The impacts of metalliferous drainage on aquatic communities in streams and rivers - Ecology of Industrial Pollution - page 88

legislation. This has been largely successful in terms of point sources, although
diffuse sources and the residual sediment pollution remain a major challenge.
There have been a number of studies into the recovery of riverine systems
following disturbance from channel modification, flooding, drought, acidifica-
tion and contamination with pesticides (see Milner 1994 ; Ormerod & Durance
2009 ). However, studies into recovery following pollution by metals and organ-
ics is less common, possibly due to the difficulty in addressing the diffuse
sources of these pollutants. However, over recent years, there have been some
efforts to remove point sources of metals, particularly where mining activities
have ceased and/or remediation strategies applied. For example, within the UK,
constructed wetlands have been used to remove metals (mostly iron) from coal
mine effluent in a number of sites (Coal Authority 2009 ) . The removal of point
sources of metals may lead to the recovery of stream communities, and there
has been some attempt to quantify rates and success of this recovery.
It is often difficult to assess recovery, due to an absence of information on the
required endpoint. This is particularly true for mining effluents where the
pollution may have been affecting the stream community for many hundreds
or thousands of years (Runnells et al. 1992 ). In this case, it is clearly impossible
to choose an endpoint that is the original community due to a lack of data.
Alternatively, a reference site may be chosen where the community can be used
as a model for the recovering community (Milner 1994 ); however, unexploited
areas that are geologically similar to mined regions are extremely rare, and
therefore, the endpoint may not be an accurate reflection of the true 'natural'
community. Recovery in urbanised areas is often even more of a challenge to
assess quantitatively, largely due to the presence of multiple sources of pollu-
tants. Langford et al. ( Chapter 13 ) provide details of the recovery of an urbanised
catchment. Function and production endpoints have also been suggested
as possible aims for remediation activities (Milner 1994 ), but in most examples
within the literature, it is a simple measure of density and/or species richness
which is used to assess recovery following remediation of metalliferous
discharges.
A study in the coal fields of southwest Virginia showed that following
remediation action total taxa richness showed consistent improvement over
time corresponding to an increase in pH from 4.70 to 6.97 and a decrease in Al
concentration (Simon et al. 2006 ). This response was also recorded following the
closure of metal mines in China (Watanabe et al. 2000 ) and Idaho, USA (Holland
et al. 1994 ). However, in none of these examples was recovery found to be
complete. More specifically Ephemeroptera did not recover, most likely due
to the longer amount of time taken for recolonisation of this group (Simon et al.
2006 ), but even when recovery is monitored over a long period of time,
complete recovery is not achieved. This may be due to a lack of suitable habitat
(Holland et al. 1994 ; Armitage et al. 2007 ), continued input of contaminants