Environmental Engineering Reference
In-Depth Information
deleterious effect is still subject to debate. An extreme position would be that
any alteration of species composition from a 'natural' state is undesirable. But
other assessors will wish to take into account some measure of the relative
desirability of the species being lost and gained. On land and in freshwater, we
have sufficient information about the distribution and abundance of individ-
ual species to be able to set conservation priorities, and could use these to judge
what constituted a deleterious change. In the marine environment, we cannot
yet do this, although there would probably be agreement that the presence of
known opportunistic species is a deleterious effect (implicit in the biological
index used by Ugland et al.
2008
) and some progress is being made in classifying
substantial numbers of marine species according to their sensitivity to disturb-
ance (Borja et al.
2004
; Borja & Muxika
2005
). In a study of temporal changes in
the benthos of the Tees estuary, Warwick et al. (
2002
) interpret a reduction in
taxonomic diversity as a 'detrimental' change, despite the fact that it was
accompanied by an increase in Shannon diversity. In terms of the underlying
species changes, the increase in Shannon diversity was caused by a reduction in
the abundance of some common species, particularly the polychaete Spiophanes
bombyx, whereas the reduction in taxonomic distinctiveness was visible only in
the presence/absence data so reflects a reduction in phylogenetic diversity in
the rarer species. By some criteria, the changes caused by pollution might be
viewed as desirable changes. Some studies of atmospheric deposition have
found higher diversity at 'polluted' sites. Mechanisms that may lead to this
include direct effects of particulate deposition adding nutrients and/or raising
the pH of acidic or nutrient poor soils (Brandle et al.
2001
) and indirect effects
whereby negative effects on vegetation lead to a change in leaf litter quality
(Fenn & Dunn
1989
). Even where there is a reduction in diversity, severe metal
contamination may produce communities dominated by species or ecotypes
that do not occur elsewhere. Microbial communities in freshwater affected by
acid mine drainage such as the Rio Tinto in Spain and Iron Mountain in
California are intriguing, supporting populations of metal- and acid-tolerant
extremophiles, although in the case of the Rio Tinto may pre-date mining
activity (Bond et al.
2000
; Edwards et al.
2000
; Gonzalez-Toril et al.
2003
; Baker
et al.
2004
). Anthropogenic contamination that allows the persistence of
metal-tolerant higher plants such as the calamine violet Viola calaminaria
(Bizoux & Mahy
2007
) could be viewed as a beneficial conservation measure
(see
Chapter 2
).
However, species with wider environmental tolerances are likely to be more
widespread than those with narrower tolerances. So changes in community
composition due to pollution may well represent reductions in rare species,
and their replacement by more common species. So if we are concerned to
protect aquatic biodiversity, we should seek to avoid levels of pollution that
produce even these relatively subtle changes.
