The surface microlayer is a thin layer found at the contact zone of two environments forming an ecotone at the atmosphere–hydrosphere interface. It is the boundary layer of extreme importance for both environments. In the years 2000–2004 surface water microlayer of an eutrophic, deep lake (577 ha, max. depth 32.2 m, Lake Jasień in Northern Poland) was analyzed (in four seasons each year) in terms of their capacity to accumulate lead, cadmium and manganese. The following surface water layers were collected using the different devices (plate method, net method) and compared: a microlayer of approx. 100 μm in thickness (SM), a microlayer of approx. 240 μm in thickness (PM) and subsurface water (about 20 cm below surface) (SSW). The highest concentrations of analyzed metals were observed in the microlayer of 100 μm, characterized by enrichment factor (EF-ratio of surface to subsurface values) of 2.61 for cadmium, 2.55 for manganese and 1.57 for lead, respectively. Enrichment factors for these metals are much higher than in respective microlayers of brackish lake situated close and studied before. Seasonal changes in concentrations of analyzed elements were correlated with changes in their concentrations in subsurface water. Statistical analysis of results showed that during a year variation in Cd and Mn accumulation in analyzed layers was significant. In contrast, variation in Pb accumulation was statistically non-significant. It means that in the surface microlayer of lake water a seasonal cycle is observed for changes in heavy metal concentrations and this variability in concentrations of analyzed substances is not accidental, but definitely periodical in character. The accumulation of analyzed heavy metals in the surface microlayers of the studied deep eutrophic lake seems to be a regular phenomenon.
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