Geoscience Reference
In-Depth Information
in twentieth century river regulation projects
may not be felt for at least another 100 years
because river adjustment is a long-term processes
(cf. Petts 1984).
Although mining in many areas of the world
is now regulated and under strict environmental
legislation, there are still areas where mining
continues to have an impact on sediment and
sediment-borne contaminant supplies to rivers.
An example of this is the Ok Tedi/Fly River in
Papua New Guinea, which, according to 1997
figures, received approximately 66 Mt of mining
waste per year from the Ok Tedi Cu-Au mine,
causing increases in the Cu- and other metal-
bearing suspended sediment load by up to five
to ten times natural background (Hettler et al.
1997). This is compounded by the steep relief in
the area, which is linked to avalanches and land-
slides in the mining area (Hearn 1995). In other
areas, it is not the mining itself, but related
activities that threaten river systems. The 1998
Aznalcóllar tailings dam spill in southwest
Spain (Grimalt et al. 1999) and the 2000 Baie
Mare tailings dam spills in Romania (Macklin
et al. 2003), which released 2
3.6.3 Other impacts
The storage of contaminated sediments in flood-
plains has been flagged as a potential serious long-
term problem and, indeed, has been described as
a 'chemical time bomb' (a concept defined by
Stigliani 1991) by many workers in river systems
(Stigliani 1991; Lacerda & Salamons 1992).
Although considerable effort is being put into
understanding the fate of sediment-bound con-
taminants (Hudson-Edwards et al. 1998, 2003),
the interplay between their physical (river bank
and bed erosion, land drainage and development),
geochemical (changes in nutrient loading, redox
and pH) and biological remobilization (plant
uptake and microbial degradation) is poorly
understood (Macklin 1996). Moreover, Macklin
(1996) warned that physical remobilization of
these contaminants is currently increasing owing
to global warming. Sediment alone has also been
flagged by many government environmental
bodies as a significant threat to river systems in
terms of its weight and volume. This has been
shown in this chapter, where processes such
as increased alluviation in regulated rivers can
have large secondary effects.
Finally, the present rapid rate of urbanization,
particularly in the tropics (Gupta & Ahmad
1999), means that rivers are, and will continue
to be, put under pressure for their resources
and hazard management (cf. Knighton 1998).
This requires more effective management that
integrates good fluvial geomorphological and
engineering practice.
10
6
m
3
and
40,000 t, respectively, of metal-, arsenic- and
cyanide-rich tailings downstream, are notable
examples of this. Events such as these overwhelm
the natural sediment load of river systems, and
cause immediate and long-term threats to the
health of ecosystems and humans. Until safer
alternatives are found for the storage of mine
waste, events such as these will probably con-
tinue to occur regularly (Macklin et al. 2003).
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