Hydrogeochemical characteristics of streams with and without acid mine drainage impacts: A paired catchment study in karst geology, SW China

• A paired catchment study was used to assess karst hydrogeochemistry of two streams.
• Chemistry of streams with and without acid mine drainage (AMD) was very different.
• The observation was supported by PHREEQC modeling of equilibrium conditions.
• Ionic fluxes of AMD-impacted water were higher than that of non-AMD-impacted water.
• The higher ionic fluxes were predominantly controlled by the oxidation of pyrite.

SummaryA paired catchment study was used to assess hydrochemical characteristics of streams in AMD (acid mine drainage)-impacted and non-AMD-impacted catchments in a karstic region, SW China. The catchments shared similar geology, slope, aspect, area and climate, but different land use since one encompassed mining activities. As a result, hydrogeochemical characteristics of the AMD-impacted water were dominantly controlled by oxidation of pyrite, while that of non-AMD-impacted were influenced by water–rock reactions. It is also coincident with the source of δ34SSO4 in both waters. Upstream, unit ion fluxes of the AMD-impacted catchment for Ca, Mg, H, Fe and SO4 were 17 g/(m2 yr), 2 g/(m2 yr), 0.0002 g/(m2 yr), 17 g/(m2 yr) and 136 g/(m2 yr), respectively, while unit ion fluxes of the non-AMD-impacted catchment were much lower than that of the AMD-impacted catchment. Along the flow, fluxes of H, Ca, Mg, Fe and SO4 decreased in the AMD-impacted water, but increased in the non-AMD-impacted water. The observation was coincident with variations of ion concentrations in both waters along the flow, supported by PHREEQC modeling of minerals such as goethite, jarosite(ss), melanterite, scorodite, calcite, and dolomite. It suggests that the transport of constituents of interest (except for Ca and Mg) is dramatically different in these catchments. Results provide important information on karst system response to AMD, together with the baseline data to understand the degree and type of impairment.