Modelagem geoambiental em manguezais: detecção de áreas contaminadas via método eletromagnético indutivo no Baixo Subaé, Baía de Todos os Santos

Abstract

In order to understand the changes resulting from both natural and anthropogenic processes as well as their effects on mangroves, this study aimed to model the dynamics of changes in the mangroves of the lower Subaé, inserted in the Todos os Santos Bay (TSB), using geotechnologies. Thus, initially the study of hydrology was carried out based on soil data, DEM ALOS/PALSAR and SCS Curve Number Method. Subsequently, using the images from the Landsat series and the Planet Scope, were produced thematic maps of land use and occupation for the period from 1984 to 2018, that were used as a basis for spatio-temporal assessment of the classes present at the influx of the Subaé River. For the survey on detailed scale, from the evaluation of the NDVI and NDWI indices and the surface temperature, were determined three areas for overflight using the UAV Phantom 4 and the airborne sensor MX-RedEdge. Finally, to verify the possible correlation between electroconductivity and soil chemical components, a electromagnetic profiling was performed using the EMP-400 sensor in conjunction with the collection of soil samples that were subjected to chemical analysis. The areas with the highest runoff rate within the SRHB are found in the lower part, mainly due to precipitation. The thematic maps of the land use and occupation allowed to monitor the expansion and contraction of mangrove areas, as well as the growth of urban areas and pastures. From the detailed analysis, it was possible to notice that the values less than 85% and 75%, for the Frontal and Lateral overlays, respectively, resulted in alignment difficulties due to homogeneous status of vegetation. The analysis of the obtained indices (NDVI and NDWI) indicated the healthy state of the mangroves. however, the electrical conductivity, when tested for spatial correlation using the Pearson's method, obtained its highest value of 0.57 for MgO, not showing a good spatial correlation, expressing that the results may have been influenced by other factors. Although the inductive electromagnetic survey did not show a good correlation for the chemical elements present in the soil, it is recommended to adopt a different approach from the one carried out in this study, observing the tidal conditions, and also test other chemical and physical factors in the soil, such as, moisture content, PH, granulometry and clay content.