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• Lulao catchment (LLC) is a small, homogeneous watershed on Guizhou Plateau, SW China. • Farmland soil (FS) has higher IRM 300mT /SIRM due to stronger pedogenesis in LLC. • Grassland soil (GS) has low IRM 300mT /SIRM & higher HIRM in LLC where a reservoir lies. • Contribution of FS vs GS to reservoir sediment is inferred with sediment's magnetism. • Changes in erosion is inferred as FS is distant from the reservoir than GS. This paper demonstrates that land use could enhance spatial discrimination of soil magnetism in a homogeneous watershed, and such differences help infer alterations in sediment sources and erosion. One sediment core was sampled from a reservoir built in 1958 and fifteen soil profiles from its catchment on the southern Guizhou Plateau, SW China. The whole watershed was covered by yellow earth developed on limestone. Magnetic measurements and granulometric analysis were performed on the soils and sediments while TOC and TN analysis on two soil profiles and 137Cs analysis on the sediment core. Information of seven years' land-use was derived from remote sensing images. The farmland and grassland soils had different magnetic characteristics while the downwards distributions of TOC and C/N were similar in the two profiles. The grassland soils had higher HIRM, lower χ fd % and IRM 300mT /SIRM. The higher χ fd % and IRM 300mT /SIRM of the farmland soils suggested stronger pedogenesis under cultivation. The average HIRM, χ fd % and IRM 300mT /SIRM were 38 and 334 10-6 A m2 kg−1, 5.7 and 3.6%, and 0.91 and 0.66 for the farmland and grassland soils. The farmland soils were finer probably due to tillage. The reservoir has been closely surrounded mainly by the grassland whereas the farmland, embedded with patches of the grassland, has occurred in the terrains relatively distant from the reservoir. The sediments of 1958–1985 had lower HIRM (156 10-6 A m2 kg−1) and higher IRM 300mT /SIRM (0.79), indicating greater contributions of the remote farmland soils mixed with grassland soils and stronger erosion. HIRM increased (229 10-6 A m2 kg−1) and IRM 300mT /SIRM decreased (0.67) in the sediments of 1985–2019, implying decreased distant-soil contributions and relatively increased input of the grassland soil closely around the reservoir. Erosion thus weakened, as proven by the finer sediments. The declining erosion was mainly due to farmland shrinkage and grassland expansion. [ABSTRACT FROM AUTHOR]

• The near-dam region contributed 10.8% of the total sediment into the reservoir. • Sedimentation mainly occurred in bending, branching and near-dam reaches. • The key factor influencing sedimentation was the incoming sediment load. • New formulas were proposed to calculate sediment trapping efficiency. Sedimentation in the Three Gorges Reservoir (TGR) affects flood control, navigation, power generation and the ecological environment. We present a comprehensive analysis of the characteristics of sedimentation in the TGR from 2003 to 2018. The data set includes field measurements (runoff and sediment) at hydrological stations and estimation for areas where measured data are not available. Based on the data set, the amount of sedimentation in the TGR was calculated with the Sediment Budget Model (SBM) and Section Topography Method (STM). Finally, the variation in sediment Trapping Efficiency (TE) in the TGR was assessed. The results indicate that sediment from smaller tributaries in the TGR region, which has been ignored in most previous studies, constituted approximately 10.8% of the total incoming sediment. The total sedimentation in the TGR was 205478 × 104 t in 2003–2018, and the contribution rates of sediment load flowing into the TGR, the water depth in front of the dam, and runoff discharge flowing into the TGR were 94.4%, 24.5% and −18.9% respectively. The average annual TE was 78.5% in 2003–2018, and it was closely related to the ratio of reservoir storage capacity to flow discharge in the flood season and to sediment concentration in the non-flood season. The results in this paper not only play an important role in the optimal operation of the TGR but also have important reference value for other large reservoirs worldwide. [ABSTRACT FROM AUTHOR]

