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Journal of Tropical Oceanography

Special Issue: 南海专题

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Distribution characteristics of dissolved carbohydrates and its influence factors in the Dafengjiang River Estuary, Qinzhou Bay, northern South China Sea

ZENG Debin1, KANG Zhenjun1, YANG Bin1,2,3, ZHOU Jiaodi1,3, LU Dongliang1, HUANG Haifang1,4, YAN Tingting1   

  1. 1. Guangxi Key Laboratory of Marine Environmental Disaster Processes and Ecological Protection Technology, Beibu Gulf University, Qinzhou 535011, China;

    2. Key Laboratory of Coastal Salt Marsh Ecosystems and Resources, Ministry of Natural Resources/Jiangsu Key Laboratory of Marine Biotechnology, Jiangsu Ocean University, Lianyungang 222005, China;

    3. Guangxi Laboratory on the Study of Coral Reels in the South China Sea, Guangxi University, Nanning 530004, China;

    4. Key Laboratory of Marine Chemistry Theory and Technology, Ocean University of China, Qingdao, 266100, China

  • Received:2025-08-24 Revised:2025-10-16 Accepted:2025-10-23
  • Supported by:

    National Natural Science Foundation of China (42166002); Guangxi Natural Science Foundation (2025GXNSFAA069339); Natural Science Foundation of Jiangsu Province (BK20241962); Guangxi Key Laboratory of Marine Environmental Change and Disaster in Beibu Gulf, Beibu Gulf University (2024KF01); Marine Science First-Class Subject, Beibu Gulf University (TRB002); Beibu Gulf Marine Ecological Environment Field Observation and Research Station of Guangxi (23-026-271)

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Abstract: The concentrations of dissolved monosaccharides (MCHO), polysaccharides (PCHO), and total carbohydrates (TCHO) were determined by 2,4,6-tripyridyl-s-triazine (TPTZ) method in the Dafeng River Estuary (DRE) during December 2022, and their distribution characteristics and influence factors were studied. The results showed that average (range) concentrations of MCHO, PCHO and TCHO in surface seawater of the DRE were 24.78 (8.52~43.71), 14.75 (9.96~21.01) and 39.53 (19.54~61.72) μmol C·L -1, respectively. TCHO accounted for an average of 52.8% ± 17.3% of the dissolved organic carbon (DOC) concentration, indicating that TCHO was a significant component of DOC in the study area. MCHO contributed an average of 59.1% ± 15.5% to TCHO, suggesting that MCHO was the dominant form of TCHO. The concentrations of MCHO and TCHO exhibited a gradual decreasing trend along the river-estuary-bay continuum, while PCHO showed the opposite distribution pattern. Both MCHO and TCHO were significantly negatively correlated with salinity and pH (P<0.01), indicating that terrestrial inputs and freshwater-seawater mixing processes were key factors controlling the distribution of dissolved carbohydrates in the DRE, and seawater acidification indirectly regulated the spatial distribution of dissolved carbohydrates in the study area by modulating biological processes. This study will provide baseline data on dissolved carbohydrates in the river-estuary-bay continuum of the Qinzhou Bay prior to the construction of the Pinglu Canal, a century-long project. These findings are of great significance for deepening our understanding of coastal carbon cycling processes and their mechanisms in the Guangxi Beibu Gulf.

Key words: dissolved carbohydrates, dissolved organic carbon, distribution characteristics, influence factors, Dafengjiang River Estuary