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

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• 作者：Bernard T. Nolan ; Kerie J. Hitt ; and Barbara C. Ruddy
• 刊名：Environmental Science & Technology
• 出版年：2002
• 出版时间：May 15, 2002
• 年：2002
• 卷：36
• 期：10
• 页码：2138 - 2145
• 全文大小：586K
• 年卷期：v.36,no.10(May 15, 2002)
• ISSN：1520-5851

文摘

A new logistic regression (LR) model was used to predictthe probability of nitrate contamination exceeding 4mg/L in predominantly shallow, recently rechargedgroundwaters of the United States. The new model containsvariables representing (1) N fertilizer loading (p < 0.001),(2) percent cropland-pasture (p < 0.001), (3) natural log ofhuman population density (p < 0.001), (4) percent well-drained soils (p < 0.001), (5) depth to the seasonally highwater table (p < 0.001), and (6) presence or absence ofunconsolidated sand and gravel aquifers (p = 0.002). Observedand average predicted probabilities associated withdeciles of risk are well correlated (r² = 0.875), indicatingthat the LR model fits the data well. The likelihood of nitratecontamination is greater in areas with high N loadingand well-drained surficial soils over unconsolidated sandand gravels. The LR model correctly predicted the status ofnitrate contamination in 75% of wells in a validation dataset. Considering all wells used in both calibration andvalidation, observed median nitrate concentration increasedfrom 0.24 to 8.30 mg/L as the mapped probability ofnitrate exceeding 4 mg/L increased from tities/le.gif">0.17 to >0.83.