SEASONAL VARIATION OF CHLORIDE INPUTS FROM ROAD SALT APPLICATION IN A MIXED URBAN/AGRICULTURAL WATERSHED IN CENTRAL ILLINOIS

Chlorides are not toxic to humans, but high concentrations are becoming an ecological and water resource threat. Therefore, to understand chloride storage on a large scale, establishing a consistent, temporal data set for understanding the transport and fate of chlorides related to the application of road salt is essential. Studies of Illinoisan streams have shown increases in chloride concentration with time, indicating storage capacity still exists. Groundwater chloride storage can vary spatially due to differences in land use, application rates, soil characteristics and subsurface geology thus making it difficult to study within a single watershed. This projects works to identity spatial and temporal changes in chloride loading in a mixed urban/agricultural watershed for a future numerical model. The study site focuses on Little Kickapoo Creek (LKC), a low gradient, perennial stream that meanders through a glacial outwash valley. Discharge measurements and water samples analyzed for major anions, specifically chloride, occurred every two weeks at seven locations along LKC. Data reveal the chloride load increases downstream. Temporal results show that chloride concentrations in the fall averaging ~120 mg/L (40-250 mg/L) increased in the winter to an average of ~ 181 mg/L (142-301 mg/L) before decreasing in the spring/early summer to an average of ~88 mg/L (50-134 mg/L). The stream chloride concentrations never reached the reported background concentration of ~15 mg/L observed in the groundwater. The increase in chloride concentrations over the winter months indicates that application rates of road salt are a controlling factor for chloride loading. Overall, this study illustrates the existing storage capacity of chlorides in a watershed due to the concentrations never reaching background level.