Results of studies of the coastal zone of Lake Ladoga in the area of Valaam Archipelago (1998–2019) at RSHU

Abstract

Ecological monitoring data of pelagic communities and environmental factors for the coastal zone of the Valaam archipelago and also littoral and sublittoral samples analyses of contrasting hydrological conditions zones are generalized. Values ranges of the focused parameters have been identified for the unique coastal zone of Lake Ladoga with a significant biotopes diversity over than 20 years of research. Phyto- and zooplankton abundance relatively high indices are characteristic of water area closed from wind and wave mixing. This area is characterized by an active vegetation period of macrophytes and highly productive macrozoobenthos formation. According to the open water area temperature (conducted since 2013) continuous data (logger) observations, a significant average monthly temperature values interannual variability is shown, warm period duration with a surface water horizon temperature value more than 10 °C is equal to 100 days. In shallow closed areas, zooplankton biomass values differ strongly from another parts of the water area. However, in some cases, extremely high values of phytoplankton biomass (up to 29.5 mg / l) were observed in Lake Ladoga open areas, associated mostly with surges. In general, the phyto- and zooplankton biomass in the Valaam archipelago open areas coastal zone is comparable with the data for the northern Lake Ladoga deep-water area, for the closed areas biomass has been lower than the published earlier data for the coastal zone of the lake. Plankton quantitative development interannual differences are caused by the hydrological conditions of specific years. Despite the relatively small coastal zone area and macrophytesmosaic distribution, this community was characterized by a high species richness (more than half of the species recorded for Ladoga). In terms of quantitative characteristics, the invertebrates littoral communities are not less then to well-studied communities of the coastal area at depths up to a meter and significantly much bigger those observed in the open lake water area. The littoral fauna (including groups of larva insects, some crustaceans and molluscs) is observed in various conditions (10-12 m depth), thus, with macrophytes distribution data, it makes possible to expand the littoral boundary zone equals to 10 m depth, instead of the previously depth equals 8.5 m. The water area, for all studied biological communities, is classified as oligo-mesotrophic.