wEPA
United States Environmental Office of Water EPA-822-R-02-019
Protection Agency Washington, DC 20460 March 2002
METHODS FOR EVALUATING WETLAND CONDITION
#9 Developing an Invertebrate Index
of Biological Integrity for Wetlands
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wEPA
United States Environmental Office of Water EPA-822-R-02-019
Protection Agency Washington, DC 20460 March 2002
METHODS FOR EVALUATING WETLAND CONDITION
#9 Developing an Invertebrate Index
of Biological Integrity for Wetlands
Principal Contributor
Minnesota Pollution Control Agency
Judy Helgen, PhD
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 e nrichment 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 EPA approval, endorsement, or recommendation.
APPROPRIATE CITATION
U.S. EPA. 2002. Methods for Evaluating Wetland Condition: Developing an Invertebrate Index
of Biological Integrity for Wetlands. Office of Water, U.S. Environmental Protection Agency,
Washington, DC. EPA-822-R-02-019.
ACKNOWLEDGMENTS
EPA acknowledges the contributions of the following people in the writing of this module:
Judy Helgen (Minnesota Pollution Control Agency), Jeanne DiFranco (Maine Department of Environ-
mental Protection), Mike Gray (Ohio Environmental Protection Agency), Peter Lowe (United States
Geological Survey), Randy Apfelbeck (Montana Department of Environmental Quality), and Russ
Frydenborg (Florida Department of Environmental Protection).
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
11
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CONTENTS
FOREWORD v
LIST OF "METHODS FOR EVALUATING WETLAND
CONDITION" MODULES vi
SUMMARY 1
PURPOSE 1
INTRODUCTION 1
PROCESS FOR DEVELOPING AN INVERTEBRATE IBI
FOR WETLANDS 3
STEP i. SELECT STUDY SITES 5
STEP 2. PLAN THE INVERTEBRATE SAMPLING 5
STEP 3. FIELD SAMPLING METHODS AND DECISIONS 8
STEP 4. SAMPLE PROCESSING PROCEDURES l5
STEP 5. METRIC ANALYSIS 18
A. SELECTION OF ATTRIBUTES 18
B. FORMING THE IBI 22
CONCLUSIONS AND RECOMMENDATIONS 23
REFERENCES 25
APPENDIXES 34
GLOSSARY 46
LIST OF FIGURES
FIGURE l: INVERTEBRATE IBI SCORE PLOTTED AGAINST AN
ESTIMATION OF HUMAN DISTURBANCE ON LARGE
DEPRESSIONAL WETLANDS IN MINNESOTA 2
FIGURE 2: FLOWCHART FOR DEVELOPING AN INVERTEBRATE INDEX OF
BIOLOGICAL INTEGRITY 4
FIGURE 3: ILLUSTRATION OF SAMPLING SITES IN A WETLAND WITH
EMERGENT VEGETATION SHOWN AS SYMBOLS 7
ill
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FIGURE 4: FRAMED SCREEN FOR SEPARATING VEGETATION FROM
INVERTEBRATES DURING DIPNETTING 12
FIGURES: ACTIVITY TRAPS USED BY MINNESOTA 13
FIGURE 6: TOTAL NUMBER OF INVERTEBRATE TAXA PLOTTED AGAINST
THE LOG OF THE CHLORIDE IN THE WATER (MG/L) FROM
LARGE DEPRESSIONAL WETLANDS IN MINNESOTA 19
FIGURE 7: INTOLERANT TAXA PLOTTED AGAINST THE LOG OF
PHOSPHORUS (MG/L) IN THE WATER OF LARGE
DEPRESSIONAL WETLANDS IN MINNESOTA 2O
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
INTRODUCTION
r I The invertebrate module gives guidance for
J. developing an aquatic invertebrate Index of
Biological Integrity (IBI) for assessing the condi-
tion of wetlands. In the module, details on each
phase of developing the IBI are given. First, in the
planning stage, invertebrate attributes are selected,
the wetland study sites are chosen, and decisions
are made about which stratum of the wetland to
sample and what is the optimal sampling period or
periods. Then, field sampling methods are chosen.
The module describes field methods used in sev-
eral States, and gives recommendations. Labora-
tory sampling procedures are reviewed and dis-
cussed, such as whether and how to subsample,
and what taxonomic level to choose for identifica-
tions of the invertebrates. Specific categories of
attributes, such as taxa richness, tolerance, feeding
function, and individual health are discussed, with
examples. Appendices to the invertebrate module
give details about the advantages and disadvantages
of using invertebrates, of the different attributes, of
various field sampling methods, and of lab process-
ing procedures as used by several State and Fed-
eral agencies. The module and appendices give a
detailed example of one State's process for devel-
oping an invertebrate IBI, with a table of metrics
with scoring ranges, and a table of scores of indi-
vidual metrics for 27 wetlands. A glossary of terms
is provided.
PURPOSE
r I The purpose of the invertebrate module is to
J. describe the advantages of using aquatic
invertebrates for assessing the condition of
wetlands, and to present approaches for develop-
ing IBIs for wetlands.
r IJ his module describes the advantages of using
J. aquatic invertebrates for assessing the condi-
tion of wetlands and presents approaches for de-
veloping an invertebrate IBI for wetlands. Pro-
cesses, methods, and examples of invertebrate IBIs
for wetlands are presented, along with summaries
of approaches currently used in several States. The
module is based primarily on work done on ponded
freshwater wetlands, but the approaches described
can be modified for other types of wetlands. The
module describes development of the IBI, but other
indexes and approaches for assessing the condition
of wetlands, particularly multivariate techniques
(Davies et al. 1999, Reynoldson et al. 1997), can
be used. A glossary of terms is also provided.
WHY USE AQUATIC INVERTEBRATES TO
ASSESS WETLANDS CONDITION?
Because they respond to many kinds of
stressors to wetlands, as shown in Figure 1.
WHAT ARE THE ADVANTAGES AND
DISADVANTAGES OF USING AQUATIC
INVERTEBRATES?
Several advantages and disadvantages of using
aquatic invertebrates are reviewed in Appendix A.
Briefly, some of the advantages of using inverte-
brates for biological assessments of wetlands are:
They are commonly and widely distributed in
many types of wetlands (Batzer et al. 1999).
They respond with a range of sensitivities to
many kinds of stressors; they are commonly
used for toxicity testing and ecological
assessments in waterbodies (e.g., see Barbour
et al. 1999, Beck 1977, Cairns and
Niederlehner 1995, deFur et al. 1999, Euliss
and Mushet 1998, Hart and Fuller 1974,
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Heliovaara and Vaisanen 1993, Helgen and
Gernes in press, Hellawell 1986, Kerans and
Karr 1994, Lewis et al. 1999, Morris et al.
1989, Rainbow 1996, Saether 1979, Servos
1999, Stuijfzand et al. 2000, Warwick 1980).
Many aquatic invertebrates complete their life
cycles in wetlands; they are exposed directly to
physical, chemical, and biological stressors
within the wetland (Clarke 1981, Driver 1977,
Hanson and Swanson 1989, Fairchild 2000,
Klemm 1982, Larson 1987, Mackie, in press;
Merritt and Cummins 1996a; Walker 1953,
1958, Walker and Corbet 1975, Westfall and
May 1996, Wiggins 1996, Wiggins etal. 1980,
Wrubleski 1987).
Aquatic invertebrates are important in wetland
food webs of wildlife (Bart et al. 1992, Colburn
1997, Deutschman 1984, Eldridge, J. 1990,
Fredrickson and Reid 1988, King and
Wrubleski 1998, Krapu and Reinecke 1992,
Swanson et al. 1977, Swanson et al. 1985,
Wissinger 1999).
They have public appeal in citizen monitoring
programs (see Module 8, Volunteers and
Wetland Biomonitoring; Helgen and Gernes
1999).
Many wetland invertebrates complete the life cycle
from egg to adult in a wetland, and therefore are
directly exposed to wetland conditions and stres-
sors. In infrequently flooded, seasonal, and tem-
porary wetlands, invertebrates will have shorter life
cycles of days to weeks (Schneider and Frost 1996,
Wiggins etal. 1980). In more regularly flooded,
more permanent wetlands, invertebrates with longer
life cycles of weeks to months, such as dragonflies
or crayfish, will be present. Populations of inverte-
brates with shorter life cycles, such as fairy shrimp
and mosquitoes, will respond more quickly to hu-
man disturbances, but they may recover more
quickly, either from resting eggs or from
recolonization by adult insects. Invertebrates with
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FIGURE l : INVERTEBRATE IBI SCORE PLOTTED AGAINST AN ESTIMATION
OF HUMAN DISTURBANCE ON LARGE DEPRESSIONAL WETLANDS
IN MINNESOTA.
