Human-Induced Changes in South American River Sediment Fluxes From 1984 to 2019

River sediment fluxes have been impacted in South America (SA), one of the continents with the highest erosion and sediment transport rates globally. However, the magnitude and spatio-temporal distribution of the main drivers of changes have been poorly identified and explored. Here, we performed simulations using a hydrological-hydrodynamic-sediment model to comprehensively estimate the spatial and temporal sediment changes and trends in SA from 1984 to 2019. We found that 51% of the main SA rivers experienced significant changes in simulated sediment transport (QST) over this period, with 36% due to Amazon deforestation and river damming and 15% due to precipitation changes. We also estimated a 10% reduction in the average sediment delivery to the oceans. Deforestation was responsible for QST changes higher than 80% in some Amazon sites, and hydropower expansion led to a greater reduction of sediment flows (80%-100%) in the Tocantins, Uruguay, Upper Parana, lower Sao Francisco, Desaguadero, and Negro rivers. In addition, our results suggest that reservoirs built in the Amazon region in the 2011-2019 period are also affecting sediment transport. Our modeling outputs provide unprecedented information about the status of river sediment dynamics in SA, and a template to develop evidence-based strategies and transboundary policies related to continental-wide sediment dynamics and the conservation and restoration of ecosystems.

Automated summary

In this study, a hydrological-hydrodynamic-sediment model was used to simulate and estimate the spatial and temporal sediment changes in South American rivers from 1984 to 2019. The results showed that 51% of the main rivers in South America experienced significant changes in sediment transport, with 36% attributed to deforestation and river damming in the Amazon, and 15% to precipitation changes. Deforestation caused the highest changes in sediment transport in some Amazon sites, while hydropower expansion led to a significant reduction in sediment flows in multiple rivers. Additionally, the construction of reservoirs in the Amazon region also affected sediment transport.