Differences And Causes Research On Hydrochemistry Between Jinci Springs And Lancun Springs Of Taiyuan Ximountain Karst Groudwater System

Lancun spring is an important water source in Taiyuan, Jinci spring is a great spring in history of Shanxi Province. Research on hydrochemistry and its controlling factors between Jinci spring and Lancun spring plays an important role in the theoretical study of Taiyuan karst water system formation and evolution, while has important practical significance on public water supply .Because of insufficient understanding on karst water-bearing system chemical composition and structure, there has not been a very good explanation on hydrochemistry differences between Jinci spring and Lancun spring. Author redivides the water-bearing system of study area according to the hydrochemical constituents, and combines structure conditions of karst development, and then reinterprets hydrechemistry datas from predecessors. Conclusions being obtain:Four gypsums universally develop in the middle part of Taiyuan Xishan Ordovician stratum. The main karst water runoff layer of Jinci spring discharge area is located between the first and second gypsum belt at the lower part of Fengfeng team. A large number of dissolved gypsum led to high SO₄^2– contents to 385.5mg / L (Wanglili,2004)in Jinci spring, accounts for over 60% in anion totally, while SO₄^2- and Ca²⁺ produced by dissolved gypsum promoted the resolution of dolostone, which eventually led to high salinity of Jinci spring. Lower Ordovician and upper Cambrian carbonate rocks mainly contain dolomite, and dolomite contents in Liangjiashan group reach to 80%. From second reservoir to Lancun , Fen river cuts to O1 strata. A large number of dissolved dolomite produced higher Mg²⁺ / Ca²⁺ ratio karst water supply of Lancun spring , so Mg²⁺ / Ca²⁺ ratio of Lancun spring is higher than Jinci spring.Ping spring which located in Jinci spring discharge region has higher TFe contents to 2.5mg / L (2003,Li xiangquan). Study on the regional geological situation found that iron was from pyrite in the upper aquifer of the C-P coal measure strata. After oxidation, pyrite went into coal measures, which was a supply for karst water through fault, resulting in relatively high concentrations of TFe. Through analyzing ³⁴S contents differences of different water sources, The result suggest SO₄^2- in Ping spring mainly from dissolved gypsum, and 5% from the acidic water generated by oxidation of pyrite in the overlying coal measure strata, which is coincident with the analysis of TFe contents.Lancun spring has a lower water temperature (15.5℃) than Jinci spring (21.25℃)(Li xiangquan,2003). According to thermal warming base rate, shallow aquifer resulted low temperature in Lancun spring through affecting the temperature of rocks; while Jinci karst spring located in Ordovician aquifer with thick overlying C-P strata, and groundwater ran through deeper aquifer with high temperature rocks, and at the same time groundwater flew slow which led to water-rock heat exchange balance, consequently, Jinci spring had a higher temperature.Finally, based on influence fators analysis of Jinci spring salinity changes from 1984 to 2001, The result suggest salinity was mainly affected by pit surface displacement and groundwater level decline. Mine displacement played a major role in karst water salinity changes. According to influence factors analysis of NO₃^- content in Lancun spring, I think NO₃^- was mainly from Fen river which was polluted by production waste and domestic sewage caused by public in Gujiao City. By comparative analysis, The result suggest water emissions in coal mine , as well as a large number of groundwater extraction is the main factor which causes karst water quality to change. Consequently, planning and management of pit surface displacement and water exploitation should be strengthened.