Antecedent snow conditions affect water levels and plant biomass of a fen in the southern boreal forest : results from an experiment using mesocosms

Biogeochemical processes in peatland environments, such as carbon sequestration and decomposition, are affected by variation in water supply. Across the boreal forest biome, climate change threatens to either alter rates of annual precipitation or skew the timing and ratio of rainfall and snowfall events. To simulate moisture variability during the ice-free season, cylindrical mesocosms (diameter 1.5 m) were installed in a southern boreal patterned fen in central Saskatchewan, Canada, to enable manipulations of antecedent snow conditions. The objectives of the study were to assess the utility of in situ mesocosms for peatland ecohydrology research and to test for effects of snow manipulations on fen plant communities. After spring thaw, initial water depths were greatest and dates of surface water disappearance were latest in the snow addition mesocosms, followed by the control and snow removal mesocosms. In contrast, maximum frost levels and frost disappearance dates in the snow addition mesocosms were intermediate to those of the control and snow removal mesocosms. Densification of snow during snow manipulation events is suggested to account for this confounding outcome. Of the nine plant taxa identified in the harvests of aboveground biomass from all mesocosms, buckbean (Menyanthes trifoliata) biomass was most strongly related to variation in surface water conditions. Climate conditions that favour persistence of either herbaceous- or graminoid-dominated communities will likely affect the carbon storage function of southern boreal fens.