A Preliminary Study of Stratification in Lake Toba: The Largest Tropical Lake in Southeast Asia

  • - Lukman
  • L. Subehi
  • R. Dina


Lake Toba, the largest tropical lake in Southeast Asia, has multi-functions as a tourism destination, fisheries, and fish culture in a floating net cage (FNC).  Stratification in a mixing lake is driven by temperature, and in the next stage designing biological processes and water quality in a lake system. This study aims to get the vertical profile of the physical and chemical parameters of Lake Toba. The observation was conducted at six stations in November 2017. Temperature, dissolved oxygen, and Chl-a profile vertically were observed using the CTD profiler, and Secchi depth was measured using a Secchi disk. The range of Secchi depth was 3.8 - 7.1 m.  The Chl-a concentration ranged from 0.8 to 3.8 ug/L and the maximum value was found at 10 - 20 m depth. The temperature gradually decreases from 25 - 26oC at the surface to 24 - 25 oC at a 100 m depth, afterward was stable. The anoxic condition have been found at <100 m water depth. The relatively low value of Chl-a indicating an oligotrophic condition, and the temperature vertical profiles indicating that the lake was stratified. Temperature stratification and the presence of FNC are presumed to affect the vertical oxygen profile.Keywords: Lake Toba, stratification, temperature, Chl-a profile, oxygen stratification