Environmental Engineering Reference
In-Depth Information
100
80
60
40
20
0
1985
1990
1995
Year
2000
2005
Figure 16.3.
Change in BMWP score along the River Don, Sheffield between 1985 and
2005. Moving northwest of Sheffield downstream to the Lower Don Valley, the four sites
are at Oughtibridge (black circle), Hillsborough (grey circle), Corporation Street (white
circle), Weedon Street (cross).
programme of fish stocking in the River Don since 1975. In the 1990s, although
there was a healthy brown trout population in the upper reaches of the Don,
further downstream, fish abundance and diversity were still impoverished,
with limited numbers of roach, gudgeon, dace, perch, brown trout and gray-
ling being sampled during fish surveys (Amisah & Cowx
2000b
).
The improvement in water quality observed in the River Don has been
mirrored in other industrial areas including Liverpool, Manchester, Leeds,
Newcastle and the Midlands (see
Chapter 13
). Further improvements in water
quality are expected as a result of the implementation of the EU Water Frame-
work Directive (WFD). The WFD is an important piece of environmental legisla-
tion that has the aim of achieving 'good ecological status' for surface waters by
2015. However, this aspiration raises some interesting issues about what we
consider to be an improvement in quality and how these judgements can be
made. While it would be hard to argue that changes in Sheffield's rivers from
lifeless, or virtually so, to their present state is not an improvement, what
would constitute further improvements and are these realistic and desirable?
Reference conditions and environmental management
The WFD defines ecological status in terms of derivations from 'undisturbed
conditions' and, hence, requires the identification of reference states to which
the current state can be compared. Reference condition for the WFD has been
defined as 'a state in the present or in the past corresponding to very low pressure,
without the effects of major industrialisation, urbanisation and intensification
of agriculture, and with only very minor modification of physico-chemistry,
hydromorphology and biology' (UKTAG
2007
). The question is, does such a state
