Nutrients in groundwaters of the conterminous United States, 1992-1995
January 1, 2000
Results of a national water quality assessment indicate that nitrate is detected in 71% of groundwater samples, more than 13 times as often as ammonia, nitrite, organic nitrogen, and orthophosphate, based on a common detection threshold of 0.2 mg/L. Shallow groundwater (typically 5 m deep or less) beneath agricultural land has the highest median nitrate concentration (3.4 mg/L), followed by shallow groundwater beneath urban land (1.6 mg/L) and deeper groundwater in major aquifers (0.48 mg/L). Nitrate exceeds the maximum contaminant level, 10 mg/L as nitrogen, in more than 15% of groundwater samples from 4 of 33 major aquifers commonly used as a source of drinking water. Nitrate concentration in groundwater is variable 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 in groundwater include well-drained soils, fractured bedrock, and irrigation. Factors that mitigate nitrate contamination of groundwater include poorly drained soils, greater depth to groundwater, artificial drainage systems, intervening layers of unfractured bedrock, a low rate of groundwater recharge, and anaerobic conditions in aquifers.
Citation Information
Publication Year | 2000 |
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Title | Nutrients in groundwaters of the conterminous United States, 1992-1995 |
DOI | 10.1021/es9907663 |
Authors | B. T. Nolan, J.D. Stoner |
Publication Type | Article |
Publication Subtype | Journal Article |
Series Title | Environmental Science & Technology |
Index ID | 70022942 |
Record Source | USGS Publications Warehouse |