EXPLORATION OF HELOPHYTE GROWTH DYNAMICS IN THE PSKOVSKOE LAKE LITTORAL ZONE USING REMOTE SENSING DATA

Abstract

The article presents the results of an assessment of the spatio-temporal dynamics of the Pskovskoe Lake littoral zone overgrowing with helophytes in the period from 1989 to 2019. Lake Pskovskoe is a shallow body of water with a high trophic status, annual water level fluctuations, and an extensive littoral zone (about 15 % of the water surface area). The said factors, coupled with global warming, create favorable conditions for the expansion of higher aquatic vegetation. A detailed analysis of the history of research of the lake water area is provided. The types of the lake overgrowing in different years with indication of the prevalent ecological groups and dominant species are suggested. Lake Pskovskoe is characterized by the helophytic – “fragmentary-belt” type of overgrowing. Data from the literature and own field data were analyzed; multispectral satellite images taken in different years were thematically processed. The process of littoral overgrowing in this period has been fluctuating, with a positive trend component. In low-water years, the occurrence of helophytic plants increased. The expansion of helophytes in relation to the averaged shoreline configuration ranged from 26.56 to 641.9 ha, i. e. 0.04–0.9 % of the lake total area. The largest helophyte expansion was noted at Talabsk station, where the overgrown area gained 7.5 hectares in the period from 2007 to 2017. Amongyear changes of the main structural parameters of the southern reed (Phragmites australis (Cav.) Trin. Et Steud., 1840), the species playing the key role in the overgrowing of Lake Pskovskoe, are analyzed. The density and biomass of the reed stands have increased over the period of observations.