CO2 and CH4 emissions from coastal wetland soils

Increasing awareness of the significance of coastal wetlands in global carbon budgets, combined with recently developed approaches such as in situ gas analyzers connected to flux chambers, has led to the wide interests in quantifying greenhouse gas exchange in these ecosystems, for which less attention was paid to than terrestrial ecosystems. Considering the high net primary production and large carbon stocks of coastal wetlands, recent researches have pointed out their conservation as an opportunity to mitigate climate change. CO2 emissions are especially low in mangrove ecosystems (257 g C m− 2 year− 1), while CO2 emissions from saltmarshes (564 g C m− 2 year− 1) are relatively similar to those from terrestrial ecosystems (592 g C m− 2 year− 1). Contrasting trends were reported for CH4 emissions, with low values in terrestrial ecosystems (0.22 g C m− 2 year− 1), intermediate values in mangroves (1.69 g C m− 2 yr− 1), and high values in saltmarshes (14.2 g C m− 2 yr− 1). The large variability in measured CO2 and CH4 fluxes at the soil-air interface suggests that emissions are highly responsive to changes in both physical and biological parameters. Anthropogenic disturbances in particular often enhance carbon decomposition and releases from soils. With a focus on coastal wetlands, this chapter gives recommendations for the use of incubation chambers, synthesizes soil-air CO2 and CH4 flux magnitudes, discusses the biotic and abiotic parameters influencing greenhouse gas fluxes, and provides future directions to fill the knowledge gaps in coastal carbon budget estimates.