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 salt (NaCl) applied to roads during the winter elevates sodium (Na+) and chloride (Cl-) concentrations in nearby soils and water bodies through surface runoff and groundwater recharge. High salinity values in wetlands lowers both plant and animal diversity and disturbs the evenness of species distribution. Here, we investigate the conditions for release and storage of road salt at Kampoosa Bog, a 0.7 km2 calcareous fen providing habitat to about twenty state endangered species. Kampoosa Bog is adjacent to a 1.9 mile stretch of Interstate 90 and Rt 7 in Stockbridge and Lee, MA, USA. We used discharge, chloride mass flux, precipitation and road salt application data collected between Nov 2017 and Nov 2020 to calculate the mass balance of Cl- at a monthly and annual scale. This site has average discharge, Cl- application and Cl- mass flux values of 0.06 m3s-1, 300 000 kg/year and 100 000 kg/year, respectively. Chloride export at the outlet stream is linearly correlated with discharge. Seasonal variations in discharge lead to seasonal variation in Cl- mass flux with high export during periods of snowmelt and high rainfall. Overall, there is a net accumulation of Cl- in the fen. The storage rate decreased from 230 000 kg/year to 126 000 kg/year between the 2019 and 2020 water years, reflecting decreases in salt application rates from 342 000kg of Cl-/year to 228 000 kg of Cl-/year in that period.