Geoscience Reference
In-Depth Information
Table 3.2 Types and sources of natural and anthropogenic inputs to fluvial sediments.
Category
Sources
Bedrock, soil, vegetation
Physical weathering through natural erosion, forest fires, tectonic
uplift, deforestation, agriculture, mining, damming and other
engineering work, urbanization
Natural sources, industry, mining and processing, acid mine
drainage, sewage treatment, agriculture, vehicle emissions and
road runoff, coal combustion, atmospheric fallout
Natural sources, mining and processing, industry, acid mine
drainage, acid deposition, agriculture
Agricultural and urban land runoff (fertilizers), wastewater from
sewage treatment
Agriculture, industrial processes that produce dioxins, sewage,
landfills
Nuclear power industry, military, natural sources
Metallic and metalloid elements (Sb, As, Cd,
Cu, Co, Cr, Pb, Hg, Ag, Tl, Sn, Zn)
Inorganic compounds (SO 4 , PO 4 )
Nutrients (C, N, P)
Organic compounds (pesticides, herbicides,
petroleum hydrocarbons, viruses, bacteria)
Radionuclides ( 137 Cs, 129 I, 239 Pu, 230 Th)
Sediment-bound contaminants enter river
systems either from point (e.g. tailings effluent
and other mine discharges, sewage discharges,
spillages) or diffuse sources (e.g. remobilization
of contaminated alluvium, agricultural runoff )
(Macklin 1996; Walker et al. 1999). Point sources
either operate only once (e.g. the Aznacóllar mine
tailings dam failure in south-west Spain, April
1998) or repeatedly (e.g. sewage discharges;
regular tailings effluent discharge into the Río
Pilcomayo, Bolivia; Hudson-Edwards et al. 2001).
Although diffuse contaminants enter rivers con-
tinuously, growing evidence suggests that they
are mainly mobilized during storm events. For
example, Kratzer (1999) suggested that runoff
from infrequent winter storms would continue to
deliver significant quantities of sediment-bound
organochlorine pesticides to the San Joaquin
River, California, even if irrigation-induced sedi-
ment transport was reduced. Muller & Wessels
(1999) showed that approximately one-third of
the annual inputs of total organic C, N, Cu, Pb
and Zn to the River Odra, Poland, were released
into the river during a major flood in 1997.
transfer and storage. Although it is possible to
directly determine fluvial sediment provenance,
indirect methods have been favoured in recent
decades (cf. Peart & Walling 1986). One of the
main types of indirect approaches is that of
sediment source 'fingerprinting', which has been
used to great effect in studies of suspended and
alluvial sediment provenance, over a wide range
of time-scales ranging from the event-level to
recent historic and Holocene. Owens et al. (2000),
for example, traced contemporary sources of
alluvium in the Rivers Tweed, Teviot and Ettrick,
UK, using composite fingerprints (metallic ele-
ment geochemistry, radionuclides, organic C,
N and P) and a numerical mixing model, and
showed that most of the sediment was derived
from pasture/moorland topsoil and channel bank
erosion (Fig. 3.6b). By contrast, Passmore &
Macklin (1994) demonstrated that pre-eighteenth
century alluviation in the River Tyne, UK, was
related to deforestation and agricultural develop-
ment during late prehistoric times. Walling et al.
(2002) used 137 Cs measurements and sediment
source fingerprinting to develop sediment budgets
that showed sediment tile drains to transfer
between 30 and 60% of sediment from two low-
land, agricultural basins in the UK.
The scientific basis of sediment fingerprinting
is that the properties of the fluvial sediment are
compared with the same properties of all poten-
tial source materials (e.g. Walling et al. 1979).
'Tracers', which exhibit conservative behaviour
3.2.1.2 Sediment provenance and source material
fingerprints
Analysis of fluvial sediment provenance can yield
important information on the types of sources
(e.g. topsoil or channel bank materials), relative
source contributions, and on patterns of erosion,
 
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