Research from Smith College on the effects of road salts and the surrounding ecosystem in Kampoosa Bog, MA
Posted Mar 7, 2025
Each winter, millions of tons of road salt are applied to highways and sidewalks to improve safety and mobility. While effective at melting ice and preventing accidents, this widespread use of salt has unintended environmental consequences that persist well beyond the winter months. Professors Amy Rhodes, Department of Geosciences, and Andrew Guswa, Picker Engineering Program of Smith College have been researching the effects of increased sodium (Na) and chloride (Cl) on wetland plants, sensitive ecosystems, and water quality in the Kampoosa Bog, an area near Stockbridge and Lee in Massachusetts (MA).
Kampoosa Bog, despite its name, is a type of wetland classified as a “calcareous fen,” and it contains endangered plant species in addition to species that are rare to the state of MA. It is located in the Paleozoic marble belt of western MA, and the bedrock geology generates high concentrations of Ca, Mg, and alkalinity that support the fen plants. An interstate highway (I-90) crosses the upstream region of the fen, and road salt has altered the geochemistry of the fen groundwater and streams by increasing Na and Cl concentrations and overall specific conductance of the water. It has been shown by Richburg et al. (2001) that regions of lower plant community diversity within the fen are associated with elevated dissolved salt concentrations in shallow groundwater, and also may be related to excessive growth of invasive plants, primarily by Phragmites australius, which is a salt-tolerant, giant reed that overtook portions of the fen.
Hannah Kreutzer '24, Helena Grilliot '24, Wayne Ndlovu '22, Prof. Amy Rhodes
Because of its ecological significance for MA and vulnerability to human disturbance, Kampoosa Bog was designated as one of MA Areas of Critical Environmental Concern, and a number of different organizations have collaborated to support scientific study and restoration of the fen from the Phragmites. Rhodes was initially inspired to get involved because of the combination of interesting chemistry questions and the potential for real-world impact. Rhodes invited Guswa to contribute to the project and over the years their research on the hydrogeochemistry of Kampoosa Bog has also been in collaboration with community partners, regional planning agencies, the Nature Conservancy, the MA Department of Transportation, the MA Natural Heritage and Endangered Species Program, which is part of Mass Division of Fisheries and Wildlife, and the University of Massachusetts, all of which have been concerned about how the influx of road salt from the interstate highway is altering the geochemistry of the fen.
Their most recent work was an outgrowth of a prior hydrogeochemical study on Kampoosa Bog (Rhodes and Guswa, 2016), which described variations in groundwater chemistry within the fen, the dynamics of dissolved salt export from its outlet stream during snowmelt events, and the levels of sodium adsorption on peat soils.
The recent manuscript with Smith College undergraduate, Wayne Ndlovu ‘22, (Ndlovu et al., 2024) focuses specifically on the mass balance of the dissolved salts, chloride in particular, and incorporates new, continuous streamflow measurements made by staff at the University of Massachusetts - Amherst. The MA Department of Transportation provided data on the amount of road salt applied to the interstate highway, which was critical for determining the mass balance. Their results show that significantly more Cl is being added to the highway region within the fen watershed than is being exported by the outlet stream, suggesting that this wetland is accumulating salt. They also showed that greater amounts of salt are stored in years when more salt is applied to the highway, and that large rain events are important for exporting salt. Seasonally, as might be expected, salt accumulates in the watershed during the winter months (when it is applied), and is exported throughout the entire year, with the outflux of salt mass being strongly correlated with streamflow.
In the peat of Kampoosa Bog, shallow groundwater, including the root zone of the plants, showed the highest concentrations of Na and Cl in the wetland; concentrations varied greatly from month to month, with periods of sustained dilution. In contrast, the deeper groundwater showed lower, less variable concentrations in dissolved salts, with a steady increase over the three-year sampling period. Further research will inform the hypothesis that a reduction in road salt application rates to the highways within the watershed would result in a decrease in Na and Cl concentrations in the streams and groundwater of Kampoosa Bog.
Organic soils can be a significant location of storage for Na from road salts due to cation exchange reactions between salt-contaminated groundwater and the organic material. Cation exchange experiments on peat are being conducted to better understand the adsorption and desorption dynamics of Na to soil in the presence of varying concentrations of calcium and magnesium. These kinds of experiments should provide insight on the storage and release of Na from a peatland, as it pertains to the soil complex.
Highly elevated concentrations of sodium and chloride persist in streams, soils, and groundwater throughout the year, not just during seasons when salts are applied to roads. Their study demonstrates that peatlands can be a significant source of storage for dissolved salts, with the highest concentrations of Na and Cl occurring in the most shallow part of the peat mat where plant roots occur. The accumulation of salt in the wetland is directly related to the amount applied to roadways. Road-safety strategies that can limit the use of halite salt (NaCl) would reduce dissolved salt concentrations over time.
As this work progresses it will continue to inform hydrologists, water resource managers, and other decision makers. Their findings in the Rhodes and Guswa (2016) manuscript were included in the Massachusetts Department of Transportation road-salt environmental status and planning report (MassDOT, 2012).