EN
This paper presents the results of research on the number, the rate of secondary production and physiological properties of neustonic (surface microlayer SM ≈ 250 μm) and planktonic (subsurface water SSW ≈10–15 cm) bacteria of the eutrophic lake (TP 30–99 μg l⁻¹; TN 0.94⁻¹.76 mg l⁻¹; chlorophyll a 26.4–56.9 mg l ⁻¹; water transparency 1.2–1.9 m). It was found that the total number of neustonic bacteria (TNB) varied from 1.28 × 10⁶ to 1.98 × 10⁶ cells ml⁻¹ and was from 1.4 to 2.0 times higher than the number of planktonic bacteria (P <0.001). TNB range for planktonic bacteria oscillated between 0.75 × 10⁶ and 1.45 × 10⁶ cells ml⁻¹. The number of heterotrophic neustonic (SM) bacteria (CFU 22 °C) was also higher by 2.0 to 13.3 times (P <0.001) being between 1.48 and 12.5 × 10³ cells ml⁻¹ while the CFU of bacteria in the SSW oscillated between 0.35 to 0.94 × 10³ cells ml⁻¹. Both the values of TNB and CFU displayed a distinct seasonal variation (P <0.001). However, the rate of secondary production of planktonic bacteria was higher (from 1.1 to 6.0 times) than the rate of production of neustonic bacteria (P <0.05) and displayed seasonal variability (P <0.001). The rate of secondary production in subsurface water ranged from 0.676 to 1.265 μgC l⁻¹ h⁻¹ while in surface microlayer from 0.118 to 0.597 μgC l ⁻¹ h⁻¹. In neuston the bacteria decomposing fat and DNA were more common than in plankton (P <0.05).