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Historical distribution characteristics of polycyclic aromatic hydrocarbons (PAHs) and their carriers (i.e., organic matter and mineral particles) in the sediment cores of the Yangtze Estuary were investigated, with emphasis laid on the role of the Yangtze River. Grain size component of sediments (clay, silt, and sand) and organic carbon (black carbon and total organic carbon) in the sediment cores were markedly affected by water flux and sediment discharge of the Yangtze River. Qualitative and quantitative analysis results showed that sands and black carbon acted as the main carriers of PAHs. The sedimentation of two-ring to three-ring PAHs in the estuary had significant correlations with water flux and sediment discharge of the Yangtze River. The relative lower level of the four-ring and five-ring to six-ring PAHs concentrations appeared around the year 2003 and remained for the following several years. This time period accorded well with the water impoundment time of the Three Gorges Reservoir. The decreased level of two-ring to three-ring PAHs occurred in the year 1994, and the peak points around the year 2009 indicated that PAHs sedimentation in the estuary also had close relationship to severe drought and flood in the catchments. The findings presented in this paper could provide references for assessing the impacts of water flux and sediment discharge on the historical deposition of PAHs and their carriers in the Yangtze Estuary. [ABSTRACT FROM AUTHOR]

Abstract: Historical profiles and sources of PAHs at two typical sediment cores (i.e., the shipping route site and the shoal site) were fully compared to probe the controlling factors, specifically the water currents, for the PAHs deposition processes in the Yangtze River Estuary. Compared with ocean water currents, river runoff affected by the water impoundment of the Three Gorges Dam greatly affected the PAHs levels and percent contribution of PAHs sources in the two cores. River runoff hindered the PAHs deposition in shoal site, while a contrary phenomenon was observed for the shipping route site. Though the PAHs in the estuary were mainly from river catchment, only low ring PAHs in the shipping route site were mainly from the upper reach of the river. Coarse sediments with higher organic carbon content also accounted for the higher deposition levels of PAHs in the shipping route site. [Copyright &y& Elsevier]

Highlights: [•] Chronological records of metal deposition at different estuarine sites were studied. [•] Sedimentary metal speciation reveal responses to upstream hydrological events. [•] The transformation of metal speciation can explain the intercepting role of dams. [•] Sediment particles and organic carbon are the proxies for the metals deposition. [Copyright &y& Elsevier]

Abstract: Batch leaching experiments, Freudlich isotherm, correlation analysis (CA) and principal component analysis (PCA) were undertaken to explore the mechanisms that govern the release of sediment–associated metals (i.e. Cd, Cu, Mn and Pb) under the salinity stress in the Yangtze River Estuary. Special attention has been paid to the role of sediments’ physico-chemical properties and metal chemical speciation. The increase of salinity promoted the metal mobility which followed the order: Cd>Mn>Cu>Pb. Sediments properties (e.g., particle component and organic carbon) governed the mobility of Cd; metal chemical speciation controlled the release of Mn, while the mobility of Cu and Pb were simultaneously affected by the two factors. Different metal release mechanisms caused by salinity changes might be explained by: the chloro-complexation for Cd, the encouragement of acidity changes for Mn, and the high affinity to Fe–Mn oxides, organic substances and specific sorption sites in the sediments for Cu and Pb. Under salinity effect, Cd and Mn exhibited higher ecological risk and mobility, while Cu and Pb seemed to be more conservative. [Copyright &y& Elsevier]