THE EFFECTS OF LONG-TERM WATER TABLE MANIPULATIONS ON PEATLAND EVAPOTRANSPIRATION, SOIL PHYSICAL PROPERTIES, AND MOISTURE STRESS

Abstract

<p>Northern boreal peatlands represent a globally significant carbon pool that are at risk of drying through land-use change and projected future climate change. The current ecohydrological conceptualization of peatland response to persistent water table (WT) drawdown is largely based on short-term manipulation experiments, but where the long-term response may be mediated by vegetation and microtopography dynamics. The objective of this thesis is to examine the changes to peatland evapotranspiration, soil physical properties, and moisture stress in response to a long-term WT manipulation. The energy balance, hydrology, vegetation, and soil properties were examined at three adjacent peatland sites in the southern sub-boreal region which were subjected to WT manipulations on the order of ±10 cm at two treatment sites (WET, and DRY) compared to the reference site (INT) as a result of berm construction in the 1950s.</p> <p>Sites with an increasing depth to WT were found to have greater microtopographic variation and proportion of the surface covered by raised hummocks. While total abundance of the major plant functional groups was altered, species composition and dominant species of vascular and non-vascular species within microforms was unaltered. Changes in vegetation and microtopography lead to differences in albedo, surface roughness, and surface moisture variability. However, total ET was only significantly different at the WET site. Transpiration losses accounted for the majority of ET, where LAI best explained differences in total ET between sites. Surface moisture availability did not appear to be limiting on moss evaporation, where lab results showed similar moisture retention capacity between microforms and sites, and where low surface bulk density was shown to be a strong controlling factor. Modelling results further suggested that, despite dry surface conditions, surface moisture availability for evaporation was often not limited based on several different parameterizations of peat hydraulic structure with depth.</p>