CHANGES IN THE ENVIRONMENTAL CONDITIONS OF MESOTROPHIC LAKES IN THE RIVER-LAKE SYSTEM OF THE MARÓZKA AND UPPER ŁYNA RIVERS (MAZURIAN LAKELAND, POLAND)
Bogusław Zdanowski*, Konrad Stawecki*, Jakub Pyka*, Julita Dunalska**, Joanna Hutorowicz*, Stanisław Prusik*
*Department of Hydrobiology, The Stanisław Sakowicz Inland Fisheries Institute in Olsztyn, Poland
**Chair of Environmental Protection Engineering, University of Warmia and Mazury in Olsztyn, Poland
ABSTRACT. This study focused on the environmental conditions in four mesotrophic lakes, Mielno, Maróz, Święte, and Łańskie, located in the catchment basin of the Marózka and upper Łyna rivers. Changes in the thermal and oxygen conditions and the trophic status of the water of these lakes were evaluated based on the results of measurements conducted in 2004-2005 and archival materials. The highest oxygen content was noted in Lake Łańskie. The oxygen concentration in the waters of the hypolimnion of this basin was two orders of magnitude higher than in those of the epilimnion. The lowest oxygen concentration was noted in Lake Święte. The waters of the investigated lakes were of the calcium – hydrogen – carbonate type, which is typical for harmonic lakes. The contents of phosphorous and nitrogen in the lakes was similar and indicated that eutrophication in the basins was moderately advanced. The organic fractions of phosphorous and nitrogen were the dominant forms in the epilimnia. The near-bottom water layers were dominated by phosphates and ammonia nitrogen, the contents of which increased during the spring-summer period as oxygen deficits increased at the bottom. The values of parameters TSISD and TSIChl indicated that lakes Mielno, Maróz, and Łańskie were mesoeutrophic, while Lake Święte was eutrophic. The phosphorous index (TSIPtot) indicated that the degree of eutrophication in the lakes was slightly higher. The deteriorating oxygen conditions in the metalimnion and hypolimnion of Lake Łańskie could lead to the rapid rise in the eutrophication of this basin.
Key words: LAKE, EUTROPHICATION, THERMAL AND OXYGEN CONDITIONS, WATER CHEMISTRY, PHOSPHOROUS, NITROGEN
Prof. dr hab. Bogusław Zdanowski, Instytut Rybactwa Śródlądowego, Zakład Hydrobiologii, ul. Oczapowskiego 10, 10-719 Olsztyn; Tel./Fax:+48 89 5240171;