Comparison of physical and chemical properties of water and floristic diversity of oxbow lakes under different levels of human pressure: A case study of the lower San River (Poland)

The oxbow lakes of the lower San River are the place where many valuable and protected vascular plants such as Salvinia natans and Trapa natans can be found. The aim of the research conducted in the San Valley in 2000 and 2004–2005 was to ascertain the relationships between biodiversity and waterbody's local flora but also to examine physical and chemical water parameters and ways of micro-catchment cultivation. The authors also attempted to measure the sensitivity of each of the species to water deterioration. Five oxbow lakes situated in the area around the town of Zaleszany were studied. All of the oxbow lakes came into existence at the same time and only differ in their size and cultivation level. In the case of the San River oxbow lakes there is no direct correlation between macrophyte distribution or presence of threatened and protected species and environmental parametres. It is only considerable human impact that results in macrophyte decrease (expressed as cover index and biodiversity index). The most valuable species i.e. Salvinia natans may be threatened by lake overgrowing and excessive eutrophication.