Environmental Engineering Reference
In-Depth Information
to coarse particulate organic matter (CPOM) (Watanabe et al.
2008
), potentially
constituting a risk to shredders. Particulate matter has also been found to be an
important source of metals in Hydropsyche exocellata (Barata et al.
2005
).
In terms of biomagnification within the food web, studies have been limited
and those that have been reviewed have shown that there is no evidence
for magnification of the metals Zn and Cu between feeding guilds, although
there may be some potential for magnification of Pb in certain circumstances
(Goodyear & McNeill
1999
).
The uptake of high concentrations of metals by macroinvertebrates is likely
to result in direct toxicity, and therefore some groups may be preferentially
removed in impacted streams. For example, collector-browsers and collector-
filterers showed a significant reduction in response to elevated levels of Cu and
Zn (Hickey & Golding
2002
). Survivorship of juvenile amphipods was also found
to be significantly reduced when fed on copper contaminated diets, and
reduced feeding was also observed in adults (Roberts et al.
2006
). In contrast,
some authors have suggested that there is no specific evidence for toxicity even
where metals are accumulated within invertebrates (Borgmann et al.
2007
). This
is because heavy metals can be stored in organisms as non-toxic species or
bound to metallothionein (Gerhardt
1993
). De Schamplherlaere et al. (
2004
)
demonstrated that, although dietary copper was effectively taken up by
Daphnia magna, this caused an increase in reproduction and growth which
was considered to be due to the storage of Cu in a non-toxic form.
The pathways by which metals are taken up by aquatic organisms within
metal-polluted environments, therefore, remain rather unclear with contra-
dictory evidence and, therefore, require further investigation. It is likely that
the mixture of metals present, the acidity of the environment and the presence
of precipitate material all influence the relative importance of metal sources
within the environment on uptake into organisms.
Ecosystem function
As illustrated in previous sections some major groups are more affected by
metals and acidity than others. This has the potential to change the structure
of the community and has been reported in response to Mn and Zn (Nelson
2000
); Al, Mn and Fe (Doi et al.
2007
); and acidification (Gu´rold et al.
2000
).
Although direct toxicity has been demonstrated, indirect effects on community
structure may also be caused by metals and acidity. Communities and food
webs within acidified streams tend to be structurally simpler due to the
absence of herbivores, which is thought to be caused by the absence of algae
as a food source due to acidity or associated metal toxicity rather than direct
toxicity to the invertebrates (Morris et al.
1989
; Nelson
2000
; Sasaki et al.
2005
).
Ledger and Hildrew (
2000
a) reported the absence of specialist herbivorous
species in conditions of low pH and high metal concentrations.
