Water isotopic and hydrochemical characteristics and causality in Tajikistan

Main ions and hydrogen, oxygen isotopes were measured in samples of lake water, river water and spring water, which were collected from various locations of the Tajikistan region during the period from September through October 2011.The spatially distributed characteristics of these hydrochemical variables are analyzed to further explore the causes of formation and their environmental significance.The results show that the ion product of water can be used to represent the environment character in different areas of Tajikistan.Ca²⁺ and HCO₃^- are the dominant ions in lake water and spring water, which are mainly come from the calcite and dolomite weathering.Ca-SO₄^2- and Na-HCO₃^- are found in few water samples resulting from the evaporation and silicate weathering.The lakes of Tajikistan are mostly located in the east mountainous area with the quality types of Mg-SO₄^2- and Na-Cl^-, impacted by long term evaporations.Slight saline and saline lakes are most common in the area induced by the arid climate condition.The hydrogen, oxygen isotopes of river and spring water in Tajikistan vary from -129.38×10^-3 to -65.19×10^-3 and -17.06×10^-3 to -9.33×10^-3 respectively.Spatially, these hydrochemical variables are enriched gradually from east to west, which indicate that the water supply of rivers and springs in the east is replenished by glacier melting and those in the west, precipitation is the main source of water supply.The relationships between hydrogen and oxygen isotopes of east and west river water are significantly different as the result of different sources of water supply.The variation of hydrogen, oxygen isotopes in lakes mainly reflect the amount of evaporated water from lake surfaces.