CREATING A MODEL THAT PREDICTS STREAM CHLORIDE CONCENTRATION AS A FUNCTION OF LAND USE CHANGE

Change in land use and land management practices result in the alteration of hydrological processes and quality of local and receiving waters. Anthropogenic activities introduce an array of contaminants into surface and groundwater with detrimental effects to the environment. Contamination of surface waters is a serious threat for aquatic biota as well as for the quality of drinking water.

The application of road salts is a common road maintenance practice in many countries and is the major source of surface water chloride in affected areas. The focus of this study is to determine the relationship between land use and stream chloride concentration and use this relationship to create a model to predict chloride concentration in streams as a result of future land use change.

The study area comprises two adjacent watersheds in Central Illinois, with similar geology and climate but varying land uses (agricultural, rural subdivision, urban). GIS tools are used to subdivide the study area into smaller sub-watersheds according to their land use characteristics and main source of chloride. Stream water samples were collected and analyzed for anionic composition for a full year. Results show increase of chloride concentrations during winter months over non-winter months of more than 20 times for an urban stream (range between 1350 and 65 mg/L), around 3 times for an agricultural stream (between 60 and 20 mg/L), as well as for a rural subdivision (between 205 and 78 mg/L). Because other sources of chloride other than road salts contribute to stream concentration, bromide and chloride ratios (Br/Cl) are used to assist in identifying sources of stream chloride within each sub-watershed.

The model is designed to create a non-linear relationship (using Spearman's rank correlation) between stream chemistry and land use type for each sub-watershed. This relationship will allow for the prediction of road salt chloride impact on a stream as the watershed land use changes.