SEASONAL SHIFT IN NITROGEN STORAGE FROM AGRICULTURAL LANDS TO SURFACE WATER BODIES

The Quality of water in the state of Iowa is a matter of great concern. Contaminants in agricultural runoff have had an adverse impact on Iowa’s surface water quality. There is no natural resource more important than water to the economy and quality of life in Iowa. Most rivers and lakes in the Midwest are being degraded from diffuse influx of agricultural leachates and sediments from land areas adjacent to these water bodies. Therefore, understanding the temporal and spatial variations in water quality is critical in developing the best management practice guidelines and other remedial measures. This research project is focused on the Cedar River, a resource that is important to our community. Samples from seven different sites were collected on a weekly basis for ten weeks. Four of the sites are on the Cedar River itself and three are on streams flowing into the Cedar River. The sampling sites are both upstream and downstream of the cities of Waterloo and Cedar Falls so that the urban effects may be noticed. Water quality was determined by measuring dissolved oxygen, pH, total dissolved solids, temperature, and turbidity using field instruments, as well as total suspended sediments using laboratory equipment.

Sites 2, 5 and 7 showed considerably higher average nitrate concentrations (18.80 ppm, 16.30 ppm and 16.33 ppm respectively) than the other four sites sampled. The general land areas around these sites are characterized by agricultural lands that receive application of commercial fertilizers. The lowest average nitrate (5.79 ppm, ranging from 2.96 to 8.54 ppm) was found at site 6. This site is characterized by suburban areas with very low agricultural impacts. Temporally, most sites showed a general increase in nitrate concentration toward the end of the summer. Throughout the summer, nitrate washes off from agricultural lands and forms a large accumulation of the nutrient in surface water bodies. This study indicates that eutrophication of surface water bodies can continue all the way to the fall season.