Environmental Engineering Reference
In-Depth Information
occur in the present UK landscape and if not, how far into the past should we go,
and do we have the appropriate data on past environments?
Two concepts frequently discussed when considering the quality of ecosys-
tems are biological integrity and ecosystem health. Biological integrity in an
ecosystem has been defined as 'the capability of supporting and maintaining a
balanced, integrated, adaptive community of organisms having species com-
position, diversity, and functional organization comparable to that of natural
habitats of the region' (Karr & Dudley
1981
). Common definitions of 'natural'
are, in essence, either being without human influence or without human
technology (Hunter
1996
; Angermeier
2000
). The terms 'balanced, integrative
and adaptive' are not further specified in the definition and without further
clarification cannot provide consistently applicable criteria for assessing eco-
system state. This leaves the concept resting mainly on naturalness. The
principle of biological integrity indices is to select and integrate indicators of
the structure and functioning of ecosystems (e.g., species richness, tolerant
taxa, trophic structure, individual health of organisms) that can detect diver-
gence from natural reference conditions attributable to human activities (Karr
& Chu
2000
). Consequently, high biological integrity is an attribute of ecosys-
tems unaffected by humans, and it provides a benchmark by which to measure
the extent of human impacts on ecosystems (Angermeier
2000
). Because integ-
rity is determined relative to a regionally defined natural reference state, it
implies an existing or historical target.
It can be very difficult to characterise the conditions of an ecosystem without
human influence or technology, given the long history and dominance of
human activities in many regions of the world (Kareiva et al.
2007
; Nilsson
et al.
2007
). Many ecosystems, such as large temperate lowland rivers, no longer
exist in a 'natural' state in many regions of the world. Alternative methods of
defining natural reference states include the use of historical or paleo-
ecological data (Gillson & Willis
2004
). However, historical data of appropriate
quality are often scarce and paleo-ecological data are essentially limited to a
selected set of organisms and habitats, such as diatoms in lakes (Swetnam et al.
1999
). Even if good historical data are available, many landscapes have been
altered by humans for hundreds to thousands of years and therefore historical
references would describe other degrees and types of human influence rather
than a natural state without human influence (Pickett & Ostfeld
1995
). And, of
course, both natural long-term change and temporal variability in the bio-
logical structure of ecosystems, as a result of natural disturbances or internal
ecological mechanisms, further complicates the separation of human induced
alteration from other processes (Bunn & Davies
2000
; Milner et al.
2006
).
Apart from the problems of defining the reference state, there is also a
fundamental practical issue, which is that return to the natural state would
require the removal of most, if not all, human activity in an area and this is
