Seagrass and macrophyte mediated CO2 and CH4 dynamics in shallow coastal waters

Seagrass meadows are among the most important coastal/ marine ecosystems for long-term carbon storage and conditioning of coastal waters. A combined air-water flux of CO 2 and CH 4 from the seagrass meadows was studied for the first time from Asia’s largest brackish–water lagoon, Chilika, India. Ecosystem-based comparisons were carried out during two hydrologically different conditions of dry and wet seasons in the seagrass dominated southern sector (SS); macrophyte-dominated northern sector (NS); the largely un-vegetated central sector (CS) and the tidally active outer channel (OC) of the lagoon. The mean fluxes of CO 2 from SS, NS, CS and OC were 9.8, 146.6, 48.4 and 33.0mM m -2 d -1 , and that of CH 4 were 0.12, 0.11, 0.05 and 0.07mM m -2 d -1 , respectively. The net emissions (in terms of CO 2 equivalents), considering the global warming potential of CO 2 (GWP: 1) and CH 4 (GWP: 28) from seagrass meadows were over 14 times lower compared to the macrophyte-dominated sector of the lagoon. Contrasting emissivity characteristics of CO 2 and CH 4 were observed between macrophytes and seagrass, with the former being a persistent source of CO 2 . It is inferred that although seagrass meadows act as a weak source of CH 4 , they could be effective sinks of CO 2 if land-based pollution sources are minimized.