SPATIAL VARIATIONS IN WATER CHEMISTY AND ITS IMPACT ON VEGETATION COMMUNITIES IN A CALCAREOUS WETLAND IN CENTRAL VERMONT

Concentrations of Na⁺ and Cl^- in the groundwater of the southern wetland at Pecks Pond in Barre, VT vary significantly from southwest to northeast, with the southwestern edge showing the highest concentrations ( 292 mg/L of Cl and 148 ppm of Na) and the northeastern side showing the lowest concentrations (48 mg/L of Cl and 15 ppm of Na). Additional variations are seen where a stream inlet enters the wetland from the southwest. The inlet water chemistry showed moderate concentrations of Na (44.87 ppm) and Cl (97 mg/L) and higher concentrations of Ca (113.60 ppm) and HCO₃^- alkalinity (148 mg/L). These spatial variations are largely driven by the influx of road-salt from Rt. 63, which borders the southwest side of the wetland. Additionally, the presence of a disperse outflow from the north to south through the center of the wetland, acts as a hydrologic barrier and limits the contamination of the eastern and northern sides of the wetland. The chemistry of the inlet may be explained by the mobilization of Ca²⁺ by cation exchange with Na⁺from carbonate-rich soil and till that underlie the stream.

Vegetation communities inhabiting the wetland are influenced both by water chemistry and water depth. A grass meadow is dominant along the southwestern edge of the wetland where Na⁺ and Cl^- concentrations are highest and the water table depth is shallow (3-5cm depth). Species with lower salt tolerance levels are present along the edge of the eastern side of the wetland, where Thuja occidentalis is dominant in a shrubby wetland community. Typha angustifolia, which has a medium tolerance to salt, is located throughout the center of the wetland where the water table is at the surface, with one exception. The area where the inlet enters the center of the wetland is dominated instead by Equisetum hyemale. T. angustifolia has a low tolerance to CaCO₃ and the chemistry of the inlet is characterized by high concentrations of Ca²⁺ and HCO₃^-. The continued accumulation of road-salts in this wetland will likely result in the expansion of the grass meadow at the expense of the more diverse shrub communities. This study illustrates not only the ability of wetlands to accumulate contaminants but also the sensitivity of wetland vegetation to disturbance and suggests that the ecological value of wetlands should be considered when applying road-salt to adjacent roads.