Water quality charateristics in Bakun reservoir and its downstream area three years after impoundment

Abstract

After 36 months of impoundment, no further studies have been carried out to assess the water quality changes and current status of the Bakun Reservoir. Realizing the high potential of the reservoir for aquaculture, tourism and recreation activities, a study was conducted to assess the water quality changes and current status of the reservoir. Physicochemical and biological parameters of temperature, potential of hydrogen ion, dissolved oxygen, total suspended solids, chlorophyll-a and total sulfide were analysed using standard method and procedures. Results show that thermocline occurred at 6 to 11 m depth and 4 to 7 m depth of Estuary of Murum River and branching of Murum River, respectively. The temperature at 20 m depth in all stations ranged from 25.03-27.60 °C. Subsurface pH of all stations fall into (6.05 to 7.37) of INWQS. Subsurface dissolved oxygen (DO) of Estuary of Linau River, in front of the intake point and Balui River (7.10 to 8.18 mg/L) fall into Class I, whereas Estuary of Murum River (5.67 mg/L) and branching of Murum River (6.63 mg/L) fall into Class II. Meanwhile, river below the dam had low DO (3.63 mg/L, Class III), high sulfide (0.19 mg/L) and TSS (17.3 mg/L). Total sulfide increased with depth in all stations, ranging from 0.03 to 0.69 mg/L. Although the reservoir was not eutrophic and categorized as oligotrophic (Chl-a<2.5 µg/L), the presence of sulfide made it less favourable for fish culture.