Influence of extensive gold mining in the southwestern Amazon on the spatial and temporal dynamics of suspended sediment transport in the Madre de Dios River

The Madre de Dios (MDD) watershed in the southwestern Amazon has experienced extensive environmental degradation and mercury (Hg) contamination due to rapid gold mining expansion. Previous studies documented increased suspended sediment concentration (SSC) using satellite-derived estimates at river inlets and outlets. However, the spatial and temporal variability of SSC along the MDD River, as well as cross-sectional patterns and grain-size distribution, remain insufficiently quantified. This study integrated harmonized surface reflectance data from Sentinel 2 and Landsat 7 and 8, combined with field campaigns, to investigate spatial and temporal SSC dynamics along the MDD River and their response to flow conditions and mining activity. The analysis focused on two phases: the initial mining expansion (1999–2009) and the subsequent floodplain mining intensification (2010–2024), across two reaches influenced by the Colorado and Inambari tributary confluences. Results revealed pronounced daily-to-weekly SSC fluctuations associated with peak flow conditions and mining activity, particularly in the upper reach, with marked attenuation downstream. Gold mining altered floodplain hydrology by reactivating tie channels and paleochannels, leading to elevated sediment inputs and atypical sediment exchange between the river and oxbow lakes. Furthermore, the vertical distribution of sediment, dominated by cohesive material representing approximately 60–90% of total SSC and remaining relatively uniform throughout the water column, provided key insights into the potential enhanced transport of Hg along the MDD River system, driven by the strong adsorptive capacity of fine sediment. These findings support improved sediment management and sustainable mining practices aimed at preserving geomorphological stability and ecological integrity in tropical environments.