2024 KIRK BRYAN AWARD: RAPID CHANGES TO RIVER SUSPENDED SEDIMENT FLUXES BY HUMANS

Although watersheds undergo dynamic, natural changes due to floods and other disturbances, humans have accelerated the rate of disruption, particularly in the past century. Resulting changes to erosion and sediment transport threaten to alter geomorphic and ecological function in rivers across the globe. Our understanding of these changes has been limited to where scientists have made repeated observations for decades, but many rivers are under- or un-monitored. To address these spatial and temporal gaps, we have developed a suite of algorithms that enables monitoring of global river suspended sediment transport using Landsat imagery, allowing for the detection of changes in suspended sediment flux since the 1980s for most wide rivers (> 50 m across) globally.

Using these methods, we estimate that rivers are transporting just 49% of their historic suspended sediment flux to global oceans, mostly due to trapping by dams in the Northern Hemisphere. Despite increased dam building in the global hydrologic south (south of 20°N Latitude), suspended sediment fluxes have increased for those rivers by 41 ± 7% since the 1980s. Erosive land use in river corridors is associated with changes at 83% of those rivers. In the tropics, mining is particularly impactful: sediment flux has increased for more than 35,000 wide-river kilometers affected by alluvial mining, 7% of tropical wide-river length. The geomorphic, ecological, and human consequences of these changes, given their global distribution, warrants increased attention by the scientific community and the public.