Responses to atrazine of respiration, nitrification, and denitrification in stream sediments measured with oxygen and nitrate microelectrodes

Atrazine from agricultural runoff commonly pollutes streams in the Midweste rn United States. Potential effects of atrazine on nitrification and denitr ification were studied in sediment cores collected from a stream receiving relatively low inputs of atrazine. Nitrate and oxygen microprofiles were me asured in these sediment cores using microelectrodes. After initial light a nd dark profile measurements, atrazine was added to overlying water resulti ng in concentrations of 0, 10, 50, and 100 mu g l(-1) active ingredient. Mi croprofiles were measured again 1 and 6 days following the addition of atra zine. Rates of oxygen respiration, nitrification, and denitrification were determined from the microprofiles using a reaction-diffusion model. Oxygen respiration increased relative to its initial value in cores exposed to all atrazine concentrations. This resulted in a shallow oxic layer in sediment cores exposed to atrazine. Nitrification was inhibited in sediments expose d to 50 and 100 mu g l(-1) atrazine and was significantly higher than contr ol in cores exposed to 10 mu g l(-1). In the light, denitrification increas ed relative to control in sediment exposed to 10 mu g l(-1) atrazine. Denit rification was inhibited by 100 mu g l(-1) atrazine in the dark. Total dail y carbon mineralization resulting from aerobic and nitrate respiration was significantly higher in cores exposed to 10 mu g l(-1) atrazine than in con trol cores. These results suggest that atrazine can significantly alter nit rogen and carbon cycling in streams. Atrazine could affect stream recovery from nitrate pollution and could reduce total organic matter retention in s treams. (C) 1999 Federation of European Microbiological Societies. Publishe d by Elsevier Science B.V. All rights reserved.