Water quality of mid Batang Rajang at Nanga Benin and Peraran, Kapit, Sarawak

This study was carried out to document the physicochemical and biological parameters as well as the river discharge at Nanga Benin and Peraran, Batang Rajang, Kapit, Sarawak due to lack of published information on water quality at these two areas after the impoundment of Bakun Hydroelectric Dam in 2011 and operation in 2012. The flTst sampling was from 7 to 9 July 2015 and the second from 8 to 11 December 2015. Turbidity values, transparency, and total suspended solids values at Peraran were higher than at Nanga Benin. However, temperature, pH, concentrations of nitrite-nitrogen, ammonia-nitrogen, and silica at Nanga Benin were higher than at Peraran. The temperature at Nanga Benin (24.67 ± 0.00 °C to 28.88 ± 0.00 0C) was higher than at Peraran (25.65 ± 0.01 °C to 26.91 ± 0.01 0C). pH value at Nanga Benin (6.82 ± 0.00 to 7.22 ± 0.01) was higher than at Peraran (6.15 ± 0.01 to 6.80 ± 0.01). Ammonia-nitrogen concentration at Nanga Benin (0.0020 ± 0.0010 mg/L to 0.0250:;1: 0.0010 mg/L) was higher than at Peraran (0.0027 ± 0.0006 mg/L to 0.0150 ± 0.0010 mg/L). Silica concentration at Nanga Benin (1.8843 ± 0.2290 mg/L to 6.9470 ± 0.5535 mg/L) was higher than at Peraran) (0.3267 ± 0.0075 mg/L to 6.4627 ± 0.3999 mg/L). While, turbidity at Peraran (19.27 ± 0.12 NTU to 290.80 ± 3.03 NTU) was higher than at Nanga Benin (0.21 ± 0.07 mglL to 61.07 ± 0.12 mg/L). The water quality downstream of the dam is affected by the amount of water release from Bakun dam