Hypoxia is generally defined as a condition characterized by a dissolved oxygen (DO) concentration of less than 2-3 mg/L (Farrell and Richards 2009). When dissolved oxygen levels fall to zero, this state is termed anoxia. Hypoxia is a phenomenon observed globally, especially in coastal regions. Notably, the Gulf of Thailand has reported instances of hypoxia.
Eutrophication
Driven by excess nutrients like nitrogen and phosphorus from river runoff, triggers algae blooms and hypoxia; as algae decompose, they consume large amounts of oxygen, leading to hypoxic conditions enhanced with long water residence times.
Water stratification
Limited vertical mixing due to density differences – often from warmer temperatures or freshwater runoff – creates a less dense surface layer, isolating the bottom layer from oxygen- rich surface waters
Climate change
Rising global temperatures due to climate change further decrease the oxygen – holding capacity of water, as warmer water holds less dissolved oxygen. Additionally, denser water column, and the increased metabolic rate of living organisms leads to a higher oxygen demand
