Meiofauna of esker groundwaters in Finland

Invertebrates from eskers situated in bedrock areas were extracted from the groundwater by sieving water pumped from monitoring wells. Water quality was determined from water samples taken concurrently. The numbers of animals were small if compared with other studies from more southern parts of Europe. The animals were concentrated in the uppermost layer close to the groundwater table, which was situated at an average depth of 4 m from the ground surface. In the uppermost layer, the total numbers exceeded 10 ind. m^sup -3^at only a few sites. The deepest occurrence of animals was at 10-12 m below the ground surface. The most abundant taxa were the harpacticoids Bryocamptus minutus and Parastenocaris phyllura followed by nematodes and the lumbriculid oligochaetes Lamprodrilus isoporus and Stylodrilus heringianus. Both lumbriculids were shrunken in size. The next most abundant taxa were Diacyclops spp., turbellarians, Moraria brevipes and larvae of chironomids. The archiannelid Troglochaetus beranecki was found at several sites. Other species found were e.g. Aeolosoma hemprichi, Bryocamptus pygmaeus, Attheyella crassa, Parastenocaris glacialis and Paracyclops fimbriatus. The abundance of animals and the number of taxa were lower when the water table was situated deeper. Anthropogenic changes increased the number of both individuals and of taxa. B. minutus had the highest number of significant correlations with the water quality variables while the electrical conductivity had the highest number of correlations with the meiofauna parameters. Diversity increased with the size of pore space. Gravel extraction seemed to increase the numbers of individuals. The species diversity was high at an artificial groundwater plant having an induced infiltration. Road de-icing did not have a severe negative influence and oxygen was not a limiting factor. Food descending from the ground surface with percolating water appears to be rapidly utilized by meiofauna.[PUBLICATION ABSTRACT]