The use of satellite images to determine the boundaries of water bodies and study the processes of eutrophication

The purpose of the work is to select the most informative spectral indices for determining the boundaries of reservoirs and diagnosing the processes of eutrophication of water bodies in the Kirov region. Five satellite images obtained from the Landsat 5 satellite were decrypted. The water color index, turbidity index, chlorophyll concentration index a, normalized vegetation index (NDVI) and normalized index of water refractive index (NDWI) for four reservoirs in the Kirov region were determined: Belokholunitskoye, Omutninskoye, Bol'shoye Kirsinskoye and Chernokholunitskoye. To confirm and correct the data of deciphering the images, we used the results of bathymetric surveys, algological and chemical analyzes of water from the reservoirs of the Kirov region, obtained during ground-based field observations in water bodies. To build index maps, we used the QGIS software product, versions 2.18 and 3.8. Scales for indices were selected empirically, highlighting areas with similar indices. The minimum and maximum values of the index in the reservoirs were taken as the boundaries of the scale. It is noted that with high turbidity (more than 8 units of turbidity by formazine) and high water color (from 42 to 398 degrees of color), the most informative indicators for identifying the boundaries of water bodies are the NDVI and NDWI indices. On satellite images taken in the spring, water color indices, NDVI and NDWI are lower than in the Slimmer. In the Omutninsk reservoir, an increase in the turbidity index during the mass development of phytoplank ton was noted. The ability to assess and compare the degree of development of phytoplankton, its spatial distribution over the water area of the Kirov region reservoirs using the turbidity indices and the concentration of chlorophyll a in water is shown. When analyzing index charts, it was noted that the maximum values of the chlorophyll concentration index a correspond to areas of the water area occupied by thickets of higher aquatic plants (Omutniniskoye reservoir)and shallow areas with delayed water exchange (Om utni risk oye, Belokholunitskoye reservoirs).