Abstract:
Oxygen concentration in the water is significantly affected by environmental condition. In this research, oxygen
concentration in the lacustrine and transition zones of the Koto Panjang reservoir is studied from June to September 2013, it
was coincidence with the minimum water level. A post facto survey method was applied and there were 4 sampling sites, in
the Lacustrine 1 (L1), Lakustrine 2 (L2), Transition 1 (T1) and Transition 2 (T2). The vertical sampling points were decided
based on the brightness of the water (in the surface, 3m, 6 m, 12 m depth and above the sediment in the bottom). The
number of vertical sampling sites was depend on the depth of the water. Results shown that the DO concentration in the
surface of the lacustrine zone was 6.14 to 8.26 mg/l and in the transition zone was 7.38-8.6 mg/l. In the bottom of the
lacustrine zone was 0 to 0.41 mg/l and that of the transition zone was 0.41-3.29 mg/l. The vertical profile of the Dissolved
Oxygen in both stations shown that the highest decrement rate of the oxygen occur from 2 secchi depth (3 m) to 4 secchi
depth (6 m). In the lacustrine zone, oxygen concentration drop into critical level (< 2 mg/l) in 12 m depth and in this
research, the oxic depth was 7.0 m in L1 and 8.0 m in L2. Whereas in T1: 6.2 m and 8.0 m in T2. During the minimum
water level, the oxic depth decrease due to decrement of water volume that lead into increment of organic matter loaded.
