Effects of climatic variations over 11 years on nitrate-nitrogen concentrations in the Raccoon River, Iowa

Nitrate-nitrogen (NO 3 -N) concentrations at public water-supply intakes on the Des Moines and Raccoon Rivers in Iowa exceeded the maximum contaminant level (MCL) of 10 mg L -1 for public water supplies established by the USEPA for extended periods of time from March through early August 1990. The excessive NO 3 -N levels followed 2 yr of less than normal precipitation in 1988 and 1989. The largest daily NO 3 -N load (771 t) transported during the last 17 yr in the Raccoon liver occurred in June 1990