Volume 11 (2011): Issue 1 (March 2011)

Lake Jasne, also known as Lake Czyste, is a well-known oligo-mesotrophic water body located in the Iława Lake District, Poland. Between May 2009 and June 2010 ciliate biomass and community composition were studied on the basis of Lugol-fixed samples taken from the surface waters and the near-bottom zone. The mean annual ciliate biomass amounted to 0.58 μgC l^-1 in the surface waters and 1.46 μgC l^-1 in the near-bottom zone, and therefore, the ciliate biomass is amongst the lowest estimates observed in oligotrophic waters. In the surface waters typical bimodal seasonal changes in biomass were recorded with two peaks observed in spring and autumn. In the near-bottom zone the peak was recorded only in spring. The ciliate community was dominated by prostomatids (mainly Urotricha spp.), both in the surface waters (77% of biomass) and in the near-bottom zone (54% of biomass).

The aim of the study was to reveal differences in the productivity of lakes varying distinctively in water mass dynamics, as shown by the examples of Lakes Track, Miodówko and Szeląg Wielki situated in the Olsztyńskie Lake District. The selected lakes are also characteristic for a high content of nutrients. The analysis of the obtained results has revealed that in the peak of the summer stagnation the productivity was the highest in the polymictic Lake Track. The content of chlorophyll a, which is a measure of primary production, in the Track waters reached the value of 123 mg m^-3 whereas the water transparency measured as the visibility of a Secchi disc was below 0.6 m. The lowest primary production in the summer was observed in the bradymictic Lake Miodówko. The transparency of water in this lake was nearly 3 m while the content of chlorophyll a merely 1.7 mg m^-3. Lake Szeląg Wielki, featuring the characteristics of a eumictic reservoir, in the peak of the summer period was noted for the average values of the analysed parameters (1.2 m water transparency, 40.3 mg m^-3 chlorophyll a).

The objective of the study (2007-09) was to determine the current trophic state of eight selected lakes - Rybiec, Niezabyszewskie, Czarne, Chotkowskie, Obłęże, Jasień Południowy, Jasień Północny, Jeleń - based on Carlson-type indices (TSIs) and, to examine the relationship between the four calculated trophic state indices: TSI(SD), TSI(Chl), TSI(TP) and TSI(TN). Based on these values, it can be claimed that the trophy level of the lakes are within the mesotrophic and eutrophic states. It was observed that the values of the TSI(TP) in the analysed lakes are higher than the values of the indices calculated on the basis of the other variables. Moreover, the differences between the indices for particular lakes, suggest that in none of the analysed lakes is phosphorus a factor which limits algal productivity.

Lakes play a very important function in water retention, particularly in areas with strong water deficiency. Water resources in lakes determine the possibility of using them for different purposes, e.g. economic development (irrigation or drinking water, water supply for industry). With ongoing processes causing a reduction in lake capacity (shrinking and shallowing), it is necessary to investigate the scale and rate of decreasing lake resources, in terms of the economic and natural consequences of this process. The aim of the study was to test changes in water resources in lakes situated in the middle and lower River Warta catchment. Special attention was paid to lakes characterised by reduced water resources in order to identify factors contributing to this phenomenon. Our current studies of 127 lakes showed a 10% decrease in water resources over 50 years (1910-1960) in the analysed part of the catchment. Our results indicated that the predominant process causing the disappearance of lakes is shallowing. This factor should be monitored carefully to avoid further lake loss.

The aim of the study was to identify patterns of ice-related phenomena on 39 selected anthropogenic water bodies in the Silesian Upland in southern Poland. The core research was conducted in the winter season of 2009/2010, between December and March. Field measurements and observations were conducted every two days during the freezing and thawing phases and every four days at the time of continuous ice cover. Data were interpolated to cover days without observations. Differences in the ice cover phenology on these water bodies were caused by natural conditions (morphometric and hydro-meteorological) and human activity (thermal pollution). Two principal groups of anthropogenic water bodies were identified in terms of the ice phenomena: lakes and ponds with a natural or quasi-natural pattern of ice phenomena and water bodies featuring various degrees of human impact. The thickness of the ice-cover was found to vary, which was a source of great danger to the users of the water bodies in the winter season.