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High Nitrate Concentrations in Some Midwest United States Streams in 2013 after the 2012 Drought
Author(s) -
Van Metre Peter C.,
Frey Jeffrey W.,
Musgrove MaryLynn,
Nakagaki Naomi,
Qi Sharon,
Mahler Barbara J.,
Wieczorek Michael E.,
Button Daniel T.
Publication year - 2016
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq2015.12.0591
Subject(s) - nitrate , environmental science , streams , hydrology (agriculture) , precipitation , watershed , manure , drainage basin , environmental chemistry , ecology , chemistry , geography , geology , biology , geotechnical engineering , cartography , machine learning , meteorology , computer science , computer network
Nitrogen sources in the Mississippi River basin have been linked to degradation of stream ecology and to Gulf of Mexico hypoxia. In 2013, the USGS and the USEPA characterized water quality stressors and ecological conditions in 100 wadeable streams across the midwestern United States. Wet conditions in 2013 followed a severe drought in 2012, a weather pattern associated with elevated nitrogen concentrations and loads in streams. Nitrate concentrations during the May to August 2013 sampling period ranged from <0.04 to 41.8 mg L −1 as N (mean, 5.31 mg L −1 ). Observed mean May to June nitrate concentrations at the 100 sites were compared with May to June concentrations predicted from a regression model developed using historical nitrate data. Observed concentrations for 17 sites, centered on Iowa and southern Minnesota, were outside the 95% confidence interval of the regression‐predicted mean, indicating that they were anomalously high. The sites with a nitrate anomaly had significantly higher May to June nitrate concentrations than sites without an anomaly (means, 19.8 and 3.6 mg L −1 , respectively) and had higher antecedent precipitation indices, a measure of the departure from normal precipitation, in 2012 and 2013. Correlations between nitrate concentrations and watershed characteristics and nitrogen and oxygen isotopes of nitrate indicated that fertilizer and manure used in crop production, principally corn, were the dominant sources of nitrate. The anomalously high nitrate levels in parts of the Midwest in 2013 coincide with reported higher‐than‐normal nitrate loads in the Mississippi River. Core Ideas Multiyear precipitation patterns can affect nitrate loading to streams. Anomalously high nitrate concentrations in 2013 in some streams followed the 2012 drought. Nitrate correlated to nitrogen fertilizer applications and multiyear precipitation patterns. High nitrate in small Midwest streams in 2013 coincides with high loading in the Mississippi River.