Estimation of the area overgrown with helophytes in large bays of Lake Ilmen using Earth remote sensing data

The article considers the processes of overgrowth of Lake Ilmen with airborne aquatic vegetation – gelophytes. This vegetation is one of the key components of the aquatic ecosystem, and largely determines its trophic state and bioproductivity. The study was performed based on the decoding of multispectral satellite images using the normalized vegetation index (NDVI). This allowed us to obtain objective information about the distribution of plant communities in the water area. The satellite images of Landsat satellites that passed the standard stages of radiometric and atmospheric correction were used as a source of information. Special attention was paid to three large bays of the lake – Arkadsky, Sinetsky and Rubelsky, which are most sensitive to fluctuations in water level. The constructed map charts of the spatial distribution of aerial and aquatic vegetation made it possible to identify patterns of their distribution in temporal and spatial aspects. It was established that under conditions of decreasing water levels, a steady tendency to increase the area of overgrowth is recorded, whereas at maximum levels, the degree of vegetation coverage does not exceed 2.38–4.86 %. The largest areas of overgrowth, exceeding 60 km², were recorded in July 2018, June 2021 and August 2023. For individual bays, peak values of overgrowth were determined. А statistically significant inverse relationship was also found between the overgrown area and the water level approximated by a polynomial curve,.