Hydrogeological, physicochemical, and thermal conditions as drivers of faunal diversity in an urban groundwater ecosystem

Shallow urban groundwater is habitat of microorganisms as well as invertebrate fauna. Both communities are assumed to be strongly influenced by multiple stressors, such as increased groundwater temperatures and enhanced local hydraulic fluctuations, acting in the urban subsurface. To date, ecological studies mainly focused on natural and arable environments, with little attention to biodiversity and the role of anthropogenic factors in urban groundwater habitats. Our project targets the subterranean regime of the city of Halle (Saale) as an ideal benchmark to explore spatial and temporal dynamics of subsurface biodiversity on the urban scale. The unique hydrogeological setting of Halle, which covers a broad range of different aquifer types, with characteristic subsurface urban warming, allows for the evaluation of selected abiotic factors related to hydraulics, hydrochemistry and temperature trends. We expect new insight into the individual and concerted role of these factors on groundwater microorganisms and fauna.First data were collected within a field campaign in June/July 2022. Physico-chemical parameters in groundwater were recorded with a multiparameter probe at each sampling point. Hydrochemical analysis including major anions and dissolved organic carbon (DOC) was conducted with the water samples from the wells and freshly pumped groundwater. Groundwater animals were collected from the bottom of the wells with a net sampler. Animals were sorted and counted at the level of higher taxonomic groups (e.g. amphipods, copepods, isopods, ostracods, oligochaetes, nematodes, and mites). In the presentation, first results on the hydrogeology, hydrochemistry, microbiology and faunal diversity of the urban center and surroundings of Halle are introduced. We show major spatial trends and how faunal abundance and diversity relates to direct urban temperature effects and zones of anoxic conditions. Moreover, research activities planned for the near future will be discussed.