Diurnal changes in water quality in Batang Ai Reservoir

Abstract

Batang Ai Hydroelectric Dam Reservoir is an important site for commercial fish aquaculture. However, little is known about the water quality changes diurnally. As water quality is important for the survival and health of the aquatic organism, this study was conducted to assess the changes in water quality over a 24-hour period at an aquaculture site in the reservoir. In-situ water quality was recorded four-hourly in November 2013 at three different depths, namely, subsurface, 10 m and 20 m. Results indicated that temperature, dissolved oxygen, and pH decreased with depth. Temperature beyond 10 m were the highest at 1 pm whilst the lowest was at 9 am for all the three depths. Temperature, dissolved oxygen and pH fluctuated the most at the subsurface and the least at 20 m. Only at subsurface, dissolved oxygen was recorded above 5 mg/L at all the sampling times. At 10 m and 20 m, dissolved oxygen were lower than 5 mg/L with anoxic condition observed at 5 pm and 1 am. The strong wind resulted in the highest subsurface DO observed at 5 pm and 9 pm. This study shows that subsurface water quality was suitable for aquaculture but not beyond 10 m depth as stratification of the reservoir resulted in low DO 10 m depth and below and the lowest DO at subsurface occurred at 1 am followed by 5 am. Weather conditions such as wind and rain affected the water quality.