Effects of eutrophication on vendace, Coregonus albula (L.). I. Limnological characteristics of selected lakes in Wielkopolska

Abstract. The aim of the study was to characterize the abiotic environmental factors influencing the occurrence and biology of vendace, Coregonus albula (L.). The analyses covered four lakes in the Wielkopolska region -lakes Dominickie, Gorzyñskie, Lubikowskie, and Strzeszyñskie. The most important natural characteristics of the lakes were analyzed, and their current trophic states were determined. Moreover, two trophic state indicators were also used -the HB index and the Carlson index. Parameters differentiating the lakes most strongly included area, depth, area-depth index, shoreline development, and fish yield index. In terms of morphometry, lakes Gorzyñskie and Lubikowskie are most suitable for optimal vendace fishery management. The least developed stratification was observed in Lake Dominickie, while the most marked stratification was noted in Lake Gorzyñskie, which had the shallowest epilimnion depth, the highest thermocline temperature gradient, and a deep, cool hypolimnion. Considerable deoxygenation was observed in the summer in the hypolimnions in all the lakes; however, oxygen deficits were also detected in the metalimnion of Lake Strzeszyñskie. Based of the analysis of physicochemical factors and trophic state indexes, good water quality was noted in all the analyzed lakes. The trophic state of Lake Gorzyñskie was designated as on the border between the mesoeutrophic and eutrophic states, while lakes Dominickie, Lubikowskie, and Strzeszyñskie were designated as eutrophic