Sedimentary records of metal speciation in the Yangtze Estuary: Role of hydrological events

Chemical speciation of Al, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Sb and Zn in two typical 210Pb-dated sediment cores (i.e., the CJ03 site and CJ06 site) in the Yangtze Estuary was investigated to reveal their different responses to upstream hydrological events. Cluster analysis and correlation analysis (CA) demonstrated that the CJ03 site, which is located in the main river channel, experienced significant influences from river hydrology. Specifically, metals in liable fractions (exchangeable, carbonate, reducible and organic fractions) were sensitive to water fluxes, while conservative fractions (residual fractions) have higher affinity with sediment inputs. By comparison, the CJ06 site in shoal correlated better with total organic carbon (TOC), and was influenced more by the surrounding cities. Evidently decreased sediment discharge and their fluctuated size composition and varied metal concentrations accorded well with the time when the impoundment of dams and disastrous flood occurred. The transformation of metals in liable speciation into conservative phases reflected the intercepting role of dams. Metals in the reducible and organic fractions were significantly affected by the varied redox conditions caused by hydrological events.