Saline lakes
Saline lakes (i.e., bodies of water that have salinities in excess of 3 grams per litre) are widespread and occur on all continents, including Antarctica. Saline lakes include the largest lake in the world, the Caspian Sea; the lowest lake, the Dead Sea; and many of the highest lakes, such as those in Tibet and on the Altiplano of South America. Although inland saline water constitutes some 45 percent of total inland water, it is largely concentrated in only a few deep lakes, principally the Caspian Sea. Saline lakes are most common in the semiarid regions of the biosphere, which encompass approximately 27 percent of total land area, because two preconditions for the formation of salt lakes occur there most frequently: a balance between input of water (precipitation and inflows) and output of water (evaporation and seepage) and the presence of endorheic drainage basins.
Despite their wide geographic distribution and large total volume, the importance of salt lakes as an integral element in biospheric processes generally has been overlooked. Indeed, not until the effects of human impact began to be noticed—from about 1960—did their environmental significance become clear. An example of this is provided by the Aral Sea, a large salt lake in Central Asia. After much of the input of fresh water was diverted before reaching the lake to be used for irrigation, the level of the lake fell, salinity rose, and vast expanses of the lake bed were exposed. As a result, the fishing industry collapsed, islands that had served as wildlife refuges became peninsulas, biological diversity and productivity fell, biota disappeared, large quantities of salt blew from the lake bed onto neighbouring lands, groundwater salinity rose, and the local climate was altered. The effects on the local human population were catastrophic as well.