Chapter 4 - Biosphere-atmosphere exchange of CO2 and CH4 in mangrove forests and salt marshes

Abstract

Coastal wetlands have one of the highest carbon sequestration rates among the world’s natural ecosystems mainly because of their high primary productivity and low rate of ecosystem respiration. Meanwhile, they are often assumed to be minor sources of methane (CH4), a highly potent greenhouse gas (GHG), under the influence of high salinity. On the other hand, frequent inundation and anaerobic environment make coastal wetlands potential sources of CH4 if other favorable conditions are met. Accurate quantification of the magnitude and direction of biosphere-atmosphere exchange of GHGs, including carbon dioxide (CO2) and CH4, is essential for a comprehensive assessment of the climatic impact of coastal wetlands. The eddy covariance technique allows for the direct, quasicontinuous, and long-term measurements of ecosystem-scale GHG fluxes and has been increasingly used in coastal wetland ecosystems. In this chapter, we briefly introduce the basics of the eddy covariance technique, followed by a synthesis of biosphere-atmosphere exchange of CO2 and CH4 in coastal mangroves and salt marshes, with a particular focus on the temporal variability and biophysical drivers.