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Environmental problems of Northern Eurasia

The Aral Sea

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Environmental Problems in Irrigated Areas

The knock-on effects of increased water withdrawals are not the only irrigation-related forms of environmental degradation in the Aral Sea basin. The irrigated cropland itself has been subject to problems of salinization and waterlogging due to poor water management, with consequent negative effects on crop yields. Problems are caused by the wasteful use of water: by applying more than can be taken up by plants, through leakage from improperly lined drainage canals, and as a consequence of inadequate drainage. The salt tolerance of most cultivated plants is relatively low, so salinization rapidly leads to declines in productivity.

The proportion of cropland adversely affected by salt problems is greater than 60 per cent in Kazakhstan, Turkmenistan and Uzbekistan, and the situation is particularly critical in the latter two countries where around 90 per cent of all cropland is irrigated (Table 22.6). One estimate of the effect on the agricultural economy suggests that soil salinization reduces crop production in Uzbekistan by as much as 30 per cent (Khakimov, 1989). The quality of cotton grown has also been adversely affected by the high salt content of the soil and irrigation water.

Table 22.6 Salinization of irrigated cropland

In an assessment of land degradation problems in Turkmenistan, O'Hara (1997b) reported that the salt content of the top metre of soil on Turkmen irrigated areas increased markedly over the period 1987-92 and that the area suffering from strong to very strong salinities increased by nearly 80 000 ha, accounting for more than 15 per cent of the total agricultural land in 1992. Over the same period, the area of non-saline soils decreased from 10.5 per cent to 4.7 per cent of the total area cultivated. Much of the country's irrigated area has also experienced waterlogging problems. Ground water levels have risen over the same period, so that in 1992 just over half the irrigated area had levels less than 2 metres below the surface. The efficiency of water use and irrigation in Turkmenistan is particularly poor. The Karakum canal is especially prone to seepage and just 15 per cent of the country's irrigation network is lined. Overall, combined water losses from conveyance and in-field systems is thought to be about 12.4 km³, almost half the total volume of water used.

Other measures of efficiency have also shown that Central Asian agriculture has been very wasteful in recent decades. In terms of productivity per agricultural worker, Lerman et al. (1996) showed that productivity in Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan was 20-30 per cent below the average for the USSR as a whole over the period 1965-90. The low efficiency on Uzbek cotton plantations was highlighted in the same study. In comparison with cotton cultivation in seven other countries, water applications per hectare were shown to be greatest in Uzbekistan and fertilizer use only exceeded in Egypt. However, the weight of cotton lint produced per unit of water applied in Uzbekistan was more than three times lower than that achieved in Australia, and Uzbekistan also came bottom of the comparative table in terms of the weight of cotton lint produced per unit of fertilizer applied.

The large amounts of fertilizers used on irrigated cropland, and similarly high levels of pesticide applications, have been a response to the need to increase crop yields and maintain them in the face of declines due to salinization and waterlogging. In 1985, fertilizer use in the Aral Sea basin exceeded the average used in Russia by 10-15 times, and the amounts of herbicides, defoliants, and other pesticides applied was more than ten times the average for the former Soviet Union (FSU) as a whole (Glazovsky, 1995b). Nonetheless, the yields of six major crops on irrigated plantations in Uzbekistan were all lower in the early 1990s than they had been in 1980 (Lerman et al, 1996). Yield declines for rice and corn over this period were both greater than one third.

Large applications of agrochemicals and increasing levels of salinization on irrigated croplands have meant that drainage water from the agricultural plantations is characterized by high salinity and is contaminated by high concentrations of fertilizer and pesticide residues. These contaminants have given rise to a number of other environmental issues in the Aral Sea basin. The declining quality of surface and ground water caused by agrochemical residues has been linked to a range of human health problems in the region as pollutants have entered the food chain via the soil and atmosphere, as well as through the water supply. A sharp increase in oesophageal cancers, high rates of congenital deformities, impaired immune function, chronic gastritis, cardiovascular disease, outbreaks of viral hepatitis, and a life expectancy in some areas of about 20 years less than for the FSU as a whole have been cited for Central Asian regions of cotton monoculture (Downing, 1995).

Several other factors contribute to the poor health situation in the region, including inadequate nutrition, poor sanitation, pollution from industries, and the post-Soviet collapse of the health care system, but the importance of agrochemical residues is not in doubt. In one study of children in Kazakhstan (Jensen et al., 1997), blood levels of the pesticide hexachlorocyclo-hexane (HCH) were found to be very high and the levels of DDT compounds were up to 20 times greater than those in healthy Swedish children.

High levels of agriculturally derived pollution also characterize several new lakes that have been formed from drainage water discharge (Glazovsky, 1995&). Water from irrigation schemes on the left bank of the Amudarya began to fill the Sarykamysh depression, to the west of Nukus on the edge of the Ustyurt plateau, in the early 1960s. At this time, the new Sarykamysh Lake had a salt content of 3-4 g l^-1, but by the late 1980s it had reached 12-13 g l^-1. Similarly high salt levels have been recorded in Arnasai Lake, about 100 km west of Tashkent, formed by diversion of drainage water from the left bank of the middle Syrdarya. It had been hoped that these lakes would provide a new fisheries industry to offset partially that lost from the receding Aral, but their fish have proved to be inedibe due to high levels of pesticides. Some of the new drainage sink lakes and irrigation reservoirs have, however, provided new habitats for migrating waterfowl displaced from the shores of the Aral. Letolle and Mainguet (1993) list six such reservoirs and drainage sinks with capacities of 1 km³ and more, associated with the Syrdarya and five associated with the Amudarya.

Rising levels of saline ground water in agricultural areas have also caused new environmental hazards outside irrigation zones. The foundations of buildings have been flooded in some areas and capillary rise of salts has resulted in damage to walls and ancient monuments. Field investigations by Akiner et al. (1992) in Khiva and Bukhara found some of the world's finest examples of Islamic architecture to be suffering severe damage to stone, brick, and ceramic tiles due to salt attack from rising levels of aggressive ground water. Much of the rise in ground water levels is likely to be of recent origin, concomitant with the post-1950s expansion of irrigation, and the speed of deterioration by salt weathering was well illustrated in the Ulughbeg madrassa in Bukhara. Salt efflorescence, break-up of bricks, and extrusion of mortar were all evident on parts of the building that had been restored in 1980, just 11 years before Akiner et al.'s fleldwork. Elsewhere in Uzbekistan, Aimbetov and Seitniyazov (1994) have noted similar effects due to the rise of saline ground water levels in the city of Nukus where salt attack has caused serious structural problems in a number of modern buildings.

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