Groundwater-surface water connectivity in the presence of riparian wetlands

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Nearly a third of the Canadian population, and up to 80% in agricultural areas, relies on groundwater resources. The global groundwater extraction rate has at least tripled over the past 50 years and we are only beginning to assess the impacts of increased usage on drinking water supplies and ecosystems. In most cases, recharge and discharge of aquifers in connection with surface water reservoirs remain poorly understood. This leads to a lack of control for the sustainable exploitation of aquifers as well as for the integrated management of water resources. The long-term objective of this research program is to determining how groundwater and surface water reservoirs are connected and how they respond to natural and human-induced changes. Specific objectives are (1) to identify the parameters and processes that drive groundwater recharge and discharge in the presence of riparian wetlands, (2) to quantify the fluxes exchanged between aquifers, riparian wetlands, and rivers at various scales and (3) to understand the impacts of environmental change on hydrological connectivity. The research program is divided in three parts. In Part I, groundwater recharge-discharge settings in the presence of wetlands will be characterized. This will be achieved on existing experimental sites by measuring geology and river corridor conditions using detailed field data and water sampling (major ions, 222Rn, stable isotopes and water temperature). Statistical analyses will help discern which parameters control groundwater recharge-discharge connectivity and time series analyses (water levels, temperature and electrical conductivity) will contribute to the identification of exchange processes. In Part II, the fluxes between aquifer, riparian wetlands and river will be simulated with fully-coupled 3D modeling and with local recharge modeling to pinpoint the scales involved in these exchanges. Global sensitivity analysis will determine numerically the processes that drive aquifer-wetland-river interactions. In Part III, the effects of environmental change on the drivers of hydrological connectivity in the presence of wetlands will be quantified. This will be done through the fully-coupled flow simulations under land use change and climate change scenarios. The effect of mitigation measures such as the implementation of river corridors leading to additional wetland areas on groundwater levels, floods and river low flows will also be simulated. Transport simulations will be performed at the local and regional scales to better understand the role of riparian wetlands as effective barriers for contaminant fluxes. This research program will pinpoint the drivers and constraints of groundwater recharge-discharge through riparian wetlands. It will also contribute significantly to identify the limits of existing approaches and to define new techniques for the study of aquifer-river fluxes in the presence of riparian wetlands. Science-based understanding of the scales at which fluxes involved in groundwater recharge and discharge through riparian wetlands need to be considered to fully assess the processes involved will be developed. The research will also significantly contribute to better define the impact of anthropogenic pressures and climate change on watersheds, and to better understand hydrological and water quality functions of riparian systems. These original contributions will be made possible by the training of numerous HQPs prepared to face the complexity of field and modeling work common to hydrogeology and environmental studies. This research program has the potential to drastically change the way groundwater and wetlands are managed and to help sustain their long term resilience within the river corridor.