| Niangziguan spring is one of the largest karst springs in China,the typical characteristics of the spring region is that the regional strata tend to be opposite to that of surface water and karst water,the main water-bearing rocks in the spring are Cambrian-Ordovician carbonates which is located downstream of the spring field,while the Carboniferous-Permian coal-bearing strata is located upstream of the spring field,the unique “reverse – type” structure model makes the upstream coal mining activities directly threaten the water quality of the downstream Niangziguan spring.In this paper,by comparing and analyzing in recent 30 years water quality data of Niangziguan spring field shows that the karst groundwater chemical composition(TDS,HB,SO42-)have a significant increase in Niangziguan spring in the years of 2014 and 2015 which means the water quality towards deteriorating development trend.Water chemistry analysis method and groundwater isotope characteristic method were used to study the cause of water quality change in Niangziguan spring area,the water quality types of karst spring water were evaluated by fuzzy evaluation method and comprehensive scoring method,and then combined the regional distribution of coal mines and temporal and spatial variation characteristics of water quality in the study area,deepen the research on the influence mechanism of coal mining on the water quality evolution of Niangziguan karst water system.Research shows: The hydrochemical types of Niangziguan group is generally dominated by SO4·HCO3-Ca·Mg,the characteristics of the water chemical components are high calcium and magnesium,low potassium and sodium in cationic aspects,while the anions show low chlorine and high sulfate,bicarbonate,and the content of sulfate and bicarbonate were negative correlation;Through the study of hydrogen and oxygen isotope,the ?D-?18O equation of karst water is obtained,it is shows that ?D=5.8262?18O-14.517(R2=0.97),the ?D and ?18O of all the water bodies in the study area are on the right side of the precipitation rainwater line,and the distance from the rain line is basically the same,all these shows that the supply sources of each water body is precipitation and there is water connection between each water body;By sulfur isotope study,found that the ?34S values in the northwest and southwest of the spring are higher,indicating that the SO42-in these areas are mainly derived from the dissolution of gypsum in the Middle Ordovician strata,the middle confluence area of the spring is the low value zone of ?34S,its value is lower than 15 ‰,in the Niangziguan spring discharge area,the elevation of the spring sample is from high to low,and from the upstream to the downstream,the values of ?34S shows that the characteristics which from small to large;According to “groundwater quality standards”(GB/T14848-93),applying the comprehensive score method and the fuzzy mathematics method are applied shows that in the water samples the water quality is lower than Class III standard that is ? and ? class water accounts for 50% of the total sample.The water of Niangziguan spring exceeded the project are HB,TDS,SO42-,Mn,NO2-N,the above shows that the karst groundwater in Niangziguan spring area is seriously polluted and the water quality is deteriorating;SO42-produced by pyrite has a great influence on spring water of Niangziguan,since 2003,the content of SO42-from pyrite in the Chengxiquan and Jiquanzhan has been increasing,especially in 2014,63% of SO42-content from pyrite in Chenxiquan.In 1998 compared with 1987 the content of SO42-from pyrite significantly increased,indicating that the increase of SO42-ions after 1987 mainly comes from coal mining activities.To sum up,the coal mining activity is the main reason for the change of the chemical composition of the Niangziguan spring water.After summary,the mine water polluted the karst groundwater through the river leakage,the vertical cross flow and the drill string pollution. |
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