Mapping capacity, demand and pressure for hydrological ecosystem services – a case-study of Canadian rivers

Mapping and quantifying the spatial configuration of ecosystem services is a crucial tool to understand the sustainability of socio-ecological systems. River systems are unlike terrestrial systems because they are connected by the flow of water across large watersheds, creating long-distance up- and downstream dependencies between sources and use of the services. These connections have important, often overseen, implications for the mapping and quantification of hydrological ecosystem services. Following the conceptual approach of terrestrial ES assessments, we developed a spatial, hydrological approach to measure the capacity for, demand for, and pressure on for hydrological ecosystem services provision linked to river systems. We applied this method to all Canadian rivers to assess their capability to provide, purify and regulate water in a desirable quantity to beneficiaries, and analyzed the degree of risk, i.e. the relative potential of failure to deliver these services, among four beneficiaries: agriculture, municipalities, industries, and hydropower. Our results present a first-time cartography of capacity for,   demand for, and pressure on freshwater provision and regulation, and indicate hotspots of risk of failure at a large scale. Our results show that, in Canada, rivers considered at risk for reduced ecosystem services provision are located in three main regions: the Prairies, where demand for and pressure from freshwater provision and regulation for agriculture is high; southern Ontario and Québec, where demand for and pressure from water provision for municipalities and industries is high; and in Northern large rivers, especially in Québec, where pressure from water provision for hydropower production is high.  The distribution of capacity, demand and pressure shows an intense but concentrated reliance on small rivers to provide water for downstream users, especially for agriculture. For Canadian large rivers, the degree of risk to freshwater provision and regulation are moderate but constant. Our cartography can inform freshwater management by identifying rivers where water provisioning is at risk, for example, where demand is reaching capacity or where water use has negative consequences on downstream ecosystem services.