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

doi:2015.30.2.121

Algae > Volume 30(2); 2015 > Article

Algae 2015;30(2): 121-137. doi: https://doi.org/10.4490/algae.2015.30.2.121

Ju-Hyoung Kim¹, Eun Ju Kang², Keunyong Kim², Hae Jin Jeong³, Kitack Lee⁴, Matthew S. Edwards⁵, Myung Gil Park², Byeong-Gweon Lee² and Kwang Young Kim^2,*

¹Faculty of Marine Applied Biosciences, Kunsan National University, Kunsan 573-701, Korea
²Department of Oceanography, College of Natural Sciences Chonnam National University, Gwangju 500-757, Korea
³School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul 151-747, Korea
⁴School of Environmental Science and Engineering, Pohang University of Science and Technology, Pohang 790-784, Korea
⁵Department of Biology, San Diego State University, San Diego, CA 92182, USA

*Corresponding Author

Email: kykim@chonnam.ac.kr

ABSTRACT

Studies on carbon flux 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 fields in this regard. In this study, the dynamics of carbon flux 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 significantly higher ecosystem production than the other habitat types. Specifically, 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-flux box model. These results indicate that the vegetative ecosystems showed significantly high capturing efficiency of inorganic carbon through coastal primary production.

Key words: CO2 flux; ecosystem production; eelgrass beds; Gwangyang Bay; macroalgal vegetation; microphytobenthos; phytoplankton; unvegetated sediment