Sediments, porewaters and diagenesis in an urban water body, Salford, UK: impacts of remediation

Abstract

Abstract:Contaminated sediments deposited within urban water bodies commonly exert a significant negative effect on overlying water quality. However, our understanding of the processes operating within such anthropogenic sediments is currently poor. This paper describes the nature of the sediment and early diagenetic reactions in a highly polluted major urban water body (the Salford Quays of the Manchester Ship Canal) that has undergone remediation focused on the water column.The style of sedimentation within Salford Quays has been significantly changed as a result of remediation of the water column. Pre-remediation sediments are composed of a range of natural detrital grains, predominantly quartz and clay, and anthropogenic detrital material dominated by industrial furnace-derived metal-rich slag grains. Postremediation sediments are composed of predominantly autochthonous material, including siliceous algal remains and clays. At the top of the pre-remediation sediments and immediately beneath the post-remediation sediments is a layer significantly enriched in furnace-derived slag grains, input into the basin as a result of site clearance prior to water-column remediation. These grains contain a high level of metals, resulting in a significantly enhanced metal concentration in the sediments at this depth.Porewater analysis reveals the importance of both bacterial organic matter oxidation reactions and the dissolution of industrial grains upon the mobility of nutrient and chemical species within Salford Quays. Minor release of iron and manganese at shallow depths is likely to be taking place as a result of bacterial Fe(III) and Mn(IV) reduction. Petrographic analysis reveals that the abundant authigenic mineral within the sediment is manganese-rich vivianite, and thus Fe(II) and Mn(II) released by bacterial reactions may be being taken up through the precipitation of this mineral. Significant porewater peaks in iron, manganese and silicon deeper in the sediment column are most probably the result of dissolution of furnace-derived grains in the sediments. These species have subsequently diffused into porewater above and below the metal-enriched layer.This study illustrates that the remediation of water quality in anthropogenic water bodies can significantly impact upon the physical and chemical nature of sedimentation. Additionally, it also highlights how diagenetic processes in sediments derived from anthropogenic grains can be markedly different from those in sediments derived from natural detrital material.

Early diagenetic vivianite [Fe3(PO4)2·8H2O] in a contaminated freshwater sediment and insights into zinc uptake: A μ-EXAFS, μ-XANES and Raman study

“…Early diagenetic sulphide mineral precipitates have been documented previously to act as sinks for trace metals in marine and brackish sediments (Parkman et al, 1996;Pirrie et al, 1999;Morse and Luther, 1999) and these minerals are routinely considered in contaminated marine sediment assessment (Ankley et al, 1996). Our study is the first to consider the incorporation of the potentially toxic element Zn in vivianite, an important mineral in anoxic environments such as acid mine drainage sites (Ueshima et al, 2004), rivers (House, 2003), lakes (Fagel et al, 2005) and urban water bodies (Taylor et al, 2003). There is a need to study the role of vivianite in the uptake of other potentially toxic elements in freshwater systems (e.g.…”

“…1). A full description of this site, 4 and its contamination and remediation history, can be found in Taylor et al (2003). The Manchester Ship Canal is up to 8 m deep, steep-sided and up to 50 m wide.…”

“…It has long been known that early diagenesis plays a particularly strong role in the short-to long-term release of the chemical species Fe, Mn, contaminant elements and P (Hamilton- Taylor et al, 1996a, b;Bryant et al, 1997;Taylor et al, 2003). The release of P from sediments during early diagenesis 3 has been recognised to be an important control on water quality in freshwater systems (Carignan and Flett, 1981;Jensen et al, 1992;Hupfer et al, 1995;Gonsiorczyk et al, 2001).…”

Sediments in urban river basins: a review of sediment–contaminant dynamics in an environmental system conditioned by human activities

“…Within contaminated sediments, metals commonly co-precipitate with Fe and Mn oxides. The chemical reduction of these oxides results in the release of these adsorbed contaminants to sediment porewaters (Dodd et al 2003;Taylor et al 2003) and thence to overlying water. The build-up of chemical species in sediment porewaters also leads to the precipitation of authigenic minerals in the sediment.…”

Mixing and Transport

“…It was shown that resuspension, through relations between particle flux and hydrodynamics, can be either the fact of dynamics of the introduction system or that of the chalk karstic aquifer.Bravo-Espinosa et al (2003) evaluated conditions of bedload transport using hydraulic, sediment, land-use, and rock-erosivity data of 22 alluvial streams. The study also looked at the performance of selected bedloadtransport equations Taylor et al (2003). examined the nature of sediment, porewaters and diagenesis in a highly polluted urban water body, the Salford Quays, UK, and the impacts of remediation.…”