Hydrochemical characteristics of groundwater before and after water-saving reform in Hetao Irrigation District, Inner Mongolia.

The purpose of the research is to validate the water environment changes of regional soil after implementing the water-saving upgrading program. The background of this research is about program implementation of water-saving upgrading in North irrigation district. The groundwater samples were analyzed scientifically and systemically in Inner Mongolia Hetao irrigation district, then the descriptive statistics, the correlation matrices, the ratio coefficient of the main ions and the graphical method (including the H..... diagram, the piper diagram and Multi-rectangular diagram) were utilized to gain the better understanding of the spatial-temporal variability of the characteristics and the evolution rule of groundwater hydrochemistry in Hetao irrigation district of Inner Mongolia. The results showed that evaporation concentration, lixiviation and cation exchange were the main hydrological chemical processes which controlled the evolution of groundwater quality in irrigation district. Compare with the 2007 (before water-saving upgrading), the absolute content of HCO₃ ^- has change from smallest to largest in anion which becoming the main anion in the groundwater on 2008 and 2009. Coefficient of variation of Ca²⁺,Mg²⁺,HCO₃ - had few change and kept in a stable content in the groundwater. In addition, coefficient of variation of Na+,Cl-,SO₄ 2- had a large change in the groundwater. As a result, Na+, Cl-,SO₄ 2- became a susceptibility factor varying with environmental factors and major variables that determined in groundwater salinization effect. The main chemical types of ground water were HCO₃—Na (middle and lower reaches), SO₄—Na (downstream) and Cl—Na (upstream) in irrigation district. Moreover, compared with the 2007, the concentration of HCO₃ ^- was increasing, but the concentration of Cl^-and Na+ were decreasing. The groundwater was changing to more desalt water and small harm for crop. There was a complex spatiotemporal variation of chemical types for ground water. To follow the direction of groundwater flow, the chemical types of groundwater had been changed from Na-Ca-Mg-Cl-SO₄-HCO₃, Na-Mg-Cl-SO₄-HCO₃ and Na-Mg-Ca-HCO₃- SO₄-Cl to Na-Cl-SO₄, Na-SO₄-HCO₃ and Na-Mg-Cl-HCO₃. Furthermore, the chemical types of groundwater had been changed from Ca-Na-Mg-HCO₃-SO₄-Cl, Na-Mg-Ca-HCO₃-SO₄-Cl and Na-Mg-Cl-HCO₃-SO₄ to Na-Cl-HCO₃-SO₄, Na-HCO₃-Cl-SO₄ and Na-Ca-HCO₃-SO₄-Cl in 2008. In 2009 the chemical types of groundwater had been changed from Na-Ca-Cl-SO₄-HCO₃, Na-Mg-Ca-HCO₃-SO₄-Cl and Na-Mg-Ca-Cl-HCO₃- SO₄ to Na-HCO₃-Cl-SO₄, Na-Cl-SO₄ and Na-Ca-Mg-Cl-SO₄-HCO₃. The Na+ had absolute predominance trend. Therefore, in chemical type aspect, HCO₃ - of anion in 2008 and 2009 was more primary chemical type than HCO₃ - of anion in 2007. The research results can give the references to evaluate the impacts of the water-saving upgrading program on water environment of regional soil. [ABSTRACT FROM AUTHOR]