The IBI has 1 0 scored metrics; the gradient combines factors of chemical pollution and alterations in the
buffer zone and near wetland landscape.
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longer life cycles, such as dragonflies, some finger-
nail clams, and snails, will experience longer expo-
sure to wetlands conditions. In some cases, recov-
ery from losses of juveniles may take longer, be-
cause of more limited seasons of egg laying by adults
and longer development times from egg to adult
(Corbet 1999).
The disadvantages of using aquatic invertebrates
for biological assessments are detailed in Appendix
A. The biggest challenge is the amount of staff time
and expertise that is needed for picking the organ-
isms from the samples and for identifications. Tech-
niques for reducing the amount of picking time, such
as using a screen under vegetation while dipnetting,
using activity traps, or by subsampling, will be de-
scribed below. Some State agencies or organiza-
tions may lack the laboratory facilities to do the work
in-house and will need to contract out the work.
When work is contracted out, it is important for
the proj ect managers to provide the contractor with
explicit protocols and procedures for identifications
and analysis in relation to the needs of the program.
An advantage of doing the work in-house is that
the staff involved can provide active input into the
development of the biological indexes and can par-
ticipate in implementing the findings into the State's
programs. Whether or not the identifications are
contracted out, it is vital to have scientists on staff
to provide active input into biocriteria development
and implementation.
In sum, disadvantages of using macroinvertebrates
are:
Sample processing takes a lot of staff time or
resources.
Organizations may lack facilities for processing
and identifying invertebrates.
PROCESS FOR
DEVELOPING AN
INVERTEBRATE IBI FOR
WETLANDS
A flow chart for developing an invertebrate
-/I IBI for wetlands is shown in Figure 2. A simi-
lar flowchart showing an example of the process
for developing an invertebrate IBI in Minnesota is
shown in Appendix K. Overall, the process in-
volves sampling invertebrate attributes of several
wetlands of similar class and region representing a
range of human disturbance or impairment, from
least to most disturbed. After sampling, the infor-
mation on the degree of impairment is related to the
measures of various invertebrate attributes to see
which of the attributes show predictable responses
to impairment. These attributes will constitute the
metrics for the IBI. Scores are assigned to each
metric to indicate the level of response to human
disturbance (see Module 6: Developing Metrics and
Indexes of Biological Integrity). The metric scores
are summed for the total IBI score. Decisions are
made as to which range of IBI scores indicates a
poor condition, i.e., not attaining designated use (if
one exists), or a moderate or excellent condition.
This module will focus primarily on the steps in the
process that relate to developing invertebrate IBIs.
Additional detail for this process can be found in
Module 4: Study Design, Module 7: Wetlands Clas-
sification, Module 6: Developing Metrics and In-
dexes of Biological Integrity, and Module 17: Land-
scape Characterization for Wetlands Assessments.
Additional information on biological monitoring of
wetlands is also available in Rader et al. (in press).
It needs to be stated that other approaches are
successful in evaluating the condition of waterbodies
with invertebrates. Multivariate methods for ana-
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STEP 1 :
SELECT STUDY
SITES
STEP 2:
PLAN INVERTEBRATE
SAMPLING
Select ecogeographic region
Decide on wetland class
Select sites within wetland classes that exhibit a
range of disturbances
Select invertebrate attributes of sensitivity, rich-
ness, tolerance, trophic structure, or other attributes
likely to respond to human disturbance
Gather literature about regional invertebrates for the
wetland class
Determine which strata of wetland to sample
Select optimal seasonal sampling period for maturity
of invertebrates
STEP 3:
FIELD SAMPLING
Select appropriate sampling methods for objectives
of the program
Pretest sampling methods to determine number of
samples to be taken per site, and to assure the
desired types of invertebrates are collected
Decide if samples will be preserved and
processed in the lab, or sorted and identified
in the field; write Standard Operating Procedures
Sample sites within the index period, at the same
time collect samples for chemical analysis and
assess the surrounding landscape
STEP 4:
SAMPLE PROCESSING
Decide to pick entire sample or subsample
Decide on taxonomic levels for identifications
establish database of taxa lists and ITIS codes
Develop Standard Operating Procedures and set up
a Quality Assurance plan for repicking and for
independent verifications of identifications
Establish a reference collection with several
specimens of each taxon
STEP 5:
METRIC ANALYSIS
Plot attribute data against human disturbance
gradient
Select most responsive 8-12 metrics
Score metrics by trisecting data or other method
Sum the metric scores for IB I, plot IBI against
disturbance gradient
FIGURE 2: FLOWCHART FOR DEVELOPING AN INVERTEBRATE INDEX OF
BIOLOGICAL INTEGRITY.
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lyzing invertebrate data are used for stream assess-
ments in the Biological Monitoring Program in Maine
(Davies and Tsomides 1997, Davies et al. 1995,
1999). Discriminant analysis of invertebrate data
predicts the degree of impairment by comparison
with known biological characteristics of the state of
Maine's four water quality management classes.
(See also Marchant et al. 1997, Norris 1995, Wright
1995, Hawkins and Carlisle in press, U.S. EPA
1998, Lake and Reservoir Bioassessment and
Biocriteria Appendix E). Reynoldson and others
(1997) found estimates of accuracy and precision
to be higher when multivariate techniques were used
for data analysis compared with multimetric meth-
ods. If multivariate analysis is used, it is important
to use a method that allows interpretation of pro-
portional attributes rather than one that is limited to
data on the presence or absence of taxa (see
Reynoldson et al. 1997). A disadvantage of multi-
variate methods is the complexity of setting up the
data analysis.
STEP i. SELECT STUDY SITES
To reduce natural variability, an ecoregion or eco-
logical region and a class of wetlands are chosen
for developing the IBI (see Module 7 on Classifi-
cation). It is necessary to select specific wetland
classes, because invertebrate assemblages may dif-
fer among classes of wetlands (in Batzer et al. 1999;
see Huryn and Gibbs, Leslie et al., Marshall et al.,
Smock et al., and others; Carlisle et al. 1999,
Weisberg et al. 1997). It is important to include
several least impaired or reference wetlands along
with a range of wetlands that are affected by human
disturbances. Sufficient numbers of least-impaired
reference wetlands and wetlands experiencing a
range of impairments are needed to detect signifi-
cant dose-response relationships between the in-
vertebrate attributes (Y axis) and the measures of
human disturbances (X axis). See the Glossary for
definitions of disturbance and human disturbance.
The impaired wetlands can be selected to target
the major types of human-caused stressors to wet-
lands, those that are most likely to be causing im-
pairment to the invertebrates within the region and
wetland class. Invertebrates exhibit a wide range
of sensitivities to human-induced stressors such as
pesticides, metals, siltation, acidification, loss of
vegetation or vegetation diversity, nutrient enrich-
ment, and changes in the oxygen regime (Adamus
1996, Beck 1977, Eyre et al. 1993, Helawell 1986,
Resh and Rosenberg 1984, Saether 1979).
Macroinvertebrates respond to disturbances in
wetland vegetation because invertebrates are de-
pendent on the vegetation as part of their food
source (Wissinger 1999), for attachment sites, refu-
gia (Corbet 1999, p. 164, Orr and Resh 1989),
and egg laying. Some dragonflies and damselflies
lay eggs on specific types of aquatic vegetation
(Sawchyn and Gillott 1974, Corbet 1999, p. 591).
STEP 2. PLAN THE INVERTEBRATE
SAMPLING
Selection of invertebrate attributes
Attributes are measures of the invertebrate com-
position to be tested to see if they show a graded
response, or dose-response, to human disturbances
such as chemical pollution, siltation, or habitat al-
teration. If a response is seen, the attribute will be
selected as a metric and scored as part of the over-
all IBI score. See Module 6: Developing Metrics
and Indexes of Biological Integrity. More detailed
information on the selection of invertebrate attributes
is given near the end of this module in Step 5 on
Metric Analysis. Appendix F lists advantages and
disadvantages of different kinds of attributes, and
Appendix I shows metrics used by Minnesota for
large depressional wetlands. Appendix G shows
the attributes used or tested by several States.
Attributes are selected from major categories of
invertebrate composition (Barbour et al. 1996, Resh
et al. 1995), such as measures of taxonomic rich-
ness, measures of tolerance proportions and intol-
erant taxa, measures related to trophic structure and
functional feeding groups (see Merritt et al. 1996,
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1999) and other measures related to longevity, in-
troduced or exotic species, and invertebrate health
or condition (see Diggins and Stewart 1998,
Hudson and Ciborowski 1996, Warwick 1980).
