WATER AND CHLORIDE MASS BUDGETS OF A PERMANENTLY FLOODED, SEASONALLY FROZEN WETLAND IN THE CANADIAN PRAIRIES

Low permeability glacial sediments and poor drainage development in the Canadian prairies creates many permanently and seasonally water-filled depressions across the landscape. Wetland pond permanence, water level fluctuations and salinity have a significant effect on their hydrological and ecological function. The objective of this study was to quantitatively assess groundwater-surface water interactions for a permanently flooded wetland using a combination of thermal, physical and geochemical methods. At a grassland site in southern Alberta, annual and monthly water budgets were combined with chloride data to characterize wetland hydrology and the dynamics of its interaction with the surrounding landscape. The wetland is situated upon 4-16 m of glacial sediments overlying interbedded sandstone and mudstone. Hydrologic connections to both local shallow groundwater systems and deeper regional aquifers were investigated. Results indicated that groundwater fluxes between the wetland and surrounding uplands occurred on a local scale, with snowmelt infiltration driving fluxes during spring and riparian evapotranspirative demand dictating local fluxes in summer. Chloride data helped constrain estimates of groundwater exchange with the wetland, especially during winter and spring thaw periods when wetland chloride concentrations changed significantly. Analysis revealed that the water cycled through the wetland does not contribute to groundwater recharge on a regional scale, but plays a vital role in sustaining pond permanence, modulating pond salinity, and maintaining habitat necessary for migratory waterfowl. Compared to ephemeral ponds present at the site, which contribute extensively to groundwater recharge during spring melt events, low permeability sediments below the wetland limited its contribution to deeper groundwater recharge.