Entwicklung von Tagebaurestseen bei Flusswasserflutung am Beispiel des Goitschesees bei Bitterfeld Abschlussbericht

Neutralization of previously acidic mining lake Goitsche by introducing river water from Mulde river, was scientifically investigated. It became obvious that erosion and elution especially in the zone of surface wave action contributes considerably to the acidity balance. Divided by sills into several subbasins and partitioned by the density stratification into discrete water layers the neutralization progressed successively. The exchange between the basins was quantified by numerical simulation and current measurements. Already when the temporarily envisaged end water level of 71.5 m above sea was reached the entire lake was neutral, except for two small water volumes at the base of the lake bed (of pH around 6), which persisted against the mixing into the waters above due to their high concentration of dissolved substances. As a consequence of flooding and neutralizing, iron originating from acid mine drainage was precipitated. Together with the iron, phosphorus was eliminated from the water body, and hence - despite the high load of introduced nutrients -the lake never turned eutrophic, and at the end of the flooding period the lake can be classified as oligotrophic or mesotrophic. The phosphorus is bound in the sediment in various chemical compositions. Prior to flooding, or before a respective basin was impacted by the flooding waters, the plankton showed a limited variety of species, as it was typical for the conditions at that time. However, abundance could at times reach levels as high as in neutral lakes. Due to the introduced river water, the plankton composition was dominated by the introduced organisms for a limited time. For the first time in 2001, a pronounced clear water period could be established, as it was typical for neutral and stratified lakes. With the inundation with river floods in August 2002 a large amount of suspended matter was carried into the lake, which left behind a sediment layer of up to 5 m at the base of subbasin Doebern, which was the first to be hit by the inundation. In this subbasin, the thermal stratification was removed, while in the other subbasins only the epilimnia were flushed. With the inundation, a high load of nutrients was carried into the lake, which could start a plankton bloom within only few days. Within a short period of time, the introduced nutrients were deposited in the sediment. The correcponding was happening to the introduced heavy metals. Hence it appeared that the inundation could impact on the lake only for a limited time, if not transport processes out of the sediment will cause further effects. (orig.)SIGLEAvailable from TIB Hannover: F04B80 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman