Pan Wu

Sources, Spatial Distribution, and Seasonal Variation of Major Ions in the Caohai Wetland Catchment, Southwest China

The Caohai Wetland, Guizhou Province, China, is a nationally important nature reserve. In this study, we examined the major ion composition of the inflows to, and the water in, the Caohai Wetland. The main sources of major ions in the wetland water were the groundwater and river water inflows, the chemical compositions of which were controlled by the local geology, aquifer water–rock interactions, and human activities. The inflowing waters were the Ca–HCO3 type. The wetland water was classified as the Mg-HCO3, Mg-SO4, Ca-HCO3, and Ca-SO4 types during the high-flow season, and as the Ca-HCO3 type in the low-flow season. The physical and chemical properties of the wetland water varied widely from west to east. Concentrations of K+, Ca+, Mg2+, Cl−, and HCO3− in the wetland water were higher in the low-flow season than in the high-flow season; K+, Na+, Cl−, and Mg2+ concentrations were higher in the wetland than in the inflowing waters in both seasons, and HCO3− concentrations were lower in the wetland than in the inflowing waters. The chemical composition of the wetland water was mainly controlled by biogeochemical processes and evaporation in the high-flow season, and by evaporation in the low-flow season.

Using stable isotopes and major ions to identify hydrological processes and geochemical characteristics in a typical karstic basin, Guizhou, Southwest China.

The investigation of hydrological processes is very important for water resource development in karst basins. In order to understand these processes associated with complex hydrogeochemical evolution, a typical basin was chosen in Houzai, southwest China. The basin was hydrogeologically classified into three zones based on hydrogen and oxygen isotopes as well as the field surveys. Isotopic values were found to be enriched in zone 2 where paddy fields were prevailing with well-developed underground flow systems, and heavier than those in zone 1. Zone 3 was considered as the mixture of zones 1 and 2 with isotopic values falling in the range between the two zones. A conceptual hydrological model was thus proposed to reveal the probable hydrological cycle in the basin. In addition, major processes of long-term chemical weathering in the karstic basin were discussed, and reactions between water and carbonate rocks proved to be the main geochemical processes in karst aquifers.

Hydrogen and oxygen isotopic composition of karst waters with and without acid mine drainage: Impacts at a SW China coalfield

Karst water resources, which are critical for the support of human societies and ecological systems in many regions worldwide, are extremely sensitive to mining activities. Identification and quantification of stable isotope (δ(2)HH2O andδ(18)OH2O) composition for all sources is essential if we are to fully understand the dynamics of these unique systems and propose successful remediation strategies. For these purposes, a stable isotope study was undertaken in two similar watersheds, one impacted by acid mine drainage, and the other not. It was found that the majority of δ(2)HH2O and δ(18)OH2O values of acid mine drainage (AMD), AMD-impacted and Main channel mix waters plotted above the local meteoric water line (LMWL), while the non-AMD-impacted water was below the LMWL. The AMD and AMD-impacted water had a similar composition ofδ(18)OH2O and heavierδ(2)HH2O than that of the other waters as a result of pyrite oxidation and Fe hydrolysis. The non-AMD-impacted and spring waters were the background waters in the study area. The composition ofδ(2)HH2O and δ(18)OH2O for the former was influenced by the re-evaporation and water-rock interaction, and that for the latter was controlled by re-condensation. Along the water flow, the Main channel mix water is recharged by AMD-impacted, non-AMD-impacted and spring waters. The composition ofδ(2)HH2O andδ(18)OH2O for the Main channel mix water was coincident with the characteristics of water mixing, supported by three-component mixing modeling of upstream spring, non-AMD-impacted and AMD-impacted waters. The composition of δ(2)HH2O and δ(18)OH2O for the Main channel mix water was mainly affected by the AMD-impacted water. These results help elucidate the impact of AMD on δ(2)HH2O and δ(18)OH2O compositions for karst waters and demonstrate the utility for impact assessments and remediation planning in these unique systems.

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

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 δ2HH2O and δ18OH2O 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 δ34SSO4 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 SO42− and is mostly depleted δ34S in sulfate.