Urban aquatic sediments - Sedimentology of Aqueous Systems - page 137

areas that can be related back to the historical pattern
of urbanization and industrialization leading to the
development of industrial estates and traffi c-free pre-
cinct areas. Secondly, the trend in frequency distribu-
tion also refl ects the many geochemical and physical
changes that occur during transport of urban sedi-
ments. These are a function of a great many processes
not only unique to urban areas in general, but pos-
sibly unique to particular urban centers. The data
collected from urban areas may therefore be site- or
ecosystem specifi c (Jennett et al. 1980), and even
event specifi c, where runoff produced from separate
storms from the same outfall varies according to
prevailing conditions related to phase of construc-
tion, traffi c movements, industrial discharges, etc.
(Morrison et al . 1984). Charlesworth & Lees' (1999)
attempt to simplify sediment transport in the urban
environment into a source-transport-deposit cascade
highlighted the diffi culty of such an approach; the
urban environment is a dynamic system in which
sediments accumulating for example in gully pots, or
the bed of a river, can become remobilized during
storms and become sources of contamination them-
selves (Deletic et al . 2000) and be transported to the
next environmental compartment dependant on pre-
vailing environmental conditions.
It is not only the sediment characteristics that can
be unique to the specifi c urban centre, but this sedi-
ment will support an ecosystem that may well refl ect
site specifi city. After traffi c as a major source of sedi-
ment, construction activity in the catchment will
provide regular pulses of particulate material. Studies
have shown that the high concentration of calcium
found in some lakes may be due to construction
activities. This kind of impact can cause an ecologi-
cal imbalance, such as, for example, the generation
of a large population of mollusks due to the increased
availability of calcium, which is used in constructing
a shell (Beasley & Kneale 2002). Thus sediments can
infl uence the development of macroinvertebrates at
the bottom of the food chain, which can lead to the
modifi cation of ecosystems. Such environmental
changes initiate qualitative modifi cations in the bio-
diversity of local species (Pompeu et al. 2005), which,
according to Wolman & Schick (1967), are refl ected
in all aquatic organisms. These impacts are refl ected
in changes at the cellular level. For example, Ono
et al. (2000) found positive correlations between
sediments generated by construction activity and

genotoxicity (damage caused to DNA) in urban
areas.
Thus, to mitigate the adverse impacts of stormwa-
ter pollution, it is essential to have appropriate man-
agement strategies and effi cient treatment designs
(Egodawatta & Goonetilleke 2007). The identifi ca-
tion of the origins of urban sediments allows an
understanding of the processes of their transference
to the river channel (Walling et al . 2002; Walling
2005) which is fundamental to developing these
strategies (Taylor 2007; Owens et al. 2001) and a
holistic approach to these problems is therefore
needed. However, urban catchments are rarely
“joined up”, with many having been artifi cially cut
off from their catchments historically (Charlesworth
& Foster 1993), and many studies have historically
broken down the urban aquatic environment into
“road reaches” (Hamilton et al . 1984; Harrison
et al . 1985), individual roofs (Quek & Forster 1993;
Thomas & Greene 1993), and gullypot catchments
(Morrison et al . 1989). The following sections there-
fore concentrate on methods by which sediment
source tracing and apportionment may be investi-
gated, the results of which can be used to inform
strategies to manage their impacts in urban environ-
ments. This is not an easy task in urban areas
(Charlesworth et al . 2000), and some of the tech-
niques developed for pristine or simpler catchments
do not transfer well to such multi-impacted
catchments.

5.5.2 Sediment source tracing in urban
areas

Source identifi cation would enable accurate evalua-
tion of the potential for pollution, which in turn
could be used to deduce the impacts and fi nally make
possible the selection of an appropriate means of
control for sources that are actively producing sedi-
ments (Porto 1995). However, there are few studies
of the urban environment in which it is possible to
trace the movement of sediment and its associated
contaminants from source to deposit in a complete
catchment (Charlesworth & Lees 1999, 2001;
Charlesworth et al . 2000; Carter et al . 2003). Add
to these diffi culties the multiplicity of sources and
the many biogeochemical reactions that change the
chemistry of the sediment, and few studies have
found a chemical or physical characteristic that