Contaminant Geochemistry and Sedimentology of Urban Rivers

URBAN RIVERS IN MANCHESTER

Recent research has shown that contaminants are increasingly entering urban aquatic systems through diffuse sources such as atmospheric deposition, urban and agricultural run-off and remobilisation of contaminants from floodplains. Furthermore, a wide range of persistent organic and inorganic pollutants may also be released directly into fluvial systems from industrial discharges and sewage outfalls. The majority of these persistent contaminants (heavy metals and organics) have been shown to be associated with the sediment component of fluvial systems, with chemical fluxes of heavy metal contaminants (e.g. Pb, Zn, Cd, Cu, Mn) being of particular interest. These metals have known pollutant properties, are toxic and are readily available to the environment.

Urban catchments and their river environments are prime sites for biodiversity and regeneration. It is therefore, important to understand urban river catchments, and the associated source and transport of contaminants. In order to recognise the source and transport of persistent contaminants through urban river catchments, knowledge of the geochemical and mineralogical association of contaminants in urban river sediments is required. Hydrological processes dominate the behavior of contaminants within the fluvial environment. Therefore, the effects of particle size, sediment surface area and the surface coating on sediment particles (both suspended and bedload) need to be studied.

During this study, bed load and suspended sediment will be collected using suspended sediment samplers and a dredge sampler. The samples will be analysed for their heavy metal (e.g. Cd, Cu, Mn, Pb and Zn), organic and nutrient (e.g. phosphorus) content, and related to particle size. Total metal contaminant concentrations will be determined using acid digestion techniques (Aqua Regia) followed by atomic absorption spectrometry (AAS) and Inductively-Coupled Plasma analysis (ICP). Further analysis will provide information on the mineralogy of the sediments using X-ray diffraction (XRD) and on the sediment particle composition and morphology using scanning electron microscopy (SEM).

The first stage of this work has been to produce a spatial data set on metal-sediment levels in a small, heavily urbanised, modified river: the River Medlock, which flows through Greater Manchester, UK. As such, no data on sediment- contaminant levels within Greater Manchester exists. The resultant spatial data set will aid management plans to clear up surface waterways. The data set will also help determine the role of sediments in contaminant transport and the impact of these sediments upon catchment water quality. Thus allowing future quality assessments to be made.