Environmental Engineering Reference
In-Depth Information
However, a change in community structure does not necessarily have an
impact upon function within the community. When we refer to function, we
are referring to the way in which an ecosystem can contribute to fundamental
processes within the landscape and may include functions such as oxygen
consumption, and production, carbon mineralisation, organic matter produc-
tion and sedimentation. One of the most common methods of assessing
impacts of pollutants on ecosystem function is through the measurement of
leaf litter processing as this can be used to monitor the effects of changes in
bacterial, fungal and invertebrate communities. To the authors' knowledge,
this is the only ecological function that has been directly assessed in rivers
receiving metalliferous discharges to date.
It is widely reported that leaf litter decomposition is reduced in waters
impacted by metals and acidity (e.g., Giesy
1978
; Carpenter et al.
1983
; Burton
et al.
1985
; Leland & Carter
1985
; Maltby & Booth
1991
; Carlisle & Clements
2005
; Batty & Younger
2007
; Auladell
2009
). The causes of this remain unclear,
although some authors suggest that the functionally dominant taxa was the
most sensitive to contamination (Carlisle & Clements
2005
) or that lethal and
sub-lethal effects affected both fungal and/or invertebrate assemblages respon-
sible for processing of leaf material (Newman et al.
1987
; Cheng et al.
1993
;
Maltby et al.
1995
). This has been directly linked to the abiotic environment
(metal and nutrient concentrations, pH and conductivity) (Woodcock & Huryn
2005
). However, other studies have shown that, although community structure
is affected by the presence of metals in impacted rivers, no corresponding
reduction in leaf litter processing was reported (Nelson
2000
). This is thought
to be due to redundancy within the system where metal-sensitive shredder
species are replaced by tolerant equivalents that perform the same function
(Schindler
1987
; Nelson
2000
; Woodcock & Huryn
2005
). In freshwaters, a
number of organisms are involved in plant litter decomposition including
tubificid worms, chironomid larvae, isopods and amphipods (Mason
1976
),
and therefore, it appears that there is potential significant capacity for redun-
dancy in the system. This has also been demonstrated in acidic streams for
organisms involved in utilising biofilm and loose (FPOM) resources where acid-
tolerant species demonstrate generalist feeding patterns maintaining the link
between invertebrates and algae through the presence of shredder detritivores
(Ledger & Hildrew
2000a
,
b
,
2005
). Therefore, ecosystem function appears to be
maintained in some cases, even in polluted conditions. However, further
research is required to determine the effects on other functions within the
ecosystem, and the limitations of redundancy.
Importance of sediments
Most studies of metal pollution have examined the response to waterborne
pollutants. This has led to a predominance of water quality legislation such as
