Remote Detection of Cyanobacterial Blooms and Chlorophyll-a Analysis in a Eutrophic Reservoir Using Sentinel-2

Abstract

Harmful cyanobacterial blooms have been one of the most challenging ecological problems faced by freshwater bodies for more than a century. The use of satellite images as a tool to analyze these blooms is an innovative technology that will facilitate water governance and help develop measures to guarantee water security. To assess the viability of Sentinel-2 for identifying cyanobacterial blooms and chlorophyl-a, different bands of the Sentinel-2 satellite were considered, and those most consistent with cyanobacteria analysis were analyzed. This analysis was supplemented by an assessment of different indices and their respective correlations with the field data. The indices assessed were the following: Normalized Difference Water Index (NDWI), Normalized Differences Vegetation Index (NDVI), green Normalized Difference Vegetation Index (gNDVI), Normalized Soil Moisture Index (NSMI), and Toming’s Index. The green band (B3) obtained the best correlating results for both chlorophyll (R2 = 0.678) and cyanobacteria (R2 = 0.931). The study by bands of cyanobacteria composition can be a powerful tool for assessing the physiology of strains. NDWI gave an R2 value of 0.849 for the downstream point with the concentration of cyanobacteria. Toming’s Index obtained a high R2 of 0.859 with chlorophyll-a and 0.721 for the concentration of cyanobacteria. Notable differences in correlation for the upstream and downstream points were obtained with the indices. These results show that Sentinel-2 will be a valuable tool for lake monitoring and research, especially considering that the data will be routinely available for many years and the images will be frequent and free.

Phycocyanin Monitoring in Some Spanish Water Bodies with Sentinel-2 Imagery

“…It should be noted that for our data, there was a direct, proportional relationship between Chl-a and PC, since the greater the Chl-a, the greater the PC, and vice versa [1], as is the case with suspended solids, since a greater number of Chl-a and PC in reservoirs means that there is more phytoplankton mass and, therefore, the amount of suspended organic matter will be higher. This is linked to eutrophication processes and, therefore, to a decrease in the availability of oxygen in water, generating hypoxic environments in which organisms that are unable to survive die and generate more organic matter, thus increasing its concentration [33]. Chl-a is the major pigment present in all plants and algae, and cyanobacteria, PC, and phycoerythrin are accessory pigments.…”

Assessment of Cyanobacterial Chlorophyll A as an Indicator of Water Quality in Two Wetlands Using Multi-Temporal Sentinel-2 Images

“…Reservoirs are significant freshwater reserves that have experienced severe, negative effects that have changed their physico-chemical composition both qualitatively and quantitatively. These changes have, in turn, had an impact on the fauna and flora [1]. With the growth of industry and agriculture, there was a significant increase in the nutrient inputs into rivers and lakes, which led to the eutrophication of the water bodies [2].…”

Pathways of Nitrogen and Phosphorus Utilization and Removal from Cyanobacteria Wastewater by Combining Constructed Wetlands with Aerobic Reactors

“…The proportion of lakes (reservoirs) where eutrophication has become a problem has increased from 23% to 30% [1] in the past three years. Additionally, frequent outbreaks of cyanobacteria have primarily occurred as a result of lake eutrophication, and these outbreaks have become a common and serious environmental issue in China [2,3]. The salvage and collection of cyanobacteria is a common approach to rapidly reducing cyanobacteria in water.…”