Seasonal Hypoxia Occurrence At Terengganu Estuary, Malaysia And its Potential Formation Mechanisms

Abstract

Hypoxia is commonly defined as oxygen depletion when the dissolved oxygen (DO) levels fall below 2 mg L-1. In this paper, physical factors contributed to hypoxic condition in the diurnal tide, Terengganu Estuary has been experimentally and analytically studies. Hourly profiles on DO, current speed and nutrient were measured during the wet and dry seasons for continuous period approximately 30 hours, which cover both high and low tide at two fixed stations, located at the river mouth and 9.50 km upstream from the river mouth, respectively. It was observed that the entire estuary was free from hypoxia during the wet season. However, hypoxia was developed at the river mouth during the dry season with lowest reading of the DO level was 0.78 mg L-1. It was demonstrated that the combination of high contamination of nutrient, low current speed, the geometrical formation and water stratification are recognized as important role in formatting the hypoxia at the Terengganu river mouth.