Nutrients in Groundwaters of the Conterminous United States, 1992-1995

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• 作者：Bernard T. Nolan and Jeffrey D. Stoner
• 刊名：Environmental Science & Technology
• 出版年：2000
• 出版时间：April 1, 2000
• 年：2000
• 卷：34
• 期：7
• 页码：1156 - 1165
• 全文大小：490K
• 年卷期：v.34,no.7(April 1, 2000)
• ISSN：1520-5851

文摘

Results of a national water quality assessment indicatethat nitrate is detected in 71% of groundwater samples, morethan 13 times as often as ammonia, nitrite, organicnitrogen, and orthophosphate, based on a common detectionthreshold of 0.2 mg/L. Shallow groundwater (typically 5m deep or less) beneath agricultural land has the highestmedian nitrate concentration (3.4 mg/L), followed byshallow groundwater beneath urban land (1.6 mg/L) anddeeper groundwater in major aquifers (0.48 mg/L). Nitrateexceeds the maximum contaminant level, 10 mg/L asnitrogen, in more than 15% of groundwater samples from4 of 33 major aquifers commonly used as a source ofdrinking water. Nitrate concentration in groundwater isvariable and depends on interactions among several factors,including nitrogen loading, soil type, aquifer permeability,recharge rate, and climate. For a given nitrogen loading,factors that generally increase nitrate concentration ingroundwater include well-drained soils, fractured bedrock,and irrigation. Factors that mitigate nitrate contaminationof groundwater include poorly drained soils, greater depthto groundwater, artificial drainage systems, interveninglayers of unfractured bedrock, a low rate of groundwaterrecharge, and anaerobic conditions in aquifers.