Integrating thermal and ecological management of urban aquifers – an example from Berlin, Germany

Aquifers under urban areas are highly impacted by human activity and altered in terms of thermal, chemical, and also ecological conditions. In particular for ecological conditions, the causes and implications of changes in faunal communities for groundwater management and use are not yet fully understood. At the same time, large and dense urban clusters, such as the city of Berlin, Germany, rely on water supply from groundwater and other sources within their city limits. 

The aim of the CHARMANT project is therefore to develop a groundwater management approach specifically designed for the complex, multifaceted conditions in the urban underground that incorporates assessment of groundwater ecosystems and thermal management of the subsurface. Long-term changes in the thermal subsurface conditions are evaluated based on repeated measurements of temperature-depth profiles, which show an increase in warming down to 100m. Likewise, warming near the surface (20 m below ground level) is spreading from the city centre towards the suburban areas, due to increased surface sealing, subsurface infrastructure and climate change. Frequent occurrence of groundwater fauna, i.e. stygophile and stygobiont species, is found to be limited to locations in the Berlin-Warsaw glacial valley in central Berlin or in the vicinity of surface waters (approx. 11 % of all measurement wells). At the same time, some of the regularly sampled wells exhibit rare mass events with hundreds or even thousands of fauna individuals, which are not linked to changes in abiotic groundwater parameters. Also, for the specific case of Berlin, occurrence groundwater fauna appears to be constraint mostly due to low contents of dissolved oxygen linked to natural hydrogeological conditions. Overall, these heterogeneous conditions make quantitative assessment of the ecological status based on existing approaches difficult.

The thermal state of the subsurface of Berlin is further assessed by thermo-hydraulic modelling that aims at identifying areas with similar groundwater conditions, so-called archetypes, whilst taking groundwater temperature as a proxy for overall anthropogenic impact. In the future, these groundwater archetypes will be linked to chemical conditions, e.g. presence of typical urban contaminants, as well as the ecological status, e.g. presence of specific groundwater fauna, in order to obtain groundwater use types. These use types represent 3D, spatially-resolved conceptual models, that facilitate the integration of aspects of spatial planning above the surface as well as different regulatory frameworks. Furthermore, the project aims at using the simplified representation of complex subsurface processes in these archetypes for communicating groundwater management strategies and enhancing awareness and active participation of citizen and other stakeholders with the aim of minimizing conflicts of groundwater use.