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

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) b...

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Bibliographic Details
Published in:Environmental science & technology 2000-04, Vol.34 (7), p.1156-1165
Main Authors: Nolan, Bernard T, Stoner, Jeffrey D
Format: Article
Language:English
Subjects:
Applied sciences
contaminants
Contamination
Earth sciences
Earth, ocean, space
Engineering and environment geology. Geothermics
Exact sciences and technology
Freshwater
governmental programs and projects
Groundwater
groundwater contamination
Groundwaters
Natural water pollution
Nitrates
Pollution
Pollution, environment geology
rogram (nawqa)
u.s. geological survey's national water quality assessment p
USA
water quality
Water treatment and pollution
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Summary: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.
ISSN:0013-936X
1520-5851
DOI:10.1021/es9907663