Metal Water-Sediment Interactions and Impacts on an Urban Ecosystem

Abstract

The EU Water Framework Directive (WFD) requirement that all surface water bodies achieve good ecological status is still a goal for many regulatory authorities in England and Wales. This paper describes field and laboratory studies designed to identify metal contaminant loadings and their distributions within water bodies located in the Lower Lee catchment (London, UK). Water and sediment samples have been collected from increasingly urbanised sites on the River Lee and its main tributaries over a two-year period with samples analysed for total concentrations of cadmium, copper, lead, mercury, nickel, tin, and zinc. Complimentary batch tests indicate a positive relationship between aqueous metal concentrations and the batch test-derived sediment metal release data, particularly during wet weather events. Field data indicate a dynamic relationship between water and sediment concentrations with both being capable of exceeding relevant environmental quality standards/sediment quality guidelines at all sites. Mean sediment metal concentrations across all sites were found to be highest for Cu (141.1 ± 111.0 µg g^-1), Pb (175.7 ± 83.0 µg g^-1), and Zn (499.9 ± 264.7 µg g^-1) with Zn demonstrating elevated mean water concentrations (17.2 ± 13.8 µg L^-1) followed by Ni (15.6 ± 11.4 µg L^-1) and Cu (11.1 ± 17.8 µg L^-1).

Keywords: diffuse and point source pollution; urban receiving waters; urban sediment quality.

Figure 1

Location maps (a,b) and schematic identifying location of sampling sites on the Lower River Lee (c).

Figure 2

Overview of mean Zn aqueous concentrations during dry weather events at sites A–E in relation to Zn sediment remobilisation (%) determined during laboratory batch tests.

Figure 3

Overview of mean Zn aqueous concentrations during wet weather events at sites A–E in relation to Zn sediment remobilisation (%) determined during laboratory batch tests.