Water Quality Assessment of Lake Maninjau After the Mass Fish Kill Event

Abstract

A mass fish kill is often occurring in Lake Maninjau. A lack of oxygen has reportedly resulted in numerous fish kills, including the recent lake Maninjau condition. Deoxygenation of lake water is a natural phenomenon that often occurs after heavy rain events and low sunlight intensity. Additionally, during the strong wind for a long period, the decrease in oxygen could be chemically triggered by the diffusion of sulfide from the bottom layer of the water column. Furthermore, this study examines water quality parameters after the mass fish mortality occurred across locations in Lake Maninjau. Field surveys were conducted by measuring physiochemical parameters and total sulfide at the Fifteen sampling points (five points in the middle and ten points around the lake) from November 26 to December 2, 2022. They were measured directly using the Horriba©U 52 water quality checker (WQC), DO meter YSI ProDO© International and the HACH spectrophotometer DR3900 method. The results show that the average DO levels at each observation point were close to 0 mg/L while the average sulfide level on the surface was 9.5 micro g/L. The average Oxidation Reduction Potential (ORP) of -79.26 mV indicates that the lake is in a reduced state and signifies that much of the dead and decaying material in the water would be slowly broken down and decomposed. Low ORP values indicate that the compound in the water is available in reduced form, which is more toxic. Our diel DO measurement show that sunlight intensity was effective in increasing oxygen concentration in the lake.