METHODS AND PRACTICAL IMPLEMENTATION OF APPLICATION OF REMOTE SENSING FOR MONITORING OF EUTROPHICATION OF RESERVOIR (ON THE EXAMPLE OF TURKISH LAKE)
Authors: Fesiuk Vasyl , Polianskyi Serhii , Kopytyuk Tetyana 
Published: June 2022

The article considers theoretical, methodological and practical aspects of the study of eutrophication of water bodies using remote sensing. Factors influencing eutrophication of reservoirs, possibilities of their geoecological monitoring with the use of remote sensing are analyzed. Over a long period of time, slowly and evolutionarily, lakes naturally change their state from oligotrophic to eutrophic and even dystrophic. However, in the XX century accelerated anthropogenic eutrophication of many lakes, other bodies of water and watercourses around the world. The main reason for this was the increased use of nitrogen fertilizers and the discharge of municipal wastewater containing phosphates from household synthetic detergents. To estimate the intensity of eutrophication processes in Turske Lake, we used remote sensing data, in particular, the vegetation index NDVI. The method of estimating the intensity of eutrophication processes in Turske Lake on the basis of remote sensing is as follows: using the EO-browser  resource sentinel-hub.com was selected satellite images Landsat-8-9 L2 for the period from 1.05 to 1.10.2017-2021. The images were then analyzed to establish relationships and relationships between NDVI index values, temperature, NDVI index dynamics during the warm season, year, 5-year period, and the influence of other factors on the eutrophication process. The following regularity of intra-annual dynamics of the NDVI index has been established: in May eutrophication is practically absent, in June NDVI indicators increase, some parts of the lake surface with positive NDVI values ​​appear. In July, NDVI values ​​continue to rise. NDVI peaks in August or early September. In some years, abnormally high NDVI values ​​are recorded at this time. Starting from the second half of September, the values ​​of the index decrease, the reservoir is released from algae, they die, settle to the bottom and form an organic component of sapropel. Although in some years, even in late September, there are still some islands of high eutrophication of the lake, especially near the northern and eastern shores. Analysis of the long-term dynamics (2017-21) of eutrophication of the lake did not reveal a clear tendency to increase over time. NDVI indicators were the lowest in 2019, and the maximum values ​​were acquired in 2017 and 2021. The density of the relationship between weighted temperature values ​​and NDVI was analyzed. The correlation coefficient is 0.88. This is a fairly high level of correlation. In addition to temperature, the intensity of eutrophication of the lake is also influenced by nitrogen-containing and phosphorus-containing compounds that enter the reservoir with runoff from agricultural lands, farms and residential areas. Global climate change is also having a negative impact. A set of measures to reduce eutrophication and improve the hydroelectric condition of Turske Lake is proposed, which includes the following measures: reducing the supply of nutrients to the reservoir, compliance with the use of water protection zones, mechanical removal of plants from the lake and reclamation canals, environmental awareness and awareness the state of the reclamation network, compliance with regulations for its use, adaptation to global climate change.

Key words: lake, eutrophication of the lake, research of eutrophication of reservoirs using methods of remote sensing, measures to reduce eutrophication and improve the current hydroecological condition of the Turske Lake.