wEPA
United States Environmental Office of Water EPA 822-R-02-016
Protection Agency Washington, DC 20460 March 2002
METHODS FOR EVALUATING WETLAND CONDITION
#6 Developing Metrics and Indexes
of Biological Integrity
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wEPA
United States Environmental Office of Water EPA 822-R-02-016
Protection Agency Washington, DC 20460 March 2002
METHODS FOR EVALUATING WETLAND CONDITION
#6 Developing Metrics and Indexes
of Biological Integrity
Major Contributors
Natural Resources Conservation Service,Wetland Science Institute
Billy M.Teels
Oregon State University
Paul Adamus
Prepared jointly by:
The U.S. Environmental Protection Agency
Health and Ecological Criteria Division (Office of Science and Technology)
and
Wetlands Division (Office of Wetlands, Oceans, and Watersheds)
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NOTICE
The material in this document has been subjected to U.S. Environmental Protection Agency (EPA)
technical review and has been approved for publication as an EPA document. The information
contained herein is offered to the reader as a review of the "state of the science" concerning wetland
bioassessment and nutrient enrichment and is not intended to be prescriptive guidance or firm advice.
Mention of trade names, products or services does not convey, and should not be interpreted as
conveying official EPAapproval, endorsement, or recommendation.
APPROPRIATE CITATION
U.S. EPA. 2002. Methods for Evaluating Wetland Condition: Developing Metrics and Indexes
of Biological Integrity. Office of Water, U. S. Environmental Protection Agency, Washington, DC.
EPA-822-R-02-016.
ACKNOWLEDGMENTS
EPA acknowledges the contributions of the following people in the writing of this module:
Billy M. Teels (Natural Resources Conservation Service, Wetland Science Institute), Paul Adamus
(Oregon State University), Mark Brown (University of Florida), Dave Cowen (Duke Engineering &
Services), Chris Faulkner (U. S. Environmental Protection Agency), Ric Hauer (University of Montana),
and Jan Smith (Massachusetts Bays National Estuary Program).
This entire document can be downloaded from the following U.S. EPA websites:
http://www.epa.gov/ost/standards
http://www.epa.gov/owow/wetlands/bawwg
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CONTENTS
FOREWORD v
LIST OF " METHODS OF EVALUATING WETLAND
CONDITION" MODULES vi
SUMMARY 1
PURPOSE 1
INTRODUCTION 1
IDENTIFY REGIONAL WETLAND FLORA AND FAUNA 3
ASSIGN TAXA INTO BIOLOGICAL ATTRIBUTES 5
CLASSIFY WETLANDS INTO REGIONAL CLASSES 11
TARGET SELECTION OF SAMPLE SITES 13
COLLECT LAND-USE AND HABITAT INFORMATION 14
ESTABLISH GRADIENT OF HUMAN DISTURBANCE 15
SAMPLE WITHIN THE WETLAND 21
SUMMARIZE SAMPLE DATA BY BIOLOGICAL ATTRIBUTES 23
EVALUATE ATTRIBUTE PERFORMANCE ACROSS A
GRADIENT OF HUMAN DISTURBANCE 24
SELECT METRICS FROM BEST PERFORMING ATTRIBUTES 25
SCORE EACH INDIVIDUAL METRIC 28
CALCULATE TOTAL IBI SCORE FOR ALL SITES 28
INTERPRET IBI AND REPORT DATA 3O
REFERENCES 32
GLOSSARY 36
iii
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LIST OF TABLES
TABLE l: CURRENT PILOT PROJECTS DEVELOPING WETLAND
BlOASSESSMENT METHODS AND ASSEMBLAGES 2
TABLE 2: ASSUMED EFFECTS OF ENVIRONMENTAL DEGRADATION ON
BIOLOGICAL ASSEMBLAGES IN STREAMS 7
TABLE 3: INVERTEBRATE METRICS AND SCORING FOR A WETLANDS
INVERTEBRATE INDEX OF BIOLOGICAL INTEGRITY (IBI) 12
TABLE 4: INDIVIDUAL METRIC SCORES FOR
INVERTEBRATE METRICS 29
TABLE 5: TOTAL IBI SCORES, INTEGRITY CLASSES, AND THEIR
ATTRIBUTES FOR STREAMS IN A REGIONAL REFERENCE 31
LIST OF FIGURES
FIGURE l: SEQUENCE OF ACTIVITIES IN DEVELOPING METRICS
AND IBI 4
FIGURE 2: MINNESOTA WETLAND DISTURBANCE ANALYSIS 17
FIGURE 3: SPECIES/AREA CURVES FOR WETLAND
INVERTEBRATE SAMPLES 22
FIGURE 4: EVALUATION OF METRIC PERFORMANCE 26
FIGURE 5: SCATTER PLOT ILLUSTRATING METRIC (GRASSLIKE TAXA
RICHNESS) RESPONSE TO A SINGLE VARIABLE (ZINC
CONCENTRATIONS) REPRESENTING THE GRADIENT OF
HUMAN DISTURBANCE 26
FIGURE 6: EVALUATION OF ATTRIBUTE PERFORMANCE OVER
A COMBINED SET OF DISTURBANCES 27
FIGURE 7: SCATTER PLOT DEMONSTRATING CLOSE CORRELATION BETWEEN
A WETLAND MACROINVERTEBRATE IBI AND A DISTURBANCE
GRADIENT DERIVED FROM A COMBINATION OF
HUMAN DISTURBANCES 27
FIGURE 8: EXAMPLE OF WETLAND INDEX OF BIOLOGICAL
INTEGRITY SCORES 3O
IV
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FOREWORD
In 1999, the U. S. Environmental Protection Agency (EPA) began work on this series of reports entitled
Methods for Evaluating Wetland Condition. The purpose of these reports is to help States and
Tribes develop methods to evaluate (1) the overall ecological condition of wetlands using biological
assessments and (2) nutrient enrichment of wetlands, which is one of the primary stressors damaging
wetlands in many parts of the country. This information is intended to serve as a starting point for States
and Tribes to eventually establish biological and nutrient water quality criteria specifically refined for
wetland waterbodies.
This purpose was to be accomplished by providing a series of "state of the science" modules concerning
wetland bioassessment as well as the nutrient enrichment of wetlands. The individual module format
was used instead of one large publication to facilitate the addition of other reports as wetland science
progresses and wetlands are further incorporated into water quality programs. Also, this modular
approach allows EPA to revise reports without having to reprint them all. A list of the inaugural set of
20 modules can be found at the end of this section.
This series of reports is the product of a collaborative effort between EPAs Health and Ecological
Criteria Division of the Office of Science and Technology (OST) and the Wetlands Division of the
Office of Wetlands, Oceans and Watersheds (OWOW). The reports were initiated with the support
and oversight of Thomas J. Danielson (OWOW), Amanda K. Parker and Susan K. Jackson (OST),
and seen to completion by Douglas G. Hoskins (OWOW) and Ifeyinwa F. Davis (OST). EPArelied
heavily on the input, recommendations, and energy of three panels of experts, which unfortunately have
too many members to list individually:
• Biological Assessment of Wetlands Workgroup
• New England Biological Assessment of Wetlands Workgroup
• Wetlands Nutrient Criteria Workgroup
More information about biological and nutrient criteria is available at the following EPA website:
http ://www. epa. gov/ost/standards
More information about wetland biological assessments is available at the following EPA website:
htto ://www.epa. gov/owow/wetlands/bawwg
V
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LIST OF "METHODS FOR EVALUATING WETLAND
CONDITION" MODULES
MODULE # MODULE TITLE
1 INTRODUCTION TO WETLAND BIOLOGICAL ASSESSMENT
2 INTRODUCTION TO WETLAND NUTRIENT ASSESSMENT
3 THE STATE OF WETLAND SCIENCE
4 STUDY DESIGN FOR MONITORING WETLANDS
5 ADMINISTRATIVE FRAMEWORK FOR THE IMPLEMENTATION OF A
WETLAND BIOASSESSMENT PROGRAM
6 DEVELOPING METRICS AND INDEXES OF BIOLOGICAL INTEGRITY
7 WETLANDS CLASSIFICATION
8 VOLUNTEERS AND WETLAND BIOMONITORING
9 DEVELOPING AN INVERTEBRATE INDEX OF BIOLOGICAL
INTEGRITY FOR WETLANDS
10 USING VEGETATION TO ASSESS ENVIRONMENTAL CONDITIONS
IN WETLANDS
11 USING ALGAE TO ASSESS ENVIRONMENTAL CONDITIONS IN
WETLANDS
12 USING AMPHIBIANS IN BlOASSESSMENTS OF WETLANDS
13 BIOLOGICAL ASSESSMENT METHODS FOR BIRDS
14 WETLAND BIOASSESSMENT CASE STUDIES
15 BIOASSESSMENT METHODS FOR FISH
16 VEGETATION-BASED INDICATORS OF WETLAND NUTRIENT
ENRICHMENT
17 LAND-USE CHARACTERIZATION FOR NUTRIENT AND SEDIMENT
RISK ASSESSMENT
18 BlOGEOCHEMICAL INDICATORS
19 NUTRIENT LOAD ESTIMATION
2O SUSTAINABLE NUTRIENT LOADING
VI
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SUMMARY
Mltimetric indexes, such as Indexes of
(iological Integrity (IBIs) are powerful
tools for informed management decisions related
to wetlands and wetland health. A number of
States are currently developing wetland
bioassessments by adapting bioassessment
frameworks originally developed for streams.
Although many aspects of stream bioassessment
may apply, wetland floral and faunal assemblages
are unique, and specific data from those assem-
blages are required to construct an IBI for
wetlands. The information in this module is
designed to provide a framework for the devel-
opment of IBIs using specific examples from
wetlands. The module describes a step-by-step
process to propose, evaluate, and ultimately
select metrics into the IBI that will best reflect the
biological condition of wetlands.
PURPOSE
r I The purpose of this module is to provide a
J. framework to help wetland and water quality
professionals develop metrics and IBIs for
wetlands.
INTRODUCTION
A s discussed in Module 1: Introduction to
-ZiWetland Biological Assessment, biological as-
sessments (bioassessments) are designed to evalu-
ate the health or biological integrity of wetlands.
Many of the States currently developing wetland
bioassessments are adapting bioassessment frame-
works originally developed for streams. This reli-
ance on stream information is in part due to the com-
paratively abundant body of knowledge and litera-
ture that has accompanied the development of
stream IBIs over the past two decades. However,
the floral and faunal assemblages of wetlands as well
as the ecological processes that occur within them
(Wissinger 1999) are unique. Therefore, although
many aspects of stream bioassessment may apply
to wetland bioassessment, specific information from
wetland biological assemblages is required to con-
struct an IBI for wetlands.
Of the 10 States currently developing
bioassessment methods for wetlands, 9 are attempt-
ing to use IBIs (Table 1). Maine and Montana use
advanced statistical tests (e.g., canonical corre-
spondence analysis) in addition to IBI (multimetric)
analyses to analyze algal data (Danielson 1998,
Apfelbeck 1999). Multimetric and statistical meth-
ods are both valid, and the framework provided by
this module can benefit the development of both
methods. This module, however, focuses on the
development of IBIs. Consult Chapter 9 of the
Rapid Bioassessment Protocols for Use in
Streams and Wadeable Rivers: Periphyton,
Benthic Macroinvertebrates, and Fish (Barbour
et al. 1999) for a detailed description of statistical
analysis.
