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The irrigation of soil is an important measure for achieving the desired agricultural productivity, especially in regions with deficit of precipitations. The presence of sodium in the irrigation water can exert an adverse influence on the soil structure by reducing the rate at which water reaches the roots of plants. The Vakhsh river basin with more than 220 000 hectares of the irrigated land area is among the largest river basins in Tajikistan, which contains irrigation channels and a collector–drainage system with lengths of about 5000 to 6000 kilometers, respectively. The Vakhsh River merging with the Pyanj River to form the transboundary Amudarya River, which is the largest river in Central Asia, is the main river of the Republic of Tajikistan. The Vakhsh River Basin (VRB) is among the largest river basins (39 100 km2) in the highest part of Central Asia. In the VRB territory, 1213 million m3/year of the waste and collector–drainage waters are formed, of which 4 million m3/year are used for irrigation and 1209.1 million m3/year flow into natural surface water bodies. Therefore, the issue of water quality in the river basin is an urgent one. This study is aimed at analyzing the chemical composition of the Vakhsh River and its main tributaries and determining the degree of their applicability for irrigation of agricultural lands. It has been established that the Vakhsh River and its tributaries meet the requirements for irrigation water when regarding the main parameters, namely, the fractions of adsorbed, soluble, and exchangeable sodium and magnesium. It has been shown that the chemical composition of rivers is primarily formed because of weathering the rocks and washing out the skin of basins. [ABSTRACT FROM AUTHOR]

Agriculture still predominates in the use of water resources in Central Asia. About 90% of the water resources generated in the region are used for irrigation. The quality of irrigation water is an important element in obtaining ecological and safe varieties of crops because, according to the data of IAEA, the transfer of radionuclides to the human body is carried out along a water–soil–plant–human body chain. Although such a chain explains the movement of radionuclides, it will also probably be implemented when pollutants enter the human body. The aim of this work is to determine the origin of the chemical composition of the Shakhdara River and its contribution to the enrichment of the main river Panj with chemical elements. Water sampling from the rivers Shakhdara and Panj is carried out in accordance with the guidelines of Sanitary Regulation "Sanitary and Epidemiological Requirements for Water Sources, Water Abstraction Points for Economic and Potable Purposes, Economic and Potable Water Supply, Places of Recreational Water Uses and Safety of Waterbodies," The elemental analysis is performed in the United States at the Laboratory of Ambient Environment and Geology of the Department of Geological Sciences of the University of Colorado (Boulder) as well as at the Laboratory of Moisture Chemistry of the Institute of Arctic and Alpine Studies. It is found upon comparing the results of chemical analyses with the criteria of various types of weathering (carbonate, silicate, evaporation of evaporites) that the formation of the chemical composition of the Shakhdara River occurs as a result of weathering of silicate rocks with the active participation of H2CO3 and H2SO4. It is established that the Shakhdara River makes a significant contribution to the enrichment of the Panj River with 3d (Fe, Co, Ni) elements as well as arsenic, vanadium, and scandium in addition to the alkaline (K, Na) and alkaline earth (Mg, Sr) elements. [ABSTRACT FROM AUTHOR]