Several invertebrate attributes are tested, and the
data for the attributes are related to measures of
human influence. From the attributes that show sig-
nificant relationships with human disturbances, a set
of 8 to 12 are selected as metrics. An attribute that
does not show a significant response to human dis-
turbances will likely be discarded. However, if there
is some reason to think the attribute might show a
response to different kinds of stressors that were
not included in the study design, it might be retained
for further testing.
It is important to plan to measure the types of in-
vertebrates that would be expected to inhabit the
class of wetland in the ecological region of interest.
The taxonomic composition of the invertebrates will
likely differ in bogs, playa lakes, temporary ponds,
prairie potholes or riparian wetlands, for example
(seeBatzeretal. 1999). Information can be sought
from regional scientific literature and from inverte-
brate biologists in the area. Whatever the class of
wetland might be, the major categories of attributes
will be represented, such as taxa richness and tol-
erant and intolerant taxa, even if the taxonomic com-
position differs. If there is little preexisting informa-
tion on species composition for the particular wet-
land class, it may be helpful to do preliminary sam-
pling in reference wetlands to develop a list of spe-
cies and then select the attributes to be tested. This
could be done when the sampling methods are be-
ing tested.
Determine which stratum or zone(s) of the
wetland to sample
One decision is whether to attempt to sample the
entire wetland and all of its habitats, or to sample
defined zones or strata within the wetland. Wet-
lands have several zones that are related to the in-
fluence of hydrology and/or plant communities. For
example, freshwater marshes have shallow water,
emergent macrophyte, and floating-leafed and sub-
mersed aquatic plant zones. Bottomland forest
wetlands may have zones ranging from aquatic to
swamp to semipermanently flooded to seasonally
then temporarily flooded (Mitsch and Gosselink
1993). It may not be necessary to sample all the
zones in a wetland to assess its condition. Either
enough of the wetland habitat should be sampled to
assess its condition, or the area most sensitive to
impairment should be assessed. In a small wet-
land, sampling all the habitats may be possible, but
in larger wetlands the work effort may necessitate
choosing strata for the sampling and maintaining a
consistency among wetlands of the habitats that are
sampled. The choice can include the following con-
siderations:
Sample in the zone or stratum that is likely to
have the greatest variety and production of
macroinvertebrates,
Sample in the zone or stratum that is considered
to be most vulnerable or most affected by human
disturbances, or
Select a habitat type that is representative of
the wetland, as opposed to unique or minor in
extent; sample enough of the habitats to integrate
the conditions in the wetland.
See also Module 4: Study Design for Monitoring
Wetlands. Examples of the zones that were se-
lected by different States involved in wetland moni-
toring are given in Appendix B.
Aquatic macroinvertebrates occur in association
with benthic sediments, emergent vegetation,
submergent vegetation, and open-water habitats.
They colonize hard substrates such as tree roots or
rocks. Some feed on the microflora that colonize
the surfaces of plants and hard substrates; some
are predators on the smaller herbivorous or
detritivorous invertebrates. Different invertebrate
assemblages are associated with these different
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FIGURE 3: ILLUSTRATION OF SAMPLING SITES IN A WETLAND WITH
EMERGENT VEGETATION SHOWN AS SYMBOLS.
Two standardized dipnetting samples are taken from the wetland about 20-30 meters apart (DN1 andDN2).
Each sample consists of three to five sweeps repeated in two efforts (represented by two DNls and two
DN2s). Ten activity traps (BT) are placed at the edge and in representative areas of the near shore emergent
vegetation zone in water < 1 m deep. Wetland is not drawn to any scale. Method is used by Minnesota
(MPCA). See Appendixes B and C.
habitats, even with different kinds of wetland veg-
etation (Burton et al. 1999, Gathman et al. 1999,
King and Brazner 1999). In preliminary studies of
coastal wetlands, some invertebrate attributes dif-
fered among types of emergent vegetation zones.
Attributes were selected that gave consistent, rather
than contradictory, responses to human disturbance
among sites across four defined plant zones (Bur-
ton etal. 1999).
The vegetated areas of wetlands have been ob-
served to have more taxa of chironomids (Driver
1977) and aquatic beetles (Aitkin 1991, Timms and
Hammer 1988) and other taxa (Dvork 1987).
Emergent vegetation areas had greater richness
when compared with open water areas that lacked
submersed vegetation (Olson et al. 1995, Voigts
1976). If fish are present, open-water areas may
have more predation by fish on invertebrates
(Hanson and Riggs 1995). Having more taxa in
vegetated areas may not reflect direct herbivory on
the plants, but the conversion of macrophytes into
detritus is an important source of nutrition for inver-
tebrates (Euliss et al. 1999). Also, as stated previ-
ously, macrophytes provide refugia, substrates for
growth of algae and small organisms, and egg lay-
ing sites.
An example of sampling locations in a depres-
sional wetland in Minnesota is given in Figure 3.
Select the optimal seasonal sampling period
The seasonal index period is the window of time
when the sampling of the wetland is optimal to ob-
tain the most representative, mature invertebrate
community and the maximum number of identifi-
able taxa. The different and seasonal life cycle strat-
7
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egies of invertebrates present a challenge as to when
to sample, especially if the sampling is to be done
just once in a season. If the wetland is sampled too
early in the year, the invertebrates may be less ma-
ture, making the identifications more difficult. If the
wetland is sampled later in the season, there may
be emergences of aquatic insects from the wetland
and immigration of adult insects that fly into the
wetland from other waterbodies. If the wetland is
sampled too late in a season, the smaller wetlands
may have dried down or become choked with veg-
etation.
The seasonal index period will differ across dif-
ferent regions of the United States and it will differ
for different types of wetlands. Invertebrates are
known to undergo seasonal changes in populations
and species that inhabit a waterbody. Ideally, the
wetland should be sampled in more than one sea-
son; however, this may not be practical for State
programs. In selecting an index period, the follow-
ing should be considered:
The invertebrates should have developed
sufficiently to be identified by biologists.
The index period should bracket a time when
as many resident taxa as possible are present.
The index period is not during a time that the
wetland is likely to dry down or become
choked with vegetation (so it is still sampleable).
The index period could attempt to precede
maximum fish predation, if any, while still
encompassing the season of maximum richness
and development of invertebrates.
The index period should be shifted somewhat
to account for unusually late or early seasons
(the main goal is to optimize the number of
invertebrate taxa present and mature).
mature of some of the invertebrates (Davies et al.
1999), Minnesota (Gernes and Helgen 1999,
Helgen and Gernes in press) samples during June
when there is greater maturity in the Odonata and
more water in the wetlands. Wetlands in the more
southern location of a study set are sampled earlier
in the index period. Montana (Apfelbeck 1999)
samples the Plains Ecoregion in April to mid-June,
the Intermountain Valley and Prairie Ecoregion from
June to August, and the Rocky Mountain Ecoregion
from mid-June to September. RapidBioassessment
Protocols for Use in Streams and Wadeable Riv-
ers (Barbour et al. 1999) contains a discussion of
the sampling seasons for stream invertebrates.
STEP 3. FIELD SAMPLING METHODS
AND DECISIONS
Before the actual sampling for monitoring wetlands
takes place, several decisions need to be made.
These decisions will be based in a large part on the
program obj ectives or information needs that the
invertebrate IBI is addressing:
What strata or zones of the wetland to sample
(see discussion of selecting sampling stratum
above and see Module 4 on Study Design)
Whether to sample once or more than once
during the season (see discussion on selecting
seasonal index period above)
Whether to sample all habitats in the stratum or
zone (multihabitat approach), or selected
habitats
Whether the approach collects the range of
invertebrates needed for the attributes
What sampling methods will be used to collect
the desired invertebrates efficiently
How many samples can be processed in the
lab
See Appendix B for the approaches taken by dif-
ferent States and Appendix H for addresses of State
contacts. Maine samples in June, to obtain the most
Recommendations for field methods
Several methods for collecting invertebrates in
wetlands are described below and listed with ad-
8
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vantages and disadvantages in Appendix C. The
following are recommended, but may not be appli-
cable or suitable for researchers or State agencies
under certain circumstances.
Sample a stratum of the wetland that contains
most of the macroinvertebrates: often the
shallow areas have emergent or submerged
vegetation; very small wetlands can be sampled
all around the edges.
Sample once during the season, after
determining when the maximum development
of the invertebrates occurs, and take more than
one sample at that time; if resources permit,
sample in two seasons taking more than one
sample on each visit date.
Sample all habitats within the stratum or zone,
or sample selected habitats if they are known
to have a wide representation of invertebrates.
