ECOSYSTEM SERVICES TRADE-OFFS OF SALT MARSHES AS COASTAL NUTRIENT FILTERS VERSUS GREENHOUSE GAS SINKS

Abstract

Salt marshes are recognized for the ecosystem services they provide as coastal nutrient filters and carbon sinks, but relying on salt marshes to attenuate nutrient pollution comes at the potential cost of enhanced greenhouse gas (GHG) emissions. In this study, we quantify and assess the trade-offs between the nutrient attenuation and carbon sequestration functions of salt marshes in Atlantic Canada. We conducted groundwater monitoring, surface and groundwater sampling, and GHG flux measurements at two salt marshes located adjacent to eutrophic estuaries in Basin Head, PEI and Rushton’s Beach, Nova Scotia. A hydrogeological model was developed to characterize the magnitude and pathways of nitrate transport into, and attenuation by, the Basin Head marsh. Our results indicate that nitrate loading is mainly via tidal flooding from the adjacent eutrophic lagoon and was estimated at 0.06 mmol N m-2 d-1 with 36% of input nitrate retained or converted in the marsh. The net climatic effect of average N2O and CH4 fluxes at Basin Head and Rushton’s Beach results in only a small reduction in the marshes carbon sink (8.3% and 5.0%, respectively).