The Hydrochemistry of High-Mountain Pamir Rivers: Factors Affecting the Chemical Composition of the Vanj River, a Tributary of the Transboundary Panj River (Tajikistan)

The Vanj River is one of the tributaries of the transboundary Panj River between Tajikistan and Afghanistan which, in turn, is considered to be one of the full-flowing tributaries of Amu Darya, the largest river in Central Asia. The Amu Darya River is the main source of water supply for the wide agricultural lands of Turkmenistan and Uzbekistan. Moreover, it is a source of drinking water supply in most localities and villages. Therefore, monitoring the ecological state and chemical composition of the Amu Darya River and its tributaries is an urgent problem. Apparently, a significant role in the formation of the chemical composition of the water of the principal river belongs to its tributaries and, because the catchment area of almost all the tributaries of the Panj River is located in the highlands of Pamir, where the processes of rock weathering develop under the conditions of climate change, the study of the effect of the weathering products on the chemical composition of rivers is an important task in terms of timely detection of heavy metals and radionuclides and their subsequent neutralization. The aim of the research is to determine the origin of the chemical composition of the water and presence of stationary sources of pollution of the Vanj River. It is found that there are no sources of anthropogenic pollution at the upper reaches of the Panj River and basin of the Vanj River, and the formation of the chemical composition of the Vanj River occurs as a result of the weathering of the basin rocks. The dependences between the chemical elements of the Vanj and Panj rivers are found by applying the Pearson correlation. It is found by the determination of the mutual ratios of alkaline earth and alkaline elements with Cl – and SO_4^2 - anions that the chemical composition of the Vanj River is mainly determined by the weathering of silicate rocks. The components enriched by the Vanj River, the main tributary of the Panj River, are found by the difference in the concentrations of the chemical elements of the Vanj and Panj rivers.