River sediment load and concentration responses to changes in hydrology and catchment management in the Loess Plateau region of China

To reduce the sediment load of China's Yellow River, soil conservation measures have been progressively implemented across the Loess Plateau region since the 1950s. The effectiveness of these soil conservation measures ( which were also coincident with reduced rainfall and streamflow) in controlling sediment movement remains to be ascertained. Here the association between sediment movement, hydrological variability, and the implementation of soil conservation measures is examined for the Coarse Sandy Hilly Catchments region of the Yellow River basin. The hypothesis that the soil conservation measures have reduced suspended sediment yields beyond that associated with rainfall reductions alone, principally by reducing sediment concentration, is examined. Annual sediment yield decreased significantly over time in all subcatchments, and the timing of the change (between 1971 and 1985) was consistent with the timing of change in streamflow. Annual mean sediment concentration in 7 of the 11 catchments exhibited a statistically significant decreasing trend over time, indicating that soil conservation practices reduced the mobilization of sediment in most areas, typically accounting for similar to 75% of the observed reductions in annual sediment yield. Lesser reductions in area-specific sediment yield at larger catchment areas after the soil conservation measures were emplaced suggests that larger rivers may be reeroding stored sediment. As these sediment stores are likely to be relatively large given the high historic yields, relatively high area- specific sediment yields may persist at larger catchment areas even with improvements to sediment management in smaller tributaries.