| Jinghuiqu Irrigation District is an important grain production bases in Guanzhong plain,which has 80 years of irrigation history since the completion of water through. In recent years,groundwater levels dropped significantly and water quality degradation will not been curb in a short time. This situation is a serious threat to human’s survival and the sustainable development of irrigation districts. For the above problems, Qiaodi town was selected to sample and analyze the groundwater, which located in Jingyang, southwest of Jinghuiqu irrigation district. Based on the groundwater quality assessment and combined with groundwater chemical composition of groundwater processes affect the formation of ions in water, by the dynamic monitoring of Ca2+、Mg2+、K++Na+、HCO3-、Cl-、SO42-、NO3- and TN in each of three wells in well irrigation area and canal irrigation, the effects of two different kinds irrigation water sources on groundwater quality was studied. In order to know whether the groundwater could be used for irrigation, the analyze of adaptability of irrigation water quality was also be done. This paper draw the following major conclusions:(1) The environment of groundwater was alkaline and brackish. The major factors affected total dissolved solids(TDS) are SO42-、Cl-、Ca2+、Mg2+ and nitrate nitrogen in the groundwater was exceeded the standers about more than half and maybe worse in the future.The law of major ion concentration was as follows: Cation, C(Na+)>C(Mg2+)>C(Ca2+)>C(K+);Anion, C(HCO3-)>C(SO42-)>C(Cl-). The hydrochemistry types of shallow groundwater samples was mainly HCO3·SO4·Cl—Na·Mg and more types of deep groundwater.(2)Combined results of Gibbs diagram, hydrogeochemical simulation, by the analysis of ion correlation, the formation mechanism of groundwater chemical composition was controlled by evaporation-concentration reaction, cation exchange and dissolution precipitation reaction. The concentration of TDS and Na+in groundwater was increased by evaporation-concentration reaction. Cation exchange could reduce Na++K+ and increase Ca2+and Mg2+. The calcite and dolomite in groundwater is oversaturated, and it will precipitate ingroundwater under certain conditions; gypsum, anhydrite, halite, mirabilite was non-saturated in groundwater, and there is a tendency to continue to dissolve.(3)The ion in groundwater in well irrigation area was higher in canal irrigation area.Ca2+has the largest coefficient of variation and significantly difference between the two irrigation areas, and Na++K+ and HCO3- has no significant difference. The law of variation of concentration of Ca2+ and Na++K+ were opposite with time, but the trends Ca2+ and Na++ K+was basically similar in one year. So the reason caused temporary change of Ca2+and Na++K+was irrigation and rainfall. The main reason why the Ca2+ had significant difference concentration between the two type irrigation areas was that ion in well irrigation water and irrigation frequency were higher than well irrigation. ion concentrations higher than canal irrigation district. Na+ had little differences between the two area, because of cation exchange and soil adsorption.(4)SAR, %Na, RSC, PI were used to evaluate the shallow groundwater quality, and the four indicators were usually used to evaluation of alkali damage. Results showed that the shallow groundwater in the study area suffered less risk of alkali damage. The evaluation results of SAR and RSC showed that groundwater quality was very suitable for irrigation in the study area. While the evaluation results of %Na and PI showed that the groundwater quality was basically suitable for irrigation in the study area. Then Wilcox diagram and USSL diagram were used to evaluate the groundwater quality in the study area, which indicated that the shallow groundwater in the study area is not suitable for irrigation for the water conductivity was too high which brought risk of salt damage to plant and soil. So we should pay more attention to the salinity if the groundwater was used to irrigate. |
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