Program     Marine Carbon Sequestration (MARCO): Multiscale Regulation and Response to Global Change       Poster Spatiotemporal variability in bacterial metabolic activity in the Pearl River Estuary: Influence of the river discharge P-SPS5-10 Xiangfu Li* , State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences Jie Xu, State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences Presenter Email: lixiangfu1988@126.com Heterotrophic bacteria play a significant role in carbon cycling in marine environments. Bacterial production (BP), respiration (BR) and growth efficiency were simultaneously determined along an environmental gradient in the Pearl River Estuary in the wet season (May 2015) and the dry season (January 2016), in order to examine bacterial carbon processing in Pearl River Estuary. Our results showed that the Pearl River discharge delivered labile dissolved organic matters (DOM) with low C:N ratio, resulting in a clear gradient in dissolved organic carbon (DOC) concentration and DOC:DON ratios. BP and BR responded differently to environmental variability. BP and the cell-specific bacterial production decreased, while the cell-specific bacterial respiration increased likely due to enhanced energetic cost for cell maintenance and require, in response to a decline in the quality and quantity of dissolved organic matter along the estuary. As a result, BP (2.09 to 144 ug C L-1 d-1) was to greater extent variable than BR (64.6 to 567 ug C L-1 d-1), leading to decreasing bacterial growth efficiency along an environmental gradient. Interactions between the freshwater and seawater from the South China Sea changed the quality and quantity of DOM, ultimately modulating bacterial metabolic activity in the Pearl River Estuary.