Geoscience Reference
In-Depth Information
Whiteley & Murray 2003). Future monitoring
programmes on RDS composition are likely to
further reinforce these temporal trends.
Urban lakes are a promising source of urban
sedimentation records. Charlesworth & Foster
(1999) showed that good records of urban
sediment supply and composition were pre-
served in two small urban lakes in Coventry,
UK. Sedimentation rates in these lakes had
changed in response to very localized catchment
processes, but both clearly showed an increase
in metal accumulation after the mid-1950s. It
was also observed that Pb inputs had decreased
over time owing to the decrease in use of leaded
petrol.
Sediments from urban canals and docks have
also been shown to preserve a good record of
localized changes in pollution and remediation.
Generally, urban canals are too shallow (
and too frequently disturbed to allow a con-
tinuous sediment record to build up. In larger
canals and docks, however, where water depths
may exceed 5 m, in the absence of dredging such
records can be preserved. One such example is
from the Salford Quays in the UK where Taylor
et al. (2003) documented the clear preservation
of pre- and post-remediation sediments and
associated contaminant levels (Case Study 6.3).
In more general terms many studies have shown
that surface sediments in urban canals con-
tain lower levels of contaminants than deeper
sediments, indicating a decrease in contaminant
input into urban sediment in recent times (e.g.
Kelderman et al. 2000; Bellucci et al. 2002;
Taylor et al. 2003). This is generally put down
to the environmental legislation reducing dis-
charge and the cleaning up of the urban drainage
and sewerage system.
<
2 m),
Case study 6.3 Sedimentation in an urban water body: Salford Quays, UK
Docks and canals commonly form the terminal receiving water bodies for urban surface runoff,
and as such act as significant sites of sediment accumulation and storage. These sediments can
contain significant levels of past and present contamination and so any physical or chemical
perturbations of the sediment can lead to the release of these contaminants back into the urban
environment. The Manchester Ship Canal (MSC) was built in 1895 to allow for direct shipping
access to the City of Manchester Docks at the eastern end of the Ship Canal (Case Fig. 6.3a).
At its eastern end the MSC begins at the confluence of three rivers (Irwell, Medlock and Irk)
N
SALFORD
Salford
Quays
Manchester
Ship Canal
Case Fig. 6.3(a)
Map showing the
location of the Salford Quays, Greater
Manchester, UK (from Taylor et al.
2003).
OLD TRAFFORD
m
500
0
