Groundwater fauna in an urban area: natural or affected?

Abstract. In Germany 70 % of the drinking water demand is met by groundwater, whose quality is the product of manifold physical-chemical and biological cleaning processes. As healthy groundwater ecosystems help to provide clean drinking water, it is necessary to assess the ecological conditions of these ecosystems. This is particularly true for densely populated, urban areas, where faunistic groundwater investigations are still scare. The aim of this study is therefore to provide a first-tier assessment of the groundwater fauna in an urban area. Thus, we assess the ecological condition of an anthropogenically influenced aquifer by analysing the groundwater fauna in 39 groundwater monitoring wells in Karlsruhe (Germany) and a nearby forest land. For classification we apply the scheme from the Federal Environmental Agency (UBA), in which a threshold of more than 70 % of Crustaceans and of less than 20 % of Oligochaetes serves as an indication for good ecological conditions. In our study 35 % of the wells in the urban area fulfil these criteria, and even in the pristine forest land only 50 % of the wells indicate fine ecological conditions. While the assessment reveals that ecological conditions in the studied urban area are predominantly not in a good ecological state, there is no clear spatial pattern with respect to land use and anthropogenic impacts. However, there are noticeable differences in the spatial distribution of species and abiotic groundwater characteristics between wells in forest land and the urban area, which indicates that more comprehensive assessment methods are required to fully capture the different effects on groundwater fauna.