Application of isotopes to study the interactions between groundwater and post-mining lakes in Lusatia (IsoGon)

Country / Region: Germany / Brandenburg / Saxonia / Lusatia

Begin of project: March 1, 2023

End of project: December 23, 2026

Status of project: May 29, 2024

Artificial channel between Blunoer Südsee and Sabrodter Lake Source: Anne Gädeke

The water balance of the Lusatian river basins has considerably been influenced by mining activities. This includes, among others, the large-scale dewatering of the active mines by lowering the groundwater table below the coal-bearing layers (up to 100 m below the surface). Following the phase-out of lignite mining in Lusatia, the overall aim is the restoration of a largely self-regulating water cycle. Due to the lowland character of the post-mining landscape in Lusatia, groundwater levels rise and groundwater reconnects to surface waters, including natural surface water bodies as well as the newly created post-mining lakes. The dynamic groundwater-surface water interactions influence the groundwater flow dynamics and the water quality development and have not yet been quantified in detail. The goal of the IsoGon project is to gain an improved understanding of these interactions.

Intake structure close to Lakoma to flood the Cottbuser Ostsee Source: Anne Gädeke

To achieve the project goal, water samples from natural surface waters, post-mining lakes, and groundwater will be analyzed for their hydrochemical composition and their isotopic signature of the water isotopes and sulfur. For example, in 2024, ~400 groundwater samples and ~700 surface water samples (from streams and post-mining lakes) will be collected as part of the montane hydrological monitoring of the Lausitzer und Mitteldeutsche Bergbau-Verwaltungsgesellschaft (LMBV). The analyses of the stable water isotopes will be conducted at the BGR Isotope Laboratory in Berlin-Spandau. Additionally, field measurements to estimate potential evaporation from the post-mining lakes are planned, particularly during summer months.
The project results enable a refined parameter definition and calibration/validation of groundwater and water balance models. Furthermore, an improved understanding of the post-mining groundwater flow paths will enhance our predictions of the water quality development within the Lusatian water bodies. Thus, the project can support the development, evaluation, and optimization of remediation and water management plans.

Goals/Milestones:

• Quantification of the groundwater – surface water interactions using hydrogeological and hydrochemical methods, as well as stable water isotopes and sulfur isotope analysis
• Estimation of the water balance, especially the potential evaporation, from post-mining lakes in Lusatia
• Refinement of groundwater and water balance models

Overview of the hydrochemical processes planned to be investigated in the IsoGon Project Source: BGR

Partner:

Lausitzer und Mitteldeutsche Bergbau- Verwaltungsgesellschaft (LMBV)