We recently concluded a study (forthcoming in the Journal of Environmental Quality) on water quality modeling in the Raccoon River Watershed in Iowa. Intensive agricultural production is a predominant use of a significant portion of the land in the Raccoon River Watershed and is a primary driver of the local economy within the watershed. Frequent detections of high nitrogen concentrations on the Raccoon River in recent years have received considerable attention due mainly to drinking water pollution in central Iowa. In addition, the Raccoon River Watershed is a part of the Mississippi River drainage basin and nutrient runoff that is carried by the river system has been cited as a contributing factor to the hypoxic conditions that exist in the Gulf of Mexico.
Intensive agriculture is often reported as the primary source of water quality degradation in the river despite the significant increases in nutrient utilization efficiency which has been achieved for corn production. The nutrient outputs of animal agriculture are also reported as a significant source of impairment of the Raccoon River.
We examine what factors cause the observed monthly variation in nitrate concentration in the Raccoon River from 1992 to 2008. We use time series econometric techniques that explicitly allow us to address very interesting time series properties of water quality data that have been ignored in most of the previous studies. We find that not only the level of fertilizer application, but also timing of the application play a key role in determining nitrate concentrations in the Raccoon River. There are substantial intra-annual variations in nitrogen concentrations and the existence of a very strong seasonal pattern. Also, variations in rainfall and temperature contribute more to the monthly variation in nitrogen concentration than do the changes in nitrogen application rates.
The development of environmental, land use and water quality policies requires balancing many complementary and competing goals. Development of sound policy requires an understanding of the factors contributing to variations in water quality measures such as in-stream nitrogen concentration levels to ensure best use of limited resources. The policy making process will be better informed as we improve our understanding of the causes of variation in water quality.
- raccoon river
- water quality