Comprehensive Assessment of Surface Water Quality in Ban Pru Toei Community Forest: Physical, Chemical, and Biological Parameters

Abstract

This study conducted an integrated assessment of surface water quality in Ban Pru Toei Community Forest (42.56 ha), Bang Khan District, Nakhon Si Thammarat Province, Thailand. Water samples were collected in triplicate from five monitoring stations along a 3.05 km transect during the dry season of January–March 2023. Mean physical parameters across all stations were: temperature 26.13 ± 0.96°C (range: 25.00–28.00°C), total dissolved solids (TDS) 11.60 ± 0.13 mg/L (range: 7.56–18.40 mg/L), and pH 6.77 ± 0.13 (range: 6.15–7.05)—all compliant with Thailand's Pollution Control Department Class 1 standards. Mean dissolved oxygen (DO) was 4.36 ± 0.10 mg/L (range: 3.23–5.60 mg/L), with Station 2 (Waterfall) recording the highest DO (4.75 ± 0.07 mg/L) and Station 5 (Canal) the lowest (3.90 ± 0.10 mg/L). Mean water hardness was 14.65 ± 0.07 mg/L (range: 8.13–25.03 mg/L), well below the 300 mg/L Class 1 threshold. Biological assessment identified 22 families across 10 orders of aquatic macroinvertebrates; Odonata (5 families) was the most diverse order, followed by Ephemeroptera and Coleoptera (3 families each). Pollution-sensitive taxa (Perlidae, Heptageniidae, Ephemeridae) were present at Stations 2–5 but absent from Station 1, which was dominated by moderately clean water indicators (Filopaludina sumatrensis, 91.8% of individuals). This spatial distribution confirmed Class 1/2 ecological status at Stations 2 and 3, Class 2 at Stations 1 and 4, and Class 3 at Station 5. A modified Water Quality Index (WQI; formula: 0.3×Physical + 0.3×Chemical + 0.4×Biological) scored Stations 2 and 3 highest (86.7/100) and Station 5 lowest (68.3/100). These findings establish quantitative baseline data for the dry season, supporting adaptive management and community-based conservation strategies for this ecologically significant watershed. Year-round monitoring spanning the wet season is recommended to provide a complete annual baseline.