Seasonal and Long-Term Dynamics in Stream Water Sodium Chloride Concentrations and the Effectiveness of Road Salt Best Management Practices

Abstract

We use a 32-year dataset from a rural, southeastern New York stream to describe the effect of long-term road salt use on concentrations of sodium (Na+) and chloride (Cl−). Mean annual stream Na+ and Cl− concentrations initially increased, reached a plateau, and then increased again. Trends in summer and winter stream concentrations were similar but summer concentrations were higher than winter, indicating that salt entered the stream via groundwater discharge. Seasonal and inter-annual variability in stream Na+ and Cl− concentrations and export were high in the latter years of the study and can be explained by increased variability in stream discharge. Stream water Na+ and Cl− concentrations were positively correlated with conductivity, and conductivity was negatively correlated with discharge during all seasons (p < 0.001). We used road salt application data from a local agency to examine effects of best management practices. Despite reductions in salt application, there was no commensurate decrease in stream water Na+ and Cl− concentrations. We estimate that the legacy of long-term salt accumulation in groundwater and soils may delay a decline in stream water Na+ and Cl− concentrations by 20–30 years. Continued research to develop road salt reduction practices is important to mitigate impacts on freshwater ecosystems and drinking water supplies.