Lakes of Indonesia: ecosystem and knowlegde-based management, the key in their sustainability

Already in 1887 lakes were ecologically divided into two types, river lakes and watershed lakes. River lakes are appendages of rivers and substantially fauna is from the river, which both should be studied together. Watershed lakes are poorly drained. According to depth of depression, accumulated water forms either marshes, wetlands or stratified lakes. Animals are independent of the surrounding land and many are endemic. In depression lakes, a steady ecological equilibrium and balance with conflicting interests has been reached over millennia and lakes try to steadily maintain it by spontaneous self-adjustments against disturbances. In 1928-1929 Sunda Expedition was an important study for tropical limnology, followed by Expedition Indodanau 1991-1993. Already 100 years ago temperature-dependent functions were necessary to understand the peculiar, often wind-driven behavior of lakes, which is important for oxygen replenishment and in avoiding formation of ―pathological‖ hypoxia and finally anoxia. Knowledge of fundamental life supporting hydrodynamic processes, nutrient load and tolerance limits against nutrient pollution are needed in lake management. Ecohydrology as a novel lake management subject needs realistic perspectives because it may disturb general lake management objectives. In the absence of adequate knowledge of ecosystems, best precautionary measure is to postpone lake utilization decisions rather than resuscitate lakes after disasters of wrong decisions. Mitigation of societal disasters should start in planning and decision making, not after the disasters are real and economic losses huge. Research of lake water, behavior of water and functions of lakes and nutrient regimes should be made first, followed by continuous monitoring of lakes.