Estimation of the level of eutrophication of coastal waters of the Baltic Sea on the basis of Earth remote sensing data

Abstract

One of the serious environmental problems is the eutrophication of water bodies, so monitoring of this process is necessary. The purpose of the study is to assess the level of eutrophication of coastal waters based on the analysis of satellite imagery data using NDVI. The NDVI value and the water area where NDVI is greater than zero were used as indicators of eutrophication. The study was carried out in the Gdansk and Kaliningrad bays of the Baltic Sea. Computer processing of images in .tif (NDVI) and .png (RGB images) formats from satellites of the Sentinel-2 and Landsat family for 2013-2021 was performed. As a result of the study, it was found that the calculation of the NVDI index and the area where this index is greater than zero is an adequate method for monitoring eutrophication, since it demonstrates areas of the water area where a high level of vegetation is observed. Compared to the calculation of chlorophyll content indices (which are very difficult to establish standard values), the calculation of NDVI is easier to interpret. The study shows that the level of eutrophication in the bays of the Baltic Sea depends on seasonality, it usually increases from May to August, and decreases in September. Annual fluctuations are also observed, in particular, a decrease in eutrophication in 2020-2021 due to the decline in economic activity and anthropogenic pollution. Sharp and rapid increases in the level of eutrophication were found, but in the study period, the ecosystems of the bays were capable of self-healing.