Dissolved organic matter cycling revealed from the molecular level in three coastal bays of China

Chen Zhao; Haibo Zhang; Penghui Li; Yuanbi Yi; Yuping Zhou; Yuntao Wang; Chen He; Quan Shi; Ding He

doi:10.1016/j.scitotenv.2023.166843

Dissolved organic matter cycling revealed from the molecular level in three coastal bays of China

Sci Total Environ. 2023 Dec 15:904:166843. doi: 10.1016/j.scitotenv.2023.166843. Epub 2023 Sep 5.

Authors

Chen Zhao¹, Haibo Zhang², Penghui Li³, Yuanbi Yi⁴, Yuping Zhou⁵, Yuntao Wang⁶, Chen He⁷, Quan Shi⁷, Ding He⁸

Affiliations

¹ Department of Ocean Science and Center for Ocean Research in Hong Kong and Macau, The Hong Kong University of Science and Technology, Hong Kong SAR, China; School of Earth Sciences, Zhejiang University, Hangzhou 310058, China.
² National Marine Environmental Monitoring Centre, Dalian 116023, China.
³ School of Marine Sciences, Sun Yat-sen University, Zhuhai 519082, China; Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519082, China.
⁴ Department of Ocean Science and Center for Ocean Research in Hong Kong and Macau, The Hong Kong University of Science and Technology, Hong Kong SAR, China.
⁵ School of Earth Sciences, Zhejiang University, Hangzhou 310058, China; School of Environmental and Municipal Engineering, Qingdao University of Technology, Qingdao 266525, China.
⁶ State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China.
⁷ State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Changping District, Beijing 102249, China.
⁸ Department of Ocean Science and Center for Ocean Research in Hong Kong and Macau, The Hong Kong University of Science and Technology, Hong Kong SAR, China; School of Earth Sciences, Zhejiang University, Hangzhou 310058, China; State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou 310012, China. Electronic address: dinghe@ust.hk.

PMID: 37678524
DOI: 10.1016/j.scitotenv.2023.166843

Abstract

As the widespread distributed and critical zones connecting the land and ocean systems, coastal bays are special units with semi-enclosed landforms to accommodate and process dissolved organic matter (DOM) in the context of increasing anthropogenic effects globally. However, compared to other common systems that have been paid much attention to (e.g., large river estuaries, wetlands), the roles of the coastal bays in coastal carbon cycling are less explored. To fill this knowledge gap, here we combined optical techniques and ultra-high-resolution mass spectrometry to systematically investigate the DOM chemistry of the three typical coastal bays in different nutrient levels, Xiangshan Bay, Jiaozhou Bay, and Sishili Bay, in China. Results show that terrestrial signals and anthropogenic imprints were observed in these three bays to various extents. Besides, Xiangshan Bay with a higher nutrient level had the DOM characterized by lower humification and aromaticity degree than Jiaozhou Bay and Sishili Bay, which not likely mainly resulted from the differences in the primary production or photochemical processing. Further examination reveals that microbial processing likely contributes to the differences in DOM chemistry among the three bays, as indicated by different proportions of potentially transformed nitrogen-containing molecules and relative abundances of the island of stability molecules. Considering the nutrient levels in different bays, we speculate that the lower nutrient concentrations would promote the efficiency of the microbial carbon pump (MCP), which hypothesized that heterotrophic microorganisms might contribute to the formation of marine recalcitrant organic carbon. Additionally, the enrichment of oxygen-rich compounds in the unique carboxyl-rich alicyclic molecule pool of Jiaozhou Bay and Sishili Bay suggests that the efficient MCP might preferentially form them in these two bays. This study emphasizes the importance of coordinating the land and ocean systems and controlling the nutrient discharge to coastal bays, thus, to potentially promote long-term marine carbon sequestration.

Keywords: Coastal bays; Dissolved organic matter; Estuarine carbon cycling; FT-ICR MS; Microbial carbon pump.