NITRATE IN AQUIFERS BENEATH AGRICULTURAL SYSTEMS

Authors: Burkart, Michael; STONER, JEFFREY - U.S. GEOLOGICAL SURVEY

Submitted to: Water Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2001
Publication Date: 6/1/2002
Citation: BURKART, M.R., STONER, J.D. NITRATE IN AQUIFERS BENEATH AGRICULTURAL SYSTEMS. WATER SCIENCE AND TECHNOLOGY. 2002. V. 45. P. 19-29.

Interpretive Summary: Nitrate in groundwater from agricultural sources is a concern throughout the world. A review of international research was used to define hydrologic and agricultural factors contributing to nitrate in groundwater. These factors were statistically analyzed using data from the U.S. to quantify relations between occurrence of nitrate and agricultural systems. Shallow aquifers are most susceptible to nitrate contamination associated with agricultural systems. Among three classes of shallow aquifers studied, those in sand and gravel are the most vulnerable and those in limestone or dolomite have a smaller contamination risk. Where any of these aquifers are overlain by permeable soils the risk of contamination is larger. Irrigation add to this risk. The agricultural system of corn, soybeans, and hogs produced significantly larger concentrations of groundwater nitrate than all other agricultural systems. The benefit of this research, for scientists and policy makers, is a better understanding of the space and time trends in nitrate contamination. This research may impact decisions by scientists to strategically locate long-term groundwater monitoring. It may also have an impact on agricultural policy to reduce nitrogen sources in areas of high groundwater vulnerability.

Technical Abstract: Research from several regions of the world provides general information to hypothesize hydrologic and agricultural factors contributing to groundwater vulnerability from nitrate contamination. Analysis of groundwater measurements from the U.S. confirm these hypotheses for a variety of agricultural systems. Shallow unconfined aquifers are most susceptible to nitrate contamination associated with agricultural systems. Alluvial and other unconsolidated aquifers are the most vulnerable and shallow carbonate aquifers provide a substantial but smaller contamination risk. Shallow aquifers located in areas dominated by irrigation are more vulnerable than in non-irrigated areas. Where any of these aquifers are overlain by permeable soils the risk of contamination is larger, particularly in areas with irrigation. The agricultural system of corn, soybeans, and hogs produced significantly larger concentrations of groundwater nitrate than all other agricultural systems with almost 25% of wells yielding nitrate exceeding 10 mg/L. Asia may experience increasing problems because of recent increases in fertilizer use based on generalization of U.S. conditions. Fertilizer-use trends may help strategically locate long-term monitoring that will help answer questions about whether and when proportional changes in concentrations of nitrate will follow these changes in fertilizer. A major contributor to groundwater vulnerability is the distribution of irrigated cropland. This practice is expanding throughout the world, but particularly in Asia. More data and research will be needed in Asia to determine if patterns of water quality degradation in irrigated areas of other regions is repeated here.