In 2006 the spatial distribution and seasonal variations in chlorophyll concentration were measured, at about two-week frequency, in Lake Gardno. In general, chlorophyll concentrations in the central part of the lake were high throughout the growth season. The minimum chlorophyll concentration was recorded in March (7.5 mg m -3 ), and the maximum value in September (303 mg m -3 ). Higher chlorophyll concentrations and lower temporal variability were measured in the central part of the lake, compared to lower concentrations and higher variability in the vicinity of the Łupawa River input to the lake. Chlorophyll concentrations were measured fluorometrically along several vertical and horizontal profiles, enabling direct observations of the dynamics of changing chlorophyll concentrations in Lake Gardno throughout the year.
Protozoan communities were studied in the coastal zone of the southern Baltic Sea. Stable environmental conditions and typical, bimodal seasonal changes in the protozoan biomass were observed at the sampling site in Sopot (2003Sopot ( -2004. At the sampling site in Ustka (2007)(2008), strong benthic resuspension and irregular impacts of fresh water resulted in atypical seasonal changes in the protozoan biomass with a summer peak only. The mean annual biomass had similar values at both sites: 43.2 µg C dm -3 in Sopot and 38.6 µg C dm -3 in Ustka. The protozoan community in Sopot was dominated by ciliates (48% of the biomass), whereas in Ustka − by heterotrophic nanoflagellates (53%).
Nutrient status, mainly the availability of nitrogen and phosphorus, is essential to understand the present state of a lake ecosystem and to predict its possible further development and proper management strategies within the drainage basin [1]. Because each lake ecosystem is influenced by lake morphometry, basin geology, and climate, nutrient sources and nutrient cycling in lake waters differ between lakes [2]. Numerous case studies are needed to formulate more general patterns of lake ecosystem functioning in relation to their specific characteristics. Lake Gardno belongs to a type of shallow lake located along the southern Baltic Sea coast and influenced by seawater intrusions. Such coastal lakes were grouped separately within the Polish abiotic typology prepared according to the requirements of the Water Framework Directive 2000/60/EC [3]. It represents the type of lake which can be considered a "shallow" lake. Shallow lakes differ in their hydraulic behavior and ecological functioning from deep lakes.
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