Using Synergy between Water Limnology and Satellite Imagery to Identify Algal Blooms Extent in a Brazilian Amazonian Reservoir

Isabel De Sousa Brandão,Wouter Verhoef,Rosildo Paiva,Augusto Saraiva,Elidiane Da Silva,Chris Mannaerts

doi:10.3390/su9122194

Isabel De Sousa Brandão, Wouter Verhoef + Show 4 more

Open Access

https://doi.org/10.3390/su9122194

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Abstract

Monitoring algal blooms from space is a very challenging task, which becomes particularly difficult when dealing with cyanobacteria blooms. Cyanobacteria are strategic organisms adapted to a wide variety of environmental conditions. In high concentrations, they form scum on the water surface, which is a concern for public health due to the production of toxins, as well as being a nuisance. Knowledge of the ecological role of these organisms is, therefore, essential when trying to estimate their extent from satellite-based data. We present a multidisciplinary approach, based on both the ecological and the optical perspective. This approach is applied in a Brazilian Amazonian reservoir using spatial and temporal scales. The ACOLITE processor is employed to perform atmospheric correction. Extent of the algal bloom is mapped with outputs such as Rayleigh reflectance atmospheric corrected images. Chlorophyll-a estimation is accomplished using a blue-green edge algorithm from the Ocean Biology Processing Group (OBPG), and shows reasonable results (R2 = 0.95; RMSE = 0.40). The SAred-NIR slope algorithm identifies the extent of the algal bloom at both the spatial and temporal scale. Unfortunately, the performance of these algorithms is most likely affected by weather conditions and glint effects. Therefore, this study recommends that cyanobacteria or phytoplankton studies in this area ensure that their ecological functioning is carefully considered when attempting to map occurrence using limited satellite imagery.

Highlights

Eutrophication in man-made reservoirs has received considerable attention over time due to its harmful effects on the aquatic environment and on human and animal health [1,2]
Our main objective was to investigate whether the combination between water limnology and satellite imagery is a suitable approach for monitoring spatial distribution and temporal frequency of algal blooms and establish their potential toxicity in the Tucuruí hydroelectric reservoir (THR)
Despite the fact that the ecological and optical approaches showed both drawbacks and advantages, the overall conclusion is that the Ocean Biology Processing Group (OBPG) algorithm is suitable for estimating the spatial and temporal variability in Chl-a concentrations

Summary

Introduction

Eutrophication in man-made reservoirs has received considerable attention over time due to its harmful effects on the aquatic environment and on human and animal health [1,2]. The increased probability of algal blooms occurring is of major concern, especially where these blooms are due to (toxic) cyanobacteria species. Under natural conditions in aquatic ecosystems, a balance exists between cyanobacteria and other phytoplankton groups [3]. Specific characteristics may allow cyanobacteria to become prevalent. These characteristics are determined by a range of features, including cellular physiology (gas vesicles within cells allow regulation of buoyancy) and physiological response (light and nutrient utilization, for example), cell size, cell structure, and general morphology [4]. The predominance of cyanobacteria over other species occurs under specific environmental conditions, including optimal light intensity and water temperature, nutrient availability and stability in the water column [2]

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