Monsoonal Effects and Hydro–Biogeochemical Characteristics in Maritime Cargo Areas of Siracha Bay, Eastern Upper Gulf of Thailand

Abstract

Nutrient dynamics play a crucial role in regulating seawater quality and maintaining ecological balance in coastal environments. While moderate nutrient inputs support productivity, excessive loading, often linked to human activities, can lead to eutrophication and oxygen depletion. This study investigated seasonal variations in marine water quality in the cargo area off Sriracha and Sichang Island, Chonburi Province, Thailand, using water samples collected from 16 locations during the dry season (March 2020) and rainy season (August 2020). Results showed elevated concentrations of ammonia (50.77±8.28 µg N·L⁻¹), nitrite (21.40±13.19 µg N·L⁻¹), nitrate (10.82±3.32 µg N·L⁻¹), and particulate organic matter (0.08±0.05%) in near-bottom waters at the loading site during the rainy season. In contrast, total nitrogen (82.98±15.29 µg N·L⁻¹) and total phosphorus (24.16±2.49 µg P·L⁻¹) were elevated during the dry season. These patterns indicate that loading activities contribute to organic matter accumulation in sediments, which subsequently release inorganic nutrients into the water column. High nutrient concentrations and low dissolved oxygen during the rainy season were associated with water column stratification. Most parameters met seawater standards, except for orthophosphate in near-bottom water during the rainy season. Further research is needed to determine the degradation rate of tapioca starch, identify associated byproducts, and evaluate its contribution to hypoxia. A systematic investigation will help clarify its long-term environmental impact and support improved water quality management in maritime cargo areas.