Multimetric indexes are numbers that integrate
several biological metrics to indicate a site's condi-
tion. They can be designed to be sensitive to a
range of factors (physical, chemical, and biologi-
cal) that stress biological systems, and they are rela-
tively easy to measure and interpret (Karr and Chu
1999). Through a multimetric approach, each met-
ric is given a rating according to whether its value
approximates, deviates somewhat from, or devi-
ates strongly from values measured in least-disturbed
ecosystems of a particular type within a region.
These ratings (e.g., excellent, moderate, fair, and
poor) can be used to make decisions about whether
the wetland condition indicates that aquatic life is
being supported.
Because wetlands vary so widely geographically,
hydrologically, biologically, and by wetland class, it
is unrealistic to expect a single "off-the-shelf
multimetric index to be applicable everywhere.
Even though techniques may vary, those that ad-
here to some basic biological, sampling, and statis-
tical principles maintain the strengths of a multimetric
1
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TABLE l: CURRENT PILOT PROJECTS DEVELOPING WETLAND
BIOASSESSMENT METHODS AND ASSEMBLAGES
SPONSORING ORGANIZATION
Minnesota Pollution Control Agency
Ohio EPA
North Dakota Department of Health
Montana Department of Environmental
Quality
Florida Department of Environmental
Protection
Massachusetts Coastal Zone Management
Maine Department of Environmental
Protection
Vermont DEC
Wisconsin DNR
Duke University
Michigan State University
USGS Patuxent Wildlife Research Center
Penn State Cooperative Wetlands Center
Volunteer Project - Mass Bays
Volunteer Project - King County, WA
Volunteer Project - MPCA,Minnesota
Audubon, and Dakota County, MN
TYPE(S) OF WETLANDS
Depressional
Starting riparian and would like
to do Vernal Pools next.
Depressional
Riparian
Depressional
Riparian
Depressional
Depressional & Others
Coastal Marshes (salt and fresh)
Casco Bay Watershed
(depressional, fringe, riparian)
Vernal Pools
White Cedar Swamps
Great Lake Fringe Wetlands
Southeast forested swamps and
Everglades
Great Lake Fringe Wetlands
Restored depressional wetlands
on Delmarva Peninsula (MD &
DE)
All types focusing first in
Juniata Watershed and then
expanding to whole state.
Salt marshes
Depressional Wetlands
Depressional Wetlands
ASSEMBLAGE(S)
Macroinverteb rates
Plants
Macroinverteb rates
Plants
Amphibians
Plants
Macroinverteb rates
Macroinverteb rates
Algae
Some plant work
Macroinverteb rates
Plants
Macroinverteb rates
Plants
Birds
Macroinverteb rates
Algae
(some plant work)
Macroinverteb rates
Amphibians
Plants
Macroinverteb rates
Fish
Macroinverteb rates
Fish
Macroinverteb rates
Macroinverteb rates
Plants Birds
Amphibians
Macroinverteb rates
Plants Amphibians
Birds
Plants
Macroinverteb rates
Birds
Amphibians
Plants
Macroinverteb rates
Note: Data compiled from information contained in EPA, Biological Assessment of Wetlands Workgroup
website, www.epa.gov/owow/wetlands^awwg/.
2
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assessment approach as well as reflect the reality
of regional variation in biological condition (Miller
et al. 1988). The goal of a multimetric index is not
to measure every biological attribute; indeed, doing
so is impossible. Rather, the goal is, first, to identify
those biological attributes that respond reliably to
human activities, are minimally affected by natural
variability, and are cost-effective to measure and,
second, to formulate them as "metrics" and com-
bine them into a regionally appropriate index (Karr
and Chu 1999).
Figure 1 provides a framework that describes how
attributes are derived, evaluated, and ultimately in-
corporated into an IBI as metrics. However, the
first and most important step is to define the objec-
tives for developing an IBI, which may influence
several steps in the development process (see Mod-
ule 5: Administrative Framework for Implementa-
tion of a Wetland Bioassessment Program). Do
not expect all the steps in IBI development to fol-
low this sequence exactly. Undoubtedly, each
proj ect will deviate from the path and will require
revisiting steps on the basis of individual circum-
stances. However, this framework provides a use-
ful way to organize actions and ensure that all ma-
jor steps in developing an IBI are addressed. In
Figure 1, the upper left portion shows the steps re-
lated to the establishment of a gradient of human
disturbance (the dose), and the upper right shows
the steps for developing attributes that will, at least
predictably, respond to that gradient (the response).
The column of steps in the lower middle shows the
process by which the dose-response relationship is
analyzed to select and score the best performing
metrics for the IBI. The remainder of this report
follows the framework provided in Figure 1 and
includes small icons to help track progress through
the sequence of activities.
IDENTIFY REGIONAL
WETLAND FLORA
AND FAUNA
The success of multimetric in-
dexes is largely dependent on
choosing metrics that reflect di-
verse responses of biological sys-
tems to human actions (Karr and
Chu 1999). Therefore, the best
multimetric indexes combine mea-
sures of condition in individuals,
populations, communities, eco-
systems, and landscapes. Work
with stream bioassessments indicates that valuable
multimetric indexes typically use one or more as-
semblages for evaluating stream condition, such as
macroinvertebrates, fish, and/or periphyton
(Barbouretal. 1999). Professionals implementing
stream bioassessments have found that monitoring
more than one assemblage greatly increases the
power of their assessment methods. Assemblages
sometimes differ in their sensitivity to environmental
stressors, such as sedimentation and eutrophica-
tion. Having more than one assemblage provides
sensitivity to a wider range of stressors and increases
confidence in management decisions. Although
more investigations are needed to confirm the rela-
tionship, preliminary results from wetland IBI de-
velopment indicate that monitoring a combination
of assemblages (e.g., plants and macro-inverte-
brates) may similarly increase the power of
bioassessments in wetlands (Gernes and Helgen
1999).
Current wetland bioassessment projects are ex-
ploring the use of several assemblages, including
algae, amphibians, birds, fish, macroinvertebrates,
and vascular plants (Table 1). It is not yet clear
which assemblages will work best in wetland
bioassessments. It is entirely likely that specific as-
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Llassity Wftllands
irtlo regional Classes
retinal
flnra ari'J fauna
Selection of fsrqaH s
Assign taxa it>
CullttU tai'n] use and
habitat informatwin
the
nt human disturbance
Summarise sampte date bv
btologtcal altributet.
I
tvaluats attriDuie
across graven! of
56lecl metrics from best
Score each Individual
*otai
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semblages may be appropriate in some wetlands
and not in others because of the wide variety of
wetland types (e.g., salt marsh, bog, and forested
swamp). For example, using wetland fish commu-
nities in bioassessments may be effective in only a
small number of wetlands, such as wetlands on the
fringes of large bodies of water. It is also likely that
some assemblages will work in some parts of the
country and not in others. For example, wetland
amphibian communities are naturally less diverse in
western states, and there simply may be too few
species to develop a typical IBI. One of the first
steps in developing an IBI, however, is carefully
considering the advantages and disadvantages of
sampling any particular assemblage (See other mod-
ules in this series to assist in the appropriate choice.)
After selecting an assemblage, it is very helpful to
make a list of the taxa (e.g., species, genera, and
families) in that assemblage that are expected to
occur in the study area. Such lists may be based on
pre-project sampling or on previous studies from a
particular regional wetland class (Sparling et al.
1996). This list will help with identifying organisms
and with the next step of assigning taxa to biologi-
cal attributes. Such lists should accommodate new
species findings, which will result from additional
sampling.
ASSIGN TAXA INTO
BIOLOGICAL ATTRIBUTES
Attributes, in the context of
bioassessments, are defined as
measurable components of a bio-
logical system (Karr and Chu
1999). They include the ecologi-
cal processes or characteristics of
an individual or assemblage of
species that may or may not pro-
vide useful information regarding
response to human disturbances.
Attributes for most IBIs are com-
monly placed in the following four general catego-
ries: species richness and composition, tolerance
and intolerance to human disturbances, trophic com-
position, and population characteristics (including
health and condition of individuals). After defining
the list of taxa, list the attributes within these cat-
egories that will change in value along a gradient of
human disturbance from least impaired to severly
damaged wetlands. Also, predict whether each at-
tribute will increase or decrease in value as wet-
lands become more damaged. This list of predic-
tions will be tested later to identify metrics, that is,
attributes empirically shown to change in value along
a gradient of human disturbance. Examples include
a change in species richness or a change in the rela-
tive abundance of tolerant organisms. (For an ex-
ample, see Module 9: Developing an Invertebrate
Index of Biological Integrity for Wetlands.) The list
of useful attributes will differ for any wetland type
depending on the assemblage monitored. Consult
other modules for more detailed discussions of po-
tential wetland attributes for algae, birds,
macroinvertebrates, amphibians, and vascular
plants. The ultimate goal in the selection process is
to test the many attributes and from these identify 8
to 12 metrics that show strong relationships across
a gradient of human disturbance. Through the pro-
cess of evaluation, many of the predicted attributes
will display limited value for detecting human dis-
turbance. Expect only about one-third of the initial
predictions to actually be good metrics.
Each attribute considered for an IBI should be
based on sound ecological theory. Although theory
can be a good guide for selecting metrics, it must
be tested with real-world data before a metric is
used. Even if the underlying theory is sound, many
variables control an attribute's response to human
disturbance, which in turn affects its utility. For ex-
ample, an attribute that works in one type of wet-
land may not work in another type because of dif-
ferences in ecological function and the prevailing
human disturbance. In stream fish IBIs, for example,
the "anomalies metric" (percentage of individuals
with lesions, tumors, or eroded fins) may function
in only extremely degraded conditions. It provides
valuable information to a region if at least some of
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the streams are severely degraded but little infor-
mation if all streams are only moderately degraded
or unimpaired. There may even be inherent differ-
ences in how an attribute responds biologically to
human disturbances. In the case of stream fishes,
the number of species typically declines with added
human disturbance; however, in some coldwater
streams, the effect may be reversed because in-
creased nutrients and temperatures may result in
increased species numbers. Thus, it is necessary to
test attributes and their underlying assumptions not
only to validate the existence of an empirical dose-
response relationship, but also to be able to under-
stand and predict the nature of that relationship. The
primary underlying assumptions that have been used
in stream IBIs are presented in Table 2. Although
not all of those assumptions have been extensively
tested in wetlands, at least some appear to be ap-
plicable to wetlands.
ATTRIBUTE CATEGORIES
Because development of multimetric indexes for
wetlands is relatively new, no one group of organ-
isms has proven superior to another for
bioassessment. In fact, several taxa or taxa groups
show promise. Regardless of the taxonomic groups
sampled, as previously stated, several studies sug-
gest that attributes and metrics can be conveniently
grouped into the following categories:
• Species richness and composition
• Tolerance and intolerance to human
disturbances
• Trophic composition
• Population characteristics (including health and
condition of individuals)
Because most multimetric studies have been con-
ducted in streams, there may be metric categories
that are yet to be considered in wetlands. There-
fore, this categorization is meant as a general guide
to the development of attributes and metrics. A
properly constructed IBI, as defined by Karr and
Chu (1999), will have some metrics from each of
these metric categories.
