Human activity has reconfigured global river sediment flux

Human activity is rapidly altering how much sediment flows from rivers worldwide into the oceans and seas, researchers report. Their findings also highlight sediment flux changes specific to key regions: while damming activity has decreased the amount of sediment flux in rivers across the global north, in the global south, increased erosion, likely driven by land use change, has increased sediment flux. Because sediment flux is crucial to river health and the stability of the economic and ecological services they provide, these new observations could help inform policy decisions and future planning and mitigation efforts. Across scales, riverine sediment flux plays a vital role in shaping landscape morphology and river, wetland, and coastal ecosystems. However, sediment flux worldwide is changing due to various human activities and impacts, including increased erosion from changing land use, sediment trapping from dam building, and compounding hydrological and sedimentological alterations due to climate change. Across many basins and particularly at the global scale, the current and future impacts of each of these changes are poorly understood, largely due to insufficient monitoring. To fill this knowledge gap, Evan Dethier and colleagues present an analysis of flux changes for 414 rivers worldwide. Deither et al. used more than 130,000 field measurements and a suite of algorithms to calibrate satellite images from 1984-2020, creating a monthly record of suspended sediment concentration (SSC) in global rivers spanning nearly 40 years. The findings show that dams have dramatically reduced sediment flux in rivers throughout the global north, resulting in SSC declines to 49% of pre-dam conditions. Across the global south, however, extensive land use change has increased erosion, increasing SSC on average by about 41% since 1980. “Although similar techniques have been used locally before, the scale, both spatial and temporal, and extensive verification of the work by Diether et al. is unprecedented, which allows the most detailed and comprehensive analysis of these trends in the data,” write Christiane Zarfl and Frances Dunn in a related Perspective.