Zoobenthic assemblages of ponds supplied with biologically treated sewage

The composition of benthic macroinvertebrate communities were studied in three interconnected earth fish ponds in the sewage treatment plant in Olsztynek. These ponds were fed with biologically treated wastewater and stocked with the common carp (Cyprinus carpio L.), tench (Tinca tinca L.), European pike-perch (Sander lucioperca (L.)) and roach (Rutilus rutilus L.). Zoobenthos was sampled monthly between April and October 2007. The dominant taxa were Chironomidae and Oligochaeta. Ceratopogonidae and Ephemeroptera were scarce. Taxon richness was low. The total densities of bottom fauna of ponds varied from 3060 ind. m−2 to 9928 ind. m−2 in pond 1 and 2, respectively. Abundance of the total zoobenthos of three ponds showed similar temporal patterns with a peak in mid summer and a minimum in early spring and fall. The fauna of ponds were partially similar and indicated high trophy and impact of fish. The presence of underground springs at the bottom of ponds no. 2 and 3 probably affected the composition of aquatic macroinvertebrate communities.