Sustainable Watershed Management: Impacts of a 30-Year Historical Record of Water Quality of the Iowa River

The effect of farming practices on water quality has been under increased scrutiny in Iowa. Overall water quality in Iowa has improved over the past 30 years, but the number of impaired water bodies in the state is not decreasing. Achieving sustainable watershed management can result in economic benefits to farmers and social benefits to the community, while preserving the ecological integrity of the aquatic ecosystem; it is through our research that we hope to elucidate better methods in order to meet this challenge. The Iowa River has been designated as an impaired water body since 1998 by the Iowa Department of Natural Resources. Coralville Reservoir, a mainstream impoundment of the Iowa River, is classified as a eutrophic lake and an impaired water body due to high bacterial concentrations. It is the primary drinking water source for Iowa City, Iowa. The Coralville Reservoir Water Quality Project was started in 1964 with the original objective of measuring the water quality of the river and reservoir. Continuous monitoring has yielded a data set of over 10,000 data points, allowing the detection of long-term water quality changes and providing insights into the natural and anthropogenic factors responsible for the changes. Preliminary analysis of the data set shows that the amount of nitrate-nitrogen in the reservoir has an increasing trend over a 30-year time span (1972–2003), while the amount of orthophosphate shows a gradual decreasing trend. Total suspended solids have decreased over the same period. Determination of the effectiveness of Best Management Practices (BMPs) on the available sediment and nutrient load by correlating historical and current rates of sediment loading to precipitation events, land use changes, agricultural practices and suburban development will be reported.