Grant: Alliance Grants

Worldwide, stormwater management (SWM) systems are being expanded and retrofitted to counter negative impacts of urbanization, including increased flooding, stream degradation, and eutrophication of receiving aquatic ecosystems. In Canada, stormwater ponds (SWPs) are the standard SWM technology for new developments although other green technologies, especially bioretention systems (BRSs), are increasingly used. Whether these technologies also support positive climate benefits remains controversial, however. For instance, SWPs and BRSs have been shown to be significant sources of the greenhouse gases (GHGs) carbon dioxide, methane, and nitrous oxide. However, they also sequester carbon (C) and reduce the surface runoff of nutrients such as phosphorus (P), hence, altering nutrient limitation patterns, trophic conditions, and GHG exchanges along the urban aquatic continuum and in receiving water bodies. To determine if SWPs and BRSs exacerbate or mitigate climate forcing, their net effects must therefore be evaluated at the watershed scale. The proposed project will address this by (1) quantifying the landscape-scale drivers and processes within SWPs and BRSs that control GHG exchanges, C sequestration, and changes in the chemical speciation and fluxes of C and P, (2) integrating the resulting knowledge into robust representations of SWPs and BRSs in coupled hydrology-biogeochemistry models for urban watersheds, and (3) using model simulations to analyze the responses of urban GHG emissions and nutrient P export to the implementation and management of green SWM infrastructure. We will initially focus on urban watersheds in southern Ontario with SWPs and BRSs whose hydrology and biogeochemistry we have already extensively characterized, hence, laying the foundation for expanding the model applications across Canada. The project's municipal and industrial partners will use the project's outcomes to (1) carry out interventions that reduce GHG emissions from existing SWPs and BRSs, and (2) develop green SWM strategies that minimize trade-offs between climate mitigation benefits and other key services, in particular, water quality protection.