Use of Classes Based on Redox and Groundwater Age to Characterize the Susceptibility of Principal Aquifers to Changes in Nitrate Concentrations, 1991 to 2010.

摘要

In this study, water samples collected from 6,593 wells in 39 principal aquifers and 5 alluvial aquifers (collected from 1991 to 2010) were assigned to four redox-age classes on the basis of concentrations of dissolved oxygen and various indicators of groundwater age. The redox-age assignments were then used to characterize the susceptibility of principal aquifers to changes in nitrate concentrations. Aquifer areas (as defined by well networks) in which at least 75 percent of the samples were classified as oxic-potentially young were considered to have a high susceptibility to changes in nitrate concentrations. Aquifer areas were considered to have a medium susceptibility if at least 25 percent and less than 75 percent of the samples were classified as oxic-potentially young. Aquifer areas were considered to have a low susceptibility if less than 25 percent of the samples were classified as oxic-potentially young.