POLISH JOURNAL OF NATURAL SCIENCES Abbrev.: Pol. J. Natur. Sc., Vol 25(1): 47–62, Y. 2010 DOI 10.2478/v10020-010-0004-z PRELIMINARY CHARACTERISTICS OF THE TROPHIC CONDITION OF LAKES LOCATED IN THE NATURE RESERVE “BEAVER SANCTUARY ON THE PASŁĘKA RIVER” Jolanta Grochowska, Renata Tandyrak Department of Environment Protection Engineering University of Warmia and Mazury in Olsztyn K e y w o r d s: eutrophication, clinograde oxygen curve, nitrogen, phosphorus, electrolytic conduc- tivity, primary production. Abstract Studied were the following lakes: Pasłęk, Wymój, Sarąg, Łęguty and Isąg, located in the nature reserve “Beaver Sanctuary on the Pasłęka River”. The hypothesis was that lakes located in a nature protection area are subject to eutrophication in a slow rate, however, the research did not confirm it. All lakes are very fertile, as shown by the concentrations of total nitrogen, total phosphorus, electrolytic conductivity and the high negative correlation between chlorophyll a and water transpar- ency. In the peak of the summer stagnation oxygen profile is represented by the clinograde curve typical for eutrophic lakes while free carbon dioxide distribution in the water column is shown by a “reversed” clinograde curve, also typical for fertile reservoirs. WSTĘPNA CHARAKTERYSTYKA TROFICZNA JEZIOR POŁOŻONYCH NA TERENIE REZERWATU PRZYRODY „OSTOJA BOBRÓW NA RZECE PASŁĘCE” Jolanta Grochowska, Renata Tandyrak Katedra Inżynierii Ochrony Środowiska Uniwersytet Warmińsko-Mazurski w Olsztynie S ł o w a k l u c z o w e: eutrofizacja, krzywa tlenowa klinogradowa, azot, fosfor, przewodność elek- trolityczna, produkcja pierwotna. Address: Jolanta Grochowska, University of Warmia and Mazury, ul. Prawocheńskiego 1, 10-957 Olsztyn, phone: +48 (89) 523 42 73, e-mail: igroch@uwm.edu.pl