Bacterioneuston Abundance and Physicochemical Properties of the Surface Microlayer of Lake Baikal

The aquatic surface microlayer is located at the atmosphere–hydrosphere boundary and occupies 70% of Earth's surface, covering all water bodies. The depth of the surface microlayer is about 50 μm. A special microbial community called neuston is formed there. The total bacterial abundance in the surface microlayer (SML) and underlying waters (UW) of LakeBaikalwas studied using epifluorescence microscopy. Physicochemical features of the surface microlayer of LakeBaikalwere revealed for the first time. The SML was sampled throughout LakeBaikalin May–June of 2013 to 2016 and in August of 2013, 2015 and 2016. SML samples were taken from a boat, mainly during calm weather, using Garrett’s metal mesh screen (a diameter of 26.5 cm). The average values of total bacterial abundance in the SML varied through years within a range of (0.93–1.49)×10⁶ cells/mL in May–June and (1.73–2.24)×10⁶ cells/mL in August; in the UW, at a depth about 15–20 cm, there were (0.79 – 0.89)×10⁶ cells/mL in May– June and (1.15–1.4)×10⁶ cells/mL in August. Significant differences and a direct relationship between the total bacterial abundance in the surface microlayer and underlying waters ofLakeBaikal in the summer period have been shown. Differences between the chemical composition of the surface microlayer and the subsurface water layer in all studied seasons were revealed. The surface microlayer was enriched with PO43-, total organic carbon and suspended particulate matter as compared with the underlying waters. A direct relationship was found between the numbers of bacteria in the surface microlayer and the suspended particulate matter concentration.

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