The Oligochaeta and the chironomida fauna in the river Someş/Szamos system

The epiphiton and benthos were examined in the Rivers Someşul Cald/Meleg Szamos, Somejul Rece/Hideg Szamos, Someşul Mic/Kis Szamos, Somejul Mare/Nagy Szamos, and „United" Somejul/Szamos to the mouth of the river system near Vasarosnameny in Hungary in 16 sections. The sampling took place between I and 22 August of 1992, and repeated between I and 21 August of 1996. Main results of the first expedition: Isochaeta michaelseni Last., Eiseniella tetraedra Savigny were dominant in high mountain river parts, Polamothrix vejdovskyi Hrabe and Tubifex nevaensis Brinkhurst on middle mountain river parts in clean water. The Oligochaeta fauna was changed because of anthropogen effects (pollution): Limnodrilus hoffmeisteri Claparede and Tubifex ignotus Ditlevsen were dominant and abundant. Tubifex nevaensis Brinkhurst was found and dominant in self-purificated river parts. High density of chironomid larvae was found in biotecton: Tanytarsus gregarius Kieffer and Prodiamesa olivacea Meigen were dominant here. Eukiefferiella brevicalcar Kieffer and Polypedilum laetum Meigen were dominant on the high mountain river parts. Polypedilum laetum Meigen and Prodiamesa bathophila Kieffer were dominant in clean water on the middle mountain river parts. The chironomid fauna was deteriorated and changed very strongly because of anthropogenic effects. Cricotopus bicinctus Meigen was almost the only species in high density in biotecton on this polluted parts of river system. Presence of Chironomus riparius Meigen indicated the self-purification of water on the lower parts of rivers. Results of the second expedition: the benthos diversity (Oligochaeta and chironomid fauna) decreased, but the density of epiphytic chironomid species increased between N3s3ud and A-Letea