Environmental Engineering Reference
In-Depth Information
drainage water from disused tin and copper mines and are grossly contamin-
ated as a result. The highest sediment metal concentrations occur in the upper
reaches of Restronguet Creek, with total Cu often in excess of 3000 m gg 1 and
total Zn as high as 4500 m gg 1 (personal observation). Metal concentrations
are lower in the sandier sediments of the Hayle estuary (450 850 m gg 1 Cu,
450 2500 m gg 1 Zn), but metals are more readily bioavailable there. Pore water
Cu concentrations in Hayle sediments are regularly in excess of 500 m gL 1 , and
we have measured concentrations of up to 3400 m gL 1 Cu (in comparison with
a maximum of 65 m gL 1 Cu in Restronguet Creek sediments and a UK EQS for
marine waters of only 5 m gL 1 ). The most marked ecological effects can be
attributed to copper contamination. Populations of several invertebrates from
these estuaries can only survive there because they have evolved enhanced
copper tolerance (Grant et al. 1989 ). Individuals of the common estuarine
polychaete Nereis diversicolor from the Hayle and upper Restronguet Creek are
able to tolerate Cu concentrations that are five times higher than those that
can be tolerated by animals from clean estuaries. Nematode communities from
both estuaries show a similar increase in Cu tolerance while microbial com-
munities from the most contaminated parts of the Hayle are 2000 times less
sensitive to Cu than those from uncontaminated sites (Millward & Grant 1995 ,
2000 ; Ogilvie & Grant 2008 ).
Work on the nematode communities in the Fal is consistent with the con-
ceptual picture described above. Nematode diversity is significantly reduced
only in the most contaminated tributary, Restronguet Creek, but community
composition is altered in other less contaminated tributaries in a pattern that
correlates with severity of contamination (Somerfield et al. 1994 ). These data
suggest that there is an alteration of the nematode communities in all tribu-
taries accept for Percuil River. The nematode communities in tributaries other
than Percuil River also show increased tolerance to copper, indicating that the
changes in community composition reflect a replacement of sensitive species
by more tolerant species (Millward & Grant 2000 ), and providing strong evi-
dence that there is an effect of pollution on these nematode communities.
Meiofaunal copepods appear to be less sensitive than the nematodes, and
changes in copepod communities can only be found in Restronguet Creek
(Somerfield et al. 1994 ).
In contrast, the microbial communities in these estuaries provide an
extreme example of how community response to environmental heterogeneity
can mask the effects of a pollutant. There is no relationship between bacterial
community composition, as quantified using T-restriction fragment length
polymorphism (T-RFLP) analysis on bacterial 16S rDNA, and the extent of metal
contamination, despite the fact that sediment metal concentrations vary by a
factor of 20, and pore water metal concentrations by three orders of magnitude
(Ogilvie & Grant 2008 ; Fig. 7.3 ). The data presented in Fig. 7.3 are for two
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