Hydrogeomorphic controls on the thermal regime of natural and restored wetlands in a glacial plain

Abstract

Wetland thermal regimes are underexplored but essential attributes of habitats and function for regulatory and action agencies to evaluate the success of nationwide restoration activities. Here we investigate regional and local controls on the hydrological and thermal regimes of small natural and restored wetlands in the St. Lawrence River Valley region of northern New York State, USA. We deployed pressure and temperature sensors in seventeen wetland ponds and adjacent groundwater piezometers to obtain hourly measurements of stage and water temperature for one year. For this humid continental climate, we observed seasonal hysteresis in air and water temperature, which extended to benthic and groundwater environments. We found the temporal behavior of wetland temperatures within this region were strongly similar across sites, suggesting two seasonal controls: regional atmospheric forcing as a primary control and local groundwater offset induced by hydrogeomorphic settings as a secondary control. In particular, wetland temperatures showed the greatest spatial variability with a consistent rank order among sites during summer (standard deviation ranging 0.9–2.8℃). Three regional hydrogeomorphic settings corresponded to varying thermal behaviors in dry summer due to different degrees of groundwater sourcing. Results demonstrate that the imprints of hydrogeomorphic controls on wetland thermal regimes are best assessed in both summer and winter, due to differences in groundwater availability of wetland thermal regimes.