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.