Evaluation of carbon fux in vegetative bay based on ecosystem production and CO2 exchange driven by coastal autotrophs

Abstract

Studies on carbon fux in the oceans have been highlighted in recent years due to increasing awareness about climate change, but the coastal ecosystem remains one of the unexplored felds in this regard. In this study, the dynamics of carbon fux in a vegetative coastal ecosystem were examined by an evaluation of net and gross ecosystem production (NEP and GEP) and CO2 exchange rates (net ecosystem exchange, NEE). To estimate NEP and GEP, community production and respiration were measured along different habitat types (eelgrass and macroalgal beds, shallow and deep sedimentary, and deep rocky shore) at Gwangyang Bay, Korea from 20 June to 20 July 2007. Vegetative areas showed signifcantly higher ecosystem production than the other habitat types. Specifcally, eelgrass beds had the highest daily GEP (6.97 ± 0.02 g C m-2 d-1), with a large amount of biomass and high productivity of eelgrass, whereas the outer macroalgal vegetation had the lowest GEP (0.97 ± 0.04 g C m-2 d-1). In addition, macroalgal vegetation showed the highest daily NEP (3.31 ± 0.45 g C m-2 d-1) due to its highest P: R ratio (2.33). Furthermore, the eelgrass beds acted as a CO2 sink through the air-seawater interface according to NEE data, with a carbon sink rate of 0.63 mg C m-2 d-1. Overall, ecosystem production was found to be extremely high in the vegetated systems (eelgrass and macroalgal beds), which occupy a relatively small area compared to the unvegetated systems according to our conceptual diagram of a carbon-fux box model. These results indicate that the vegetative ecosystems showed signifcantly high capturing effciency of inorganic carbon through coastal primary production.