Rare earth element geochemistry of the sediments from small rivers draining southeast China

Representative suspended and floodplain sediment samples were systematically collected from three small rivers in Zhejiang and Fujian provinces. Two chemical phases (leachates and residues) were separated by 1N HCl leaching and the leachates account for 32%~82% of the total REE concentration. The absorption on Mn-Fe (hydro)oxides and clay minerals are the main hosts of acid-leachable REEs. The REE compositions of the leachates can potentially indicate the whole weathering history of the sediments to some extent. Silicate minerals and stable heavy minerals like zircon are important hosts of residual REEs, and the residual fractions are reliable for the indication of sediment provenance. The weathering products of river basins and Changjiang-derived sediments pumped by strong tide into the estuaries are the main sources of these rivers sediments. REE fractionation is demonstrated during extreme chemical weathering and hydrodynamic sorting processes, and thus it should be cautious to use the bulk REE compositions of these river sediments to indicate the sediment provenance. Slight positive Gd anomalies occur both in the leachates and residues, which do not indicate the presence of anthropogenic Gd, but reflect the geochemical compositions of the materials in Eastern China.