VARIABILITY OF WATER QUALITY IN RELATION TO FARMING ALONG THE RACCOON RIVER IN WEST DES MOINES, IOWA

Agriculture regularly impacts surrounding surface water via the runoff of chemical applicants. Manure runoff and nitrogen-based fertilizer runoff are largely responsible for heightened levels of contaminants such as nitrates. Contaminants have larger impacts as they travel through the hydrosphere to aquatic systems and water resources. This work aims to determine the impact of farming activities on surface water quality along the Raccoon River in West Des Moines, Iowa. In the most recent assessment by the Iowa Department of Natural Resources, the section of the Raccoon River covered in this research was listed under impaired following an integrated report of varying parameters. Other previous assessment cycles consistently showed E. coli and nitrates as impairments on this river. This analysis over the selected portion of the Raccoon River assesses how water quality varies spatially and temporally throughout the crop season and how the surface water quality of the Raccoon River is impacted by surrounding land use (urban vs rural). Data collected included temperature, PH, conductivity, total dissolved solids, total suspended solids, turbidity, alkalinity, phosphate, and concentrations of chlorine, nitrate, and sulfate. Seven sampling locations were selected over five sample dates spanning from before planting to after harvesting. Water quality variance over time at each sampling site and variation in water quality across separate sites was determined following data collection. Across all seven sampling sites, nitrate (NO₃^-) values peaked in the summer, averaging around 20-30 mg/L across all seven sampling locations. A tributary to the river surrounded by forest saw the lowest concentrations of nitrates throughout the sampling periods. Rural locations were of similar values, ranging from ~20 – 40 mg/L. Site 4 showed the highest concentration across the data - 39.7 mg/L. A gradual decrease in nitrate concentration followed, resulting in not detectable levels (less than 0.5 mg/L) across all sites in early August/September. Correlation between the application of fertilizers in early crop growth and nitrates increase in surface water was observed. This analysis can be used to help the state regulatory agencies develop their best management practices and assess Iowa's current nutrient reduction strategies.