De-icing salt (NaCl) applied to roads can elevate Na+ and Cl- concentrations in nearby soils and water bodies through surface runoff and groundwater recharge.Wetlands adjacent to these roads retain this salt. For this study, wetlands classified as either rain-fed true bogs or groundwater-fed acidic fens and freshwater marshes located close to major and minor roads were sampled. Surface water, groundwater and peat/organic mud samples were collected from the true bogs (Arcadia Bog (AB) and Mill Valley Road Bog (MVRB) of Belchertown), acidic fens (Trout Brook wetland (TB) and Quag Bog (QB) of Templeton and Gardiner), freshwater marshes (Fitzgerald Lake (FL) and East Templeton Pond (ETP) of Northampton and Templeton) and vernal pool in Belchertown.
Field measurements and major ion chemistry data show that NaCl contamination is higher in acidic fens and freshwater marshes because of groundwater recharge and their closer proximity to major roads. Lower Na+ and Cl- concentrations were recorded in true bogs. While a 1:1 relationship between Na+ and Cl- is expected in the road salt contaminated water samples, Cl- concentrations are higher by ~20% suggesting that Na+ is adsorbed onto the negatively charged exchange sites in the peat or organic mud. The total cation exchange capacity (CEC) of the peat and organic-rich mud samples vary across the wetlands. Generally, true bogs and acidic fens have relatively higher CEC (22 cmolc/kg < CEC < 34 cmolc/kg). On the other hand, FL has the lowest CEC (12 cmolc/kg) while ETP has a CEC of 25 cmolc/kg. Calculated as charge fractions, H+ is the dominant exchangeable cation in true bogs (~60%) while exchangeable Ca2+ is dominant in acidic fens and freshwater marshes (~50%). Na+ charge fractions are highest at ETP (20%), followed by FL and QB (~6%), TB (3%) and < 0.15% in the true bogs (AB and MVRB). At all sites, Na+, Ca2+, Mg2+ and H+ charge fractions increase as their porewater chemistries increase which is an indication of adsorption. However, K+ is desorbed from the exchange sites lowering its charge fraction and increasing its concentration in the porewater.
A poster deriving from SURF program with Prof. Amy Rhodes, Professor of Geosciences.