Effect of Road Salt Application on Seasonal Chloride Concentrations and Toxicity in South-Central Indiana Streams

Contemporary information on road salt runoff is needed for management of water resources in regions experiencing urbanization and increased road density We investigated seasonal Cl- concentrations among five streams in south-central Indiana that drained watersheds varying us degree of urbanization and ranging in size from 9.3 to 27 km(2) We also conducted acute toxicity tests with Daphnia pulex to assess the potential effects of the observed Cl- concentrations on aquatic hie Periods of elevated Cl- concentrations were observed during the winters of 2007-08 and 2008-09 at all sites except the reference site The highest Cl- concentration observed during the study was 2100 mg L-1 and occurred at the most urbanized site The Cl- concentration at the reference site never exceeded 22 mg L-1 The application of road salt caused large increases in stream Cl- concentrations, but. the elevated Cl- levels did not appear to be a significant threat to aquatic life based on our toxicity resting Only the most urbanized site showed evidence of salt retention within the watershed, whereas the other sites exported the road salt relatively quickly after its application, suggesting storm drams and impervious surfaces minimized interaction between sods and salt-laden runoff During winter :a these sites, the response in stream Cl- concentrations appeared to be controlled by the timing and intensity of road salt application, the magnitude of precipitation, and the occurrence of air temperatures that caused snowmelt and generated runoff