Application of isotopes to study groundwater surface water interactions in the German Lusatian mining district – a first characterization

The hydrology and hydrogeology of the German Lusatian mining district has strongly been impacted by open pit lignite mining. During active mining, mines are dewatered to lower the groundwater tables below the coal-bearing layers (up to 100 m below the surface). Following the phase-out of current mining activities, groundwater levels will rise and groundwater will reconnect with surface water. The groundwater-surface water interactions strongly influence flow patterns and dynamics as well as hydrochemistry and water quality, and are still largely unknown.

It is therefore planned to systematically select up to five representative post-mining lakes to conduct detailed measurement of climatological parameters and stable isotopes (deuterium, oxygen-18, and sulphur-34). The overall goal of this work (IsoGon project) is the characterization of surface water-groundwater interactions and the quantification of evaporation losses from the post-mining lakes in Lusatia. In this contribution, we summarize our planned project activities, state of the project, current understanding of the subject and our objectives of further planned work.