Hydrochemistry and Quality of Irrigating Water in the Middle Reaches of the Syr Darya River in the Territory of the Republic of Tajikistan

The main consumer of water in the region is irrigated agriculture. Approximately 97% (93 800 million m3/year) are consumed by irrigated agriculture, whereas the other sectors, such as urban utilities and industry consume ~2700 million m3/year. Climatic changes towards warming will not only reduce the available water sources, but also increase the demand for them from agricultural crops, as higher temperatures increase the evaporation rate. It is expected that the total deficit of water in the two main rivers of Central Asia (Syr Darya and Amu Darya) in 2050 will attain 43 km3/year. Moreover, the monthly runoff regimes will essentially change. The total irrigated area of the Syr Darya River basin is 3.4 million ha, and the total use of the natural Syr Darya basin runoff is 30–150%. According to preliminary forecasts, the population in the Central Asia region is expected to grow by 30% to 2050 as compared to 2015 to attain >88 millions of people, so the areas of irrigated lands are planned to expand to solve the problem of food security in each country of this region. By 2025, the area of irrigated lands in the region must attain 11.8 million ha. This means that a lack of water will lead to the extended use of backwater for irrigation. This paper is devoted to studying the dynamics of the chemical composition of the Syr Darya River from the point of crossing the Tajikistan border to the point of passing to the neighboring Uzbekistan territory. Using the results of the chemical analyses of water samples, an attempt to estimate the utilization of water from the Syr Darya River for irrigation has been made. It has been established that, according to the principal indicators, just the content of adsorbed, soluble, and exchangeable sodium in the Syr Darya River fully meets the requirements to irrigation water.