Evaluating the influence of road salt on water quality of Ohio rivers over time

Anthropogenic inputs have largely contributed to the increasing salinization of surface waters in central Ohio, USA. Major anthropogenic contributions to surface waters are chloride (Cl^?) and sodium (Na⁺), derived primarily from inputs such as road salt. In 2012–2013, central Ohio rivers were sampled and waters analyzed for comparison with historical data. Higher Cl^? and Na⁺ concentrations and fluxes were observed in late winter as a result of increased road salt application during winter months. Increases in both chloride/bromide (Cl^?/Br^?) ratios and nitrate (N-NO₃^?) concentrations and fluxes were observed in March 2013 relative to June 2012, suggesting a mixture of road salt and fertilizer runoff influencing the rivers in late winter. For some rivers, increased Cl^? and Na⁺ concentrations and fluxes were observed at downstream sites near more urban areas of influence. Concentrations of Na⁺ were slightly lower than respective Cl^? concentrations (in equivalents). High Cl^?/Br^? mass ratios in the Ohio surface waters indicated the source of Cl^? was likely halite, or road salt. In addition, analysis of ³⁶Cl/Cl ratios revealed low values suggestive of a substantial dissolved halite component, implying the addition of “old” Cl^? into the water system. Temporal trend analysis via the Mann–Kendall test identified increasing trends in Cl^? and Na⁺ concentration beginning in the 1960s at river locations with more complete historical datasets. An increasing trend in Cl^? flux through the 1960s was also identified in the Hocking River at Athens, Ohio. Our results were similar to other studies that examined road salt impacts in the northern US, but a lack of consistent long-term data hindered historical analysis for some rivers.