Species richness and composition
Attributes in this category are usually the most
common feature of IBIs. In general, these attributes
display a declining response to added human dis-
turbance (Karr 1981). Normally, a population must
be viable at a site for some period of time before
one can consistently detect a species presence
(Karr and Chu 1999). The absence of a species at
a site (especially a species with low dispersal abili-
ties) may suggest that viable populations are not
being maintained. Overtime, species assemblages
have evolved that are capable of withstanding or
rapidly recovering from most natural perturbations.
For example, invertebrates often adapt to tolerate
the frequent drying that is typical in many wetland
habitats (Sharitz and Batzer 1999). However,
changes in the chemical, physical, and biological en-
vironment caused by humans often cannot be toler-
ated; thus one or more species declines in abun-
dance or becomes extirpated (Karr et al. 1986,
Euliss andMushet 1999, King andBrazner 1999).
This observation is true particularly for the most in-
tolerant taxa of an assemblage. For example, in a
Minnesota study, impairment to wetlands resulted
in a reduction in the number of kinds of dragonflies,
damselflies, mayflies, caddisflies, and chironomids
(midges), with very few intolerant taxa being ob-
served at the most impaired sites (Gemes and Helgen
1999).
Attributes within this category generally include
overall taxa richness as well as richness for taxa
that are particularly sensitive to specific kinds of
degradation (e.g., impairments to benthic habitats)
(Kerans and Karr 1994, Fore et al. 1996). Group-
ings may include taxon (or taxa) (e.g., number of
dragonfly and damselfly genera), specialized habi-
tat (e.g., submerged aquatic plant species), or a
combination of both. Attributes within the category
have often been refined by restricting the groupings
6
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TABLE 2: ASSUMED EFFECTS OF ENVIRONMENTAL DEGRADATION ON
BIOLOGICAL ASSEMBLAGES IN STREAMS
Number of native species, and those in specialized taxa or guilds,
declines*
• Number of sensitive species declines
• Percent of trophic and habitat specialists declines
• Total number of individuals declines*
• Percent of large individuals and the number of size classes decrease
• Percent of alien or nonnative species or individuals increases
• Percent of tolerant individuals increases
• Percent of trophic and habitat generalists increases
• Percent individuals with anomalies increases
* In some instances, particularly in oligotrophic environments, reverse
relationships may be observed.
Source: Modified from Hughes and Oberdorff 1999.
Note: Effects on wetland biological assemblages may be different.
7
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to native species. However, the taxonomy and geo-
graphic origin of many wetland organisms is poorly
known, which may limit the use of certain taxa in
this regard.
Tolerance and intolerance to
human disturbances
Tolerance, as it relates to IBI development, im-
plies a general tolerance of a species, or group of
species, to several human disturbances, rather than
tolerance to a specific variable. Therefore, in at-
tribute development, a concept can be applied in
several ways to any organism, or group, that dis-
plays these tendencies. Metrics such as percent-
age of exotic species, number of intolerant species,
and percentage of dominant species are ways of
expressing characteristics that sometimes are re-
lated to tolerance. Some taxa are very intolerant
(i.e., are very sensitive) to a variety of perturba-
tions, whereas others are adept at exploiting par-
ticular types of disturbances. For example, in Min-
nesota wetlands, increasing levels of impairment
resulted in fewer intolerant plant species, such as
iris (Iris sp.), slender riccia (Ricciafluitans), and
common bladderwort (Utricularia macrorhiza),
and increased coverage of tolerant species, such as
reed canarygrass (Phalaris arundinacea), duck-
weed (Lemna sp.), and cattail (Typha sp.) (Gernes
and Helgen 1999).
Intolerant species may be among the first to be
decimated after perturbation and the last to recolo-
nize after normal conditions have returned (Karr et
al. 1986). Endangered or threatened species should
not automatically be considered intolerants, because
their low numbers may be due to factors other than
human disturbance. They might, for example, be
glacial relics (Karr etal. 1986). Trends (increases
or decreases) in distribution or abundance from his-
torical data can be examined to help assign taxa to
these attributes. Tolerance rankings may also be
based on factors that indicate the ecological con-
servatism of taxa (those taxa adapted to a specific
narrow range of biotic and abiotic factors) (Wilhelm
andLadd 1988, Andreas andLichvar 1995). How-
ever, because of a lack of information for many
wetland taxa, empirical, rather than theoretical, ap-
proaches may be necessary or preferred to estab-
lish tolerance rankings. For example, taxa that are
represented in the least impaired sites and tend to
disappear in the most impaired sites would be
empirically defined as intolerant. Similarly, taxa that
tend to increase in disturbed sites would be defined
as tolerant (Gernes and Helgen 1999).
The mere presence of intolerant taxa is a strong
indicator of good biological condition. The relative
abundance of these taxa, in contrast, is often diffi-
cult to estimate accurately without extensive and
costly sampling efforts (Karr and Chu 1999).
Therefore, intolerant taxa should be represented
simply as the number of intolerant species per unit
sample effort. In contrast to intolerant taxa, the pres-
ence alone of tolerant taxa says little about biologi-
cal condition, because tolerant groups inhabit a wide
range of places and conditions. However, note that
many wetland organisms can tolerate the stressful
levels produced by a variety of natural environmental
disturbances (Wissinger 1997, Euliss et al. 1999,
Higgins and Merritt 1999), and care should be taken
to base tolerance designations on human distur-
bances and not natural ones.
Tolerance attributes should be expressed as the
percentage of tolerant individuals from either a single
species or a grouping of highly tolerant species.
Note that if a high number of tolerant or intolerant
species is included in the composition of attributes,
the usefulness of those attributes will be diminished.
In general, it is recommended that only about 10%
(no fewer than 5% or no more than 15%) of taxa in
a region should be classed as intolerant or tolerant.
The point of these metrics is to highlight the strong
signal coming from the lowest and highest ends of
the biological integrity continuum, without being
swamped by the weak or intermediate signals from
in between (Karr and Chu 1999).
8
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Trophic composition
Because the food base is central to the mainte-
nance of a community, information about trophic
composition may be important to an IBI. All or-
ganisms require a reliable source of energy. The
dominance of trophic generalists occurs as specific
components of the food base become less reliable,
and the opportunistic foraging habits of the gener-
alists make them more successful than trophic spe-
cial! sts(Karretal. 1986). Sometimes entire groups
of specialized organisms have been reduced or ex-
tirpated from ecosystems as a result of human dis-
turbances. For example, top carnivores such as
ospreys and bald eagles have disappeared from
regions as a result of eggshell thinning and repro-
ductive failure associated with the bioaccumulation
of chlorinated hydrocarbon pesticides from aquatic
food webs (Carson 1962, Rudd 1964, Thomann
1989). Depending on the type of disturbance, pri-
mary producers and invertebrates of wetlands may
also respond as the ecosystem begins to function
improperly. Some wetland invertebrates will re-
spond to both bottom-up (e.g., enrichment, exotic
plants) and top-down (e.g., heavy metal
biomagnification, exotic fish) alterations in the food
web (Rader 1999). For example, the benthic com-
munities of contaminated Louisiana bayous sup-
ported a "poor trophic mix" of macrobenthic inver-
tebrates, and fewer predatory invertebrates and
suspension feeders were found at those sites than
elsewhere (Gaston 1999). Thus, the trophic struc-
ture of a community can provide information on
patterns of consuming and producing organisms that
are affected by impairment.
In general, attributes in this category can be de-
signed to assess trophic balance and structure. For
example, the biota of stream ecosystems in good
condition usually will not be overly dominated by
omnivores or trophic generalists and will normally
contain at least some trophic specialists, including
top carnivores that form the apex of many aquatic
food pyramids (Karr et al. 1986). However, ma-
nipulations of top carnivores have been shown to
have little effect in some ecosystems, such as wet-
lands (Batzer 1998), whereas such manipulations
have had a significant effect in others, such as lakes
(Carpenter etal. 1987). Furthermore, surface wa-
ter levels in most natural wetlands fluctuate widely.
Such variation also affects water and substrate
chemistry, nutrient availability, vegetation, primary
production, detritus processing, and the presence
of vertebrate predators (Wissinger 1999). There-
fore, caution should be exercised in developing
trophic attributes for wetlands, and particular at-
tention should be paid to those attributes involving
functional feeding groups. Karr and Chu (1999)
observe that despite widely accepted theory,
metrics pertaining to functional feeding groups
among benthic macroinvertebrates may or may not
be good indicators; their dose-response relation-
ship to human influences must be carefully tested
and established for multiple data sets and circum-
stances before they are used in a multimetric index.
Population attributes
The attributes in this category assess characteris-
tics of populations such as reproduction, growth,
and condition of individual organisms within the
populations (Fore et al. 1996). Ecosystems can
maintain themselves only if the populations of or-
ganisms that characterize the ecosystems are able
to compensate for loss of members by reproduc-
ing. Human disturbances that negatively affect re-
production are ordinarily indicated by an accom-
panying reduction in the proportion of reproductive
specialists. In addition, conditions must be favor-
able for the young of a population to survive, dis-
perse, and grow to sexual maturity (Pickett and
White 1985, Wissinger and Gallagher 1999). For
example, the eggs of some species, such as fairy
shrimp, require aerated soil for development; there-
fore, these species rely on the drying up of tempo-
rary ponds for reproduction. Any alterations of the
frequency and duration of ponding in wetlands that
contain these species would greatly influence the
viability of populations. In another example, cer-
tain invertebrates have become extremely special-
9
-------
ized in their dependence on the fluid of pitcher plants
(e.g., Sarreciniapurpured) to reproduce and carry
out their life cycle. At least some of these inquilines
(organisms that live within the abode of another
species) are poor dispersers and may be slow to
colonize isolated wetland habitats that have become
fragmented as a result of human disturbance
(Giberson and Hardwick 1999). Therefore, at-
tributes that characterize population structure and
patch dynamics can be effective indicators of hu-
man disturbance.
measure and score. Recognizing the tendency for
moderate levels of nutrient and thermal enrichment
to elevate fish abundance, Oberdorff and Hughes
(1992) scored this metric so that very high abun-
dances received lower metric scores than moder-
ate numbers did; only very low abundances received
the lowest score. This scoring adaptation is an ex-
ample of the need to evaluate metric performance
along disturbance gradients before applying the IBI
in resource assessments (Hughes and Oberdorff
1999).
Certain structural and functional attributes of wet-
land vegetation and algae are also included in this
category. Many of these attributes have been used
in and out of the context of IBI to assess a wide
variety of human disturbances (e.g., hydrologic
changes, nutrient enrichment, sediment loading, and
accumulation of heavy metals). For example, in-
creased algae biomass is one of the most widely
used indicators of eutrophication in aquatic eco-
systems (see Module 11: Using Algae To Assess
Environmental Conditions in Wetlands). Likewise,
the percent coverage of submerged aquatic veg-
etation has been a useful indicator of nutrient en-
richment in many estuarine environments (see Mod-
ule 16: Vegetation-Based Indicators of Nutrient
Enrichment in Freshwater and Estuarine Wetlands).
Minnesota has used increased persistent plant lit-
ter, resulting from human-induced changes in the
composition of the plant community, as an IBI at-
tribute to indicate reduced detrital energy to drive
wetland ecosystems (Gernes and Helgen 1999).
