U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

Transport and Concentrations of Selected Herbicides and Nitrate in the Sangamon River, Illinois, April 1991 - March 1992

Abstract

The Sangamon River, located in east-central Illinois, drains some of the most intensively used agricultural land in the Midwest. Effects of agricultural practices in the drainage basin on stream-water quality were investigated by collecting surface-water samples from April 1991 through March 1992 at Monticello, Illinois. Samples were analyzed for concentrations of selected herbicides and nitrate. Total load was calculated and compared to estimated application totals of each compound in the drainage basin above Monticello.

During the study period, 1,607 pounds of atrazine were transported by the river; this mass represents 1.4 percent of the total annual application of 113,700 pounds. The river transported 669 pounds of cyanazine--a mass equal to 1.6 percent of the total annual application of 41,900 pounds. About 353 pounds of alachlor were transported by the river (0.31 percent of the 112,300 pounds applied). About 12,100 tons of nitrogen fertilizer were applied, and 3,393 tons of nitrate as nitrogen were transported by the river (28 percent of the total amount applied). However, other natural and human-derived sources of nitrate could have contributed to this total load.

The timing of chemical application and the quantity of rainfall and runoff after herbicide application affected the concentrations. Herbicide concentrations were highest in early spring during storms immediately following application. Peak concentrations for atrazine, cyanazine, and alachlor occurred in May; these concentrations were 21, 16, and 8.8 micrograms per liter, respectively. Nitrate concentrations were at or above the U.S. Environmental Protection Agency's maximum contaminant level of 10 milligrams per liter from the beginning of the study until June 11, 1991. Nitrate concentrations then remained less than the maximum contaminant level until November 1991.