Patterns and environmental drivers of greenhouse gas fluxes in the coastal wetlands of China: A systematic review and synthesis.

Coastal wetlands play an increasingly important role in regulating greenhouse gas (GHG) fluxes and thus affecting climate change. However, the overall magnitude, trend, and environmental drivers of GHG fluxes in these wetlands of China remain uncertain. Herein, we synthesized data from 70 publications involving 187 field observations to identify patterns and drivers of GHG fluxes across coastal wetlands in China. Average methane (CH4), nitrous oxide (N2O) fluxes, and carbon dioxide (CO2) emissions (ecosystem respiration) across coastal wetlands were estimated as 2.20±0.31 mg·m-2·h-1, 16.44±2.96 μg·m-2·h-1, and 388.76±42.28 mg·m-2·h-1, respectively. GHG emissions varied with tidal inundation, where CH4 and CO2 emissions during tidal inundation were lower than during ebbing. CH4 and CO2 emissions from wetlands decreased linearly with increasing latitude, while N2O did not. CH4 fluxes were positively related to air temperature and aboveground biomass, and CO2 emissions were positively related to soil organic carbon. N2O fluxes were lower with increasing soil pH, and CH4 and CO2 emissions were greater with increasing soil moisture. Based on the results of sustained-flux global warming potential and sustained-flux global cooling potential models, our paper indicate that the fluxes of CH4 and N2O in coastal wetlands have a positive feedback to global warming, which is mainly driven by the CH4 emission. Our synthesis improved understanding of the roles of coastal wetlands in the ecosystem C cycle under global change. We suggest that long-term field observations of GHG fluxes across a wider range of spatiotemporal scales are urgently required to improve the prediction accuracy in GHG fluxes and the assessment of net GHG balance and its contribution to the GWP of coastal wetlands.