Individual abundance is a common surrogate for
system productivity, and some types of highly de-
graded sites are expected to support fewer indi-
viduals than are high-quality sites (Karr 1981).
However, Karr and Chu (1999) suggest that abun-
dance may be a poor candidate for a multimetric
index because it varies too much, even when hu-
man disturbance is minimal, and it is also difficult to
Sites with especially severe degradation often yield
a high number of individuals in poor health (Mills et
al. 1966, Brown etal. 1973,Baumannetal. 1982,
Sanders etal. 1999). Parasitism has been shown
to reflect both poor environmental condition and
reduction in reproductive capacity (sterility) in fish
(Mahon 1976). Indications of poor health include
individuals with tumors; limb, mouthpart, or other
structural malformations; heavy infestations of para-
sites; and discoloration, excessive mucus, edema,
rash, orhemorrhaging. For example, malformation
in chironomid mouthparts has been used to indicate
impairments to water from sedimentation, eutrophi-
cation, and contamination (Warwick 1980). Re-
cently, increasing numbers of amphibian populations
with unusually high frequencies of morphological
abnormalities (>5%) have been reported through-
out North America; however, the ecological signifi-
cance of these observations remain poorly under-
stood (Ouellet 2000, Helgen et al. 2000). Leonard
and Orth (1986) found increases in the incidence
of disease and anomalies in stream fish only after
substantial degradation was evident, indicating that
this metric may be sensitive at only the most se-
verely impaired sites. In cases in which only low to
moderate levels of impairment occur, the metric has
been dropped; however, it should be considered
wherever the possibility exists for changes in the
incidence of diseased or deformed organisms
(Hughes and Oberdorff 1999).
10
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LESSONS LEARNED FROM THE
BIOLOGICAL ASSESSMENT OF
WETLANDS WORKING GROUP
These lessons should be treated as general rules of
thumb and not absolutes. Nature keeps reminding
us that when dealing with biology and ecology, there
are always exceptions to the rules. The following
lessons on attributes and metrics are based on the
experience of the Biological Assessment of Wet-
lands Working Group (BAWWG) members:
• Explicitly define attributes. To aid in testing at-
tributes and to improve communication with
others, it is very important to explicitly define
attributes. There are many ways to examine an
attribute. For example, tolerance can be de-
scribed in the following ways:
• Number of tolerant individuals
• Percentage of tolerant individuals (number
of tolerant individuals/total number of indi-
viduals)
• Number of tolerant species or taxa
• Percentage of tolerant species, or taxa
(number of tolerant taxa/total number of tol-
erant taxa)
• Be careful in using measures of abundance. Al-
though Karr and Chu (1999) suggest that abun-
dance may be a poor candidate for a multimetric
index, BAWWG members have found some
exceptions to this rule. For example, the abun-
dance, or biomass, of algae may be a useful
attribute, but further testing is needed.
• Avoid combining attributes. In general, restrict
ratios to relative abundance or proportions in
which the total number of individuals or taxa is
used as the denominator. Avoid using attributes
such as the number of water boatmen taxa di-
vided by the number of midge taxa. Also be
careful about adding attributes together, such
as the number of sedge taxa plus the number of
rush taxa plus the number of grass taxa. Ratios
and sums of attributes can hide valuable sig-
nals, can be difficult to interpret, and are often
more variable than the individual attributes (Karr
and Chu 1999). It may be more effective to
test each attribute independently. However,
BAWWG members have found some excep-
tions to this rule. For example, Minnesota uses
a metric that combines the number of mayfly
and caddisfly genera plus the presence of drag-
onflies and fingernail clams (Table 3).
CLASSIFY WETLANDS
INTO REGIONAL CLASSES
Successful biological monitor-
ing begins with a judicious clas-
sification of sites. Classification
is an essential step in develop-
ing bioassessment methods.
Biological assemblages are in-
fluenced by natural variations in
wetland types (e.g., landscape
position, source of water) and
by variations in the amount and
type of human disturbances. Classification is a way
to account for the effects of natural environmental
influences on wetlands and helps avoid comparing
wetlands of unlike classes. Yet, excessive empha-
sis on classification, or inappropriate classification,
can impede development of cost-effective and sen-
sible monitoring programs. Using too few classes
fails to recognize important distinctions among places
and can produce insensitive metrics; using too many
adds unnecessary costs to the development of
biocriteria. The challenge is to create a system with
only as many classes as needed to represent the
range of relevant biological variation in a region and
the level appropriate for detecting and defining the
biological effects of human activity in that place (Karr
and Chu 1999).
It is important to remember that for the purpose
of developing bioassessment methods, classifica-
tion is a way to help minimize "noise" and make it
easier to identify signals of human disturbance. Clas-
1 1
-------
TABLE 3: INVERTEBRATE METRICS AND SCORING FOR A WETLANDS INVERTEBRATE
INDEX OF BIOLOGICAL INTEGRITY (IBI)
METRIC
DESCRIPTION
RANGE
SCORE
REF
AG
SW
Richness metrics
Total taxa
Chironomid
ETSD
Leech taxa
Odonata
Snails
# Genera chironomids, caddis-
flies, mayflies, damselflies,
dragonflies, leeches, snails,
macrocrustaceans, presence
of Chaoborus and clams
# of genera of Chironomidae
larvae
# Genera of Ephemeroptera,
Trichoptera, plus presence of
Sphaeriidae and Dragonflies
# Genera of Hirudinidae found
in BT and DN samples
# Genera of Dragonfly &
Damselfly larvae
# Taxa of snails to
species most cases
28 -46
20-27
12 - 19
13 - >20
6- 12
> 70%
4 or more
2-3
> 70%
4- 5
2-3
0 - 1
4-6
3
0-2
5 - 7
3-4
0 - 2
5
3
1
5
3
1
5
3
1
5
3
1
5
3
1
5
3
1
5
1
3
2
6
4
2
5
1
4
1
1
3
3
2
5
4
3
5
2
5
1
4
4
1
5
2
6
4
6
5
6
5
2
8
1
3
8
1
6
4
Tolerance/Intolerance metrics
Intolerant
Taxa
# Intolerant taxa:
Leucorrhinia,
Libellula, Tanytarsus, Pro-
cladius, Triaenodes, Oecetis
4 or more
2-3
0 - 1
5
3
1
5
1
8
11
Proportion metrics
Corixidae
Erpobdella
3 Dominants
% Corixidae of Hemiptera plus
Coleoptera from BT samples.
% Erpobdella in BT and DN
samples of the total
abundance in DN samples.
% top 3 dominants of total
abundance in DN samples
< 30%
30 - 70%
> 70%
0- 11%
>11 - 22%
> 70%
34 - 55%
> 55 - 80%
> 70%
5
3
1
5
3
1
5
3
1
5
1
6
5
1
2
2
3
3
2
3
1
6
1
1
5
4
6
3
2
9
2
Abbreviations: BT, bottletrap; DN, dipnet; number of sites scoring in range is given for Reference sites (Ref),
agricultural (Ag) and stormwater (SW) influenced wetlands (Gernes andHelgen 1999).
12
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sification is not the end product, and there is no
perfect classification system. Also, classification is
an iterative process. Try applying an existing clas-
sification system (e.g., Cowardin et al. 1979, USDA
1981,Brinson 1993, Omernik 1995, Omernikand
Bailey 1997) and then lump and split as needed to
produce groups of biologically similar wetlands that
respond in similar ways to anthropogenic influences.
For further discussion of classification issues and
approaches, including some wetland bioassessment
examples, see Module 7: Wetlands Classification.
TARGET SELECTION OF
SAMPLE SITES
After wetlands are classified,
sample sites should be selected.
Module 4: Study Design for
Monitoring Wetlands describes
the options for developing sam-
pling schemes for a wetlands
monitoring program, including ran-
dom sampling, targeted sampling,
and before/after or control/impact
designs. The members of
BAWWG recommend the use of a targeted sam-
pling design when developing bioassessment meth-
ods for wetlands. They have found that random
sampling often fails to capture enough least impaired
reference wetlands or enough of the severely de-
graded wetlands. Also, random sampling may not
consider important factors such as accessibility to
sites and the selection of relatively permanent ref-
erence sites that will not be subjected to a great
deal of future human disturbance. The process of
testing attributes and selecting metrics depends on
plotting data on a graph with an attribute value on
the y-axis and a gradient of human disturbance on
the x-axis. It is very important to select enough
reference wetlands and severely damaged wetlands
to anchor both ends of the disturbance gradient. It
is also important to select enough wetlands with
varying degrees of human disturbance in order to
reveal a signal in the attribute if there is one. Based
on the experience of the BAWWG members, tar-
geted sampling is probably the best way to ensure
that this is accomplished. The development of hu-
man disturbance gradients is discussed further in
this module in the sections "Collect Land Use and
Habitat Information" and "Establish Gradient of
Human Disturbance."
One challenge to the characterization of reference
conditions is that there are few, if any, places left
that have not been influenced by human actions. In
many regions, what are described as least impaired
wetlands may in fact be very degraded, because
accessible less-degraded sites cannot be found.
This may complicate the development of an IBI but
does not prohibit it. A common pitfall is the failure
to canvass a wide enough area for sites that may be
less impaired. It may be advantageous to survey
neighboring areas and expand the geographic range
to find similar wetlands in better condition. An-
other failure is to not include an adequate number
of most impaired sites. Sampling only from the least
impaired end of the gradient creates problems be-
cause it does not represent the full range of site deg-
radation and it prohibits analysis of the relationship
between biological attributes and highly negative
human influences.
Biological communities in wetlands with a high
proportion of degrading land uses (e.g., commer-
cial, residential, agricultural) in their vicinity or wa-
tersheds can sometimes be assumed, for purposes
of developing an IBI, to be potentially stressed.
However, forested wetlands, and in particular, for-
ested wetlands with dense canopies, should not
automatically be considered the least impaired. This
is because in some regions, some wetlands are nor-
mally dominated by herbaceous vegetation due to
persistently high water table levels and/or other natu-
ral influences. Some of these herbaceous vegeta-
tion sites may in fact be in better condition than are
forested wetlands. However, if herbaceous wet-
lands historically prevailed in an area, their invasion
by woody vegetation could be a sign of stress, not
an indication of good health.
13
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As mentioned previously, it is important to select
sites that are minimally impaired reference sites and
severely damaged sites as well as some in between
to represent the full gradient of human disturbance.
The number of sites that are needed depends on
the number of wetland types within a given class,
the ecological variability of the wetland types, the
kinds and amount of human disturbances, and the
size of the region. The number of sites should be
sufficient to show a gradient of human disturbance
for each wetland class in the region. See Module
7: Wetlands Classification for more detail on classi-
fying wetland types. Sampling an adequate num-
ber of sites will provide confidence in the sensitivity
of the metrics showing a response.
COLLECT LAND-USE AND
HABITAT INFORMATION
Before starting the field sampling,
gather information about the study
sites through published sources
and field reconnaissance. The
overall goal of this step is to col-
lect information to help verify that
wetlands are classified correctly,
provide data for constructing hu-
man disturbance gradients, and
provide insights into why biologi-
cal communities are damaged dur-
ing the IBI interpretation phase. A wealth of infor-
mation can be collected about sites without even
leaving the office. Information sources include the
following:
• U. S. Geological Survey quadrangle topographic
maps. These maps can provide baseline infor-
mation on slope, elevation, land use, and the
hydrological network in the vicinity of the study
wetland.
