Carbon balance in tropical freshwater wetlands on the coastal plain of the Gulf of Mexico

Wetlands play an important role as carbon stores; however, these ecosystems also contribute to the emission of greenhouse gases (GHG). In this study, we compared the carbon balance (CB) in coastal freshwater marshes and swamps. We use three different methods, which are described in the literature. The first is based upon the CB basis (Carbon-emission subtracted to Carbon-sequestration), without considering the global warming potential (GWP) of GHG. The second method is a CB considering the GWP, and the third method estimated the wetland function as carbon sink or source, by using a dynamic model with different horizon times (20, 100 and 500 years). With the first method, the studied wetland soils functioned as carbon sinks. Using the second method, the carbon in the form of GHG was up to 5 times more than sequestered carbon, however, the methodology does not consider the dynamics of gases in the atmosphere. By using a dynamic model that integrates productivity, plant respiration, the half-life of the gases and soil carbon emitted as methane, it was found that these ecosystems are net sinks carbon at horizon times of 500 years. This outlines a need to conserve and restore wetlands, and demonstrates the wetlands role as carbon sinks without concerning that they are sources of GHGs.