Problem identification on surface water quality in the Mun River Basin, Thailand

The largest Mekong River Tributary in Thailand, the Mun River nurtures more than 10 million people, although degradation of its water quality has been reported. This study aims to illustrate spatio-temporal patterns of water quality across the basin. Water quality datasets acquired from field sampling, questionnaires, and long-term monitoring were analyzed. The findings show seven surface water quality characteristics, which were significantly spatiotemporally dependent. During the monsoon, water quality was often found with high coliform bacteria. Salinity problem was substantial, particularly during the early monsoon in the upper northern part. The dry-season water quality was even worse, exhibiting high loadings of organic compounds, coliform bacteria, nutrient, and low dissolved oxygen. This poor water quality was found in Lam Takhong Sub-Basin and the lower basins-including the lower part of the main river, Huai Samran Sub-Basin, and Lam Se Bai Sub-Basin. The degrading water, with a rotten smell and algae bloom, was affecting the quality of supplied water, as reported by the local agencies. Discharge of household wastewater could respond to the poor water quality, exhibiting high BOD and PO43-, whereas agriculture contributes to high N-to-P ratio characteristics. Suggestions on water quality management should focus on solutions for salinity, control of direct discharges of household wastewater, promoting good agricultural practices, and properly disinfecting tap water.