SEASONAL VARIABILITY IN CONTAMINANT TRANSPORT CHARACTERISTICS OF A WATERSHED

Natural events like rainfall, or flooding, destroys aquatic ecosystems through river bank erosion, river-bed siltation, and deteriorating water quality. The extent of damage can be quite different from one season to another based on differences in hydrologic events. This project investigates seasonal variability in the distribution of land derived nutrients in a moderately large system of streams in Iowa. The study is expected to bring insights into the geo-hydrologic relationships between Iowa’s agricultural lands and adjacent water bodies. Hydrologic sampling was conducted in the Cedar River watershed of northeast Iowa, including the main channel Cedar and 5 of its tributaries. The long term goals of this project are to (1) conduct geo-hydrologic mapping to identify probable hotspots of pollution by soil runoff nutrients; and (2) delineate avenues of nutrient and sediment transport caused by high intensity rain events and flooding. Preliminary data show E.Coli values to fluctuate largely due to site specific land use with generally higher values toward rural areas. In September 2013, total suspended sediments (TSS) and dissolved oxygen (DO) had average values of 30.5 mg/L and 9.80 mg/L respectively. Although average DO increased with lower temp in October and November, both rural and urban areas showed spatially similar values. TSS values dropped by 50% from September to October, still without significant spatial variations during a sampling event. The lowest chloride concentration was 18.34 mg/L in a rural site and the highest was 26.59 mg/L in an urban site. Although higher chloride values are generally expected from degraded pesticides in agricultural lands, the observation to the contrary is attributed to the vertical infiltration of dissolved chloride on farmlands during intense rain events. The average nitrate is 15 mg/L with a range of 12.54 mg/L at a suburban site to 18.29 mg/L at a rural site. Although nitrogen is also expected to be impacted by infiltration loss, excessive amounts of residual fertilizer from fields possibly kept the rural values higher. The project was done post summer, and it is clear that nutrient and TSS distributions in the watershed are much more uniform than what is expected during summer time. No particular high flow avenues of nutrient transport are observed during this study.