|Central Eurasian Water Crisis: Caspian, Aral, and Dead Seas (UNU, 1998, 203 pages)|
|Part I: introduction|
|3. Major environmental problems in world lakes|
The collapse of aquatic ecosystems and loss of biodiversity in natural lakes is the ultimate result of all the above-mentioned five processes.
Freshwater ecosystems are by no means as rich in plant and animal species as terrestrial ecosystems, but they are highly specialized with a high percentage of endemic species. For instance, the current number of fish species is said to amount to 22,000, of which one-third live in freshwater environments. In relation to the very limited area of inland waters, this percentage is surprisingly high and indicates the diversity of freshwater environments and the profound effect of geographical isolation.
Lake ecosystems, with their unique environment and biota, very vulnerable to or intolerant of disturbance from outside. This is shown by the frequent invasion of alien species and their explosive prolification in many lakes. The opportunities for such immigration are ever increasing owing to the development of intercontinental travel and transportation. Waterweeds of New World origin are flourishing and suppressing native species in Old World lakes (e.g. Elodea canadensis, E. nuttallii, Egeria densa) and vice versa (e.g. Myriophyllum spicatum). It is said that Nile perch, a big carnivorous fish introduced into Lake Victoria, have already exterminated some 200 native fish species, a greater part of which are endemic to the lake (Chamberlain, 1993). The recent invasion by zebra mussel (Dreissena polymorpha) from Europe of the Great Lakes of North America offers another very remarkable example (Nalepa and Schlosser, 1993). Similar cases are known from many other lakes.
Lake ecosystems are also vulnerable to environmental changes. The excessive advance of such processes as siltation, water level decline (and resultant salinization), acidification, toxic contamination, and eutrophication may lead to the eradication of high plants and animals in the lake. We are thus losing highly characteristic gene pools in lake ecosystems from time to time.
The exploding world population and developing industries are always thirsty for fresh water. A critical shortage of freshwater resources may possibly arrive sooner than that of food in the near future. As this brief review shows, the critical situation of world lake environments should properly be placed among the important environmental problems of global scale because of its worldwide occurrence and profound influence on human life. In order to halt its further advance, concerted international efforts are indispensable. The International Lake Environment Committee sincerely hopes that the Fifth World Lake Conference (Stresa, 1993), together with the preceding and subsequent conferences, will take significant steps forward in responding to the challenge of this problem.