| The distribution area of karst geology in Shanxi province is the largest in North China. The karst ground water has become the most important water-supply resources in Shanxi provinces for urban, industrial and agriculture because of its merits of concentrated water quantity, stable flow and high water quality. The Jinci spring belongs to Xishan karst fissure water system, which not only was nominated as a famous karst water spring in Shanxi province but also played an important role in water supply both to Jinci agriculture system. The flow of Jinci spring decreased drastically as large amount of karst groundwater was exploited. Meanwhile, sewage from Gujiao industrial state and polluted water producing accompanied by large amount of coal mining, both caused serious pollution to local karst groundwater system since 1980 s. Changes of karst groundwater chemical field, ascend of pollutant irons ratio and the deterioration of water quality were directly caused by hydrodynamic condition changes and environmental pollution.The groundwater chemical characteristics and their evolution process were researched by combined methods of water chemical analysis,multivariate statistical analysis and water chemical simulation based on the synthesized analysis of geological and hydrogeological conditions.The main results are as follows:(1) The chemical index values of karst groundwater from recharge area to discharge area show as: An increased trend of water temperature showed up along the flow direction. PH value declined from north to south. The water turned from alkaline into neutral gradually. TDS value generally increased,both the anions and cations showed an increasing change tendency, however the degree was different.Ca2+ and SO42- increased 7.39 and 17.47 times respectively.The results showed that the hydro geochemistry types changed initially from HCO3-Ca ? Mg to HCO3 ? SO4-Ca and HCO3 ? SO4-Ca ? Mg, and then became SO4 ? HCO3-Ca ? Mg, finally, transformed into SO4-Ca ? Mg and SO4 ? Ca.(2) The EOF decomposition method was used to depart the ground water chemical field timely and spatially, the results showed that the distribution characteristics analyzed in space is same to(1) that pH value reduce but TDS,Ca2+,Mg2+,HCO3- and SO42- increase gradually. On the other side, the values of pH, Mg2+,K++Na+,HCO3- and Cl- fluctuated around the mean value from 2001~2014; the values of Ca2+ and SO42- both showed decreased trends,the significant trends of decreasing appeared after 2008 and 2009 respectively.According to groundwater quality evaluation results, from north to south of the spring area, water quality changed from class II to class IV gradually. In the recharge and runoff regions, water quality mainly classified to class II. Water quality was low in eastern part from the piedmont faults, which classified to class IV.(3) The water samples were separated into three groups according to their chemical characteristic relations based on the results of cluster analysis method. Samples in same group had the relatively tight correlation. The first group is located in the recharge runoff area of spring field. The second and third group are located discharge area and north-east of discharge area. The formation of karst water chemical composition is analysised using the factoranalysis method, the main effects of different groups and the same set of different kind of water chemical composition is different. Through the combination analysis of correlation method and chemometrics, the results were gained that major ions of karst groundwater mainly came from mineral dissolution except Na+ and SO42-,which had other resources.(4)The calculation of saturation index reflect the static state of dissolution and sedimentation of major minerals in the progress of water rock interaction were determined. Calcite in all water points is oversaturated in groundwater, Dolomite is dissolved in the most of water points. There was also no obvious change pattern both for Calcite and Dolomite along the flow path.The gypsum and hard gypsum transformed from dissolved state to saturated state gradually and had obvious increasing trend along the flow path. The partial pressure of CO2 in karst water is higher than that in air and lower than that in soil. Through the calculation of the erosion modulus, the amount of gypsum dissolution was increased significantly, calcite was over saturated and associated with dolomitization process. The sediment of calcite was greater than the dissolution of gypsum, but a large number of new pores would be formed by the impact of groundwater.(5) Mass balance simulation and reacted path simulation were performed on seven typical profiles in the spring area, the results showed that the diversity of hydro geochemical reactions were huge from different regions of the karst groundwater system; significant differences also existed in northeastern, central and southwestern part of the spring area. the phenomenon indicated that the karst groundwater hydro geochemical reactions was significantly controlled by groundwater dynamic fields and local geological structures. |
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