Characterizing groundwater and surface water contribution to ecosystem services: A Canadian national-scale framework

Environment and Climate Change Canada is implementing the ten-year Nature Smart Climate Solutions Fund (NSCSF) to mitigate net greenhouse gas emissions while providing multiple co-benefits to biodiversity and human well-being. Accounting for these co-benefits involves the need to characterize ecosystem service flows across a broad range of sites within the Canadian landscape.  To support this objective, a standardised approach has been developed to assess water-focused ecosystem services at NSCS pilot sites, across three ecozones, and ranging in size from 12.5 to 635 ha. Four of the pilot sites are restoration targets, with a degraded landcover base-case scenario, and four are securement targets, with a natural land cover base-case scenario. The national scale Canada1Water (C1W) hydrogeological data and modelling framework was adopted, thus ensuring consistent data fidelity and model structure across sites. The fully integrated hydrologic modelling was implemented in HydroGeoSphere and is an unique solution for ecosystem services assessment, because groundwater, soil moisture, and surface water (ponds, wetlands, and streams) are dynamically coupled and simulated under transient climatology that includes both flood and drought conditions. Recognizing that NSCSF site sizes vary considerably, the model construction methodology also ensures consistent spatial resolution to facilitate comparison of land cover efficacy towards ecosystems services between sites. Outputs from the modelling are used to assess landcover influences on stream/river flow rate, cumulative discharge; wetland water storage; groundwater recharge, discharge, and storage; soil moisture; and cumulative evaporation and transpiration. The simulated hydrologic influences are then normalized (0 to 2 for the restoration sites and 0 to -2 for the securement sites) and plotted on a cumulative-step plot that translates hydrologic differences into visualized differences in water-focused ecosystem services. This approach, leveraging C1W for its ability to facilitate national scale hydrologic analysis, could form the basis of a highly efficient water-focused ecosystems services assessment at all NSCSF sites.  Subsequent to the eight pilot case studies, an alternative quasi 2-dimensional column modelling solution is being implemented. This approach removes the model mesh development overhead and permits user selection within a web-based or GIS environment. While lacking some of the advantages of a full three-dimensional solution, it provides the advantage and flexibility of being deployed across thousands of sites without the need for apriori knowledge of site locations.