Assessment of the environmental carrying capacity of pollutants in Tam Giang-Cau Hai Lagoon (Viet Nam) and solutions for the environment protection of the lagoon

Tam Giang-Cau Hai lagoon is the largest lagoon in Viet Nam. It has two inlets that exchange water with the sea: Thuan An inlet in the north and Tu Hien inlet in the south. Every year, Tam Giang-Cau Hai lagoon receives a large amount of wastewater from five coastal districts with various waste sources such as residences, aquaculture, livestock and industry among others. Due to the low water exchange through the two inlets, wastewater is discharged into the lagoon and pollutants accumulate in the water. This results in pollution concentrations in the water exceeding the environmental limits and causing adverse effects on aquatic life. This paper presents the environmental carrying capacity (ECC) of the lagoon based on calculations from the Delft-3D model using three scenarios: 1) ECC following Vietnamese regulations; 2) maximum ECC or dangerous scenario (which the water body can no longer purify itself or becomes a dead water body); 3) proposed ECC for the protection of aquatic life. Based on the study results, some solutions have been proposed to protect the lagoon with the construction of wastewater treatment plants being the most important action to reduce pollution load in the lagoon.