Análise das práticas agrossilvopastoris na bacia hidrográfica do Rio dos Mangues, BA

Abstract

The removal of vegetation cover in the Rio dos Mangues Watershed (BHRM), especially riparian forests, intensifies geomorphological phenomena and compromises water quality. The use of pesticides in agrosilvopastoral activities increases nitrates and phosphates, the main contributors to the eutrophication of water bodies, and exposes soils and water resources to harmful pesticides, adversely affecting biodiversity and public health. This study assesses the environmental quality of the BHRM, focusing on morphometric analysis and temporal land use and land cover changes from 1990 to 2018, to relate these results to the water quality provided to the population of Porto Seguro. Quantum GIS – QGIS 3.22.2 softwares was used to extract and generate geomorphological and land use and cover data, verifying interventions in Environmental Protection Areas (EPAs), as defined by the Brazilian Forest Code. To evaluate the presence of pesticides in the water, indicators of organic and inorganic substances representing health risks were used, in accordance with CONAMA's resolution for raw water. This allowed for an analysis of the relationship between land use and water quality in the study area. Morphometric results revealed significant indices, such as circularity (0.150), compactness (2.58), and form factor (0.41), indicating a low potential for flooding. However, unregulated land occupation increases surface erosion and mass movement in Permanent Preservation Areas (PPAs), contributing to the siltation of water bodies. Segmented land use analysis showed an expansion of agricultural activities, posing a risk to runoff dynamics and sediment transport in the watershed. In segments 1 to 4, a high concentration of rural properties and agrarian reform settlements resulted in significant vegetation cover reduction and increased vulnerability to erosion and water contamination. In segments 5 to 7, permanent preservation areas face usage conflicts due to proximity to agricultural areas, requiring sustainable management measures. Segments 8 to 10, which have greater vegetation cover, are crucial for aquifer recharge and maintaining the watershed's flow.The detection of pesticides in surface waters throughout 2022 and early 2023 revealed the presence of 15 pesticides, 9 of which are banned in both Brazil and the European Union. The predominance of insecticides is particularly concerning due to their environmental toxicity, affecting non-target organisms, including pollinators and natural predators. The spatial distribution of pesticides showed variable concentrations, reflecting land use dynamics and hydrological characteristics of the watershed. During the sampling campaigns, detection varied by time and location. In June 2022, Endrin Aldehyde had the highest concentration (~380 μg/L-1

) in Field 1, and Heptachlor Epoxide (~100 μg/L-1

) in Field 3. In October 2022, Molinate and Methyl Parathion had significant concentrations in Field 1 (~10-20 μg/L-1 ). In February 2023, DDT and its metabolites (DDE, DDD) were found in various parts of the watershed, indicating persistence and bioaccumulation.The rapid growth of agrosilvopastoral activities poses a significant risk not only to fluvial morphodynamics but also to water quality. This study highlights the importance of public policies to protect and restore native vegetation areas, especially in high-slope regions, mitigating erosion and water contamination risks. The creation of vegetated buffer zones along watercourses can reduce surface runoff and improve water quality. Moreover, it is crucial to promote environmental awareness among landowners to ensure the proper use of natural resources. This work not only achieved its objectives but also paved the way for future investigations, emphasizing the importance of an integrated approach to the management and conservation of water resources in agricultural regions.