• National Resource Conservation Service soil
surveys. These surveys are an invaluable source
of information on wetland soils and their char-
acteristics. Hydric soils are mapped and de-
scriptions of soil characteristics and how they
vary by soil horizons are provided.
• National Wetland Inventory maps. These maps
are useful for identifying the presence of wet-
lands and estimating wetland size. They also
include the Cowardin et al. (1979) classifica-
tion.
• U. S. Department of Agriculture aerial photos.
If available, these photos are very useful for
gathering information on the landscape surround-
ing wetlands. They can also be used to recon-
struct historical changes in land use by analyz-
ing a series of photos taken over past years.
• Geographic Information System (GIS) data-
bases. Many state and local units of govern-
ment have digital land-use and other informa-
tion available on GIS databases. Often, this
information can be linked to other available data
(e.g., percent impervious surface and point
source discharges) to locate and display geo-
graphically referenced sources of impairment.
Such information is also increasingly available
from many online websites. The layering and
interactive features of GIS databases greatly
enhance landscape-level assessments (see
Module 17: Land-Use Characterization for
Nutrient and Sediment Risk Assessment).
However, the scale and quality of GIS infor-
mation should be closely examined in view of
the intended use. Other information, such as
low-altitude photographs, may be needed to
supplement GIS information in order to derive
a meaningful estimate of the gradient of human
disturbance.
In addition to landscape features, onsite wetland
characteristics are important in establishing gradi-
ents of human disturbance. Onsite investigations
should provide general information on landscape
setting, hydrologic features, and vegetative cover
of the wetland. Such observations can generally be
made from visual assessments from the wetland's
edge. Obvious stressors, such as hydrologic alter-
14
-------
ations (e.g., ditches and dikes), should be identi-
fied. The extent of vegetation cover and the char-
acteristics of buffer areas should be noted. Buffer
areas should also be clearly defined (e.g., the 100
m of land surrounding the wetland boundary at full
pool), and land uses within those buffers should be
described. Examples of other data that should be
recorded at each site include the following:
• Topography and landscape features that sur-
round the site. Many characteristics should be
recorded, including the shape of the wetland;
adjacent land use; the general distribution of
wetland vegetation and open water; the inter-
spersion of plant communities; the type of buffer;
hydrological features, including surface water
inflows and outflows; and human-made water
control structures. This information should be
included on a site sketch map.
• Patterns in the vegetation community, such as
the number of community types and their loca-
tion in relation to each other, the vegetation
strata present, the dominant species, and pres-
ence of nonnative or invasive species.
• Evidence of human disturbance (if any). One
way to approach this question is to prepare a
stressor checklist that can be used to survey
each site (see "Establish Gradient of Human
Disturbance" below for potential stressors).
• An estimate of the size of the wetland.
• Photographs of the site.
ESTABLISH
GRADIENT OF
HUMAN
DISTURBANCE
Once sites have been classified by
natural factors, it is essential to cat-
egorize the same sites according to
degrees of human disturbance.
This step is important to ensure that
metrics are sensitive. Human disturbance serves as
the gradient along the x-axis to which biological at-
tribute data along the y-axis are compared. Deter-
mining the human factor and the likely range of the
gradient must be done before sampling begins, not
as an afterthought, because post hoc categorization
may reveal that the full range of human disturbance
was not captured, thus requiring additional sam-
pling to develop a useful IBI.
To help establish sampling sites that reflect the full
range of human disturbance, it can be useful to first
identify and perhaps prioritize the main types of dis-
turbances in a region, such as hydrologic modifica-
tion, eutrophication, sedimentation, and chemical
contamination. U.S. Environmental Protection
Agency (EPA) and State reports (305b, 303d) can
be used with other sources, particularly interviews
with local conservation groups and resource agen-
cies, to obtain an initial indication of watersheds
whose wetlands might be candidates for designa-
tion as least or most impaired sites. In rare instances,
detailed descriptions may exist of a wetland's bio-
logical communities before its alteration and devel-
opment of the surrounding watershed. In such in-
stances, the historic condition can be used to define
the least impaired reference condition.
In some cases, human disturbance may comprise
a single impairment, such as vegetation removal by
grazing. For example, Montana used a simple dis-
crete disturbance gradient based on grazing and
farming for wetlands in a rural landscape (Apfelbeck
1999). Three classes were identified: wetlands that
are currently grazed or farmed, wetlands that were
grazed or farmed but not within the recent past,
and wetlands that have either never been grazed or
never been farmed or at least not within recent his-
tory. In most circumstances, diverse and often
subtle human activities interact to affect conditions
in watersheds, bodies of water, or wetlands. As a
result, it may be advantageous to develop a gradi-
ent that integrates several human disturbances to
account for multiple stressors.
15
-------
Where there is adequate information, the devel-
opment and use of an index may greatly enhance
the establishment of the gradient of human distur-
bance. Such an index incorporates values that rep-
resent the various degrees and combinations of pre-
vailing human disturbances for all sites, not just the
least and most impaired, as illustrated in the Minne-
sota Wetland Disturbance Analysis (Figure 2). Al-
though there is no standard protocol for construct-
ing such an index, human disturbance should not be
represented simply by a single score from a single
source of disturbance. Instead, it should be devel-
oped by combining scores from several prevailing
disturbances from both the landscape and the wet-
land. Possible landscape-level disturbances in an
index include the following:
• Percentage of the watershed within impairing
land uses (e.g., cropland, pastureland, and ur-
ban land)
• Presence, condition, and width of wetland
buffer
• Proximity of wetland to other natural habitats
(e.g., wetlands, natural grasslands, and forest)
• Percentage of other natural habitats in close
proximity (e.g., a 1-km radius) of the wetland
• Impoundment of runoff or flow by dams or
berms located upstream or upslope
Possible local human disturbance factors in an in-
dex include the following:
• Impoundment of runoff or flow by excavations
(pits) within wetlands
• Redirection of runoff or flow within wetlands
• Extraction of water from the wetland (e.g., for
irrigation)
• Removal of vegetation (e.g., through logging,
grazing, mowing, and controlled burning)
• Flattening of wetland microtopography
• Steepening of wetland topography (especially
shorelines)
• Persistent disturbance of wetland soils or
vegetation through compaction, tillage, or
trampling
• Drainage of wetlands through ditching or tiling
• Water or atmospheric deposition
• Simplification of shoreline complexity
• Pollution (e.g., thermal and chemical)
The type of land cover that surrounds a wetland
is generally one of the most dominant influences on
wetland condition (see Module 17: Land-Use
Characterization for Nutrient and Sediment Risk
Assessment). GIS information can be useful in
mapping and analyzing land-use patterns and other
spatial relationships that broadly affect wetlands.
For example, several recent GIS studies have found
significant negative correlations between watershed-
wide agricultural or urban land uses and stream ffils
(Lenat and Crawford 1994, Richards et al. 1996,
Roth et al. 1996, Wang et al. 1997). When consid-
ering the influence of particular land uses, it is im-
portant to consider their distance from a wetland,
the intervening slope, and the time period (current
or recent or distant past) at which they occurred.
Land use of the surrounding landscape should be
assessed within a meaningful radius around the wet-
land (e.g., 300 m), with greater weight given to land
use in areas upstream or upslope of a site, that is,
the "contributing watershed." Although GIS infor-
mation can be a powerful tool for defining a distur-
bance gradient, it is not a replacement, or a good
surrogate, for the IB I itself or for biological moni-
toring (Karr and Chu 1999). To supplement GIS
mapping data, onsite visits are generally required to
improve the assessment of human disturbances.
Several states (i.e., Ohio, Oregon, Florida, and
Maryland) have prepared data forms to assist in
the assessment of onsite conditions for rapid field
assessment of environmental risks or disturbances
16
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FIGURE 2: MINNESOTA WETLAND DISTURBANCE ANALYSIS
PRELIMINARY DRAFT RATING FORM (2/08/01)
The forms shown below are presented to show the concepts and framework under development
in Minnesota for rating the degree of human disturbance to wetlands and their immediate land-
scape. These forms are to be completed while referencing various, current digitized spatial
information, such as land use, wetland border, aerial photos, digital raster graphs, hydrologic data
themes and field notes from site visits. These forms and the corresponding evaluation method are
likely to be considerably revised and changed as the scores and method are further tested against
additional data sets (Helgen and Gernes in press).
Site:
Study:
Raters:
Date:
points
Factor 1. Buffer landscape disturbance
Extent and Intensity
Best— as expected for reference site, no evidence of disturbance
Mod.— predominately undisturbed, some human use disturbance
Fair— significant human disturbance, buffer area nearly filled with human use
Poor— nearly all or all of the buffer human use, intensive land use surrounding wetland
(0)
(6)
(12)
(18)
BEST
MOD.
Mature (>20 yr.) woodlot,
forested
Mature prairie
Other long recovered area
Other wetlands
Old field, CRP or rangeland,
Restored prairie (<10 yr.)
Young (<20 yr.) second growth woodlot
Shrubland
FAIR
POOR
Residential with unmowed areas
Active pasture
Less intensive agriculture
Turf park, Golf course
Newly fallowed fields
High road density in buffer area
or impervious surfaces
Urban development
Industrial development
Intensive residential/ mowed
Intensive agriculture
Mining in or adjacent to wetland
Active construction activity
Remarks or comments:
17
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points
Factor 2. Landscape (immediate) Disturbance
Extent and Intensity
Best—landscape natural, as expected for reference site, no evidence of disturbance
Mod. --predominately undisturbed, some human use disturbance
Fair— significant human disturbance, landscape area nearly filled with human use
Poor— nearly all or all of the landscape in human use, isolating the wetland
(0)
(6)
(12)
(18)
BEST
FAIR
MOD.
Mature (>20 yr.) woodlot,
forested
Mature prairie
Other long recovered area
Other wetlands
Old field, CRP or rangeland,
Restored prairie (<10 yr.)
