overall ecological integrity, which describes the state of an ecosystem with respect
to biology as well as physical and chemical factors [8]. Therefore, the purpose of
using biota to assess environmental conditions is that they integrate the effects of all
environmental factors to which they are exposed over their entire life-spans and
habitat ranges [8, 9]. However, because biota are responsive to such a multitude of
environmental factors acting over multiple temporal and spatial scales, determining
clear and unambiguous relationships between biota and anthropogenic impairment
remains a challenging and active area of research.
This chapter addresses the development of numerical indices, based on biological assemblage-level data, to make inferences regarding anthropogenic stress to
freshwater ecosystems. We follow the framework of Fauth et al. [10] in defining the
terms community and assemblage. Communities refer to all organisms within the
spatial boundaries of the system of interest. For bioassessment, the spatial boundaries of communities are generally artificial constructs, rather than distinct, natural
boundaries, and are chosen based on some combination of scientific, logistical, and
political criteria. The term assemblage refers to a taxonomically defined subset of a
given community, for example, the benthic macroinvertebrate assemblage of a
stream system.
The general objective of all bioassessments is to separate the signal of anthropogenic impairment effects from the noise of effects related to natural variations in
space and time that are not related to anthropogenic impairment. Evaluation of the
relative importance of these two effects requires measurement or estimation of
variables related to anthropogenic impairment, which we refer to hereafter as
stressors, as well as those related to natural variation, which we refer to as natural
environmental variables.
The assemblages chosen for bioassessments depend on the expertise and
resources available to investigators, public interest, and on those that are most
expected to respond to anthropogenic stress. Algae, fish, and macroinvertebrates are
the most commonly used assemblages, and numerous examples of useful
bioassessment indices exist for each. Investigations comparing these assemblages
commonly show that they respond differently to anthropogenic stress, and each
represents a unique aspect of ecological integrity [11–13]. Therefore, we focus on
describing the analytical methods used for the development of contemporary
indices, not on comparing the usefulness of different assemblages. We do not
address descriptions of field and laboratory methods, but do note that sampling
methodology [14, 15], sampling effort [16, 17], and taxonomic resolution [18, 19]
have important and well-documented effects on bioassessments. Our focus is on
perennial streams and rivers, as these systems dominate the literature and are the
focus of most bioassessment programs. We also provide examples from lakes,
impoundments, and wetlands when they enhance our discussion. The analytical
methods presented here are also applicable to other aquatic systems and assemblage
types.
Biological integrity is defined by one or a series of bioassessment metrics, which
are quantitatively defined aspects of assemblages that are expected to vary in
response to impairment. Some investigators favor the use of multiple metrics,
Principles for the Development of Contemporary Bioassessment Indices for. . .
235
to biology as well as physical and chemical factors [8]. Therefore, the purpose of
using biota to assess environmental conditions is that they integrate the effects of all
environmental factors to which they are exposed over their entire life-spans and
habitat ranges [8, 9]. However, because biota are responsive to such a multitude of
environmental factors acting over multiple temporal and spatial scales, determining
clear and unambiguous relationships between biota and anthropogenic impairment
remains a challenging and active area of research.
This chapter addresses the development of numerical indices, based on biological assemblage-level data, to make inferences regarding anthropogenic stress to
freshwater ecosystems. We follow the framework of Fauth et al. [10] in defining the
terms community and assemblage. Communities refer to all organisms within the
spatial boundaries of the system of interest. For bioassessment, the spatial boundaries of communities are generally artificial constructs, rather than distinct, natural
boundaries, and are chosen based on some combination of scientific, logistical, and
political criteria. The term assemblage refers to a taxonomically defined subset of a
given community, for example, the benthic macroinvertebrate assemblage of a
stream system.
The general objective of all bioassessments is to separate the signal of anthropogenic impairment effects from the noise of effects related to natural variations in
space and time that are not related to anthropogenic impairment. Evaluation of the
relative importance of these two effects requires measurement or estimation of
variables related to anthropogenic impairment, which we refer to hereafter as
stressors, as well as those related to natural variation, which we refer to as natural
environmental variables.
The assemblages chosen for bioassessments depend on the expertise and
resources available to investigators, public interest, and on those that are most
expected to respond to anthropogenic stress. Algae, fish, and macroinvertebrates are
the most commonly used assemblages, and numerous examples of useful
bioassessment indices exist for each. Investigations comparing these assemblages
commonly show that they respond differently to anthropogenic stress, and each
represents a unique aspect of ecological integrity [11–13]. Therefore, we focus on
describing the analytical methods used for the development of contemporary
indices, not on comparing the usefulness of different assemblages. We do not
address descriptions of field and laboratory methods, but do note that sampling
methodology [14, 15], sampling effort [16, 17], and taxonomic resolution [18, 19]
have important and well-documented effects on bioassessments. Our focus is on
perennial streams and rivers, as these systems dominate the literature and are the
focus of most bioassessment programs. We also provide examples from lakes,
impoundments, and wetlands when they enhance our discussion. The analytical
methods presented here are also applicable to other aquatic systems and assemblage
types.
Biological integrity is defined by one or a series of bioassessment metrics, which
are quantitatively defined aspects of assemblages that are expected to vary in
response to impairment. Some investigators favor the use of multiple metrics,
Principles for the Development of Contemporary Bioassessment Indices for. . .
235