Impact of long-term drainage on summer groundwater flow patterns in the Mer Bleue peatland, Ontario, Canada

This is the authors' abstract. We don't add key points for this paper.

Long-term impacts of a drier climate on coupled hydrology and carbon cycling in northern peatlands are poorly understood. We used a historic drainage ditch, separating an area from the main peatland, as an analogue for long-term drying in a northern temperate bog. The objective was to identify the impact of drier conditions on ecohydrological processes and groundwater flow patterns in an area now wooded and an area that maintained bog character. Groundwater flow patterns alternated between downward flow and upward flow in the bog area and were mostly upward orientated in the wooded area. Flow patterns were in agreement with changes in post-drainage hydraulic conductivities, storage capacity of the peat and hydraulic gradients. Compared to the bog, hydraulic conductivities in the wooded area were one to three orders of magnitude lower in the uppermost 0.75 m (paired t-test, p<0.05) of peat but partly higher below. Bulk density had increased and the water table level was lower and more strongly fluctuating. Our findings suggest hydraulic gradients and flow patterns have changed due to increased evapotranspiration and interception with the emergence of a tree cover. The smaller size of the now-forested area relative to the remaining bog area appeared to be important for the hydrological change. When water supply from undisturbed areas was large, enhanced runoff to the drainage channel had little effect on hydrologic patterns and vegetation pattern, whereas in the smaller, now forested area pervasive changes in vegetation and hydrologic processes occurred. This finding raises questions about tipping points with respect to the impact of drying on bog ecosystems that need to be addressed in future research.