Response of Peatland Ecohydrology to Changing Precipitation Frequencies

English Abstract:

Sphagnum moss, the primary peat-forming vegetation in ombrotrophic peatlands, require sufficient surface moisture for growth and survival. Climate change projections for some regions include more intense but less frequent precipitation events that are predicted to lead to lower water tables and drier surface conditions. Recent studies have highlighted the importance of precipitation in these systems; however, few studies consider how the temporal distribution of rainfall will impact moisture within the moss layer, particularly among different land cover types. As such, the main objective of this study was to investigate the feedbacks between soil moisture, evapotranspiration (ET), and the rates of photosynthesis and respiration of Sphagnum moss under varying precipitation frequencies, and in the presence of common vascular vegetation. Soil cores were taken from a pristine Southern Ontario peatland containing three different plant communities (Sphagnum, Sphagnum and sedges, Sphagnum and ericaceous shrubs) and watered at varying frequencies (3X/week, 1X/week, 0.5X/week) while maintaining a constant total water supply between treatments. To assess the importance of changing precipitation frequencies on the moisture state of Sphagnum moss, the vertical distribution of soil moisture and ET rates were measured among the different plant cover types. Preliminary results suggest that precipitation frequency is particularly important for the moisture state of Sphagnum in cores with ericaceous shrubs, as higher ET rates led to drier surface conditions than in cores without shrubs. The implications of varying moisture conditions under the three precipitation regimes for rates of photosynthesis and respiration of Sphagnum is also discussed. This study highlights the importance of considering the temporal distribution of precipitation when predicting climate change impacts on ecohydrological feedbacks in Northern peatlands, and indicates that this response can vary among different land cover types.