Assessment of ecological status in small urban streams of Prague agglomeration.

The purpose of this research was to compare ecological status of a few small urban watersheds in Prague agglomeration (the Botic creek, the Zátisský creek and the Komoranský creek) with different sources of pollution, different sewer systems and with different hydraulic regimes of the recipient. Concentrations of selected heavy metals (Cd, Cu, Ni, Pb, Zn) were measured in water and sediment samples and in different species of benthic organisms. The biological assessment of macrozoobenthos has also been carried out using two biotic indexes: the saprobic index and the ASPT. The assessment of the environmental risk in an aquatic environment has been based on three different coefficients: the Distribution coefficient (Kd), the Hazard Quotient (HQ) and the Metal Pollution Index (MPI). In the Botic creek there was found out chronic load of bottom sediment by heavy metals. There is higher ecological risk of sediment toxicity in this creek. Outlets of combined sewer system in the Botic creek degrade water quality and consequently deteriorate biological indicators. In the Zátisský creek the main problem is connected with storm sewer outlets. The comparison of the Zátisský creek with the reference stream, the Komoranský creek demonstrates strong hydraulic impact, which induces frequent changes of watercourse morphology reflecting on the composition and representation of benthic macroorganisms.