Determining conditions for storage and release of road salt pollution in a calcareous fen: A hydrological and geochemical analysis of Kampoosa Bog, Stockbridge and Lee, MA

Abstract

De-icing salts applied to roads during winter can contaminate nearby soils and water bodies through groundwater and surface runoff. High salinity in wetlands adjacent to roads lowers both plant and animal diversity and also disturbs the evenness of species distribution. Therefore, it is critical to understand how changes in road salt application rates and hydrological events impact wetland water quality. In this study, we investigate (1) chloride accumulation rates and (2) the conditions for storage and release of road salt at Kampoosa Bog, a 0.7 km2 calcareous fen. Kampoosa Bog, located in Stockbridge and Lee, MA, USA, is adjacent to a 1.2 mile stretch of Interstate 90 (Turnpike) and provides habitat to approximately twenty state endangered species. High frequency (15-minute) measurements of discharge and specific conductance from November 2017 through October 2020 are combined with road-salt application rates to quantify chloride outflux and storage within the watershed at monthly and annual scales. During that time period, 583,000 kg of chloride were applied to the Turnpike. Annual net storage of chloride in the watershed ranged from 167,000 kg to 30,000 kg, and we estimate that approximately 50% (284,700 kg) of the applied chloride from November 2017 through October 2020 was retained. Chloride accumulation in the fen has led to increases in groundwater chloride concentrations in the fen. Groundwater samples collected in shallow (5ft) wells had chloride concentrations of about 220 mg/l, which is close to the EPA chronic criterion threshold (230 mg/l). Monthly outflux of chloride from the fen tends to be low (<500kg/month) in the dry late summer to fall months. The greatest monthly chloride outflux (35,000kg/month) occurred in May 2020. Despite some variability in the data, initial evidence suggests chloride outflux from the fen is strongly tied to high discharge events.