Use a dipnetting method with a standardized
and repeatable protocol; combine this with
activity traps to collect the motile predators (see
discussion of these and other methods below).
Determining the number of samples to take:
species richness and sampling effort
Once these decisions have been made, the sam-
pling methods should be pretested in the field to
ensure they collect the invertebrates that are needed
for the attributes and to determine the numbers of
samples that will be needed. In practice, States,
Tribes, and researchers often have to balance the
limitations of resources against the requirements for
validation of data. It is useful to test methods in
reference wetlands to determine how many samples
are needed to obtain the desired representation of
the invertebrate fauna.
It is well known in ecological research that the
number of species or taxa collected frequently in-
creases with the sampling effort (Magurran 1988).
A quantitative sampling method (e.g., cores or
Gerking samplers) will yield data on the density of
taxa or species per unit area sampled. A
semiquantitative sampling method (dipnetting, ac-
tivity traps), as described below, will record the
number of taxa per total sample count. This is called
numerical taxa richness. In either case, the number
of species or taxa usually increases with sample size,
i.e., with the number of samples taken or the area
sampled. For the purposes of comparing sites, it is
essential that the number of samples and area
sampled be the same at all sites.
Several samples should be taken with consistent
methods at all sites to determine how many samples
are necessary to collect a desired percentage of the
total number of species collected. Ideally, enough
samples will be collected to achieve the plateau level
at which taking more samples does not increase the
number of species. However, this may not be prac-
tical, because a plateau may not be reached even
with many samples (see Mackey et al. 1984).
Sparling et al. (1996) collected multiple samples at
the same sites and recorded the increases in the
percent of total invertebrate taxa with the increase
in the number of samples analyzed. In 1,2,3,4, 5,
and 6 samples there were, cumulatively collected,
40%, 56%, 60%, 64%, 68%, and 72% of the in-
vertebrate taxa, respectively. In addition to com-
paring the taxa gained by added sampling effort,
the effects on the final evaluation of the wetland,
which lead to the IBI or other index score, should
be gauged for each level of effort. To reduce vari-
ability, a minimum of three samples is recommended,
although each method should be tested for its vari-
ability if possible.
It may not be possible to do a power analysis at
the beginning of IBI development. Power analysis
determines how many samples need to be taken to
obtain enough statistical power to detect differences
among sites using the IBI scores. To do this, sev-
eral samples would be taken in each of several
wetlands that have a range of human disturbances.
For discussions of power analysis and the number
of samples to take, see Eckblad (1991), Allan
9
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(1984), and Green (1989). Several papers may
be helpful (Davies et al. 1995, 1999, Davies and
Tsomides 1997, Fore et al. 1994, Rankin and Yoder
1990, Rathbun and Gerritsen in press). Variability
in the biological data may increase with greater im-
pairment, as seen in biological monitoring in Ohio
streams (Rankin and Yoder 1990, Yoder 1991).
Select the appropriate sampling methods
The methods appropriate for sampling will depend
on the type of wetland and the goals of the sam-
pling. Appendix B describes sampling protocols
used by several states with advantages and disad-
vantages. The emergent or submerged vegetation
in wetlands presents a challenge for sampling. Se-
lected methods used in wetlands studies are sum-
marized in Appendix C with advantages and disad-
vantages. More detail on the methods can be ob-
tained from references cited in the text to follow.
See Batzer et al. (in Rader et al. in press) on sam-
pling invertebrates in wetlands.
There is a need for comparisons among the most
commonly used sampling methods for sampling in-
vertebrates, particularly for differences in inverte-
brate composition and attributes. Brinkman and
Duffy compared Gerking samplers, cores, activity
traps, and artificial substrates (1996) and found
Gerking samples collected significantly more taxa
than cores. Hyvonen andNummi (2000) compared
activity traps with corers, finding fewer active in-
vertebrates in core samples. Some of the articles
cited below have comparative studies of methods.
Is a quantitative sample necessary?
A quantitative sampling method collects inverte-
brates by trapping the column of water and/or the
bottom sediments from a known dimension of bot-
tom area. This permits calculating the number of
invertebrates per unit area of wetland bottom.
Quantitative methods may be particularly useful in
assessing the productivity of wetlands in relation to
waterfowl production. They are not as necessary
for developing IBIs (Karr and Chu 1999). Ex-
amples of quantitative sampling methods for
macroinvertebrates are the Gerking box sampler
(Gerking 1957, Anderson and Smith 1996); the
stovepipe sampler (see Wilding sampler in Welch
1948, Turner and Trexler 1997); and various meth-
ods for collecting (Gates et al. 1987) or coring the
benthic sediments (Hyvonen and Nummi 2000,
Swanson 1978, 1983). Some have used an Ek-
man grab sampler mounted on a pole.
The Gerking box samplera quantitative
sampler
The Gerking box sampler is lowered into the wa-
ter until the open bottom of the sampler (0.3 m2) is
pushed into the sediments leaving the open top pro-
j ecting above the water's surface. Everything within
the sampler is collected from the sediments, veg-
etation, and water column. A flat 1 mm mesh plate
is slid across the bottom before the sampler is pulled
up and drained, and the sample is rinsed into a sieve.
The advantages of this device are the quantitative
estimates of the invertebrates and the fact that it
captures many of the organisms from the benthos,
vegetation, and water column. Gerking samplers
collect greater abundance and greater numbers of
invertebrate taxa than activity traps or artificial sub-
strates (Brinkman and Duffy 1996). The chief dis-
advantage of the Gerking box is the labor involved
in processing the large samples that it collects. In
addition, the device is bulky, requiring two people
to carry it to the site and a crew of three to four to
operate. It is not useful if woody vegetation is present.
This method has been used in projects at the Patuxent
National Wildlife Refuge (see Appendix B).
Core samplera quantitative sampler
The advantage of using core samplers is the
quantitation per unit bottom area of wetland and
the shorter collection time. A disadvantage is the
fact that core samples contain fewer invertebrate
taxa than Gerking samplers or sweep nets (Hyvonen
and Nummi 2000, Cheal et al. 1993) and the or-
ganisms have to be processed from the mud. Cores
10
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sample a smaller bottom area than the Gerking box
and they do not capture the motile taxa. The fre-
quently anaerobic benthic sediments of some wet-
lands would not be expected to have the range of
taxa found in other habitats. Cores are appropriate
if the goal is to analyze the benthic invertebrates,
such as oligochaete worms, benthic molluscs, and
chironomids, or if the type of wetland has low wa-
ter or saturated conditions (see Hershey et al. 1998).
Only 2 taxa of chironomids were collected from
cores pooled from benthic sediments in depressional
wetlands, whereas a mean of 12 taxa were col-
lected by a dipnet method (Helgen et al. 1993).
In samples that include benthic sediments, such
as cores or stationary samplers, the organisms can
be floated from the sediments in dense (30%) su-
crose or salt solutions (Anderson 1959, Ritchie and
Addison 1991). As much sediment as possible is
washed out of the sample with running water on a
No. 30 (600 mm) mesh sieve. After water is
drained from the residual debris and sediment, the
30% sucrose solution is added to float out the or-
ganisms from the residual. This technique is mostly
limited to muddy benthic sediment samples that are
very difficult to pick.
Semiquantitative sampling methods
Dipnet or sweep net samples. Dipnetting, also
referred to as sweep netting, is probably the most
common method for sampling invertebrates in shal-
low vegetated wetlands (see Appendix C). With
consistent, standardized protocols, dipnetting yields
semiquantitative data on invertebrate abundances
and taxa richness. Without a consistent effort,
dipnetting yields only qualitative results. See Ap-
pendix B for methods used by different States to
produce semiquantitative data with dipnetting. Re-
peatability is dependent on the standardization of
protocols and the training and skill of the field crews.
Ways to assure repeatability in dipnetting proto-
cols include:
Defining the number of sweeps (Minnesota,
Florida)
Defining the amount of time for sweeps
(Montana, Ohio, Merrittetal. 1996, 1999)
Defining the distance of sweeps and the number
(Florida, Maine)
Doing consistently repeated efforts at each site
(Minnesota)
Dipnetting samples a large area and the range of
wetland habitats. Dipnets have been considered a
useful method because they capture a high richness
of species, comparable to that obtained with the
Gerking box sampler (Cheal et al. 1993, Kaminski
1981). Dipnets collect more taxa than are collected
by cores or artificial substrates (Mackey et al. 1984),
and collected more taxa of chironomids than cor-
ers, artificial substrates, or activity traps in Minne-
sota (Helgen et al. 1993). An advantage of
dipnetting is that experienced crews can collect
samples quickly over a wide range of habitats.
