|Central Eurasian Water Crisis: Caspian, Aral, and Dead Seas (UNU, 1998, 203 pages)|
|Part I: introduction|
|3. Major environmental problems in world lakes|
Everywhere in the world, lakes and reservoirs are becoming more and more important as the most dependable sources of water in large amounts. Lakes and reservoirs are more attractive water sources than rivers and underground water for big water consumers such as cities and industrial centres. In terms of size, number, and distribution, man-made lakes today are quite comparable with freshwater natural lakes.
On all the continents, however, the environments in those lakes and reservoirs are deteriorating rapidly and extensively due to various human impacts. Both the quantity and the quality of lakes' water resources are being threatened in that an increasing number of lakes have already lost not only their value as sources of water but also such traditional roles as the space for fisheries and waterborne transportation.
For this very reason, the International Lake Environment Committee (ILEC) was established soon after the First World Lake Conference held in Japan in 1984. Since 1986, ILEC has made efforts to formulate guiding principles and programmes on the environmentally sound management of lakes and their watersheds along the line of sustainable development policies. Its activities have so far included the publication of lake management guideline books (Jørgensen and Vollenweider, 1989; Jørgensen Löffler, 1990; Hashimoto, 1991; Matsui, 1993; Jørgensen, 1993), convening training courses in lake management, symposia, and workshops, promoting environmental education in schools of several countries, supporting a series of World Lake Conferences, and, above all, compiling environmental data on world lakes. Detailed limnological and socio-economic data on some 220 lakes have already been accumulated and are being published by a joint project of ILEC, the United Nations Environment Programme (UNEP), and Lake Biwa Research Institute (LBRI and ILEC, 1988, 1989, 1990, 1991). Descriptive information on more than 500 lakes is also available for reference.
Figure 3.1 shows the range of water volume in relation to mean transparency for 145 lakes whose data had been published before 1990. The range covered is very wide, amounting to the order of 107, though most of the lakes are in a narrower range of 102-104 km3. Transparency appears to depend on lake size, but certain lakes, e.g. shallow lakes on windy plains such as Lake Winnipeg (Canada) and Lake Balaton (Hungary), tend to have exceptionally small Secchi depth values.
A preliminary synthesis of the accumulated data on world lakes and reservoirs revealed the global prevalence of six types of environmental disruption as major problems of urgent concern (fig. 3.2): decline of water level, accelerated siltation, acidification, eutrophication, toxic contamination, and extermination of ecosystems and biota.