Land cover and topographic controls on groundwater recharge on the Oak Ridges Moraine

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Land use and climate changes have major implications for hydrologic processes and water resources. I will study how such changes impact groundwater recharge and streamflow on the environmentally-sensitive Oak Ridges Moraine in southern Ontario - a key regional hydrogeologic resource. The Moraine is undergoing both land use and climate change, the hydrologic implications of which are unclear. This is partly due to uncertainty in the ability of drainage basins to store and release water to streams. Adjacent streams on the Moraine discharge greatly different amounts of groundwater, and it is not known whether this results from differences in recharge, subsurface storage and release properties, or both. This variability also suggests differences in residence time of water in the basin before it leaves as streamflow. Data on water residence times is critical when predicting if and when surface hydrologic changes (due to land use and/or climate change) may induce a streamflow response.***Our ability to predict surface and subsurface water response to land use and climate change partly depends on our knowledge of how such changes control water infiltration, recharge, and discharge. This work will study differences in infiltration and recharge for land uses ranging from urban to forest, and particularly the potential for depression-focused recharge. This is produced when hillslope runoff enters topographic depressions and infiltrates. It leads to greater and faster recharge in depressions than on adjacent uplands, with important implications for water and contaminant movement to deeper groundwater, as well as the capacity of subsurface material to filter contaminants. Frozen ground is critical in the transfer of rain and snowmelt to depressions; however, empirical evidence for this process on the Moraine's hummocky landscape is lacking. Cost-effective methods will be developed to estimate recharge for the Moraine's land use and specific topographic conditions. Frozen soil development will be determined for these land uses to assess how recharge may be altered by land use change. Basin capacity to store recharge inputs will be obtained from detailed 3-d geologic data, and water residence times will be derived from environmental tracers. Data will be used in model predictions of recharge response to land use and climate changes, and results will help assess coupling between infiltration, water residence times and streamflow. The integrated field- and modelling-based approach will link the potential for depression-focused recharge with water storage and release from drainage basins and associated water residence times, and will assess how such linkages may be modified by climate and land use changes. These results will be key inputs for the groundwater models that are critical components of sustainable water resource management on the Oak Ridges Moraine and elsewhere in Canada.