See Appendix C for more details of dipnet pro-
cedures. In Florida, 20 0.5-m sweep net efforts
are distributed in proportion to the representation
of the habitat type, with emphasis on the "produc-
tive habitats" (Florida DEP 1994, 1996, and FL
SOP). In Minnesota, 3 to 5 sweeps are done twice
for each sample, i.e., a total of 6 to 10 sweeps per
sample, and 2 samples are collected per wetland
(Gernes and Helgen 1999, Helgen and Gernes in
press). In Ohio, a 30-minute multihabitat dipnetting
is done and invertebrates are handpicked from sub-
strates that could not be sampled by dipnet
(Fennesseyetal. 1998). Montana samples all habi-
tats in the wetland for 1 minute, 3 to 4 times, de-
pending on the wetland size and complexity, or until
at least 300 organisms are collected into one
composited sample (Apfelbeck 1999). Merritt,
Cummins, and others have used 30-second sweeps
with D-frame nets to assess the status of vegetated
riparian systems (Merritt et al. 1996b, 1999,
1 1
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FIGURE 4: FRAMED SCREEN FOR SEPARATING VEGETATION FROM
INVERTEBRATES DURING DIPNETTING.
W hardware cloth 12" x 16" screen sits on a pan of water contained in a larger tray. Vegetation is
placed on top of the screen and invertebrates are encouraged to drop into water in pan over a period ofl 0
minutes. Process is done two times for one sample.
Cummins and Merritt in press; Cummins et al.
1999). A time-constrained dipnetting protocol may
be difficult when wetlands are particularly mucky
or habitats are farther apart.
A disadvantage of dipnetting is the amount of veg-
etation and other debris that gets trapped in the net.
This adds greatly to the picking time needed in the
lab. Unless debris is removed in the field, it in-
creases the amount of sample that must be pre-
served. Minnesota reduces the vegetation in
samples by laying the net contents on a framed Va"
12" x 16" hardware cloth screen that sits on a pan
of water contained in a floatable tray (see Figure 4
and Appendix C). The vegetation is gently teased
apart periodically over a 10-minute period and the
invertebrates are encouraged to drop into the wa-
ter in the pan beneath the screen. This process is
done twice for one dipnet sample, then the pan of
water is poured through 4" cylindrical 200 micron
mesh sieves. Florida reduces the amount of veg-
etation in its multihabitat dipnet samples by washing
it in the net and removing the larger pieces of veg-
etation, as does Ohio.
Some habitats are not amenable to dipnetting, e.g.,
areas with a lot of woody debris or roots or very
dense vegetation, or water that is too shallow.
Coring methods may be necessary in very shallow,
saturated wetlands or during drought cycles
(Hershey et al. 1998). Also, dipnetting tends to miss
some of the very motile invertebrates, e.g., the large
predatory beetles and bugs. This problem is over-
come by combining the use of dipnets and activity
traps.
Multihabitat dipnetting methods. The multi-
habitat dipnetting method takes samples from most
of the habitats within the wetland. The sampling
can be distributed among the habitats in proportion
to the habitat type or by other consistent protocols
such as time constraints. Training field crews to
assess the habitats and to sample consistently using
12
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standardized protocols is important. See Appen-
dix C for the variations on the multihabitat method
used by Florida, Montana, and Ohio.
Advantages of the multihabitat method are that
the sample represents the complexity of the wet-
land and collects most of the invertebrate taxa, ex-
cept the very motile taxa. Disadvantages of the
method are the time needed for processing the large
composite sample, or, alternatively, the need to
subsample or use a minimum count (e.g., 200 or
300) or organisms (see Appendix C). Multihabitat
samples tend to have a lot of vegetation and debris,
unless it is removed in the field. Also, wetlands
may differ in habitat types (Burton et al. 1999).
While it would be preferable to preserve sepa-
rately the samples from each habitat, for efficiency,
the sample is usually a composite of collections from
all the habitat types. Separate preservation would
require added effort in the field. An advantage of
keeping the collections from the habitat types sepa-
rate would be in the analysis of the data to deter-
mine which habitats show the most response to hu-
man disturbance.
Activity trapsa semiquantitative method. An
activity trap is a passive sampler usually containing
a funnel-shaped opening and an enclosed container
(jar or cylinder) that receives and traps organisms
that swim into the trap. With a funnel opening around
2.5cm diameter, macro-invertebrates can pass into
the trap. When placed horizontally in the wetland,
activity traps (AT) give semiquantitative data on the
motile wetland invertebrates, effectively trapping the
motile predators (e.g., the leeches, aquatic beetles,
and bugs) better than dipnets (Hilsenhoff 1987b,
1991, Turner and Trexler 1997). They are less suit-
able for collecting the nonmotile types of inverte-
brates (Hyvonen and Nummi 2000).
Activity traps are variously styled as funnel traps
(Swanson 1978, Fennessey et al. 1998, Hanson et
al. 2000, Gernes and Helgen 1999, Helgen and
Gernes in press, Murkin et al. 1983, Swanson
1978). They are left out at least one night, so the
night-active invertebrates swim or crawl into the
funnel openings. The style of trap that is used by
Minnesota is pictured in Figure 5. Traps used by
Minnesota and Ohio EPA are described in Appen-
dix C.
-
FIGURE 5: ACTIVITY
TRAPS USED BY
MINNESOTA.
Ten activity traps are placed
horizontally in near shore area of
wetlands, a. Trap is held to W 4 ft
dowel by a sliding bracket of 3 " thin
wall PVC. A wingnut unites this and
the larger bracket that holds the
bottle; b. funnel is cut from the top
end of a 2 liter beverage bottle. Four
grooves 1/8 x 2" are cut into rim of
funnel to snap into bottle, c. bottle is
held by a 4"PVC open bracket, (see
WikD. in References)
13
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Activity traps should be placed in shallow water
(<1 m to a few cm deep), because the active inver-
tebrates, such as predaceous beetles and bugs, feed
there. If they are placed too deep, fewer inverte-
brates are collected. Typically, the traps are placed
horizontally, although vertical placement has been
used, primarily for zooplankton with smaller open-
ing size in the funnel (Whiteside and Lindegarrd
1980). The traps are usually retrieved after 24 to
48 hours, depending on the water temperature, with
a longer period in colder water.
An advantage of activity traps is that they provide
semi quantitative data. Also, less training and time
are required to set out and collect several traps in a
repeatable way. Activity traps collect a sample that
is clean of most vegetation and requires less pro-
cessing time. Minnesota averaged 2.3 hours of pro-
cessing time for 10 activity traps per wetland.
A disadvantage of activity traps is the need to re-
visit the site to collect the traps after one or two
overnights. Activity traps do not collect the range
of macroinvertebrates needed for the IBI. They
must be used in conjunction with another sampling
method, such as dipnetting, if the goal is to have a
broad representation of the invertebrates for the IBI
attributes. There is also a concern that predation
within the trap might alter the invertebrate compo-
sition. One study (Elmberg et al. 1992) suggests
that fish, but not invertebrate predators, may affect
richness, but not abundance, of the invertebrates.
Another disadvantage of activity traps is the pos-
sible collection of large numbers of tadpoles so dense
they seem to exclude macroinvertebrates. Decom-
position was advanced even after 24 hours in the
water (Peter Lowe, Patuxent Wildlife Research,
personal communication; Sparling et al. 1995).
Dead organisms in the traps might attract some
predators to the traps, although this has not been
evaluated.
More study is needed on the effectiveness of the
different designs for activity traps, particularly the
size of the funnel opening and how it might affect
the size of organisms, including vertebrate preda-
tors, that can enter the traps. The effect of trap
volume and whether the trap is enclosed (plastic or
glass) versus open (screen) should be reviewed for
predation impact that might be reduced by declin-
ing oxygen levels in the enclosed traps. Minnesota
excludes air bubbles in activity traps to reduce ac-
tivity of predators inside the traps (Ralph Gunderson,
St. Cloud State U., MN, personal communication).
Finally, more study is needed on the relation be-
tween water temperature and efficiency of funnel
traps for active macroinvertebrates. Murkin et al.
(1983) suggest that water temperature was not sig-
nificantly correlated with the abundance of inverte-
brates in activity traps, but temperature does affect
invertebrate activity (Henrikson and Oscarson
1978).
