Geochemische Modellierung zukünftiger aquatischer Zustände des Braunkohletagebaus Espenhain sowie Erstellung eines dafür geeigneten Stoffaustragsmodells / Geochemical modelling of the future water quality of the open-cast lignite mine espenhain and the development of a suitable substance transfer model

The flooding of a closed-down open-cast lignite mine, if done in an aimless procedure, may inhibit a later utilisation as recreational area. This is due to the acid features of pyrite which is dissolved from some layers of embankments during flooding. In order to prevent the pH value to decrease during and after the flooding procedure, the computer program FAL has been established by Fachgebiet Gewässergütemodellierung (University of Hannover) to simulate and forecast the quality conditions arising with dissolved minerals. FAL takes into account all kinds of input sources, such as precipitation, ground and drained water, as well as the expected dispersal (by waves, erosion, rill erosion etc.) from uncovered and bare embankments. As output, FAL creates a file to be fed into the geochemical equilibrium model PHREEQC.The subject of the present work is the numeric balance of all incoming and outgoing substance transfers with respect to the future water body. The resulting data are used with the vertical hydraulics/quality simulation model LAC, which provides a nonstationary calculation of the mixing and stratification processes and of oxygen balance and algal growth.