Seagrass and macrophyte mediated CO(2) and CH(4) 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.