Stepwise decreases of the Huanghe (Yellow River) sediment load (1950–2005): Impacts of climate change and human activities

The sediment load delivered from the Huanghe (Yellow River) to the sea has decreased sharply to 0.15×10 9 metric tons per year (0.15 Gt/yr) between 2000 and 2005, and now represents only 14% of the widely cited estimate of 1.08 Gt/yr. The river seems to be reverting to the pristine levels characteristic of the middle Holocene, prior to human intervention. Datasets from 1950 to 2005 from four key gauging stations in the main stream reveal distinct stepwise decreases in sediment load, which are attributed to both natural and anthropogenicimpacts over the past56yr. Completions of tworeservoirs,Liujiaxia(1968) and Longyangxia(1985), intheupper reaches of the river and their joint operations have resulted in stepwise decreases in sediment load coming from the upper reaches. Effective soil conservation practices in the middle reaches since the late 1970s, combined with the operation of the Sanmenxia and Xiaolangdi reservoirs, have also caused stepwise decreases in sediment load at Huayuankou in the middle reaches, but the decrease differs from that observedinthe upper reaches.Decreaseinprecipitationisresponsible for 30% of the decreasein sediment load at Huayuankou, whilethe remaining 70% is ascribed tohuman activities inthe river basin, of which soilconservation practices contribute40% tothe total decrease. Sediment retention within reservoirs accounts for 20% of the total sediment load decrease, although there was notable sediment retention within the Xiaolangdi reservoir from 2000 to 2005. The remaining 10% of the decrease in sediment load is a result of the operation of reservoirs in the upper reaches. In the lower reaches, 20% of the sediment passing Huayuankou has been lost as a result of channel deposition and water abstraction. Soilconservation practices and the operation of reservoirs have lowered the content of coarser sediment (DN0.05 mm) at Huayuankou, and reduced channel deposition in thelowerreaches.In contrast,sediment loss owing to water abstraction in the lower reaches has increased considerably as water consumption for agricultural needs has increased. Therefore, the combined effectsof climatechange and human activities inthe upper, middle, and lower reacheshave resulted in stepwise decreases in the sediment load delivered from the Huanghe to the sea. The Huanghe provides an excellent example of the altered river systems impacted by climate change and extensive human activities over the past 56 yr. Further dramatic decreases in sediment load and water discharge in the Huanghe will trigger profoundgeological, morphological,ecological,andbiogeochemical responses intheestuary, delta, andcoastal sea. © 2007 Elsevier B.V. All rights reserved.