Artificial substrates. Artificial substrates are
passive samplers that are made of hard substrates
(plates, tiles, or objects that mimic the natural sub-
strates) that are placed in the water for a few weeks
to allow colonization on the substrates by certain
aquatic invertebrates. The substrates are colonized
by epiphytic fauna and have been used to collect
information on a number of attributes (King and
Richardson, in press; King and Richardson, sub-
mitted). They were useful in studies on the impact
of mosquito control agents on chironomids (Liber
etal. 1998, Ferrington 1994). More taxa of chi-
ronomids were found on artificial substrates on plates
that were placed up in the aquatic macrophytes than
on plates placed on the bottom (Liber et al. 1998,
Ferrington 1994). A disadvantage of artificial sub-
strates is the lack of collection of actively swimming
invertebrates and consequent lower taxa than ob-
tained with dipnets (Turner and Trexler 1997).
14
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Advantages of using artificial substrates are:
They yield a clean sample relatively free of
debris.
The data are semiquantitative (based on area,
size and number of plates).
They are easy to deploy in the field.
Disadvantages of artificial substrates are:
They collect chironomids, oligochaetes, snails,
and other epiphytic taxa, but not Odonata or
other active invertebrates collected by other
methods.
The need to put the samplers out and collect
them several weeks later, with the possibility of
loss or disturbance of samplers overtime.
STEP 4. SAMPLE PROCESSING
PROCEDURES
Several decisions need to be made concerning
sample processing:
Whether to preserve samples in alcohol in the
field or chill and bring back live
Whether to pick samples in the lab or do much
of the picking in the field
How to conduct the sample picking in the lab
Whether to pick the entire sample or a
subsample
Appendix D lists some options for the above
choices, along with advantages and disadvantages.
If samples are preserved in alcohol or another pre-
servative, there should be adequate ventilation for
sample processing staff even after the samples have
been rinsed and placed in water. The following are
recommended, but other options may be needed
depending on the circumstances of the researchers
or State agencies. Whatever the protocols are, they
must be used consistently.
Preservation of the sample in the field is
preferable, so the processing of the sample takes
place in controlled conditions in a laboratory.
Picking the samples should be done in the
laboratory, not under varying field conditions
of climate and lighting.
Staff who pick the samples should have some
training in aquatic invertebrates, but they need
not be the taxonomists who do the
identifications.
Picking the sample in the lab should be done
either under a microscope or in a glass tray over
a light box with a magnifying lamp.
The sample should be picked into partly sorted
categories to expedite identifications.
If the entire sample is picked, it is more efficient
to collect a sample that has reduced vegetation
and debris.
Preservative should be rinsed off samples
picked in water; adequate ventilation should be
provided for staff doing the picking and the
identifications.
Subsampling or picking the entire sample?
It is recommended the entire sample be picked if
the sampling method and resources permit this. To
make this more efficient, it is helpful to collect
samples that are not overloaded with vegetation and
debris. When wetlands are sampled with a repeat-
able, consistent sampling effort, picking the entire
sample improves proportion metrics of total sample
count, taxa richness, and variability in metrics
(Doberstein et al. 2000, Ohio EPA 1988,
Courtemanch 1996) and allows better compara-
bility among sites. However, with stationary samples
such as the Gerking box, stovepipe, or Wilding sam-
plers, or with certain multihabitat dipnetting meth-
ods, there may be a lot of vegetation and debris. In
such cases, a subsampling process may be neces-
sary. See Appendix C for some methods to re-
duce debris in these samples.
15
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A sample can be subsampled by using a gridded
screen or a grid underlying a glass tray. Random
squares or rows are selected to ensure that a de-
fined proportion (at least 20%) of the sample grid
is picked. There are sample splitters and other
methods, but these need to be tested and their use
may be difficult with debris-laden samples from
wetlands.
Alternatively, picking the sample until a minimum
number of macroinvertebrates, typically 100,200
or 300, is found will reduce the picking effort. There
are disagreements on the validity of taking this kind
of subsample. Forissues of subsampling see Sovell
and Vondracek (1999), Barbour and Gerritsen
(1996), Courtemanch (1996), Vinson and Hawkins
(1996), Somers et al. (1998), and Doberstein et al.
(2000).
Some investigators facilitate the sample picking
by staining the invertebrates with Rose Bengal stain
(100 mg Rose Bengal in 1,000 mL preservative,
see Lackey and May 1971).
Taxonomic resolution and identifications of
invertebrates
The level of taxonomic identifications, to order,
family, genus, or species, will depend on the at-
tributes or metrics that are used, the degree of cer-
tainty needed in the wetland assessments, and the
ease or difficulty of identifying the particular groups
of invertebrates. More information about the con-
dition of a waterbody is obtained when organisms
are identified to the genus or species level. Among
genera within a family there are often differences in
sensitivities to factors causing impairment, likewise
among the species within a particular genus. A very
rapid assessment approach or a citizen monitoring
program might identify to the family level.
It is recommended to identify the invertebrates
to the lowest possible taxonomic level, at least
to genus and to species where possible, because
of the different sensitivities within some
taxonomic groups.
It is recommended, where possible, to have the
identifications done by biologists who are on
staff and trained in taxonomy; these staff can
also participate in the development of biological
monitoring tools and help guide the biological
monitoring program.
It is recommended that reference collections be
maintained with several specimens of each
organism that was identified, and to have these
identifications verified by outside taxonomists if
the taxonomist on staff lacks expertise in
particular groups (e.g., chironomids).
It is recommended that a database management
staff person be dedicated to the biological
database and participate with the biological staff
in its development of the program.
It is recommended that the taxonomic names
be coded in the database with the national
Integrated Taxonomic Information System
(rriS) codes (www.itis.usda.gov); unique codes
will be needed for the taxa that are not yet
coded by ITIS.
It i s recommended that the known functional
feeding groups for each taxon be built into the
database so that functional feeding group
attributes can be tested.
Identifications at least to the genus level are rec-
ommended for biological assessments to be used
for resource agency decisions. A number of excel-
lent keys and sources are available (for example,
Merritt and Cummins 1996a; Hilsenhoff 1995,
Thorpe and Covich 1991, Walker 1953, 1958,
1975,NeedhamandWestfall 1954,Klemm 1982,
Westfall et al. 1996, Clarke 1973, 1981, Mackie
in press, to name a few). Some taxa will be identi-
fied to the lowest practical level, depending on avail-
able taxonomic sources, staff expertise, and work
effort for identifications. For some groups or life
stages, reliable taxonomic keys may not be avail-
16
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able. For other groups, such as the fingernail clams
and leeches, identifications are difficult because of
the time needed to process the shells to view the
hinge teeth, or to relax certain leeches and dissect
the reproductive structures. Some snails can be iden-
tified to species, others only to genus level.
Once the choices are made, they should be con-
sistently applied in the assessment protocol by all
staff working on the identification of the samples.
For the total taxa metric, a clear definition of which
taxa to be included must be determined for the stan-
dard identification procedures in the lab. The staff
biologists need to keep track of changes in tax-
onomy and maintain literature sources used for the
identifications. The ITIS codes should be regularly
updated (see Appendix E).
Some agencies contract out the identifications of
certain special groups, such as chironomid larvae
to genus level. If chironomids are identified only to
the four subfamily/tribe levels, information about
condition is lost compared to identifications to the
genus level, where more than 12 to 16 genera may
be found in one wetland (Diggins and Stewart 1998,
Helgen and Gernes 1999, Gernes and Helgen in
press, Beck 1977).
For some of the functional feeding group metrics,
taxonomy is carried to the level needed to describe
the function (Merritt and Cummins 1996a). In this
case, all Odonata would immediately be classed as
predators, or all members of a family might be
classed in one functional feeding group. In other
cases, identifications to lower taxonomic levels are
needed to define the functional feeding groups (see
Mihuc 1997). Therefore it is prudent to identify the
macroinvertebrates to the lowest possible taxonomic
level, genus or species, where possible.
Immature specimens and morphospecies
Some specimens will be too immature to identify
to genus and will have to be left at the higher level
of identification, e.g., family. Others may be dam-
aged and not identifiable. In some cases the expe-
rienced taxonomist may be able to extrapolate, with
caution, from other specimens in the collection.
Some specimens will be identified to genus but will
be distinctly different from others in the same genus
in the sample. These specimens must be recorded
so that they are recognized as an additional species
in the sample, i.e., as a "morphospecies" (Oliver
and Beattie 1996). If species are carefully identi-
fied as distinct morphologies, this level of identifi-
cation can produce accurate measures of species
richness, but only when the experienced biologist is
certain the differences are not simply due to differ-
ing stages of development.
It is important to define standard protocols for
counting the number of different taxa when the iden-
tifications of different taxa are at different levels of
taxonomic resolution. For the counting rules used
by Maine, see Davies and Tsomides (1997).
