The chemical evolution of tributaries to Lake George (Essex County), New York (USA), 1970–2024: recovery from acidic atmospheric deposition and the impact of road salt

•Acidic atmospheric deposition from air pollution (elevated sulfate, nitrate) and salinization from highway deicing (normally sodium chloride) have significant impacts on terrestrial and aquatic ecosystems. Lake George, New York (USA), is the largest waterbody totally within the Adirondack Park, a U.S. region identified by the National Acid Precipitation Assessment Program as containing surface waters sensitive to acidification. Lake George also is typical of temperate lakes at risk for elevated sodium and chloride concentrations from winter deicing. •We evaluated the ionic composition of 18 Lake George tributaries using >4300 samples, intermittently collected from 1970 to 2024. Sulfate, in response to the Clean Air Act and Amendments, declined above road salting areas, reaching “steady state” about 2019 for sulfate (a 90% decline) and base cations. Chloride from road salt has increased irregularly, starting before 1970. Watershed soil accumulated considerable Na+ during ion exchange by 2016, displacing Ca+2, Mg+2, and K+ from soils to Lake George. This trend then reversed as total (Ca+2 + Mg+2 + K+) declined more than Na+, which converged on Cl−. Consequently, the Ca+2, Mg+2, and K+ concentrations in Lake George now are being diluted but remain elevated. Continued salt loading since before 1970 has resulted in soil depletion of exchangeable Ca+2, Mg+2, and K+, even as Na+ and Cl− declined from reduced salt use. Base cations in runoff from some salt-impacted tributaries are approaching the weathering rate. Elevated Ca+2 made Lake George susceptible to invasion by non-native bivalve species. The Lake George outlet lags behind tributary chemistry changes by a few years.