Avaliação do impacto do garimpo na Bacia do Rio Tapajós/PA

Abstract

The Tapajós River is the fourth largest tributary of the Amazon River in terms of liquid discharge, with an average annual flow of approximately 13,500 m³/s. Its waters exhibit a characteristic light-green coloration associated with low suspended sediment loads. However, this fluvial system has been impacted for decades by anthropogenic activities, particularly gold mining, which significantly affects channel morphology and hydrosedimentary processes, compromising water quality and river dynamics. This research aimed to analyze the impacts of gold mining on the fluvial geomorphology of the middle and lower reaches of the Tapajós River and its main tributaries. Specific objectives included: (1) evaluating the suspended sediment flux balance; (2) identifying changes in water coloration and suspended sediment concentration (SSC) through satellite imagery; and (3) examining morphological changes in tributary channels affected by mining activities. The study utilized fluviometric data from the National Water Agency (ANA) and the HyBAM Observatory, information from the MapBiomas project, spectral data from Tapajós River waters, and SSC estimates obtained through MODIS sensors and PlanetScope imagery. Results indicate that in the Itaituba region, the Tapajós River exhibits an average annual suspended sediment flux (Qs) of 4.02 million tons and a specific yield (Qsp) of 8.79 t•year⁻¹•km⁻². Between 1985 and 2022, the area occupied by mining activities increased fourfold, reaching 0.55% of the study area. A strong correlation was observed between mining expansion and increased SSC in the Tapajós River, particularly near Fordlândia (Pearson correlation coefficient = 0.84; R² = 0.71). In the analyzed tributary channels, exposed soil area increased by over 300% between 2019 and 2024, with average bank widening of 118 meters and pronounced sedimentation processes. The study concludes that the integrated use of remote sensing and fluviometric data from ANA and the HyBAM Observatory is essential for monitoring hydrosedimentary dynamics in the region. This reinforces the need for continuous investment and effective governance focused on environmental management of the Tapajós basin.