Grundwasseranbindung von alten Tagebaurestseen im Niederlausitzer Braunkohlentagebaugebiet

Groundwater with high acidity often leads to strongly acidic residual lakes in the vicinity of abandoned open pit lignite mines. Residual lake 77 (RL77) in Lower Lusatia (Germany) belongs to a sequence of residual lakes accomplishing groundwater drainage. A two-part high resolution three-dimensional groundwater model was set-up for the estimation of groundwater discharge into RL77. The objective of the simulations was to quantify the hydraulic component of the mass balance of the lake. The calculated total discharge could be distinguished with respect to water entering from the dump areas (11.3 l s ^?1 ) and from the undisturbed sediments (3.1 l s ^?1 ). The discharge was further distinguished with respect to the vertical entrance location into the temporarily stratified lake. It showed that groundwater discharged into the epilimnion of the lake at a rate of 9.7 l s ^?1 and into the hypolimnion at a rate of 4.7 l s ^?1 . Both the large fraction of water from the dump areas and the preferential entrance into the oxygen rich epilimnion of the lake have an adverse effect on lake water quality.