Environmental Engineering Reference
In-Depth Information
from diffuse sources (Holland et al. 1994 ; Prat et al. 1999 ; Simon et al. 2006 )or
insufficient remediation of the pollutants (Watanabe et al. 2000 ). It is, therefore,
evident that the success and the rate of recovery will depend on a number of
factors such as the type of disturbance, the duration, habitat conditions and
availability and the location of potential colonisers as previously reported
(Williams & Hynes 1977 ; Niemi et al. 1990 ; Robinson et al. 1990 ; Wallace et al.
1991 ). A source of organisms is absolutely vital to recovery. Battaglia et al.
( 2005 ) noted that the lack of colonisation of clean sediment was due to an
absence of colonising organisms. The community structure that does result
will depend upon the clean communities that act as a source (Beltman et al.
1999 ). It is not as simple as this, however, as macroinvertebrates also require
suitable biotic habitats such as macrophytes and algae as well as clean
sediments (Laasonen et al. 1998 ).
Although previously it has been suggested that, in terms of recovery, the
amount of time will be longer after physical disturbance than chemical dis-
turbance (Smith 2003 ), it is clear that the time involved may be significant due
to the difficulty in remediating all diffuse sources of metals within any given
catchment. In addition, in order for recovery to be successful, the source of
contamination must be completely removed as even short periods of contamin-
ation such as low pH can significantly affect the success of recovery (Bradley &
Ormerod 2002 ; Felten & GuĀ“rold 2006 ). Even where sites have been remediated,
pollutants that remain in sediments or floodplains can still affect the river
course (Hutchinson & Rothwell 2008 )
(see the section on Importance of
sediments).
Conclusions
Historically, metalliferous discharges to the aquatic environment have had
significant impacts upon the associated communities, and although there have
been advances in the treatment and prevention of these contaminant sources,
diffuse pollution and new metal contaminants still pose a significant threat to
the environment. It is clear that metals do directly and indirectly affect organ-
isms within the environment, but where this is mixed with acidity, it is
difficult to separate out their specific effects. Recent advances in biochemical
analyses provide an opportunity to elucidate the specific stress responses in
both flora and fauna to individual and mixed pollutants which may aid in
prioritising treatment of specific compounds or discharges.
The impact of metals on organisms within the aquatic environment has
focused upon either specific organisms or communities; however, it is clear
that ecosystem function is a potentially important consideration when assess-
ing the impacts of pollutants. Ecosystem function response to metals has only
been assessed in any detail in terms of organic matter decomposition, where a
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