NONPOINT SOURCE AND WATER QUALITY TRENDS IN THE PEARSON CREEK WATERSHED

The Pearson Creek Watershed (61 km2) drains both the City of Springfield and more rural, agricultural areas. Water quality of the creek is affected by unknown toxicants potentially responsible for the decline in aquatic life. The purpose of this study is to complete an assessment of pollutant concentrations found within the watershed and to support efforts to develop a Total Maximum Daily Load (TMDL) for Pearson Creek. From November 2007 to December 2008, 15 sampling sites were monitored 2 to 3 times per month during both baseflow and runoff conditions. Analtyes of interest included total nitrogen, total phosphorus, total lead, total cooper, total zinc, Escherichia coli, total coliform, and total suspended solids. Water quality parameters included pH, temperature, conductivity, dissolved oxygen, and turbidity. Microbial source tracking was also performed on base flow samples. Rating curves were used to correlate discharge and water quality for exceedance probability analysis. In the upper portion of the watershed, water discharged from the Danforth No. 1 spring contained elevated levels of copper, E coli, and lead. The middle portion of the watershed contributed the majority of TP and TSS load. Human E. coli DNA was found at mainstem sites at and below where urban land use and septic tank density increased. When bacteria from human sources were present they were up to 22% more abundant than bovine bacteria. TN levels exceeded TMDL recommended concentration limits 99% of the time. Median lead concentrations at all sites were above the continuous concentration criteria for aquatic life. Annual watershed yields of pollutants at the Pearson Creek continuous flow gage are as follows: 1.9 Mg TN/km², 0.09 Mg TP/km², 26.3 Mg SS /km², 3.6 Mg Pb/km², and 4.2 Mg Zn/km². Pearson Creek water quality is being impaired by multiple nonpoint sources from urban, agricultural, and historical mining areas.