Effects of mining activities on evolution of water quality of karst waters in Midwestern Guizhou, China: evidences from hydrochemistry and isotopic composition

Abstract

Zhijin coal-mining district, located in Midwestern Guizhou Province, has been extensively exploited for several decades. The discharge of acid mine drainage (AMD) has constituted a serious threat to local water environmental quality, which greatly affected the normal use of local people. The Permian limestone aquifer is the essential potable water supply for local people, which covered under the widely distributed coal seams. To investigate the origin of the water, the evolutionary processes, and the sources of dissolved sulfate in the karst waters, the mine water, surface water, and groundwater near the coal mines were sampled for stable isotopes (H, O, and S) and conventional hydrochemical analysis. The results of hydrochemistry and isotopic composition indicate that the regional surface water and partial karst groundwater are obviously affected by coal-mining activities, which is mainly manifested in the increase of water solute concentration and the change of hydrochemical types. The isotopic composition of δH and δO indicates that the major recharge source of surface water and the groundwater is atmospheric precipitation and that it is influenced obviously by evaporation in the recharge process. The surface water is mainly controlled by the oxidation of pyrite, as well as the dissolution of carbonate rocks, whereas that of natural karst waters is influenced by the dissolution of carbonate rocks. The resulting δS values suggest that the dissolved sulfate source in the surface water is mainly pyrite oxidation but atmospheric precipitation for the karst groundwater. Given the similar chemistry and isotopic composition between surface water and partial groundwater, it is reasonable to assume that most of the dissolved sulfate source in part of the groundwater was derived through the oxidation of pyrite in the coal. Furthermore, the contamination of the surface water and partial groundwater from the coal seam has occurred distinctly in the catchment, which is enriched in SO and is mostly depleted δS in sulfate.

Major ion compositions, sources and risk assessment of karst stream under the influence of anthropogenic activities, Guizhou Province, Southwest China

“…As shown in the Fig. 5 , the δ 34 S in the of Youyu stream was between −5.68‰ and −8.23‰, with an average of −7.44‰, is mainly distributed near the coal end element and in the range of rivers polluted by Guizhou coal mines ( Cao et al, 2018 ; Li et al, 2018 ). Which indicates the SO 4 2 – ions in the river water are mainly affected by the coal mine wastewater.…”

“…Moreover, previous studies have shown that agricultural land and coal mines, municipal sewage, etc . may be natural sources of release of trace elements in the water environment ( Li et al, 2018 ; Njuguna et al, 2020 ; Wang et al, 2017 ). High concentrations of trace elements in the aquatic environment pose potential risks ( Zhan, Wu & Jin, 2022 ).…”

Seasonal variations of microbial community structure, assembly processes, and influencing factors in karst river

“…As one of the most prevalent forms of nitrogen pollution in WWTP, NH 4 + originated primarily from wastewater plant discharges, the same source of antibiotics. SO 4 2− is mainly derived from both natural (dissolution of soluble sulfate, oxidation of sulfide minerals, and atmospheric precipitation) and anthropogenic inputs(agricultural fertilizers, domestic sewage, industrial wastewater, and mine waste water) (Li et al, 2018). In the study area, the [Mg 2+ ]/[Ca 2+ ] values ranged from 0.39 to 1.14 with average 0.65, which indicated that the chemical composition is mainly influenced by low-magnesium minerals such as calcite and gypsum.…”

Analysis of Hydrogeochemical Characteristics of Tunnel Groundwater Based on Multivariate Statistical Technology

“…The karst area has a complex geological structure, widespread faults and caves, and rich mineral resources, and the karst groundwater system is extremely sensitive to tunnel construction. Although some scholars have studied the hydrogeochemical processes induced by mining activities in the karst areas of Southwest China [15,16], however, there are no reports on groundwater chemistry in the karst tunnel fracture zone; the existing research on groundwater related to tunnel mainly focuses on the influence of groundwater level decline and water pressure on the safety of lining structure, lack of understanding of groundwater and surrounding rock matrix water-rock interaction. As a result, it is critical to conduct groundwater chemical processes and water quality research for karst tunnels.…”