Program

Recently, the global sediment flux into the sea has drastically decreased under the influence of human activities, resulting in considerable changes in the geomorphology and eco-environment of estuarine, coastal and continental shelf regions. In order to evaluate the impact of human activities(mainly dam building) on the Changjiang River sediment discharging into the sea, the spatial–temporal variations in the sediment load of different tributaries of the river were analyzed to reveal the quantity, grain size and composition patterns of the sediment entering the sea.We attempt to (1) analyze the effect of dam emplacement on the sediment load of different tributaries; (2) identify the spatial–temporal variation patterns of sediment load within the main stream of the Changjiang associated with dam emplacement; (3) reveal the quantity, grain size and composition features of the sea-going sediment during different periods; and (4) delineate the variations in sediment load originating from the tributaries of the Changjiang for different historical times.We have used the Mann–Kendall (M–K) test to analyze long-term hydro-meteorological temporal series.Before using the M–K test, the autocorrelation and partial autocorrelation functions were used to examine the autocorrelation of all the hydrological data.We have got four results:(1)The total RSCI values of the seven tributaries and the main stream of the Changjiang reveal stepwise increasing trends. The changes of the total RSCI and sediment load of the tributaries and the whole Changjiang catchment indicate that the stepwise decrease of sediment load is apparently related to the significant increase of the total RSCI.(2)The trends, derived on the basis of the M–K method, of sediment load of the seven tributaries indicate that the downstream sediment load began to decrease earlier than the upstream sediment load. (3)The variations of sediment load discharging into the sea, measured at the Datong station, indicated that there are four stepwise reduction stage period: 1956–1969,1970–1985, 1986–2002 and 2003–2010. Further, the sediment load decrease may be related to sediment load decrease of different tributaries.(4)The sediment grain size downstream of the reservoirs becomes significantly finer,suggesting that the sediment grain size from the upstream Changjiang exhibited a continuous decreasing trend.