Ciliated protozoa and water quality in the Parma River (Northern Italy): long-term changes in the community structure

Ciliated protozoans from sediments of the River Parma (Northern Italy) were collected from 7 stations, selected according to their hydrological, chemical, and physical characteristics, and to river zonation during autumn 1989. Fiftythree species were observed. A saprobic evaluation of the river was made using the taxocenoses observed, and the results were compared with data collected in 1978, when the River Parma still received untreated sewage. In 1989 the hilly section of the stream was found to be more polluted than in 1978, but in the plain section, the saprobic indices were now slightly lower. The marked change in the ciliate community of the hills was accompanied by an increase in organic load, which caused the disappearance of some typical species and dampened the diversifying effects of other environmental factors, producing comparatively similar community structures in that whole zone.