Environmental Engineering Reference
In-Depth Information
CHAPTER FOUR
The impacts of metalliferous drainage
on aquatic communities
in streams and rivers
LESLEY C. BATTY, MONTSERRAT AULADELL
AND JON SADLER
Introduction
Metals are naturally occurring elements of the Earth's crust that can be released
into the aquatic environment through the processes of weathering and erosion,
where they are present in trace amounts and do not normally constitute an
environmental problem. However, the activity of humans has increased the
release ofmanymetals to the environment. It is difficult to assess what the natural
background levels would have been in affected areas, particularly where the
influence has been prolonged, but it has been reported that in mining areas
concentrations of metals in waters and associated sediments can be 3 4 orders
of magnitude higher following mineral ore extraction (Runnells et al.
1992
;
Helgen & Moore
1996
). Although some of the metals released by human activities,
such as Fe and Zn, are essential elements for the successful growth and functioning
of biota, the presence of these substances in elevated concentrations or in other
chemical forms can be potentially toxic. In addition, many metals, such as Pb and
Cd, have no known role in biological functioning and can be toxic to organisms at
very low concentrations. Therefore, the release of metals into the environment
poses a significant threat to the fauna and flora of receiving water courses.
The release of metals to the environment has a strong historical dimension
and can be traced back many hundreds, if not thousands, of years; the extrac-
tion of metal ores, for example, is reported to date back to the Bronze Age in the
UK (e.g., Ixer & Budd
1998
), and evidence of environmental impacts is found to
occur as far back as pre-Roman times (Rothwell
2007
). However, it was not until
the major increase in industrial activity in the form of mining, smelting, and
processing of ores and coal within the eighteenth and nineteenth centuries
that significant environmental and human health impacts were noted (Goudie
1993
). The metals were either released directly into the river systems through
surface runoff (including spoil heap discharge) and direct drainage from adits
