MR&CT analysis of the qualitative and quantitative structure of macrozoobenthos in selected oxbow lakes of Northern Poland

Macrozoobenthos inhabiting six oxbow lakes in the basins of the S upia, yna, and Vistula rivers was investigated during spring, summer, and fall 2002-2006. The researched reservoirs - re-opened, dredged, with a sluice, natural open, natural semi-open, and natural closed - differed in degree of succession and type of connection with the relevant river. In order to determine the dependency of macrozoobenthos structure on type of oxbow lake and season, multivariate regression and classification tree method (MR&CT), and indicator species analysis were applied. The tree obtained revealed that the natural, semi-open oxbow lake differed distinctly from the others and was a favorable habitat for Diptera (mainly - Chironomidae larvae), Bivalvia, and Gastropoda. The latter taxon turned out to be an indicator for summer, while Insecta and Bivalvia dominated in spring and fall. Meliorated oxbow lakes (re-opened, dredged, with a sluice) were characterized by balanced density of all the macrozoobenthos organisms and the lack of indicator taxa. In turn, high trophy was indicated by Oligochaeta abundant in natural open and natural closed oxbow lakes, and in a reservoir with a sluice.