Demonstration of the Bzura River restoration using diatom indices

Abstract

The quality of running waters is reflected in the composition of benthic diatom assemblages. The biological assessment of changes in the composition, and thus of changes in water quality, was carried out in the lowland mid-sized Bzura River, Central Poland, over the period of 30 years. The benthic diatom material consisted of samples collected in two investigation periods, in 1972 and in 2003–2004. The methods applied were three diatom indices, IPS — Specific Pollution Sensitivity Index, GDI — Genetic Diatom Index and TDI —Trophic Diatom Index, and the OMNIDIA computer program, which are commonly used in Europe. The aim of the study was demonstrating the process of restoration that occurred in the river. The Bzura was included to the most polluted ones in Poland till 1996. Since 1998 a gradual improvement in water quality has been observed, which is caused by a number of biological-technical measures, mostly a proper organization of sewage management in most cites located on the river. In 1972 the IPS classified Bzura water into Water Quality Class IV-V, while in 2003–2004 it reached much higher values, i.e. Class III–IV. On the basis of the GDI Class III was determined in the whole river in 2003–2004, while its values indicated Class III–IV in 1972. The trophic index, TDI attributed Bzura water to the eutrophic to hypereutrophic zone in 2003–2004, and to one degree better water, i.e. from the mesoeutrophic to eutrophic zone, in 1972.