Contracting out the identifications
of the invertebrates
Contracting the services of taxonomic experts is
an option when staffing levels or limitations in ex-
pertise and facilities prevent analyzing the inverte-
brates "in house," especially for particular inverte-
brates that require specialists to identify. Contract-
ing some invertebrate taxonomy can free the staff
to develop the indexes and analyze and report data.
This can be a cost-efficient way to obtain reliable
data, however it entails staff time in forming and
tracking contracts.
It is important to give the contractors clear guid-
ance on the groups of invertebrates to identify, the
taxonomic levels, the protocols, and the attributes
desired, and not to let the contractor make these
decisions. It is important to have in-house staff with
expertise in macroinvertebrates give guidance for
the work of any outside consultants. It is recom-
mended to have all of the macroinvertebrate groups
17
-------
identified to allow calculation of new or improved
metrics that may not have been previously used.
are discussed below, with a rationale for the ex-
pected responses.
STEP 5. METRIC ANALYSIS
A. SELECTION OF ATTRIBUTES
Selecting invertebrate attributes
As stated in Step 2, attributes are candidate
metrics that are measures of the invertebrate com-
munity. They are tested to see if they show a dose-
response to increasing levels of impairment, such
as chemical pollution, unnatural hydrologic or habi-
tat alterations, or siltation. If a response to impair-
ment is seen, the metric will be scored and its score
will contribute to the overall IBI score for a wet-
land.
An IBI is more robust if it is composed of 8 to 12
metrics selected from different categories of at-
tributes that represent patterns of responses to
changes in the physical, chemical, and biological
integrity of the wetland and its surrounding land-
scape. The maj or categories of attributes and their
expected responses to increases in impairment (in
parentheses) are:
Measures of taxa richness (decrease)
Measures of tolerance (increase) and
intolerance (decrease)
Measures of trophic structure and functional
feeding groups (varies)
Measures of life cycles, such as longevity and
reproduction (decrease)
Measures of poor condition or poor health of
individuals (increase)
Advantages and disadvantages and expected re-
sponses to human disturbance of these and other
categories of attributes are reviewed in Appendix
F. Attributes in use by several States are given in
Appendix G. Some of the categories of attributes
Taxa richness
Taxa richness is the count of the number of types
of invertebrates that inhabit an ecosystem. The taxa
richness, primarily genera or species, of a wetland
is enumerated by counting up all the types of inver-
tebrates collected from the sampling effort. It is
important to use a standard protocol for counting
invertebrate taxa when the taxonomic level for the
identifications differs among taxa. The number of
taxa commonly declines as human disturbance in-
creases (Barbour et al. 1995, Kerans and Karr
1994, Fore et al. 1996). This attribute shows a
high statistical power for detecting differences among
sites (Sandin and Johnson 2000). However, there
are exceptions, e.g., when low-nutrient wetlands
receive more nutrients (Rader and Richardson
1994), or forested canopy areas are opened up
over wetlands that were shaded and less produc-
tive before the forest clearing (King et al. 2000).
Plotting the taxa richness against the measure of dis-
turbance will show the response curve. If there is a
unimodal response, with a peak of taxa richness at
the intermediate level of human disturbance, the met-
ric may not be useful.
In Figure 6, the number of invertebrate taxa de-
creases as the concentration of chloride increases
in the water in the wetland. The increased chloride
may alter the active pumping systems of inverte-
brates for maintaining osmotic balance in body flu-
ids. Urban wetlands (Urb) receiving stormwater
runoff are especially high in chloride.
Tolerance
Tolerant taxa inhabit a wide range of habitats and
tolerate a wide range of conditions. The number of
tolerant taxa may not change with impairment, but
the relative abundance of tolerant organisms tends
to increase as the amount of impairment to the site
increases. This might be measured by the propor-
tion of known taxa, or by the proportion repre-
18
-------
es
H
1
0
80
70
60
50
40
30
9n
^
D
o o o° D
0° °
* o D
* D D A A
" * °
D D A
I A
D A A
A PA
A
A
*Ref
D Ag
AUrb
0.5 1 1.5 2
Log Chloride in Water
2.5
FIGURE 6: TOTAL NUMBER OF INVERTEBRATE TAXA PLOTTED AGAINST
THE LOG OF THE CHLORIDE IN THE WATER (MG/L) FROM LARGE
DEPRESSIONAL WETLANDS IN MINNESOTA.
Total taxa included the number of genera of mayflies, caddisflies, dragonflies, damselflies, chironomids,
beetles, bugs, macrocrustaceans, plus the number of genera or species of snails and leeches and the
presence/absence of fingernail clams and Chaoborus. Chloride range 1-110 mg/L.
sented by the dominant two or three taxa to the
sample count.
Tolerance values assigned to stream invertebrates
are based largely on organic enrichment from data
sets of stream invertebrates (Hilsenhoff 1987a). The
Hilsenhoff Biotic Index for streams (HBI, see
Hilsenhoff 1987a, 1995) is calculated from toler-
ance values assigned to species of various stream
invertebrates in relation to their sensitivities to or-
ganic pollution. New England has a list of family-
level tolerance values derived primarily from EPA's
listing (EAMd-Atlantic Regional Operations 1990)
with some regional modifications. Hilsenhoff also
has developed a family-level HBI, the FBI, for a
rapid field assessment or organic pollution
(Hilsenhoff 1988).
Tolerance values assigned to stream invertebrates
may not be applicable to wetlands invertebrates
because many wetlands invertebrates are tolerant
of, or adapted to, the fluctuating oxygen conditions
in wetlands. In addition, there are many inverte-
brates in wetlands that are "wetland specialists":
water boatmen; backswimmers; diving beetles and
marsh beetles; fairy shrimp, clam shrimp, and tad-
pole shrimp; mosquitoes; marsh flies; biting midges;
horse and deer flies; the snails in the families
Physidae, Lymnaeidae, and Planorbidae; and fin-
gernail clams (see Wissinger 1999). For these and
other species that are predominantly wetland spe-
cialists, there is little or no existing information on
their tolerances to human caused impairments.
Attributes that relate to tolerances of
macroinvertebrates in wetlands need to be derived
19
-------
for the invertebrates of the wetland class and re-
gion. Decisions about which taxa are "tolerant" need
to be based on examination of data sets from a range
of high-quality and impaired wetlands. Tolerant taxa
might be present in the range of wetlands, but they
would show a proportionate increase in wetlands
with greater human disturbance. The designations
of tolerance then need to be tested on another data
set for validation. Karr and Chu (1999) suggest
that about 10% of the taxa, or 5% to 15%, be de-
fined as either tolerant or intolerant. One caution
on designations of tolerance values, if done at the
genus level, is the possibility that the species within
a genus may differ in their tolerances (Hilsenhoff
1998). It is preferable, but not always possible, to
designate species rather than genera as tolerant or
intolerant.
Intolerant taxa, by definition, are more likely to
disappear under impaired conditions. Their pres-
ence indicates good conditions. Preliminary deter-
minations of intolerant species would require the
examination of the data set to see which taxa tend
to disappear from the more impaired wetlands but
are found in reference sites. Again, designations of
intolerant taxa need to be tested with other data
sets. An example of intolerant taxa, originally de-
rived from data on depress!onal wetlands and ap-
plied to a new data set on large depressions is shown
in Figure 7.
Trophic function and functional feeding
group attributes
Trophic function attributes relate to the type of
food eaten by the invertebrates: herbivores con-
sume algae and plant material, predators consume
animals, omnivores eat both plant and animal mate-
rial, and detrivores consume decomposed particu-
late material. The proportion of predators is ex-
pected to decline as impairment increases (Kerans
and Karr 1994). Many wetlands are lacking in fish
predators and are dominated by invertebrate preda-
tors such as leeches, dragonfly and damselfly lar-
vae, and juvenile and adult aquatic beetles and bugs
(D
8
7
6
4
3
1
0
* o o
O 0* D A 0 AA A
D DA A A D D
DAOODAB
OQ D D A A D
»Ref
DAg
AUrb
-2 -1.5 -1 -0.5
Log Phosphorus in Water
0
0.5
FIGURE 7: INTOLERANT TAXA PLOTTED AGAINST THE LOG OF PHOSPHORUS
(MG/L) IN THE WATER OF LARGE DEPRESSIONAL WETLANDS IN MINNESOTA.
The types of intolerant taxa were derived from a previous project on depressional wetlands. The intolerant taxa
were two genera ofdragonflies (Leucorrhinia, Libellula^), two ofcaddisflies (Triaenodes, Oecetisj, two chironomid
genera (Tanytarsus, Procladius^) and fingernail clams (Sphaeriidae). P range 0.015-1.38 mg/L.
