Aral Sea Environmental Issues

During planning for a major expansion of irrigation in the Aral Sea basin, conducted in the 1950s and 1960s, it was predicted that this would reduce inflow to the sea and substantially reduce its size. At the time, a number of experts saw this as a worthwhile tradeoff: a cubic meter of river water used for irrigation would bring far more value than the same cubic meter delivered to the Aral Sea (6, 22-25). They based this calculation on a simple comparison of economic gains from irrigated agriculture against tangible economic benefits from the sea. Indeed, the ultimate shrinkage of the Aral to a residual brine lake as all its inflow was devoted to agriculture and other economic needs was viewed as both desirable and inevitable.

These experts largely dismissed the possibility of significant adverse environmental consequences accompanying recession. For example, some scientists claimed the sea had little or no impact on the climate of adjacent territory and, therefore, its shrinkage would not perceptibly alter meteorological conditions beyond the immediate shore zone (). They also foresaw little threat of large quantities of salt blowing from the dried bottom and damaging agriculture in adjacent areas (22). This theory rested, in the first place, on the assumption that during the initial phases of the Aral's drying only calcium carbonate and calcium sulfate would be deposited on the former bottom. Although friable and subject to deflation, these salts have low plant toxicity. Second, it was assumed that the more harmful compounds, chiefly sodium sulfate and sodium chloride, which would be deposited as the sea continued to shrink and salinize, would not be blown off because of the formation of a durable crust of sodium chloride. Some optimists even suggested the dried bottom would be suitable for farming (22).

Although a small number of scientists warned of serious negative effects from the sea's desiccation, they were not heeded (14, 24). Time has proved the more cautious scientists not only correct but conservative in their predictions. A brief discussion of the most pronounced impacts follows.

Bottom exposure and salt and dust storms. The Aral contained an estimated 10 billion metric tons of salt in 1960, with sodium chloride (56%), magnesium sulfate (26%), and calcium sulfate (15%) the dominant compounds (22). As the sea shrank, enormous quantities of salts accumulated on its former bottom. This results from capillary uplift and subsequent evaporation of heavily mineralized ground water along the shore, seasonal level variations that promote evaporative deposition, and to winter storms that throw precipitated sulfates on the beaches (25-27).

Much of the 27, 000 km2 of bottom exposed between 1960 and 1987 is salt-covered. In contrast to earlier predictions that were based on a faulty understanding of the geochemistry of a shrinking and salinizing Aral, not only have calcium sulfate and calcium carbonate deposited but sodium chloride, sodium sulfate, and magnesium chloride have as well (24). Because of the concentration of toxic salts in the upper layer, a friable and mobile surface, and lack of nutrients and fresh water, the former bottom is proving extremely resistant to natural and artificial revegetation (26, 28).

However, the most serious problem is the blowing of salt and dust from the dried bottom. There is as yet no evidence of the formation of a sodium chloride crust that would retard or prevent deflation (24). The largest plumes arise from the up to 100-km-wide dried stripe along the sea's northeastern and eastern coast and extend for 500 km (11, 25). Recent reports state traces of Aral salt have been found l000 km to the southeast of the sea in the fertile Fergana Valley, in Georgia on the Black Sea coast, and even along the arctic shore of the Soviet Union (29, 30).

Soviet scientists report major storms as beginning in 1975 when they were first detected on satellite imagery. Between 1975 and 1981, scientists confirmed 29 large storms from analysis of Meteor (a high-resolution weather satellite) images (11). During this period, up to ten major storms occurred in 1 year. Recent observations by Soviet cosmonauts indicate the frequency and magnitude of the storms is growing as the Aral recedes (31). Sixty percent of the observed storms moved in a southwest direction which carried them over the delta of the Amu Dar'ya, a region with major ecological and agricultural importance (11). Twenty-five percent traveled westward and passed over the Ust-Yurt plateau, which is used for livestock pasturing.

An estimated 43 million metric tons of salt annually are carried from the sea's dried bottom into adjacent areas and deposited as aerosols by rain and dew over 150, 000 to 200, 000 km2 (11, 13, 32). The dominant compound in the plumes is calcium sulfate but they also contain significant amounts of sodium chloride, sodium sulfate, magnesium sulfate, and calcium bicarbonate (33). Sodium chloride and sodium sulfate are especially toxic to plants, particularly during flowering. In spite of the expected increase in the area of former bottom, salt export is predicted to diminish slightly to 39 million metric tons per year by the year 2000 as a result of the exhaustion of deflatable materials, the leaching of salt into deeper layers, and through the process of diagenesis of the older surface (32).