Dissolved oxygen and temperature stratification analysis for early warning system development in preventing mass mortality of fish in lake Maninjau, West Sumatera - Indonesia

Abstract Lake Maninjau is caldera lake which lies at Sumatera island, Indonesia. The objective of this paper is to analyse dissolved oxygen (DO) and water temperature (WT) stratification related to mass mortality fish. The WT and DO stratification were measured by logger version CTD profiler with a depth interval of 1 m in March 2018. Based on analysis at 12 stations of measurement from buoyancy frequency value showed various stratification. The top layer (epilimnion) had a thickness of 2 m and the concentration of DO was 4.8 mg/l – 13.5 mg/l. Meanwhile, the hypolimnion layer formed at various depths ranged from 9-20 m to the bottom of the lake with concentration of DO was close to zero. These two layers are separated by a thermocline (metalimnion), which acted as a buffer. When the surface temperature of the lake was cooler than the lower one, then the density was increased, the turnover occurred. Then, the concentration of DO at the upper layer of the lake decreased, caused mass mortality fish. The process of the mass water reversal was monitored through temperature stratification and DO measurements in real time, as criterion for early warning system of mass mortality of fish.