Aspectos tróficos da ictiofauna do Rio Paraopeba e Rio das Velhas: uma abordagem comparativa utilizando a ferramenta de isótopos estáveis para dois rios impactados

Abstract

The use of stable isotopes has become an important tool for ecologists, and in the case of ichthyology, they have been assisting in obtaining information about fish communities and trophic structure in various hydrographic basins around the world. In this study, we reconstructed, with the help of stable isotopes of carbon and nitrogen, the trophic niches of fish assemblages from two of the largest tributaries of the São Francisco River in its upper course, the Paraopeba River and the Velhas River. The former, besides being impacted by the discharge of domestic and industrial sewage from the Metropolitan Region of Belo Horizonte (RMBH), also suffers from the presence of ore tailings introduced into the river following the rupture of the B1 dam in Brumadinho in 2019; the latter suffers from the daily discharge of a large amount of sewage from the RMBH. Thus, our main objective was to evaluate the state of the Paraopeba River nearly three years after the dam rupture, comparing it with a river with a similar degradation history. Fish and their potential food resources were sampled at eight points along the Velhas River (in 2015 and 2016) and four points along the Paraopeba (in 2021), including upstream and downstream locations of the impacted regions. Our results indicate that the current state of trophic diversity in the fish communities of the Paraopeba River, post-impact of the tailings dam rupture, already compares to the trophic diversity of some points in the Velhas River basin. In some points, the community exhibits greater trophic diversity than corresponding locations in the Velhas River basin that are impacted by continuous effluent discharge from the RMBH. However, due to its particular characteristics, it was indicated from Layman metrics that the impact extends further along the Paraopeba River channel. Unlike the Velhas River, the Paraopeba does not have well-preserved tributaries that can contribute to improving water quality and ichthyofauna along its course. These results demonstrate that different strategies need to be used to evaluate and address the lack of previous data in the case of major environmental impacts and indicate the possibility of using basins impacted by different sources as a valid method of comparison, provided they have a high degree of similarity in fauna, area, history of anthropogenic actions, among others.