Abstract: Heavy metal contamination of bottom sediments of the Changjiang River is widely reported, however, the potential source and methods of transportation of these heavy metals in the contaminated sediments is poorly defined. This paper examines the correlation between heavy metals and geochemical indices, including Fe2O3, Al2O3, total organic carbon (TOC) and black carbon (BC), as well as magnetic susceptibility (MS). Using these indices we investigate the contamination characteristics of heavy metals in the sediments by with Principal Component Analysis (PCA). Results from 83 sediment samples collected in the lower reach of Changjiang River (from Nanjing to Shanghai) show that the first principal component accounts for 52.23% of the total variance, corresponding to the heavy metals, Co, Cr, Cu, Ni and Zn, and conservative components of Fe2O3, Al2O3 and TOC. This result indicates that heavy metal distributions are controlled by the transportation and sedimentation of fine particles which is also confirmed by particle size analysis. The second principal component explains 24.81% of the variance and is dominated by Cd, Pb and MS, which, collectively, result chiefly from industrial and transportation activities and, for MS, fly ash production. The third principal component accounts for 7.91% of the variance and corresponds solely to Hg. Principal component analysis/multiple linear regression (PCA/MLR) was used to estimate the contribution of the three principal components to each heavy metal. PCA/MLR results suggest that more than 50% of Co, Cr, Cu, Ni and Zn were influenced by the particle size effect. Particle size effect and fly ash account for 37.1% and 27.7% of As. Cd and Pb were mainly explained by fly ash. 98.9% of Hg was related to PC3, which represented black carbon (BC). Our study indicates that the combination of geochemical and multivariable statistical methods clearly characterizes the geochemistry of heavy metals in sediment of the lower reaches of the Changjiang River and suggests that power plants are the main source of heavy metal pollution. [Copyright &y& Elsevier]

Abstract: Long-term changes to the Yellow River delta in China have received considerable attention not only because of the growing economic importance of the delta region but also because they provide a clear example of the dominant role played by anthropogenic effects upon a large dynamic river delta. This paper presents a detailed study on the morphological consequences of reduction in river sediment load and influence of human activities based on sediment load data at three gauging stations in the upper, middle and lower reaches of the Yellow River basin from 1950 to 2007. The results indicate that sediment loads at all three gauging stations display a gradually decreasing trend over the past 58years. The primary reason for this decrease is shown to be due to various human activities, including the construction of Longyangxia and Liujiaxia reservoirs in the upper reaches, water–soil conservation practices and the commissioning of Sanmenxia and Xiaolangdi reservoirs in the middle reaches. It is estimated that water–soil conservation practices which are a major factor to the decrease of sediment load at Huayuankou gauging station account for 40% of the total amount of reduction, sediment trapping by Sanmenxia and Xiaolangdi reservoirs account for 30% of the total amount of reduction and the 10% decrease is caused by human activities in the upper reaches. The remaining 20% decrease is attributed to precipitation decrease. The reduction of sediment load has directly impacted on the lower Yellow River and the delta region, causing alternate changes between siltation and scouring in the lower river channel along with an increased rate of erosion over the whole Yellow River delta. [Copyright &y& Elsevier]

Abstract: Draining toward the South China Sea, the Pearl River is the third largest river in China. Based on datasets begun in the 1950s of water and sediment flux at the main gauging stations and measured deposition rates in some reservoirs, this paper examines the impact of dam construction on the sediment flux of the Pearl River. The results and conclusions are as follows: (1) The total storage capacity of reservoirs in the Pearl River basin had reached 65 km3 by 2005, which is 23% of the annual water discharge of the Pearl River. (2) The total deposition rate in the reservoirs has now probably reached 600 Mt/yr, one order of magnitude higher than the annual sediment flux into the sea (40 Mt/yr in 2000–2005). (3) The sediment flux of the Pearl River has shown a drastically decreasing trend since the mid-1980s, which is attributed mainly to deposition in the reservoirs. (4) A further decrease in sediment flux into the sea is expected to occur in the Pearl River in future decades because of the construction of new dams. This drastic decrease in sediment flux may be very import for the environments of the river channel, the estuary and the coastal areas, which need to paid considerable attention in scientific research and management. [Copyright &y& Elsevier]