Simple Model of Changes in Stream Chloride Levels Attributable to Road Salt Applications

Increasing stream chloride (Cl-) concentrations have been observed over the last several decades in regions that receive regular road salt. In many cases, these increases occur even when road salt application has remained nearly constant, indicating the presence of multiyear attenuation within watersheds. This paper presents a simple mixing model to interpret the relationship between Cl- inputs and Cl- in stream discharge. The model was applied to data collected between 1972 and 2003 from Fall Creek in central New York, and the results indicate that stream salt concentrations may continue to increase for several decades. The estimated average residence time of road salt in the watershed was approximately 50 years, although the uncertainty in road salt application history suggests residence times of 40-70 years are reasonable. Hydrologists may be able interpret historical road salt applications and stream salt responses as essentially a regional tracer experiment to gain insights into macroscale watershed characteristics that could dominate average water residence time. DOI: 10.1061/(ASCE)EE.1943-7870.0000458. (C) 2012 American Society of Civil Engineers.