Plausible causes of temporal variation in suspended sediment concentration in the upper Changjiang River and major tributaries during the second half of the 20th century

In the second half of the 20th century, suspended sediment concentration (SSC) varied in different ways in the upper Changjiang River and major tributaries due to the changing human activity and precipitation. The variation in annual precipitation (Pm) can explained only 16%–37% of the variation in suspended sediment concentration, and thus variation in precipitation is not the main cause for the variation in suspended concentration. Using the analysis of double-mass curve, the effect of human activities on the variation in suspended concentration has been studied. The suspended concentration of the lower Jinshajiang River increased from 1983 due to large-scale mining and road and urban construction. The double-mass curve for the Minjiang shows three periods where the relationship between SSC and Pm changes because of reservoir construction and reforestation. The SSC of the Jialingjiang River decreased from 1984 because marked sediment-reduction effect has been achieved by soil and water conservation measures. The SSC of the Wujiang River increased from 1968 and then decreased from 1983, the former can be related to the vegetation destruction that enhanced soil erosion and the latter to the construction of reservoirs that trapped sediment. Compared to the 4 tributaries, the suspended sediment of the main stem of the upper Changjiang River shows smaller variation in SSC. The results of a multiple regression analysis show that the contribution percentages of SSC of the Jinshajiang, Minjiang, Jialingjiang and Wujiang Rivers to that of the upper Changjiang are 28%, 13%, 44% and 15%, respectively.