|Stygobionts in waterworks|
In areas where groundwater as a resource of potable water is running short, the increasing demand for clean water requires to use surface water resources. An established purification procedure for surface water consists in slow sand filtration. Although the functioning of slow sand filters is not yet fully understood meiofaunal organisms play a role which abound in them.
We investigated a slow sand filter located in the upper Ruhr valley (see photo) and identified more than 130 species. Up to 20% of them are typical inhabitants of groundwater called stygobionts. Crustacea are the dominant among them. There are copepods (mostly Diacyclops languidoides and Graeteriella unisetigera, Phyllognathopus viguieri and Chappuisius inopinus), Ostracods (predominantly Pseudocandona zschokkei), Isopods (Proasellus cavaticus) and Amphipods (Niphargus fontanus, Niphargopsis caspary, Eucrangonyx subterraneus) .
Meiofauna presumably plays an important role in the purification process. The distribution of species in time and space has been analysed for five different depth in the course of one year. Species assemblages could be identified for different depths by means of statistical analyses. Drift of organisms out of the slow sand filter is regarded as a nuisance for water supply. Abundance of drifting organisms per unit volume is 1.500 times lower than the abundance of fauna within the slow sandfilter.