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ORIGINAL RESEARCH article

Front. Mar. Sci.
Sec. Coastal Ocean Processes
Volume 11 - 2024 | doi: 10.3389/fmars.2024.1511427
This article is part of the Research Topic Advanced Monitoring, Modelling, and Analysis of Coastal Environments and Ecosystems View all 18 articles

Seasonal Dynamics of Dissolved Organic Matter in a Small Tropical Estuary-Coastal Bay Continuum: Distribution, Transformation, Flux, and Global Perspectives

Provisionally accepted
Pengfei Liu Pengfei Liu 1Kuan Jiang Kuan Jiang 1Qi Tan Qi Tan 1Fajin Chen Fajin Chen 1Renming Jia Renming Jia 2Chao Wang Chao Wang 1*
  • 1 College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang, China
  • 2 Fourth Institute of Oceanography, Ministry of Natural Resources, Beihai, China

The final, formatted version of the article will be published soon.

    The export and transformation of riverine dissolved organic matter (DOM) at the river-sea interface are critical to understanding carbon budgets in tropical regions, yet remain underexplored in small watersheds. This study analyzed dissolved organic carbon (DOC), chromophoric (CDOM), and fluorescent DOM (FDOM) over five cruises from summer 2021 to summer 2022 in the Suixi Estuary-Zhanjiang Bay continuum, a eutrophic tropical transition zone in the northwestern South China Sea. Seasonal variations were pronounced for DOM in the continuum and two endmembers. Freshwater DOM, dominated by terrestrial organic materials, was closely tied to soil leaching and erosion, correlating with precipitation patterns. Conversely, seawater DOM, enriched in protein-like FDOM, varied with the West-Guangdong Coastal Current and its associated primary production. Linear decreases in DOM with increasing salinity indicate that conservative mixing largely shapes DOM distributions in the continuum, especially for humic-like FDOM. Non-conservative processes, including flocculation, phytoplankton production, and microbial transformation, variably alter DOM components across seasons. The Suixi River in summer contributed considerably but disproportionately to the annual DOM flux (47-59%), due to intense soil leaching processes that mobilize refractory terrigenous DOM. The deviation observed in the Suixi River's DOC-CDOM relationship from that of global rivers, coupled with a distinctive single-peak pattern between the carbon-specific absorption coefficient and water yield in global rivers, highlights the critical role of watershed nature in influencing river-exported DOM composition. The notably high DOC and CDOM yields for the Suixi River further emphasize the importance of small, tropical rivers in shaping the estuarine and coastal carbon budget.

    Keywords: Suixi River, Zhanjiang Bay, dissolved organic carbon, chromophoric dissolved organic matter, fluorescent dissolved organic matter, Mixing behavior

    Received: 15 Oct 2024; Accepted: 23 Dec 2024.

    Copyright: © 2024 Liu, Jiang, Tan, Chen, Jia and Wang. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

    * Correspondence: Chao Wang, College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang, China

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