Influence of regulation on ichthyofauna and benthos of the Różanka stream

Abstract

Abstract The regulation of streams worsen the living conditions of natural communities of water fauna. The aim of the paper was the analysis of the structure of ichthyofauna and macrozoobenthos communities in the regulated part and in the almost natural fragments of the small piedmont stream. In the 1980s the upper section of the stream bed was regulated. Five sampling sites were chosen with the different degree of anthropogenic changes. The regulation of the stream decreased the variety of the habitats. Such changes led to the almost complete disappearance of fish in the regulated part of the stream. The density of invertebrate s in the natural sites amounted from about 16.5 thousand to almost 30 thousand organisms per 1 m2 in site 4 while in the regulated sites the density was about 10.5 thousand in site 2. In the community of benthos in sites 1 and 2 dipterans dominated. The general density of stoneflies was the smallest in site 1. Most of the mayflies were indicated in the natural sites 4 and 5. The caddisflies were mostly congested in site 4. Gammarus was the most numerous and had the biggest biomass in the natural sites. The ichthyofauna in the regulated sites consisted of only 3 species: gudgeon, chub and minnow. In site 1 only gudgeon was caught. However, the total of 12 species were found in the natural sections. Density of ichthyofauna on the regulated sites amounted to from 1 to 6 individuals per 100 m2. Whereas, on the natural sites the density was 126 indiv. 100 m-2 (site 4) and 116 indiv. 100 m-2 (site 5). Gudgeon was most abundantly represented in site 4. In the biomass chub prevailed. Chub was also dominant in the biomass in site 5, but the bleak was the most numerous. The key findings of our research confirm that the regulation of the Rozanka stream led to almost complete disappearance of fish despite quite clean water and a lot of potential food.