Environmental Engineering Reference
In-Depth Information
observation). Warwick included the least contaminated tributary of the
Fal, Percuil River, in this comparison. Sediments here still contain around
200
m
gg
1
Cu, which is about an order of magnitude higher than background
concentrations. So it is possible that macrofauna in all the tributaries of the Fal
estuary, including Percuil River, are adversely affected by metal pollution. If so,
the difference in macrofauna between the Fal and other muddy estuaries in
South West Britain could be a consequence of metal contamination. However,
the low diversity of macrofauna and the limited number of uncontaminated
control sites limits the extent to which these conclusions can be drawn, and it
is entirely possible that the differences reflect other environmental character-
istics, as the sediments in the Fal system are rather finer grained than other
estuaries in South West Britain. In the case of nematode communities, we do
have evidence that there is no alteration in community composition in Percuil
River, as community composition in the Helford River is very similar (Millward
1995
). So the conclusion from all these studies is that there are probably effects
of metal contamination on the fauna of the Hayle and most of the Fal system.
But these effects are only apparent on some components of the biota. Multi-
variate statistical analyses detect changes in nematode composition in moder-
ately contaminated sites, but this is only possible because environmental
conditions are sufficiently homogeneous. For bacteria, ecological monitoring
methods fail to detect impacts that are clearly demonstrated by the enhanced
metal tolerance of the same microbial communities.
Have we reached the methodological limits of detecting effects
of pollution in the field?
There were considerable successes in the development and validation of multi-
variate statistical methods to detect ecological change in the 1980s and early
1990s (see Warwick & Clarke
1991
; Clarke & Warwick
2001b
). However, since
then, there seems to have been only limited progress in the development of
ecological monitoring methods in the marine environment. This limited pro-
gress appears to result from the difficulty of controlling for nuisance variables
other than the severity of pollution rather than any intrinsic limitation of the
statistical methods. Unless some novel solutions can be identified to deal with
this limit, it may be that we cannot progress further. Methods such as the
extent of taxonomic distinctiveness (Clarke & Warwick
2001a
) show some signs
of an association with pollution effects, but the association has not proved to
be strong enough for these methods to have entered into widespread use as
monitoring tools (Warwick et al.
2002
). Freshwater faunas are rather species
poor and in rivers water velocity is the strongest control on which species
occur. It has therefore proved possible to identify pollution-sensitive and pollu-
tion-tolerant taxa and construct indices such as the BMWP (or NWC) score
(National Water Council
1981
).
It has also been possible to predict the
