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<正>Sediment in rivers plays an essential role in the river and watershed ecosystem.Recently,Dethier et al.[1] used an empirical model,which was developed using the data in America and Taiwan Province in China,to estimate suspended sediment concentration(SSC) and generate a long-term record of SSC and sediment fluxes in 414 major rivers worldwide since 1984.The authors concluded that the widespread decreases in river sediment fluxes in the North Hemisphere (NH) resulted from the dams,while the increases in river sediment fluxes in the South Hemisphere were possibly related to changes in land use.Regardless of the discussion on whether such an empirical model could be extrapolated to the global rivers for accurately retrieving SSC from Landsat imagery,the elucidation of the continuous declines in SSC in the NH rivers since1980s was incomplete.As Dethier et al.[1] demonstrated,the spatial and temporal variations in river sediment were regulated by climate change and human activities [2],including precipitation,land cover and land use,damming,and dredging activities [3-6].
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