Variation and evolution of groundwater chemistry in the middle and lower reaches of the Tarim River

The change of the groundwater environment in arid areas has played a pivotal role in economic and ecological stability.And the groundwater water chemical type is a concentrated reflection of the groundwater chemical composition,is a system response of the way of the whole water and groundwater circulation characteristics.Then know about the distribution of the groundwater water chemical type not only can help to know the regional groundwater hydrogeochemical characteristics,but also have an important meaning for the further study about the regional groundwater circulation characteristics and the hydrodynamic field characteristics.While the characteristics of area underground hydrological geology and the properties of hydrogeochemical plays an important role in the direction and evolution of groundwater migration rule.So,to research the variation characteristics and the evolution law of groundwater water in chemical space and time can better reveal the interaction mechanism of the groundwater and the environment.Furthermore,it has a real significance for maintaining the ecological system’s healthy and stability in the arid areas.Based on the data of groundwater chemistry collected from 57 monitoring wells of 14 monitoring sections during 2006-2010,the temporal and spatial variation and evolution of groundwater chemistry in the middle and lower reaches of the Tarim Rive were analyzed.The results showed that the changes of groundwater salinity,TDS and concentrations of ions in the monitoring wells were greater than the pH,the ion contents of the groundwater samples were dominated by Na+and Cl-.Most of the higher salinity wells were Cl-SO4-Na-Mg type,in which the ions change little;and a few low-salinity wells were Cl-Na(Mg)type,in which the ions change much.Hydrochemical type of groundwater evolve from Cl-SO4-Na、Cl-Na-Mg and Cl-SO4-Na-Mg types to Cl-SO4-Na-Mg and Cl-Na types gradually in the middle reaches,from Cl-SO4-Na-Mg、Cl-Na-Mg to Cl-Na、Cl-HCO3-Na and Cl-Na-Mg type in the low reaches.The temporal variations in groundwater chemistry evolved from Cl-SO4-HCO3-Na to Cl-SO4-Na-Mg and Cl-Na in 2006,and from Cl-SO4-Na to Cl-SO4-Na-Mg then Cl-Na in 2010;In the low reaches,the temporal variations in groundwater chemistry evolve from Cl-SO4-Na to Cl-SO4-Na-Mg then Cl-Na(Mg) type water in 2006,from Cl-SO4-Na-Mg to Cl-Na(Mg)directly in 2010.All of the waters fall within the upper Gibbs boomerang envelope,suggesting that the chemical compositions of the waters in the middle and lower reaches of the Tarim River are controlled by evaporation and crystallization.The factors affecting hydrochemical characteristics formation were climate,hydrology,hydrogeology and human activity,including the projects of sluice,irrigation and sinking well.