MONITORING AND ASSESSMENT OF SURFACE WATER QUALITY IN THE THA THONG RIVER INFLUENCED BY DOLOMITE MINING ACTIVITIES, SURATTHANI PROVINCE, THAILAND

Abstract

Maintaining surface water quality within regulatory standards is important local communities and ecosystems. The present study aims to monitor and assess the surface water quality in the Thathong River, Surat Thani Province, specifically within the dolomite mining zone throughout the rainy season (May - July 2025). Water samples were taken from 9 monitoring stations to determine physicochemical parameters and amounts of heavy metal. Water temperatures varied from 30.3 to 33.1 °C, electrical conductivity (EC) from 345 to 406 µS/cm, total dissolved solids (TDS) from 173 to 202 mg/L, and total suspended solids (SS) from 1.01 to 34.01 mg/L, with a TDS/EC ratio of 0.50.  The value of pH ranged from 7.9 to 8.6, dissolved oxygen (DO) from 9 to 12 mg/L, and biochemical oxygen demand (BOD) from 0.02 to 2 mg/L. The average mean of nitrate-nitrogen and orthophosphate was 2.14 ± 0.84 mg/L and 0.20 ± 0.01 mg/L, respectively. Low quantities of copper, iron, manganese, and lead were discovered, while cadmium and arsenic were not detectable. All detected heavy metals were below the Thailand’s class 3 surface water quality standard. The findings provide baseline information to support long-term monitoring and water resource management in mining - influenced catchments. According to spatial analysis, land-use activities and soil erosion within mining sites was associated with nutrient accumulation and water - quality deterioration. These results provide essential baseline information for managing water resources and for planning policies and regulations to support long-term environmental monitoring and preservation.