Geoscience Reference
In-Depth Information
Atmospheric
input
Construction
material
Building
wear
Exhaust
emissions
Vegetation
Pedestrian
debris
Soil material
Fig. 6.3
Schematic diagram of the
sources of sediment comprising
road-deposited sediments.
Road wear
Tyre wear
Vehicle wear
6.2
SEDIMENT SOURCES AND SEDIMENT TRANSPORT
PROCESSES
of sources, and partly due to the heterogeneous
nature of most RDS deposits. Volumetrically, the
most important component of RDS comes from
soils and building material. Soil material, which
may be derived from a range of distances, con-
tributes both minerogenic and organic material.
For example, a study by Hopke et al. (1980)
recognized that soil material formed approxim-
ately 75% of RDS. Building material contributes
quartz sand, concrete and cement to RDS, and
these are believed to be relatively inert. In urban
areas undergoing extensive development, how-
ever, the volume of building material input to
RDS can be large, and may have important con-
sequences for air quality, sediment volumes and
particulate-associated contaminants discharged
into drainage systems and rivers.
Iron oxides are abundant in RDS and as a
result mineral magnetic analysis has been applied
to study source apportionment in these sediments.
Mineral magnetic analysis can discriminate
soil-derived iron oxide particulates from those
derived from fossil-fuel combustion (Oldfield
et al. 1985), and as such has great potential in
urban sediment sourcing. Application of mineral
magnetic analysis has shown the importance
of non-soil derived material in RDS, including
vehicle and industrial combustion, construction
material and asphalt abrasion (e.g. Beckwith et al.
1986; Xie et al. 1999; Lecoanet et al. 2003). In a
study of RDS in Manchester, UK, Robertson et al.
(2003) concluded that vehicular sources were the
primary contributor to iron oxide material (see
Case Study 6.1). Although the application of
mineral magnetic analysis has helped to identify
6.2.1 Sediment and contaminant sources
Sediments within urban environments originate
from a wide range of sources, both natural and
anthropogenic. In this chapter sediment sources
to subaerial environments (road-deposited sedi-
ments) and subaqueous environments (rivers,
canals/docks and lakes) will be considered
separately. Although both environments receive
a broadly similar range of source material,
the differences in the physical and chemical
characteristics between the environments lead
to contrasting intrinsic and extrinsic sources
dominating.
6.2.1.1 Road-deposited sediment
Compared with sediment in natural environ-
ments, road-deposited sediment (RDS) has a wide,
and diverse, range of sources (Fig. 6.3). Sources
are either intrinsic to the road surface, which
are predominantly anthropogenic in nature, or
extrinsic, which are predominantly naturally
derived. Intrinsic sources include vehicle exhaust
emissions, vehicle tyre and body wear, brake-
lining material, building and construction mater-
ial, road salt, road paint and pedestrian debris.
Extrinsic sources are soil material, plant and
leaf litter, and atmospheric deposition.
There are very few studies that have attempted
to quantify the importance of these sources to
RDS, partly as a consequence of the wide range
