In the years 2009-2010 limnological research was carried out on 13 lobelia lakes of the Tricity metropolitan area. These lakes, of unique value not only on the scale of the country, are undergoing degradation due to increasing anthropogenic pressure. Grade of degradation of these lakes, depends on geoecosystem type, which they are representing. Geoecosystem type of the lake, defines the rate of natural eutrophication of reservoir. In this article types of geoecosystems of analysed lobelia lakes where defined in accordance with the guidelines of Bajkiewicz-Grabowska (1981, 1983, 1987, 2002. The obtained results indicate that only one of the analysed lakes (Zawiat Lake) is likely to retain a low trophic level. Four lakes (Głębokie, Kamień, Borowo, Techlinko) represent geoecosystems with a moderate rate of natural eutrophication. The remaining of the analysed lobelia lakes are threatened with fast water eutrophication, which is demonstrated by a high catchment vulnerability to activate areal load, and a low resistance of the lakes (resulting from their natural properties) to external supply. The obtained results correspond to field measurements and make it possible to indicate actions aimed at protecting the group of the analysed lobelia lakes.

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Abstract:The paper presents the changes in the water surface area of Lakes Udzierz and Mątasek located in the headwaters of the catchment of the River Mątawa (tributary of the River Vistula). The assessment of the rate of changes was based on Polish and German topographic maps as well as orthophotomaps. The analysed lakes turned out to be two of the fastest disappearing Polish lakes. In the last century ) the water surface area of Lake Udzierz decreased from 148.87 to 69.60 ha and that of Lake Mątasek from 29.5 to 0.64 ha. The average rate of loss of the lake surface area during this period was from 0.53 to 0.98% per annum. Such drastic morphometric changes in the studied lakes are, on the one hand, mainly due to poorly conducted drainage and, on the other hand, the eutrophication of the lake waters intensified by the anthropogenic impact.

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Lobelia lakes are valuable elements of the natural environment. They are characterised by low trophy, mainly in-forest location and a high transparency of water. However, similarly to other surface waters, they are subjected to increasing anthropogenic pressures, a good indicator of which is the level of surfactants, also called surface-active agents (SAAs). The aim of the study was to evaluate the intensity of anthropogenic pressures in 13 selected lobelia lakes and 14 streams in the catchments of these lakes in Northern Poland, based on SAA concentrations in the waters of these water bodies. We collected one water sample from each of these water bodies and determined the concentrations of cationic, anionic and non-ionic SAAs. We then compared the results with data concerning the ways in which these catchments and water bodies are used. While ionic (cationic and anionic) SAAs were found to be present in all the 27 samples (with concentrations ranging from 0.05 to 0.51 mg dm ) with three samples largely exceeding the maximum concentration values reported by other authors. We concluded that SAAs are a real threat to the aquatic geoecosystems of lobelia lakes and that the pressures of tourism and leisure have the greatest impact.