taken from small-watershed sites exceeded the EPA's maximum contaminant level, indicating a potential health risk to nearby residents with shallow wells (9).…”

Correlação entre uso da terra e qualidade da água subterrânea

“…Nos trabalhos feitos por Nolan et al (2002) e Squillace et al (2002), a degradação da qualidade da água subterrânea foi classificada e avaliada utilizando-se um círculo com raio de 500 m, centrado no poço. Em outros estudos, o uso da terra foi estudado dentro de raios variando de 100 a 3.200 m BRUCE;McMAHON, 1996;TROJAN et al, 2003).…”

“…Deste modo, os métodos de análise multivariada de dados têm sido cada vez mais utilizados em estudos ambientais devido à sua fácil aplicação e por reduzirem o número de dados em subgrupos menores correlacionados entre si, além de identificarem as variáveis que são responsáveis pela dispersão das observações BRUCE & McMAHON, 1996;NOLAN et al, 2002;SQUILLACE et al, 2002;TROJAN et al, 2003). Embora a utilização de um raio de influência arbitrário possa parecer simplista por não levar em conta as variáveis hidrodinâmicas do aquífero, considera-se possível sua utilização em …”

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

“…Nitrate is a highly soluble nutrient [12]. When nitrogen is applied to soil as a fertilizer or in manure, NO3 is often leached to below the root zone without reaching the target crop [1].…”

“…In a comprehensive survey of domestic wells and wells of rural public water supply systems, Lockhart et al [16] showed that citrus, fruit and nuts, forage crops (often receiving dairy manure), and proximity to dairies were associated with the highest nitrate concentrations, while vineyards were among the agricultural land uses associated with the least nitrate concentration in domestic wells. Few data exist on N leaching rates from alfalfa, but observed groundwater concentration in regions with alfalfa as dominant crop (without corn rotation) are typically low in nitrate concentration [62,63]. Environmental crop modeling systems including nitrogen hazard indices [64,65], indicate that perennial crops and low or no N-input crops play a prominent role in protecting groundwater quality [1,66].…”