ORIGINAL RESEARCH article
Front. Mar. Sci.
Sec. Coastal Ocean Processes
Physico-Biochemical Controls on Dissolved Oxygen Dynamics in the Eastern Upper Gulf of Thailand: Field Observations and Numerical Modeling
Provisionally accepted
- 1Department of Marine Science, Faculty of Fisheries, Kasetsart University, Bangkok, Thailand
- 2Sriracha Fisheries Research Station, Academic Research and Support Centers, Faculty of Fisheries, Kasetsart University, Chon Buri, Thailand
- 3Department of Marine Science, Faculty of Science, Chulalongkorn University, Bangkok, Thailand
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Hypoxia poses an increasing threat to coastal ecosystems, particularly in semi-enclosed estuarine systems such as the Upper Gulf of Thailand (UGoT). This study investigates the spatiotemporal dynamics of dissolved oxygen (DO) along the eastern UGoT, with a focus on the Siracha area, by integrating field observations with a coupled three-dimensional hydrodynamic–biogeochemical model. Temporal and spatial measurements in 2020 revealed pronounced seasonal and vertical variability in DO, with hypoxic events closely associated with strong salinity stratification, elevated river discharge, and phytoplankton decay. The model further identified five progressive stages of hypoxia development in the UGoT: reduced extent (November–May), onset (June), quasi-stable (July–August), expansion (September), and redistribution (October). Unusual DO profiles, characterized by minimum concentrations at mid-depth rather than near the bottom, were also observed. Model simulations indicated that these atypical profiles resulted from the intrusion of cold offshore bottom water into the study area. Nearshore DO dynamics were found to be significantly modulated by offshore circulation, stratification, water quality conditions, and tidal forcing. Scenario simulations further demonstrated that riverine nutrient loading is the primary driver controlling the hypoxia budget, while reaeration and tidal mixing also contribute substantially. Overall, the results underscore the critical interplay between physical and biogeochemical processes in shaping DO dynamics and hypoxia development in the UGoT and its eastern coast. These findings highlight the need for continuous autonomous monitoring and targeted riverine nutrient management to mitigate hypoxia in the eastern UGoT, serving as a representative example of shallow coastal systems near river mouths.
Keywords: Hydrodynamic model, Hypoxic model, Monsoon, Riverine nutrients, stratification
Received: 18 Sep 2025; Accepted: 04 Dec 2025.
Copyright: © 2025 Kaewkhong, Pokavanich, Khaodon and Charoenpong. 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: Tanuspong Pokavanich
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