Using δ34S-SO4 and δ18O-SO4 to trace the sources of sulfate in different types of surface water from the Linhuan coal-mining subsidence area of Huaibei, China

Many studies have been carried out on the water environment in coal-mining subsidence area, which have mainly focused on the two aspects of nitrogen and phosphorus as well as heavy metal pollution in water. However, little attention has been paid to the problem of sulfate pollution. The surrounding conditions of subsidence area in Linhuan are complex, and there are a large number of coal gangue accumulation and coal mining activities. The sulfate pollution in water body is serious, while the specific sulfate source remains unclear. In the present study, the mining subsidence area in Linhuan, Huaibei was selected as the main study area, and 21 water samples were systematically collected from river water, subsidence area water and mine drainage. The conventional hydrochemical indexes were analyzed, and sulfur and oxygen isotopes were used to trace sources of sulfate in river water and subsidence area water. Our results showed that the total dissolved solid content was high in surface water, the hydrochemical type of Huihe River water was mainly Na+-Ca2+-HCO3-, and the hydrochemical type of subsidence area water was mainly Na+Cl--SO42-. Before flowing through the mining area, sulfate in the main stream of Huihe River was mainly derived from two aspects: the dissolution of evaporative salt rocks in the upper reaches. The sulfate in the Baohe River tributaries was mainly derived from the combined effects of atmospheric precipitation. The two rivers converged and were discharged into the subsidence area, causing serious sulfate pollution and affecting the water quality in the subsidence area. The delta S-34(SO4) value and SO42- content showed a good correlation in river water, subsidence area water and mine drainage, indicating that the SO42- content in the subsidence area was mainly affected by double-ended sources. Besides the impact of the Huihe River, the discharge of local mining waste water was also an important sulfate source, reflecting the effect of coal-mining activities on the water environment.