Nitrate leaching hazard index developed for irrigated agriculture

Excerpt

In 1991, the National Water Quality Assessment Program was initiated. The U.S. Geological Survey (USGS) as the lead agency worked with other federal, state, and local agencies to understand the spatial and temporal occurrence of water quality degradation, including the effects of both human activities and natural environmental factors. The results of this initiative were published as, “The Quality of Our Nation's Waters” (USGS, 1999), with specific reference to the influence of agricultural nutrients and pesticides on water quality.

Some of the highest levels of nitrate were reported to occur in streams and groundwater in agricultural areas. However, the USGS study found that nitrate concentrations vary considerably from season to season as well as between watersheds across the United States. A graphical plot of fertilizer nitrogen inputs to agricultural land versus median nitrate concentrations in underlying shallow groundwater aquifers produced a complete scatter of points (p 47. USGS, 1999) and the range of groundwater nitrate concentrations was the same for all levels of nitrogen input. This phenomenon underscores the strong influence of differing natural features and land management practices upon the movement of contaminants through the soil to reach underlying aquifers. Recognition of these differences can …