Implications of Predicted Hydrologic Changes on Lake Senftenberg as Calculated Using Water and Reactive Mass Budgets

Lake Senftenberg, Germany, is a post-mining lake that was flooded 30 years ago. It is anticipated that the levels of the surrounding post-mining lakes will rise, and that this will lead to a reversal of groundwater flow and consequently to an increase of acidifying groundwater flux into the lake. A tool to predict the future water quality of Lake Senftenberg has been developed. Present and future groundwater fluxes were calculated using a 3D hydraulic model of the surrounding aquifers. Oscillating hydraulic fluxes within the saturated and the unsaturated zones of the island within the lake, caused by continuous lake level changes, were calculated using a 2D sub-model. Mass fluxes into the lake from the aquifers, from the island, and from the River Schwarze Elster were determined by sampling or by laboratory experiments and were coupled with the hydraulic fluxes. The fluxes of acidifying components from the island sediments and sulfide oxidation products from drained zones were determined in laboratory experiments. Sediment erosion due to rill and gully formation after significant lake level change were calculated. The amount of acidifying compounds released from the eroded sediments was determined by laboratory experiments. The input of alkalinity due to the sedimentation of biomass was estimated. Gaseous partial pressures and mineral phases were used to describe the geochemical boundary conditions of the resulting lake water.