Sieved Transport and Partitioning of Metals in Plain River Networks with Sedimentary Resuspension and Implications for Downstream Lakes

Abstract

This study showed that metal transport and partitioning are primarily controlled by suspended solids with seasonal flow regimes in plain river networks with sedimentary resuspension. Eight metal species containing iron (Fe), manganese (Mn), cadmium (Cd), chrome (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn), in multiple phases of sediments, suspended solids (>0.7 μm), colloids (1 kD-0.7 μm) and water solution (<1 kD) were analysed to characterize their temporal-spatial patterns, partitioning and transport on a watershed scale. Metal concentrations were associated with suspended solids in the water column and decreased from low flow to high flow. However, metal partitioning between suspended solids and the dissolved phase (colloids and water solution) was reversed and increased from low flow to high flow with decreased concentration of total suspended solids and median particle size. Partition coefficients ( k p ) showed differences among metal species, with higher values for Pb (354.3–649.0 L/g) and Cr (54.2–223.7 L/g) and lower values for Zn (2.5−25.2 L/g) and Cd (17.3–21.0 L/g). Metal concentrations in sediments increased by factors of 1.2 to 3.0 from upstream to downstream in watersheds impacted by urbanization. The behaviours of metals in rivers provide deeper insight into the ecological risks they pose for downstream lakes, where increased redox potential and organic matter may increase metal mobility due to algal blooms. Areas of heavy pollution and their transport routines were also revealed in our research.

Keywords: metal pollution, particle size, flow regime, partition coefficient, Sediment resuspension, river networks