EVALUATING CONTROLS ON TURBIDITY IN A SMALL LOW-ORDER STREAM IN SOUTHEASTERN MINNESOTA

Logan Creek drains a predominantly agricultural area in the Whitewater River watershed approximately 15 miles east of Rochester, Minnesota. Based on agricultural practices, Logan Creek is highly susceptible to soil erosion-induced turbidity spikes. A gaging station, installed in June 2001 by the Minnesota Pollution Control Agency, was established to monitor the water quality of the stream. The station includes a YSI 6820 multi-parameter sonde (with dissolved oxygen, temperature, specific conductance, pH, and turbidity probes), a Druck pressure transducer, and a Campbell Scientific CR-10 data logger which logs data at a 15 minute interval. Additionally, a weather station measured precipitation. Almost five years worth of data has been collected thus far. In order to discern controls on turbidity within the watershed, we correlated turbidity with other parameters for 17 discrete events that occurred during 2004. We found the R² value for the relationship between maximum event turbidity and average event discharge to be 0.75. The R² value for maximum turbidity versus total event precipitation was 0.70. These numbers indicate discharge and precipitation significantly control turbidity levels in Logan Creek. These results suggest that turbidity in this designated trout stream could be reduced by managing storm water runoff from the surrounding agricultural area. Future analyses will focus on delineating trends in the seasonality of high turbidity events.