Environmental Engineering Reference
In-Depth Information
While there is considerable evidence of a relationship between diversity and stability, the rela-
tionship depends not only on the number and distribution of species, but also on the types of organ-
isms present. For example, it has been shown that the relationship between diversity and stability is
not only a function of diversity but also the presence of function groups that can adapt to a changing
environment. See McCann (2000) for a discussion of diversity and a discussion of the relationships
between stability and diversity. Biodiversity and stability then depend not only on the number of
entities and the evenness of the distributions (in space and time), but also on the differences in their
functional traits (activities or behaviors that change ecosystem properties) and the differences in
their interactions (Hooper et al. 2005).
One major environmental issue is the loss of biodiversity. It is not only the rapidly increasing rate
of extinctions that is of concern, but also the decline in populations and ranges, and the homogeni-
zation of populations, in terms of species composition and genetics. Studies reported by Naeem et
al. (1999) indicated that:
•
Human impacts on global biodiversity have been dramatic, resulting in unprecedented
losses in global biodiversity at all levels, from genes and species to entire ecosystems.
•
Local declines in biodiversity are even more dramatic than global declines, and the benei-
cial effects of many organisms on local processes are lost long before the species become
globally extinct.
•
Many ecosystem processes are sensitive to declines in biodiversity.
•
Changes in the identity and abundance of species in an ecosystem can be as important as
changes in biodiversity in inluencing ecosystem processes.
7.8 BIOLOGICAL INTEGRITY
As in the introduction to this chapter, in response to degrading conditions in aquatic systems, a
national goal was established as relected in the CWA to “restore and maintain the chemical, physi-
cal and biological integrity of the Nation's waters.” While established as a national goal, the CWA
did not include language to deine “biological integrity” or to determine either how to accomplish
that maintenance or restoration or to determine when the goals were achieved. To do so requires
deining speciic and scientiically supportable ecological end points and measures of how those end
points can be used to quantify the condition of the nation's waters.
In order to design regulations to implement the CWA and establish a deinition of “biological
integrity,” in 1975, the U.S. EPA hosted a national forum on the “Integrity of Water” and invited
well-known experts in several disciplines (Ballentine and Guarraia 1977). Two deinitions of bio-
logical integrity that were informally proposed at the forum were:
Biological integrity may be deined as the maintenance of community structure and function character-
istic of a particular locale or deemed satisfactory to society. (Cairns 1977)
the capability of supporting and maintaining a balanced, integrated, adaptive community of organisms
having a composition and diversity comparable to that of the natural habitats of the region. (Frey 1977)
Since then, the concept of biological integrity has evolved to mean a balanced, integrated,
adaptive system having a full range of ecosystem elements (e.g., species and assemblages) and
processes (e.g., biotic interactions and nutrient and energy dynamics) expected in areas with no
or minimal human inluence (Karr and Dudley 1981; Karr 1991; Karr and Chu 2000; Davies and
Jackson 2006).
The methods for the evaluation of biological integrity that have evolved from this effort are based
on the establishment of base or reference conditions, which can then be compared with the impacted
condition in order to determine the state of well-being of the system. The methods developed for
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