Impact of land use and seasonality on faecal coliform abundance and physicochemical water quality in Batang Layar river, Sarawak, Malaysian Borneo

Batang Layar, a biodiverse tropical river in Sarawak, is a vital water source for the local communities. However, it is threatened by contamination from agricultural runoff and untreated sewage, posing public health risks. This study examines seasonal variations, land use impacts on faecal coliform concentrations, and physicochemical water quality. Water sampling at five (5) sites during wet (December 2023) and dry (June 2024) seasons used a YSI ProDSS Multiparameter Water Quality Meter for in-situ analysis. Faecal Coliform Count (FCC) and Total Coliform Count (TCC) were conducted alongside DOE-WQI (Department of Environment-Water Quality Index) that incorporates pH, dissolved oxygen (DO), suspended solids (SS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), and ammoniacal nitrogen (NH ₃ -N). Results showed higher concentrations of FCC in the wet season (228.94 cfu/100 mL- 992.87 cfu/100 mL), exceeding DOE recreational standards (< 400 cfu/100 mL), particularly near schools and settlements, likely attributed to sediment resuspension and non-point sewage runoff during high flow. WQI analysis showed sites LS1, LS2, and LS3 are consistently Class I throughout both wet and dry seasons, while LS4 and LS5 shifted from Class II in the wet season to Class I in the dry season, exhibiting a seasonal water quality fluctuation. Principal component analysis (PCA) and correlation matrices show a significant relationship between water quality parameters across land use and seasonal variations. This study highlights the importance of integrated water resource management (IWRM), which considers seasonal dynamics and land-use impacts to protect aquatic ecosystems and ensure sustainable water quality in Batang Layar river.