INVESTIGATING THE IMPACT OF RAINFALL ON WATER QUALITY INDEX VALUES WITHIN THE DRY RUN CREEK WATERSHED IN NORTHEAST IOWA

During this study, nine sites within the Dry Run Creek Watershed in northeast Iowa were sampled and studied to determine the National Sanitation Foundation’s Water Quality Index (NSFWQI) values. The NSFWQI is a 100 point scale based on nine testable parameters. The interpreting scale ranges from very poor to excellent. This study was chosen in part because of the DNR’s 2002 decision to place Dry Run Creek on the impaired waters list due to the lack of aquatic life. Also in 2003 the river was found to have excessive amounts of E.coli and nitrates based on an IOWATER snapshot.

Over the course of five weeks, each site was tested on the nine parameters of the NSFWQI, including E.coli per 100mL of samples and total suspended sediments (TSS). Temperature and rainfall totals were collected from the website of the Weather Channel Interactive, Inc. Sites were classified as either “urban” or “rural” based on the surrounding land use activities. Three sites were labeled rural and six urban. Upon completion of this study it was found that factors such as episodic rainfall and land use activities associated with agriculture and urban development are primarily responsible for the low water quality index values. High E.Coli values in the urban sites are more strongly correlated with rainfall than those in the rural sites. It indicates that even though agriculture has always been identified as a source of water pollution over the last few decades, urbanization is becoming an increasingly important contributing factor. Rapid deterioration of surface water quality is also demonstrated by the high suspended sediment loads immediately following storm events. It is clear from this study that WQI values can serve as an important indicator of pollution “hot-spots” in the Dry Run Creek watershed. It is recommended that temporal as well as spatial variations in the WQI values be monitored by the state agencies to come up with the proper remedial measures.