Towards sustainable development of the environmentally degraded arid rivers of China--a case study from Tarim River

Increases in water resources development and utilization over the last 30 years have led to significant environmental and hydrological degradation of the Tarim River basin. Water discharge in the lower reaches has been seriously compromised. A total of 300 km of the lower reach has been drained between the 1950s and 1970s. The water table fell from 2-3 to 4-10 m between the years 1960 and 1980, and the annual rate of fall of the water table was 20 cm from 1980 to the present. The area populated by Populus euphtatica has declined by two thirds and the biomass has decreased by half between the years 1958 and 1978 in the Tarim River basin. From the 1950s to the 1990s, the area of P. euphratica/E. angustifolia forest, the main tree species of the region, declined by 3,820 km2 in the lower reaches of the Tarim River basin, while the shrub and meadow area declined by 200 km2. Such hydrological changes have resulted in a marked degradation of aquatic habitats and have caused substantial land desertification. A total of 12,300 km2 of desertified lands formed between the 1960s and 1990s. During the past 30 years, the salt content of the Tarim River has increased gradually according to observational data from the Alar Hydrological Station. The maximum salt content in 1960 was 1.28 g L(-1), but in 1981-1984 it reached 4.0 g L(-1), and in 1998 was 7.8 g L(-1). Based on the present organic carbon content in desertified lands, total emissions of C into the atmosphere in the last 30 years have been 112.2 Tg, representing 28.3% of organic carbon in the 0-1.0 m soil layer due to the hydrological degradation. Among factors contributing to these problems, human activities are foremost. Solving these problems will require raising the level of scientific and technological expertise in the monitoring, conservation, protection, and rehabilitation of water resources and associated habitats. Presently the greatest priority is to expand and improve water conservation studies.