Variabilidade espacial e temporal do transporte de sedimentos suspensos na confluência dos Rios Japurá e Solimões

Abstract

The production and transport of suspended sediments are key processes for understanding the geomorphological dynamics and evolution of Amazonian fluvial systems, particularly those characterized by high sediment loads. Climate change, hydrological variability, and anthropogenic activities such as alluvial gold mining intensify erosion and alter sediment regimes, emphasizing the need for continuous monitoring. Given the scarcity of in situ data, remote sensing has proven to be an effective tool for investigating the spatial and temporal variability of suspended sediments. This study analyzes the transport of suspended sediments at the confluence of the Japurá and Solimões rivers between 2001 and 2021, integrating three scales of analysis to: estimate the temporal variability of suspended sediment concentration based on remote sensing and in situ data; characterize a suspended sediment flux balance in the confluence region; and investigate the influence of natural and anthropogenic factors on the variability of suspended sediments. Hydrosedimentary balance calculations, granulometric and hydrodynamic analyses, and land use and land cover change mapping associated with gold mining activity were performed. The results indicate that the Solimões River exhibits higher suspended sediment concentrations than the Japurá River and floodplain (channels and lakes) within the confluence region, especially during high-water periods. The Paraná Aranapu functions as a main sediment transfer pathway from the Solimões to the Japurá River before their confluence. Granulometric analyses revealed a predominance of fine-grained material (silt and clay) in floodplains and river islands, while sand bars consist mainly of fine sand fractions. The sediment flux balance demonstrated an increase in flux after the confluence, confirming the contribution of the Japurá River, which drains eroded sediments from the Colombian Andes. Bathymetric and hydrological measurements highlighted areas of high ADCP backscatter signal and elevated sediment concentration along the Solimões riverbank and channel bottom. Over the 21-year period, reduced forest cover and expanded pasture and mining areas were observed, suggesting that these anthropogenic changes influence both watercolor and the regional sediment regime