Young (<20 yr.) second growth woodlot
Shrubland
POOR
Residential with unmowed areas
Active pasture
Less intensive agriculture
Turf park, Golf course
Newly fallowed fields
High road density or impervious
surfaces in immediate landscape
Urban development
Industrial development
Intensive residential/mowed
Intensive agriculture
Mining in or adjacent to wetland
Active construction activity
points
Factor 3. Habitat alteration—immediate landscape
(within and beyond buffer)
Severity and extent of alteration
Best— as expected for reference, no evidence of disturbance
Mod.— low-intensity alteration or past alteration that is not currently affecting wetland
Fair— highly altered, but some recovery if previously altered
Poor— almost no natural habitat present, highly altered habitat
(0)
(6)
(12)
(18)
18
-------
Vegetation removal disturbances
Mowed, Grazed
Tree plantations
Tree removal
Shrub removal
Course woody debris removal
Removal of emergent vegetation
Substrate/soil disturbances and sedimentation
Other
Remarks or comments:
Factor 4. Hydrologic alteration
points Severity and degree of alteration
Grading/bulldozing
Filling
Dredging
Other
Vehicle use
Sediments input (from inflow or
erosional)
Livestock hooves
Fish stocking or rearing
Other
Best— as expected for reference, no evidence of disturbance
Mod.— low-intensity alteration or past alteration that is not currently affecting wetland
Fair— less intense than "poor," but current or active alteration
Poor— currently active and major disturbance to natural hydrology
(0)
(7)
(14)
(21)
Ditch inlet
Tile inlet
Point source input
Installed outlet, weir
Dredged
Graded or fill
Other
Berm or dam
Road bed or RR bed
Levee
Unnaturally connected to other waters
Dewatering in or near wetland
Source water changes
Drainage
Remarks or comments:
19
-------
Factor 5. Chemical pollution
points
Severity and degree of pollution
Best— chemical data as expected for reference and no evidence of chemical input
Mod.— selected chemical data in low range, little or no evidence of chemical input
Fair— selected chemical date in mid range, high potential for chemical input
Poor— chemical input is recognized as high, with a high potential for biological harm
(0)
(7)
(14)
(21)
Checklist:
High Cl cone, (water)
High P cone, (water)
High N cone, (water)
High Cu cone, (sediment)
High Zn cone, (sediment)
Known MMCD treatment
Evidence of altered DO regime
Other treatment
High input potential
Other
Remarks or comments:
Additional factors and concerns
points Used in exceptional cases as described below
Maximum of (4) additional points added to the cumulative disturbance
total for reasons described below. Apply on factors 4 and 5.
Factor 1 - Buffer and landscape
Factor 2 - Landscape (immediate disturbance)
Factor 3 - Habitat alteration
Factor 4 - Hydrologic alteration
Factor 5 - Chemical pollution
Additional factors
Total final disturbance score
Site:
20
-------
to wetlands (e.g., the Ohio Rapid Assessment for
Method for Wetlands) (Ohio EPA 2001). Inde-
pendent observers should be able to repeat the as-
sessments of disturbances and obtain the same re-
sults, that is, the assessments should be highly pre-
cise. Nonetheless, a relatively high degree of judg-
ment usually is required to assess, a priori, the rela-
tive level of human disturbance a site is likely to be
enduring. Many impairments are not clearly visible
or assumable (e.g., subsurface drainage tile and
chemical contamination).
SAMPLE WITHIN THE
WETLAND
After wetlands have been prop-
erly classified and selected, sam-
pling within a wetland may begin.
One approach for sampling is to
collect data from all habitat zones.
Another approach is to find a
single zonal transition area that
may be indicative of the entire
wetland (a wetland equivalent to
the riffle zone used in streams).
The goal is not to measure every attribute of a wet-
land, but rather to find efficient indicators of health
that are expressed adequately with a minimal amount
of sampling. For example, a Minnesota study col-
lected data from the nearshore shallow emergent
zone and based all comparisons on that area. That
approach led to accurate assessments without the
need for the more time-consuming sampling from
each zone. In addition, human access to some parts
of wetlands may be difficult or impossible, which
would preclude sampling from every zone.
Although sampling from a single zone may, in cer-
tain instances, provide enough information to accu-
rately assess wetland health, there are instances
when it will not. For example, in streams, it is often
necessary to survey several habitats (e.g., riffles,
pools, runs, and backwater areas) to collect the
variety of taxa needed for IBIs to be sensitive to
the array of possible impairments. If the decision is
made to sample several zones, the number of
samples that need to be collected will increase as
the area of the wetland and its heterogeneity in-
crease. At a minimum, samples should be collected
from the following zones if they are present: per-
manently inundated areas, seasonally inundated ar-
eas, and areas saturated but seldom inundated. For
purposes of IB I development, within these three
zones, samples should be collected in a manner that
will yield unbiased data from the widest variety of
disturbance conditions and serai stages. For quan-
titative metrics (such as relative abundance and per-
cent cover) to be used in multimetric indexes, ran-
dom or systematic (grid- or transect-based) loca-
tion of sampling or observation points within zones
may be justified, and a much larger number of
samples will be necessary. The sampling strategy
must be clearly described and the number of samples
must be adequate to capture the variablity of the
attribute being measured. For more detail on sam-
pling, see Module 4: Study Design for Monitoring
Wetlands.
In general, the number of samples or observa-
tions per zone should be roughly proportional to
the area of the zone if the goal is to characterize the
wetland as the assessment unit. (However, a fixed
number of samples should be taken to avoid prob-
lems with increasing species richness with increas-
ing sample numbers.) One approach to address
sample adequacy is to construct species/area curves
to determine the number of samples required to
produce diminishing returns (an asymptotic curve)
in the cumulative number of species of the target
taxa (De Vos and Mosby 1969) (Figure 3). An-
other approach is to plot the cumulative coefficient
of variation (in, e.g., the diameters of trees that were
measured) against the number of samples (e.g., the
number of trees measured). Other approaches for
estimating sampling adequacy may be preferred,
depending on assessment objectives (see Elliott
1970). Also, the boundaries of the unit to which
21
-------
the collected data will be extrapolated need to be
clearly defined and stated. For example, will a few
samples collected on the fringe of a large roadside
wetland be claimed to represent the entire wetland
or only the roadside fringe?
A basic premise of IBI is that the biota have been
sampled in their true relative abundance without bias
toward taxa or size (Karr et al. 1986). As this
assumption is relaxed, the reliability of inferences
based on the IBI is reduced. However, with any
single method, there are inherent biases that affect
the tendency to capture or notice particular organ-
isms. Therefore, method limitations should be well
understood. Standard sampling protocols should be
adhered to, and the resulting metrics should be tai-
lored to the known limitations of the methods, pro-
tocols, and sampling equipment. In addition, data
collected by one sampling method should not be
mixed or compared with data collected by another
method.
Temporal variations may also affect the quality of
the sample or limit its comparison with other data.
This may be true particularly in temporary or sea-
sonal wetlands that support organisms that are
equally as periodic in nature. Therefore, it is im-
portant to know the best time of the year for the
collection of certain taxa and to specifically relate
that information to the protocols that govern sam-
pling. When sampling assemblages or habitats with
specific sampling periods tied to weather conditions,
such as amphibians in vernal pools, it may be im-
portant to maintain flexibility in sampling periods to
be able to adjust to the time of emergence. Other
sections of this document discuss this in greater detail.
Several methods may be appropriate for sampling
the biota of wetlands, and it is important to be able
to duplicate these methods from site to site and to
be as consistent as possible. Sampling should al-
ways be conducted in a way that maintains both
precision and accuracy (see Module 4: Study De-
sign for Monitoring Wetlands).
0
12
15
Number of Samples
FIGURE 3: SPECIES/AREA CURVES FOR WETLAND
INVERTEBRATE SAMPLES.
Demonstrates the asymptotic relationship (leveling of the curve) that should be considered for the determining
the level of sampling effort (preliminary data from Sparling et al.).
22
-------
In addition to sampling the biota, most projects
involving the development of bioassessment meth-
ods also sample some physical and chemical at-
tributes of the study sites (Sparling et al. 1996;
Fennessy et al. 1998; Gernes and Helgen 1999).
This information is particularly useful for verifying
that wetlands are classified properly and for inves-
tigating how a wetland is damaged. Data or meth-
ods from existing functional assessments may be
useful for helping to characterize the structural char-
acteristics of wetlands. For example, the
hydrogeomorphic approach (Brinson 1993) or state
rapid assessments can provide valuable informa-
tion to support the development of IBIs for wet-
lands. Ohio EPA (2001), for example, uses infor-
mation from its Ohio Rapid Assessment Survey to
gather information on structural characteristics of
wetlands. Ohio EPA also collects additional infor-
mation from water quality tests. Collecting physi-
cal and chemical information for wetlands that can
be useful for developing IBIs should include hydro-
logical indicators and soil characteristics.
Hydrological indicators include the following:
• Presence of conducted stormwater or agricul-
tural drainage
• Water marks, stained leaves, sediment depos-
its, or soil saturation in the top 30 cm (see U. S.
Army Corps of Engineers 1987)
• Water chemistry parameters (If the system is
seasonally flooded and water chemistry data
are required, this information must be taken into
account when developing the sampling design.
It may be necessary to sample water chemistry
at different times than vegetation sampling. Pa-
rameters to analyze might include pH, dissolved
oxygen, conductivity, total phosphorus, nitro-
gen, total suspended solids, chloride, metals (in
some instances), and total organic carbon)
• Percent salinity and conductivity
• HGM class, for data on site hydrology
• Temporal and spatial patterns of water area and
depth
Soils can be easily characterized using a stan-
dard soil probe. The following soil data should
be recorded in each vegetation community type:
• Thickness of the organic layer
• Soil texture
• Color as determined by a Munsell Color (1975)
soil chart
• Presence of mottles and their size and color as
well as the presence of oxidized root channels
Depending on the study goals, it may be neces-
sary to collect soil samples for analysis. Standard
analysis includes pH, percent organic matter, nutri-
ents, and perhaps metals. Total phosphorus can be
a good indicator of disturbance and the deposition
of heavy sediment loads. Also, calcium levels in
the soil may be a good index of stress severity.
SUMMARIZE SAMPLE
DATA BY BIOLOGICAL
ATTRIBUTES
A spreadsheet or database is use-
ful at this point to summarize
sample data. Many spreadsheet
applications (e.g., Lotus 1-2-3
and Microsoft Excel) are easy to
learn, but they can be cumber-
some and difficult to use for ex-
ploratory analysis. Database ap-
plications are more difficult to
learn, but they offer more features
and flexibility for conducting exploratory analysis
and constructing lists based on certain parameters.
Some states use a combination of spreadsheets, da-
tabases, and statistical software. Regardless of the
type of computer software used, the data from field
23
-------
data sheets must be entered into a computer and
summarized on the basis of the list of attributes. Field
data sheets often include a list of species or taxa
with a number next to those found at a site. The
number depends on the assemblages monitored
(e.g., the number of individuals or the percent cover
of a species). After the data are entered into the
computer, they must be summarized based on the
attributes.
EVALUATE ATTRIBUTE
PERFORMANCE ACROSS A
GRADIENT OF HUMAN
DISTURBANCE
The need to test and validate bio-
logical responses of attributes and
metrics across degrees of human
disturbance is a core assumption
of the IBI (Karr and Chu 1999).
Ideally, metrics that are incorpo-
rated into a multimetric index
should be relatively easy to mea-
sure and interpret. They should
change in a predictable fashion.
The metric should be sensitive to a range of bio-
logical disturbances and not narrowly focused on
one particular aspect of the community (e.g., spe-
cies richness). Most importantly, metrics must be
able to discriminate between human disturbances
and the background "noise" of natural variability.
Human impact should be the focus of biological
monitoring (Karr and Chu 1999).
The process for selecting metrics for use in a
multimetric index involves testing a large set of bio-
logical attributes (candidate metrics) and then se-
lecting the ones that are most sensitive to various
aspects of human disturbance. Although large num-
bers of attributes may need to be explored while
developing a multimetric index, it is inevitable that
there will be spurious relationships when consider-
ing large numbers of disturbance-attribute pairings.
A good metric will show a strong signal (response)
to increased disturbance and does not give mixed
signals. Attributes that show large variation (ex-
tremely wide ranges in response when data from a
variety of sites are plotted) will have less utility. For
example, the following simplified graphs show some
acceptable relationship for metrics:
The simplified graphs below show relationships that have limited acceptability. Exceptions are noted with
the two middle two panels, which indicate peak attribute responses with intermediate levels of disturbance.
