Using digital maps to identify areas of mass development of phytoplankton in small freshwater reservoirs
Based on the results of field observations and interpretation of space images, the authors of the article have analyzed the spatial distribution and temporal dynamics of phytoplankton development in four reservoirs of the Kirov region (Russia) from 2015 to 2021. Characteristic features of reservoirs are high color and turbidity of water, high content of organic substances in water. To identify areas of mass development of phytoplankton, the authors calculated four spectral vegetation indices. These are the normalized difference algoindex (NDAI), the normalized difference vegetation index (NDVI), the chlorophyll a concentration index (TBDO) and the normalized difference turbidity index (NDTI). The initial data for the calculation were satellite images from the Sentinel-2 satellite, posted on the resource EarthExplorer (U.S. Geological Survey). Based on the results of the calculation of spectral indices in the QGIS software product, the authors built digital maps of the studied reservoirs. They noted that phytoplankton developed mainly in coastal shallow areas of reservoirs. The mass development of algae and cyanobacteria was most often observed in July and August. This is typical for reservoirs of temperate zone. The most intense “blooming” of water was in July and August 2016, 2018, 2020 and 2021. At the same time, the following species dominated in phytoplankton samples: Anabaena lemmermannii P.G. Richter, A. spiroides Klebahn, A. planctonica Brunnthaler, Aphanizomenon flos-aquae Ralfs ex Bornet & Flahault.