Characteristics of Hydrogen and Oxygen Stable Isotopes of Different Water Bodies in Peixian Coal Mining Subsidence Area in Jiangsu Province, China

As a result of long-term well mining activities, a large area of coal mining subsidence has formed in the mining area in Peixian County, Jiangsu province, an important energy base in eastern China. This subsidence filled by water made the local water cycle become more complicated and severe geological hazards easy to occur. Oxygen-stable isotope, playing an important role in the study on water-cycle mechanism, is a substantial way to track different sources of water in nature. In this study, we took samples from different water bodies of soil water, the surface waters (river, lake and collapse pit) and the groundwater (well water) seasonally in a year. The analyses of δD and δ18O were further conducted to trace the transforming relationships between these water bodies. The findings are as follows: (i) precipitation is the main charge source of soil water, along with significant evaporation processes; (ii) with soil depth increasing, δD and δ18O of soil water showed a trend like that first decreasing to a certain value and then stabilizing and finally increasing to the bottom of soil profile; (iii) when the reclamation soil experienced longer time, the values of soil water δD and δ18O increased in the whole profile, and this character was more obvious in deeper layers than in shallower and in surface layers; (iv) indicated from the isotopic characters of different water bodies and precipitation that precipitation was the main source of recharge of collapse pit water, and the infiltrated soil water and ground water experienced mixing with river water and precipitation by the water pathways conducted through the entire Cenozoic coal seam by mining.