Attributes with such responses may make appropriate metrics with proper adjustments in metric scoring.
X-Axis = Increasing Human Disturbance
Y-Axis = Attribute Value
D
D D
D D D
D D
D
D
X-Axis = Increasing Human-Disturbance
Y-Axis = Attribute Value
24
-------
SELECT METRICS FROM
BEST PERFORMING
ATTRIBUTES
For most taxa, at least 5 metrics
(but preferably 8-12) should be
defined and selected to construct
a multimetric index. Each metric
should reflect the quality of a dif-
ferent aspect of biota that re-
sponds in a different manner to
disturbances to wetlands
(Margalev 1963, Fausch et al.
1990, Hughes andNoss 1992).
Therefore, whenever possible,
care should be taken to select metrics from several
different metric categories (e.g., species composi-
tion and richness, tolerance and intolerance, trophic
composition, and population characteristics) to en-
sure that response is derived from a range of influ-
ences and that redundancies are minimized. In gen-
eral, the wider the range of environmental influences
represented by the metrics the better (Table 2). For
example, if long-lived taxa requiring years to ma-
ture are present, one can infer that the spatial and
temporal components they require are also present.
Excessive production of herbivorous species may
be indicative of excessive nutrients. High levels of
toxic substances may be inferred from the frequent
occurrence of individuals with disease or other
anomalies (Karr and Chu 1999).
The performance of each attribute should be evalu-
ated by assessing how well it does the following:
(1) increases or decreases along a gradient of hu-
man disturbance, (2) separates the least from the
most impaired sites, (3) provides similar values for
similarly impaired sites, and (4) provides a unique
(nonredundant) discriminatory response (Karr et al.
1997). Several graphical approaches and statisti-
cal tests may be used to evaluate attribute perfor-
mance. Each may be used either individually or in
concert with another to screen out attributes that
do not perform acceptably and retain those that do.
One frequently used approach is to create bar graphs
or box plots showing means or medians and vari-
ances of a particular attribute at sites believed to be
least and most impaired (Mundahl and Simon
1999). Several commercial software programs can
do this. The degree of separation between the least
and most impaired sites can then form the basis for
retaining or discarding the attribute for subsequent
analyses (Figure 4). The statistical significance of
the separation can be confirmed using standard sta-
tistical tests such as t tests.
Another frequently used approach is to compare
attribute data not just from the extreme sites, but
from all sites across the spectrum of human distur-
bance. For that comparison, the disturbance gra-
dient can be based on a single variable representing
one or more human disturbances or several vari-
ables or an index representing multiple human
disturbances (Figures 5 and 6). The relationship
can be expressed either graphically (scatter plot)
or by a comparison of correlation coefficients, such
as Pearson's correlation coefficient (Figure 5).
Based on the degree of correlation, certain attributes
may be retained and others may be eliminated
(Figure 7).
Attributes that contain many of the same taxa may
be considered redundant, and although some re-
dundancy is acceptable, seek to reduce double
counting or using the same taxa over and over. Re-
dundancy can be tested statistically, for example,
through factor analyses (Hatcher 1994) or by sim-
ply examining similarities in the taxa groupings that
form each attribute. Simple tables can be con-
structed to compare metric performance over the
various tests.
25
-------
FIGURE 4: EVALUATION OF
METRIC PERFORMANCE.
Examples of bar graphs illustrating the
degree to which attributes separate
least- from most-disturbed sites
(expressed in mean percentages).
Based on degree of separation two of
the attributes may be retained for
further evaluation (% Odonates and
% Exotic Plants) while the other may
be eliminated (% Trophic Generalists)
(hypothetical).
% Odonates % Exotic
Plants
% Trophic
Generalists
16
14
$ 12
! 10
2
5 8
I—
a) 6 -
I 4-
O
2
0
+
^
•
n n
+
• A A
CA
D n D+ n AD
^ E> + A
GACA A
• • Al «O A
I
1 1.2 1.4 1.6 1.8 2
Log Zn (sediments)
• Ref
DAg
AUrb
R2 = 0.36
At
A
2.2 2.4
FIGURE 5: SCATTER PLOT ILLUSTRATING METRIC (GRASSLIKE TAXA
RICHNESS) RESPONSE TO A SINGLE VARIABLE (ZINC CONCENTRATIONS)
REPRESENTING THE GRADIENT OF HUMAN DISTURBANCE.
R2 = Pearson's correlation coefficient; Ref = reference wetlands; Ag = wetlands with agricultural
impairments; Urb = wetlands with urban impairments (Helgen and Gernes in press).
26
-------
FIGURE 6: EVALUATION
OF ATTRIBUTE
PERFORMANCE OVER A
COMBINED SET OF
DISTURBANCES.
Ref = reference wetlands; AgLo =
wetlands with low levels of
agricultural impairment; SwMo =
wetlands with moderate levels of
stormwater impairment; AgHi =
wetlands with high levels of
agricultural impairment; and SwHi
= wetlands with high levels of
stormwater impairment. Based on
the relationship, one attribute
(number ofOdonate genera) may be
retained, while the other (number of
leech genera) may be eliminated
(Gernes and Helgen 1999).
Odonata and Influence Categories
7
« 6-
re
§ 5-
•o
24
o
re 3-
0)
C 9 -
CO -^ (Jl O
* A
* m A
• X XX
• MAM X4K
A X
01 2 3 4 5 £
Disturbance Category
*Ref
•Agio
AsWMo
XAgHi
XSWHi
FIGURE 7: SCATTER
PLOT DEMONSTRATING
CLOSE CORRELATION
BETWEEN A WETLAND
MACROINVERTEBRATE IBI
AND A DISTURBANCE
GRADIENT DERIVED FROM
A COMBINATION OF
HUMAN DISTURBANCES.
Ref = reference wetlands; Ag =
wetlands with agricultural
impairments; Urb = wetlands with
urban impairments (Helgen and
Gernes in press).
50
45 -
40 -
00
« 3!
1 30 H
01
w 25
15 -
10
Invertebrate IBI and Disturbance
D
A
20 40 60
Disturbance Score
80
100
27
-------
SCORE EACH INDIVIDUAL
METRIC
The metric evaluation process
should cull attributes, even
those that may show some re-
lationship to the gradient of hu-
man disturbance, to select
those few metrics that are
highly sensitive to impairments
yet not redundant, to form the
IBI. The selected metrics then
can be scored by assigning val-
ues, such as 5, 3, or 1, depend-
ing on whether the data they represent are compa-
rable to, deviate somewhat from, or deviate greatly
from values exhibited by the least impaired wet-
lands (Karr et al. 1986). Some metrics will de-
crease with added human disturbance (positive
metrics) and others will increase (negative metrics);
each should be scored accordingly. Several tech-
niques have been used to score metrics, each with
the objective of assigning relative values to reflect
the degree to which each metric departs from ex-
pected conditions. Scoring may be accomplished
by determining the range in values (minimum and
maximum) for each metric and then dividing those
data into equal thirds. Metric values falling in the
higher third of the range are assigned a score of 5,
those in the middle third scored a 3, and those in
the lower third scored a 1; if the data are negatively
correlated, the scoring is reversed (Table 3).
Another scoring alternative has been used in
streams, in which a variable, such as size of stream
drainage, is known to influence a metric's response.
In such cases, a trisection technique is used to di-
vide and score scatter plot data (size of stream drain-
age vs. metric value) to account for the influence of
the variable (Lyons 1992). Although yet to be docu-
mented for wetlands, it is possible that similar influ-
ences exist and should be taken into consideration
when individual metrics are scored. Maximum spe-
cies richness lines or lines that represent the upper
limit of scoring for other metrics can be calculated
though regression analysis; species/area curve plot-
ting; or by best-fit lines, using professional judg-
ment. Care should be taken to avoid outliers in
data that may skew the scoring. This process should
be as objective as possible; rules should be de-
signed for the scoring procedure. Note that scor-
ing should apply only to wetlands in the same class.
For example, take care to avoid having the best
bog receive a score of 25 out of 50 and the best
marsh a 49 out of 50, which would incorrectly im-
ply that bogs are not as healthy as marshes. A pris-
tine bog should receive a 50 compared with other
bogs, and a pristine marsh should receive a 50 com-
pared with other marshes.
CALCULATE TOTAL IBI
SCORE FOR ALL SITES
An IBI is composed of the
summed response signatures of
the individual metrics that col-
lectively provide a relative mea-
sure of biological condition and
individually point to likely
causes of degradation at differ-
ent sites (Karr et al. 1986,
Yoder and Rankin 1995). An
IBI score can be calculated for
each site by applying the scoring criteria to the data
from each site (Table 4). If the metrics selected are
closely correlated to the gradient of human distur-
bance, then the IBI that is derived from the com-
posite of those metrics will be also (Figure 7). Once
metric scores have been totaled, various interpre-
tations can be made. For example, the same appli-
cation can be used for other wetlands in the region
and before and after studies can be performed to
assess the relative effect of various conservation
practices on wetlands. Biological criteria can be
established to help support water quality obj ectives.
Or, analyses can be performed to determine which
28
-------
TABLE 4: INDIVIDUAL METRIC SCORES FOR INVERTEBRATE METRICS
SITE
i
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
CHIRO
5
5
3
3
5
1
3
1
3
3
3
3
3
1
3
3
3
3
1
1
3
1
1
1
1
ODON
5
5
3
5
5
5
3
3
3
1
1
3
1
3
1
1
1
1
1
3
1
3
1
1
1
CORIX%
5
5
5
3
5
5
5
5
5
3
1
3
1
5
3
1
3
3
3
3
1
1
1
1
1
LEECH
5
5
5
5
3
3
5
5
3
3
3
1
3
5
3
5
3
3
3
3
3
1
3
3
3
ETSD
5
5
5
5
5
5
3
3
1
3
3
3
3
1
3
1
1
1
3
3
1
1
1
1
1
ERP%
5
5
5
5
5
5
3
5
3
1
3
5
5
5
5
5
5
3
5
3
5
1
1
1
1
TAXTOT
5
3
5
5
3
3
1
5
3
5
3
3
3
3
1
3
3
5
3
1
1
3
3
1
1
INTOL
5
5
5
3
5
5
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
3DOM%
5
5
3
5
5
3
5
3
3
3
3
3
3
1
3
1
1
1
1
1
1
3
1
3
3
SNAIL.TX
5
5
5
5
1
3
5
1
3
3
5
1
3
1
3
3
3
1
1
3
3
3
3
3
1
TYPE
Ref
Ref
Ref
Ref
Ref
Ref
Ag
Ag
Ag
Ag
SW
SW
SW
SW
SW
SW
Ag
SW
SW
SW
Ag
Ag
SW
SW
Ag
IBI
50
48
44
44
42
38
34
32
28
26
26
26
26
26
26
24
24
22
22
22
20
18
16
16
14
CONDITION
Exc
Exc
Exc
Exc
Exc
Exc
Mod
Mod
Mod
Mod
Mod
Mod
Mod
Mod
Mod
Mod
Mod
Poor
Poor
Poor
Poor
Poor
Poor
Poor
Poor
Chiro, Chironomid genera; Odon, Odonata genera; Corlx%, Corixidae proportion; Leech, leech genera; ETSD, ; Erp%, Erpobdella proportion; TaxTot,
total taxa; Intol, # of intolerant taxa; 3Dom%, proportion of dominant 3 taxa; Snail Tx, snail taxa. Type Ref, reference wetland; Ag, agricultural-
influenced wetland; SW, stormwater-influenced wet and. Exc, excellent; Mod, moderate
Note: Condition classification = 37-50 as excellent, 24-36 as moderate, and 10-23 as poor (Gernes and Helgen
1999).
