COASTING INTO 2020: A DECADE OF DISCOVERIES FOR BLUE CARBON ECOSYSTEMS

Abstract:

Over the past decade, coastal ecosystems have received scientific and policy attention for their nature-based climate mitigation potential. From seagrasses, to mangroves, to marshes to tidal freshwater forests, vegetated tidal wetlands show high rates of atmospheric carbon uptake coupled with carbon-rich soil formation processes, which lead to some of the highest observed annual rates of long-term carbon sequestration, from centuries to millennia. Although coastal wetlands represent less than 2% of global wetland acreage, they are distinct wetland types, due to historic processes of ecosystem development and past and future projected losses due to sea level rise and land-use change. At the terrestrial-aquatic interface, coastal wetlands are frequently narrow, linear, and patchy features comprising a landscape that is variable and complex in time and space, especially for subsurface conditions. While measurements and metadata remain limited, community-contributed improvements and syntheses of mapping, modeling, and measurements have advanced projections at continental scales, and pointed toward key uncertainties in research. Geomorphology is emerging as a key driver of both carbon burial rates and stock vulnerability. Salinity is emerging as a key driver of atmospheric fluxes, such as methane and gross primary productivity. Confidence in maps of both relative elevation and tidal influence will be essential improvements for reducing uncertainty in upscaled estimates of net ecosystem carbon balance. Future rates of carbon sequestration from the atmosphere and storage within coastal wetlands is largely a three-dimensional function of both immediate and long-term feedbacks of carbon accumulation, deposition and erosion, which requires incorporation of both large-scale events such as storms and in-situ species-level processes. Towards these projections, coupled physical and biogeochemical models – whether process-based or statistically-determined – will be needed to address growing uncertainty in response to active coastal modification, both human and naturally induced. Improved coordination and emergent networks among coastal scientists suggest that confidence in estimations, accounting and projections of carbon and greenhouse gas fluxes will continue to advance.