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Climate change and anthropogenic activities cause multiple changes in groundwater systems. Particularly, these processes lead to an increase in groundwater temperature under densely populated urban areas. While physico-chemical effects have been widely studied, the consequences for groundwater ecosystems are scarcely understood. However, a thorough understanding of how this sensitive ecosystem responds to various stressors, such as temperature, in urban environments is critical for a sustainable resource management.Thus, the aim of this study is to provide an assessment of the groundwater fauna in and around the city of Karlsruhe, Germany. We examine the ecological status of an urban aquifer by analysing fauna and physico-chemical parameters in 39 groundwater monitoring wells between 2011 and 2022. For classification, we apply the groundwater ecosystem status index (GESI), in which a threshold of more than 70% of crustaceans and less than 20% of oligochaetes serves as an indication for very good and good ecological conditions. Our study reveals that only 35% of the wells in the residential, commercial and industrial areas, and 50% of wells in a natural forest area fulfil these criteria and can be classified as natural and unstressed groundwater habitats in 2011-2014. In 2022, however, all wells in the forest area show a very good or good ecological status, irrespective of changes in diversity and number of individuals. Repeated measurements in 2022 also show significant changes in groundwater fauna with only slight changes in the physico-chemical parameters over time. A significantly decreasing number of individuals per well together with a decreasing biodiversity both in the forest and urban areas is observed.Overall, no clear spatial patterns in the ecological status are found with respect to land use and other anthropogenic impacts, such as groundwater temperatures. Nevertheless, we observe noticeable differences in the spatial distribution of groundwater species in combination with abiotic groundwater characteristics, such as groundwater temperature and geological settings. Monitoring wells in forest areas are characterized by lower groundwater temperatures, lower nitrate concentrations, and higher dissolved oxygen concentrations, indicating a link between abiotic groundwater characteristics and land use. In addition, these monitoring wells contain larger numbers of amphipods, which are considered as indicators of healthy ecosystems.The results of our study reveal heterogeneous and time-varying conditions in urban and natural groundwater as a habitat, which do not allow a clear assessment of the ecological status with existing assessment approaches. In the future, additional indicators, such as groundwater temperature, local geology, presence of indicator species, delineation of site-specific characteristics and natural reference conditions, should be therefore also considered in ecological groundwater assessments.

In Germany, 70 % of the drinking water demand is met by groundwater, for which the quality is the product of multiple physical–chemical and biological processes. As healthy groundwater ecosystems help to provide clean drinking water, it is necessary to assess their ecological conditions. This is particularly true for densely populated urban areas, where faunistic groundwater investigations are still scarce. The aim of this study is, therefore, to provide a first assessment of the groundwater fauna in an urban area. Thus, we examine the ecological status of an anthropogenically influenced aquifer by analysing fauna in 39 groundwater monitoring wells in the city of Karlsruhe (Germany). For classification, we apply the groundwater ecosystem status index (GESI), in which a threshold of more than 70 % of crustaceans and less than 20 % of oligochaetes serves as an indication for very good and good ecological conditions. Our study reveals that only 35 % of the wells in the residential, commercial and industrial areas and 50 % of wells in the forested area fulfil these criteria. However, the study did not find clear spatial patterns with respect to land use and other anthropogenic impacts, in particular with respect to groundwater temperature. Nevertheless, there are noticeable differences in the spatial distribution of species in combination with abiotic groundwater characteristics in groundwater of the different areas of the city, which indicate that a more comprehensive assessment is required to evaluate the groundwater ecological status in more detail. In particular, more indicators, such as groundwater temperature, indicator species, delineation of site-specific characteristics and natural reference conditions should be considered.

Functioning, healthy groundwater ecosystems are essential for high quality drinking water, and they minimize costs of processing groundwater for drinking purposes. GroundCare is a multidisciplinary project, which is led by the Helmholz Institute in Munich, Germany and funded by the BMBF (German federal Ministry of education and Research). The aim is to parametrize and to quantify groundwater ecosystem services as a basis for sustainable water management and water pollution control by biomonitoring. In other words: the development of biological assessment techniques. Multiple parameters are evaluated (physico-chemical parameters, microbial and fauna community composition, ecotoxicological effects). Invertebrate fauna is investigated at five sites all across Germany. During the project, molecular identification through DNA Barcoding and Metabarcoding of groundwater invertebrates is being implemented and compared to traditional morphological bio-assessment. The subterranean fauna can be used as bio-indicators to validate groundwater conditions, in particular surface water intrusion. For the water suppliers, surface water intrusion means an increased risk of contamination. The discrimination of epigean from stygobiotic fauna is the simple and basic idea of this approach. A very specific kind of water treatment is used by the water works in Würzburg (Bavaria), one of the fife study sites, which is located directly along the Main river bank. Uncommonly, they use part time river bank filtration if land-side groundwater levels are low. Another possibility is the extraction of Main River water by near-bank wells, followed by intensive water treatment and then the water is infiltrated again. The question asked was, whether the fauna indicates this specific situation or not. In the area, three types of subsurface waters can be distinguished, which are land-side groundwater, riverbank water and artificially infiltrated Main river water. Representative bores were sampled four times over one year for invertebrates. First results clearly show that the faunal patterns reflect these different hydrological situations.