Zooplankton in the Nida River (the Upper Wkra River) subjected to revitalization treatments

This paper focuses on the qualitative and quantitative characterization of zooplankton in a section of the Nida (the Upper Wkra) River subjected to revitalization treatments. At four established sites, biological samples were taken for analyses. In total, 44 taxa of zooplankton were determiend in the collected material. The upper section of the Wkra River, along which two sites were set up, was in general more varied in species composition, and the structure of biocenosis was shaped by rotifers and protozoa (mainly ameba species) in nearly equal halves. At the other two sampling sites, localized below, along a further section of the watercourse, the structure of zooplankton was poorer. It was colonized by larger numbers of individuals belonging to a few species of rotifers, among which Keratella cochlearis var. tecta, Trichocerca similis and T. pusilla are the species indicating a raised level of the trophy of the river water.