Chemical characteristics and environmental significance of SO42- and sulfur isotope in the karst watershed of the Niangziguan spring，Shanxi Province

The Niangziguan spring watershed is located in the hinterland of the Taihang mountains, eastern Shanxi Province, with an area of 7,217 km2. The middle Ordovician limestone dominates its aquifer group, and the lower Ordovician is the aquifer floor of the aquifer system in most areas except the drainage area and part of the recharge area. The middle-upper Cambrian aquifer formation is mainly located in the eastern and northeastern margins of the spring watershed. The karst groundwater in the spring area is supplied by the recharge of atmospheric precipitation infiltration and river leakage, and the Niangziguan spring and karst water exploitation are the discharge sites. The karst groundwater in Niangziguan spring is the primary source of water supply in Yangquan City, which accounts for more than 70% of the total water intake in the city. In recent years, the total hardness and sulfate radical of karst groundwater in this spring area have increased, and the water quality has been deteriorating. Therefore, it is very important to clarify the characteristics and sources of sulfate in karst groundwater of the spring area. On the basis of previous studies, this work tests and analyzes the chemical composition and sulfur isotope of karst water in the Niangziguan spring area were tested and analyzed, and studies the influencing factors of hydrochemical characteristics and the source of sulfate in karst water to provide scientific basis for the development and protection of karst water. The research shows that， (1) SO42- of karst water in the northwest and southwest of the watershed is mainly derived from the dissolution of gypsum. (2) The karst water near the Wenhe /Taohe /Nanchuanhe rivers of the central confluence area is recharged by the river water which is polluted by the mine pit water, or polluted by the drilling string in some areas. In the karst water, SO42- mainly comes from the coal mine water. (3) The SO42- in the Chengxi spring is mainly derived from coal mine water, while SO42- of the Wulong spring and Jiquan spring is mainly derived from the gypsum dissolution. (4) In the northeast of the spring and the east of the river, SO42- comes from meteoric precipitation and gypsum dissolution, and is also affected by stratum lithology.