Methane and nitrous oxide emissions complicate blue carbon assessments

The role of coastal wetlands as natural ‘blue carbon’ sinks may be counter-acted by emissions of methane (CH4) and nitrous oxide (N2O). Site-specific fluxes of these two potent greenhouse gases from coastal wetlands show high spatial and temporal variability , making global estimates sensitive to statistical assumptions and uncertainties. Here, we review the magnitude of CH4 and N2O fluxes from mangroves, saltmarshes and seagrasses and identify direct and indirect drivers that can control production and consumption pathways. Significant research is required to better quantify fluxes and to understand factors causing flux variability from different transport pathways before restoration of coastal blue carbon ecosystems can be reliably used for climate mitigation.