29
-------
metrics are contributing most heavily to sites with
low scores, thus helping to diagnose causes of im-
pairments for particular sites (Figure 8).
INTERPRET IBI AND
REPORT DATA
Perhaps the greatest benefit of
an IBI is that it summarizes and
presents complex biological in-
formation in a format that is eas-
ily communicated to managers
and the public. Most people
can understand plant and ani-
mal IBIs more easily than they
can understand complex statis-
tical calculations or abstract
chemical and physical wetland
functions. To help with the interpretations, integrity
classes can be developed to classify sites, along
with narrative descriptions of relative biological con-
dition (Table 5). Although an IBI score is helpful
for quickly communicating the overall condition of
a wetland, most of the valuable information lies in
the individual metrics. When bioassessment results
are reported, the IBI score should be accompa-
nied by (1) a narrative description of overall biotic
condition in comparison to reference wetlands of
the same region and wetland type, (2) numeric val-
ues of each metric, and (3) narrative descriptions
of each metric in comparison to reference condi-
tions of the same region and wetland type. For more
information about how IBIs can be used to improve
wetland management, refer to Module 5: Adminis-
trative Framework for Implementation of Wetland
Bioassessment Program
Range of Possible
Scores
Reno Crow Orchard
Wetlands
Winter
D# Snail Taxa
• # Odonata Taxa
D# Leech Taxa
• # Intolerant Taxa
D#ETSD
• # Midge Taxa
D% 3 Dominants
D% Erpobdella
• % Water Boatmen
D Total #Taxa
FIGURE 8: EXAMPLE OF WETLAND INDEX OF BIOLOGICAL
INTEGRITY SCORES.
From a Minnesota study for wetlands showing the range in scores and contribution of each metric
(Gernes and Helgen 1999). Reno and Crow are reference sites, Orchard receives urban stormwater,
Winter has heavy influences from agriculture.
30
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TABLE 5: TOTAL IBI SCORES, INTEGRITY CLASSES, AND THEIR ATTRIBUTES
FOR STREAMS IN A REGIONAL REFERENCE
TOTAL IBI SCORE
(SUM FOR 12
INTEGRITYMETRIC
RATINGS)
50-60
40-49
30-39
20-29
10-20
CLASS
Excellent
Good
Fair
Poor
Very Poor
ATTRIBUTES
Comparable to the best situations in the regional subclass without human
disturbance; contains all species expected for the region, including the most
intolerant forms; exhibits balanced trophic structure and reproductive success.
Species richness somewhat below expectation, especially due to the loss of themost
intolerant forms; some species are present with less than optimal abundances; trophic
structure and reproduction shows some sign of stress. Presence of some invasive or
non-native species.
Signs of additional deterioration include loss of intolerant forms, fewer species, highly
skewed trophic structure (e.g., increasing frequency of omnivores or tolerant species);
older age classes or top predators may be rare.
Dominated by omnivores, tolerant forms, and habitat generalists; few top carnivores;
reproductive and condition factors commonly depressed; hybrids or diseased
individuals often present. Invasive or non-native species abundant.
Dominated by highly tolerant forms or invasive species; hybrids may be common;
disease, lesions, parasites, and other anomalies may be regular. Complete absence of
less tolerant forms.
Source: Modified from Karretal. 1986.
Note: Narrative description of integrity classes may differ substantially for wetlands.
31
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GLOSSARY
Assemblage An association of interacting popu-
lations of organisms in a wetland or other habitat.
Examples of assemblages used for biological as-
sessments include algae, amphibians, birds, fish,
macroinvertebrates (e.g., insects, crayfish, clams,
snails), and vascular plants.
Attribute A measurable component of a biologi-
cal assemblage. In the context of biological as-
sessments, attributes include the ecological pro-
cesses or characteristics of an individual or assem-
blage of species that are expected, but not empiri-
cally shown, to respond to a gradient of human dis-
turbance.
Benthos The bottom fauna of bodies of water.
Biological assessment Using biomonitoring data
of samples of living organisms to evaluate the con-
dition or health of a place (e.g., a stream, wetland,
orwoodlot).
Biological integrity "the ability of an aquatic eco-
system to support and maintain a balanced, adap-
tive community of organisms having a species com-
position, diversity, and functional organization com-
parable to that of natural habitats within a region"
(Karr and Dudley, 1981).
Biological magnification The increase in con-
centration of some material in organisms compared
with its concentration in the environment.
Biological monitoring Sampling the biota of a
place (e.g., a stream, a woodlot, or a wetland).
Biota The plants and animals living in a habitat.
Community All the groups of organisms living
together in the same area, usually interacting or de-
pending on each other for existence.
Competition Utilization by different species of
limited resources of food or nutrients, refugia, space,
ovipositioning sites, or other resources necessary
for reproduction, growth, and survival.
Composition (structure) The composition of the
taxonomic grouping, such as fish, algae, or
macroinvertebrates, relating primarily to the kinds
and number of organisms in the group.
Continuum A gradient of change.
Disturbance "Any discrete event in time that dis-
rupts ecosystems, communities, or population
structure and changes resources, substrate avail-
ability or the physical environment" (Picket and
White 1985). Examples of natural disturbances are
fire, drought, and floods. Human-caused distur-
bances are referred to as "human influence" and
tend to be more persistent over time, e.g., plowing,
clearcutting of forests, conducting urban stormwater
into wetlands.
Diversity A combination of the number of taxa
(see taxa richness) and the relative abundance of
those taxa. A variety of diversity indexes have been
developed to calculate diversity.
Dominance The relative increase in abundance
of one or more species in relation to the abun-
dance of other species in samples from a habi-
tat.
Ecosystem The community plus its habitat; the
connotation is of an interacting system.
Ecoregion A region defined by similarity of cli-
mate, landform, soil, potential natural vegetation,
hydrology, and other ecologically relevant variables.
Functional feeding groups (FFGs) Groupings
of different invertebrates based on the mode of food
acquisition rather than the category of food eaten.
The groupings relate to the morphological struc-
tures, behaviors, and life history attributes that de-
termine the mode of feeding by invertebrates. Ex-
amples of invertebrate FFGs are shredders, which
chew live plant tissue or plant litter, and scrapers,
which scrape periphyton and associated matter from
substrates (see Merritt and Cummins 1996a,b).
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Functional groups A means of dividing organ-
isms into groups, often based on their method of
feeding (e.g., shredder, scraper, filterer, predator),
type of food (e.g., fruit, seeds, nectar, insects), or
habits (e.g., burrower, climber, clinger).
Gradient of human influence The relative rank-
ing of sample sites within a regional wetland class
based on the estimation of degree of human distur-
bance (e.g., pollution and physical alteration of
habitats).
Habitat The sum of the physical, chemical, and
biological environment occupied by individuals of a
particular species, population, or community.
Hydrology The science of dealing with the prop-
erties, distribution, and circulation of water both on
the surface and under the earth.
Impact A change in the chemical, physical (in-
cluding habitat), or biological quality or condition
of a body of water caused by external forces.
Impairment Adverse changes occurring to an eco-
system or habitat. An impaired wetland has some
degree of human influence affecting it.
Index of Biologic Integrity (IBI) An integrative
expression of the biological condition that is com-
posed of multiple metrics. It is similar to economic
indexes used for expressing the condition of the
economy.
Intolerant taxa Taxa that tend to decrease in
wetlands or other habitats that have higher levels of
human disturbances, such as chemical pollution or
siltation.
Least impaired site Sample sites within a re-
gional wetland class that exhibit the least degree of
detrimental effect. Such sites help anchor gradients
of human disturbance and are commonly referred
to as reference sites.
Macroinvertebrates Animals without back-
bones that are caught with a 500-800 micron
mesh net. Macroinvertebrates do not include
zooplankton or ostracods, which are generally
smaller than 200 microns in size.
Metric An attribute with empirical change in value
along a gradient of human disturbance.
Most impaired site Sample sites within a re-
gional wetland class that exhibit the greatest degree
of detrimental effect. Such sites help anchor gradi-
ents of human disturbance and serve as important
references, although they are not typically referred
to as reference sites. Such sites may be referred to
as impaired or disturbed sites.
Munsell color The color of soil based on its
chroma and hue as determined by a chart in the
bookMunsell Soil Color Charts (Munsell Color
1975).
Mottles Spots or blotches of different color or
shades of color interspersed within the dominant
color in a soil layer, usually resulting from the pres-
ence of periodic reducing soil conditions.
Omnivores Organisms that consume both plant
and animal material.
Population A set of organisms belonging to the
same species and occupying a particular area at the
same time.
Predator An animal that feeds on other animals.
Reference site As used with an Index of Bio-
logical Integrity, a minimally impaired site that
is representative of the expected ecological condi-
tions and integrity of other sites of the same type
and region.
Taxa A grouping of organisms given a formal taxo-
nomic name, such as species, genus, and family.
The singular form is taxon.
Taxa richness The number of distinct species or
taxa that are found in an assemblage, community,
or sample.
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Tolerance The biological ability of different
species or populations to survive successfully
within a certain range of environmental conditions.
Tolerance (range of) The set of conditions within
which an organism, taxa, or population can survive.
Tolerant taxa Taxa that tend to increase in wet-
lands or other habitats that have higher levels of
human disturbances, such as chemical pollution or
siltation.
Trophic Feeding; thus, pertaining to energy trans-
fers.
Wetland(s) (1) Those areas that are inundated
or saturated by surface or groundwater at a
frequency and duration sufficient to support, and
that under normal circumstances do support, a
prevalence of vegetation typically adapted for life
in saturated soil conditions [EPA, 40 C.F.R.§
230.3 (t)/USAGE, 33 C.F.R. § 328.3 (b)]. (2)
Wetlands are lands transitional between terrestrial
and aquatic systems where the water table is
usually at or near the surface or the land is
covered by shallow water. For the purposes of
this classification, wetlands must have one or
more of the following three attributes: (a) at least
periodically, the land supports predominantly
hydrophytes, (b) the substrate is predominantly
undrained hydric soil, and (c) the substrate is
nonsoil and is saturated with water or covered by
shallow water at some time during the growing
season of each year (Cowardinetal. 1979). (3)
The term "wetland" except when such term is part
of the term "converted wetland," means land that
(a) has a predominance of hydric soils, (b) is
inundated or saturated by surface or ground
water at a frequency and duration sufficient to
support a prevalence of hydrophytic vegetation
typically adapted for life in saturated soil
conditions, and (c) under normal circumstances
does support a prevalence of such vegetation.
For purposes of this Act and any other Act, this
term shall not include lands in Alaska identified as
having a high potential for agricultural develop-
ment which have a predominance of permafrost
soils [Food Security Act, 16U.S.C. 801(a)(16)].
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