Hydrodynamic processes and their impact on eutrophication in two distinct types of bays near the Beibu Gulf coast: insight from dual water isotopes

Junhui Wu; Ruixue Cao; Qibin Lao; Guangzhe Jin; Xuan Lu; Chunqing Chen; Fajin Chen; Shuwen Zhang

doi:10.1016/j.marenvres.2026.107840

Hydrodynamic processes and their impact on eutrophication in two distinct types of bays near the Beibu Gulf coast: insight from dual water isotopes

Mar Environ Res. 2026 Mar:215:107840. doi: 10.1016/j.marenvres.2026.107840. Epub 2026 Jan 5.

Authors

Junhui Wu¹, Ruixue Cao², Qibin Lao², Guangzhe Jin², Xuan Lu³, Chunqing Chen⁴, Fajin Chen², Shuwen Zhang⁵

Affiliations

¹ Institute of Marine Science, Shantou University, Shantou, China; Guangdong Provincial Key Laboratory of Marine Disaster Prediction and Protection, Shantou University, Shantou, China.
² College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang, 524088, China; Key Laboratory for Coastal Ocean Variation and Disaster Prediction, Guangdong Ocean University, Zhanjiang, 524088, China; Key Laboratory of Climate, Resources and Environment in Continental Shelf Sea and Deep Sea of Department of Education of Guangdong Province, Guangdong Ocean University, Zhanjiang, 524088, China.
³ Polar and Marine Research Institute, College of Harbor and Coastal Engineering, Jimei University, Xiamen, 361021, China.
⁴ College of Ocean and Meteorology, Guangdong Ocean University, Zhanjiang, 524088, China.
⁵ Institute of Marine Science, Shantou University, Shantou, China; Guangdong Provincial Key Laboratory of Marine Disaster Prediction and Protection, Shantou University, Shantou, China. Electronic address: zhangsw@stu.edu.cn.

PMID: 41520593
DOI: 10.1016/j.marenvres.2026.107840

Abstract

Quantitative understanding of hydrodynamic processes and nutrient supply in different types of small bays remains limited. By combining water isotopes, hydrological parameters, and nutrient analysis, our findings revealed that Qinzhou Bay (a bay with multiple riverine inputs) is significantly influenced by coastal diluted water (49 %), while Tieshangang Bay (a bay without riverine input) is mainly influenced by high-salinity seawater outside the bay (61 %) during the early rainy season. However, despite these differences, Tieshangang Bay receives a greater proportion of nutrient supply from diluted water (69-95 %) compared to Qinzhou Bay (58-87 %). This disparity is related with the higher seawater intrusion into the Tieshangang Bay, which creates an internal salinity front that inhibits nutrient diffusion outside the bay. The barrier effect of the front hinders the expansion of terrestrial nutrients out of the bay, and accumulates in the bay, exacerbating the seawater eutrophication in the inner Tieshangang bay. This results in a significantly higher degree of eutrophication in Tieshangang Bay compared to Qinzhou Bay. Our study provides valuable insights into the hydrodynamic processes and their impact on eutrophication in different types of bays, emphasizing the importance of the existence of rivers for nutrient transport in small bays.

Keywords: Beibu Gulf; Dual water isotopes; Hydrodynamic processes; Nutrients; Water masses.

MeSH terms

Bays* / chemistry
China
Environmental Monitoring*
Eutrophication*
Hydrodynamics*
Salinity
Seawater / chemistry