Abstract
The water quality of the transboundary Pyanj River in the formation zone and along the riverbed before merging with another tributary of the transboundary Amu Darya River-the Vakhsh River was studied. The water quality on the upstream river corresponds to the very soft class (> 1.5 mmol/dm3) and in the middle and the downstream to the soft class (1.5-3.0 mmol/dm3). At the upper, middle and lower reaches of the Pyanj river the concentration of alkaline earth exceeds alkali metals (Ca2+ + Mg2+> Na+ + K+) at HCO3- > SO42- + Cl- and according to the Handa classification they are characterized by temporary rigidity. To assess the criterion of applicability of the Pyanj river water for irrigation the coefficient of sodium adsorption (SAC) was calculated for water samples from the upstream (Khorog), middle (Darvaz) and the downstream (Lower Pyanj) of the Pyanj river that were equal to 0.88; 1.07; 1.71, respectively. The SAC values for all water samples (from the upper, middle and lower reaches) of the Pyanj river indicate their good qualities for irrigation of agricultural land. The concentration of heavy metals in the Pyanj river is significantly lower than the maximum permissible concentration (MPC).