Altimetry and environmental impact assessment in Mãe-Bá lagoon, Espírito Santo – Brazil


Publication date: 24/03/2022

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DIEGO LANG BURAK External Examiner *

Summary: The assessment of environmental impacts on water resources is a multidisciplinary topic, as it demands diverse knowledge. Among these, we can mention geoprocessing, water chemistry, nutrient cycling, legislation, ecology, toxicology, among others. The morphometric characteristics of a pond are essential to understand its functioning, as they can influence the quality of the water. Such characteristics can be measured through bathymetric studies, from echo sounders or from images derived from satellites. In this case, interpolators (mathematical models) are used to construct three-dimensional spaces. Through these three-dimensional models, it is possible to determine the bathymetric characteristics of the water resource. The study of the conformation of the water resource is the first step in the assessment of environmental impacts. The bathymetric characteristics will influence the physical and chemical composition of the water, which in turn influences the composition of zooplankton and phytoplankton communities, affecting the entire ecosystem. It is known that shallow ponds are much more sensitive systems, as the water turbulence itself increases the possibility of sediment suspension, modifying the physical and chemical characteristics of the water (due to organic matter turnover), which may increase the trophic state of the environment. In addition, turbidity can suspend toxic substances, such as trace elements deposited in the sediment. These events can increase the toxicity of this environment for the local ichthyofauna, which in the long term can cause irreversible damage to the ecosystem. Genotoxicity tests, such as the micronucleus test or comet assay, can aid in a safe environmental diagnosis. Our objective was to use Landsat 8 images together with artificial intelligence models such as Random Forest to obtain the potential of sensing images to predict bathymetry in a lagoon and evaluate the environmental quality through genotoxicity tests of a coastal lagoon. For this, we used two types of bathymetry, the first one was performed by means of geodetic GNSS receivers, dual frequency, in real time (RTK) coupled to an echo sounder and the second was used images derived from satellites (Landsat 8) with the processing from the data using the Randon Forest package of the R program. We also performed the water analysis and the quantification of trace elements in the lake sediment. Finally, genotoxicity tests were performed using the micronucleus test and the comet assay. The use of bathymetric techniques using images derived from the Landsat 8 satellite OLI sensor is a good alternative in lagoons, provided they do not present advanced eutrophication stages. A high concentration of Ni and Cr was detected in the sediment, but despite the genotoxicity tests being positive, it is not possible to identify the cause of this genotoxicity. It is not possible to point out the mining company as the main source of Ni and Cr in the lagoon, as analyzes carried out in a control lagoon showed high levels of Ni and Cr. Therefore, we conclude that Mãe-Bá lagoon has been suffering a strong anthropic pressure and that it may be being potentiated by its morphometry and environmental characteristics of the place.

Keywords: Coastal lagoons; bathymetry; trace elements; genotoxicity; micronucleus test; comet assay.

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