-------
(Fairchild et al. 1999, Wissinger 1999). In the fish
IBI, the proportion of individuals that are top carni-
vores (Simon and Lyons 1995) is expected to show
a decrease in response to human disturbance. More
work is needed in testing of attributes of trophic
function against gradients of human disturbance in
wetlands.
Attributes of functional feeding groups (FFGs)
merit further exploration. Such groups are based
on the mode of food acquisition rather than the type
of food eaten (Merritt and Cummins 1996b, Merritt
etal. 1996,1999). Merritt's work in defining func-
tional feeding groups of many macroinvertebrates
has laid a foundation for the analysis of FFG at-
tributes. The FFGs of each taxon, if defined, should
be included in databases to facilitate the testing of
FFG metrics.
In streams, the analysis of functional feeding groups
has been useful for understanding the changes in
stream ecology from losses of riparian vegetation
or conversion from a shaded, leafy stream to an
open system in which algae, rather than leaf litter,
become the primary food source for the inverte-
brates (Merritt et al. 1999, see also Rawer-lost et
al. 2000, Hannaford andResh 1995, Resh 1995).
Cummins and Merritt (2001) and Cummins et al.
(1999) have analyzed FFGs in wetland riparian
areas.
Functional feeding group attributes that decreased
with increasing human disturbance in streams were
the proportion of grazers and the proportion of
predators (Kerans and Karr 1994). An attribute
that tended to increase as human disturbance in-
creased was the relative proportion of filterers
(Kerans and Karr 1994). Much more testing is
needed of functional feeding group attributes in re-
lation to human disturbance in wetlands. See Merritt
et al (1996) for criteria levels for FFG ratios for
evaluating ecosystem parameters in streams.
Some functional feeding group attributes have
shown greater variability than taxa richness mea-
sures, partly because some of the FFG attributes
have been expressed as ratios (e.g., scrapers/gath-
erers) rather than proportions (Resh 1988, Resh
1994, Stan Szczytko, University of Wisconsin,
Stevens Point, WI, personal communication). Ra-
tios are susceptible to variability if both of the vari-
ables are changing. Other FFG attributes are ex-
pressed as proportions and these may be more ro-
bust when tested in wetland systems. Taxonomic
levels needed for FFGs vary widely. Some groups,
e.g., Odonata, can be entirely classed as preda-
tors, whereas others (see Merritt and Cummins
1996a) will require identifications to genus or spe-
cies level. It is recommended that identifications
be done routinely to the lowest taxonomic level.
Other invertebrate attributes to consider
Other attributes can be considered; some are in
Appendix F. Some can be found in the literature
(Barbouretal. 1996, Resh etal. 1995, Kerans and
Karr 1994). A few that might apply to wetlands in
the future are discussed below.
Condition or health of individual
invertebrates
In the fish IBI, there is a metric that records the
number of deformities, erosion, lesions, and tumors
in individual fish in the sample (Sanders et al. 1999).
This metric is most responsive in highly contami-
nated areas, as was found in Ohio. To date, mal-
formations have been recorded in some aquatic in-
vertebrates, i.e., chironomids and dragonflies. In
chironomids, malformations have been shown to be
more numerous in response to contaminants (Palmer
1997, Hudson and Ciborowski 1996a,b; Warwick
1980 1990). Minnesota has data on malforma-
tions in chironomids from 43 wetlands (done by
Leonard C. Ferrington), but has not yet developed
a metric. Malformations were found in the cast
exoskeletons (exuviae) of dragonflies in Minnesota,
first in a report from rivers and bog/fen areas
(Steffens and Smith 1999) and then from some large
21
-------
depressional wetlands (Smith 2000). There is little
monitoring data on malformations in most inverte-
brates. Therefore, it is unknown whether malfor-
mations are increasing in invertebrates the way they
appear to have increased in frogs in the 1990s in
northern North America (Helgen et al. 2000, Hoppe
2000, Ouellet et al. 1997, Northeast Natural Re-
source Center 2000).
increases in wetlands. In the Floristic Quality As-
sessment method (Fennessy 1998) for using plant
communities to assess wetlands, plant taxa that have
a higher fidelity for particular types of habitats, i.e.,
a higher coefficient of conservatism, will give the
Floristic Quality Assessment Index a higher score
(see Module 10, Using Vegetation to Assess Envi-
ronmental Conditions in Wetlands).
A possible attribute to indicate the health of in-
vertebrates is the proportion of coverage of aquatic
insects by bacteria as an indicator of nutrient en-
richment in wetlands, based on recent work by
Lemly and King (2000).
Introduced or exotic species
There are numerous exotic or introduced species
in freshwaters of the United States (see Cox 1999,
Mack et al. 2000). Some of these invade wet-
lands. As an attribute, the number of exotic taxa or
the proportion would be expected to increase as
human disturbances increase. Introduced fish will
alter the invertebrate composition (Hanson and
Riggs 1995). In Minnesota, the huge oriental mys-
tery snail, Cipangopaludina chinensis, has been
found in urban wetlands, probably after being dis-
carded from aquaria. It consumes submersed
aquatic plants and creates open areas in the veg-
etation. The rusty crayfish, Orconectes msticus,
has been expanding its range and introduced into
lakes and wetlands (Helgen 1990), where it con-
sumes the macrophytes.
Generalists and specialists
Attributes that address the proportion or richness
of generalists and specialists could be explored (see
Wissinger 1999, Mihuc 1997). A community with
a high proportion of wetland specialists is thought
to reflect more competition and evolution of spe-
cialists, whereas one with a high proportion of gen-
eralists may indicate less competition and more use
of the same resources. The number of specialist
taxa, or the proportion of specialist individuals, might
be expected to decrease as the human disturbance
B. FORMING THE IBI
To form the invertebrate IBI, the attributes are
plotted as a scatter plot against stressors or human
disturbance gradients (e.g., Figure 1, see Fore et
al. 1996, Karr and Chu 1999). Eight to 12 at-
tributes that show a response are selected and
scored. Another method of visualizing metrics is to
plot the attribute data using box-and-whisker plots
to show the spread of values of an attribute in ref-
erence sites compared with the range in the impaired
sites (Barbour et al. 1995, Barbour et al. 1992).
Attributes that show very little overlap between ref-
erence sites and impaired sites are chosen as metrics
and scored.
There are various ways to score the metrics. The
examples given below are for assigning scores with
a 1, 3, 5 system for metric data that are showing a
linear or regular response to disturbance. Other
scoring ranges can be used. For metrics whose
data indicate a nonlinear response to the gradient
of human disturbance, other methods, such as as-
signing scores on either side of inflection points,
need to be used (Karr and Chu 1999). It is impor-
tant that the study sites used to assign scores to
metrics include the full range of impairment and the
fullest range of biological response values for the
metrics.
The range of the data values for the metric can
divided evenly into three parts from the lowest
data value to the highest data value. The low
sector is assigned a score of one, the middle is
given a three, the top third is given a five. This
22
-------
method assumes the data ranges include a range
of values from the most impaired to the least im-
paired wetlands, and the data values respond
evenly to the human disturbances (Karr and Chu
1999, Helgen and Gernes in press, Gernes and
Helgen 1999).
The data for a metric are plotted in rank order
for the sites. Then the sites are divided into thirds
and the associated data values are assigned scores
of 1, 3, or 5 for the low, middle, and top third of
ranked sites.
The metric values for the reference sites are ar-
ranged in quartiles. The values for the top three
quartiles (top 75th percentile) are assigned a
score of 5. The range of values from the upper
range of the lowest quartile to the lowest data
value is divided in two and assigned a 3 or 1
(Barbouretal. 1996). This method assumes there
is an adequate number of reference sites includ-
ing some with the least amount of human distur-
bance or no disturbance. See Module 6: Devel-
oping Metrics and Indexes of Biological Integ-
rity. Once the metrics are scored, a matrix of
scores is made in a table for all the sites such as
the table in Appendix J. The scores are added
to the total IBI score and the IBI scores are di-
vided to indicate three or more categories of
condition. Appendix I shows the scoring criteria
for the 10 metrics used by Minnesota for large
depressions. It indicates how many wetlands that
were designated as reference, agricultural or
storm water-influenced received the scores of 5,
3, orl.
CONCLUSIONS AND
RECOMMENDATIONS
7 Biological assessment of wetlands by
invertebrate metrics should be increased
because the invertebrate metrics are sensi-
tive to a broad range of impairments to the physi-
cal, chemical, and biological integrity of wetlands.
This will require:
More work on the development of
invertebrate IB Is for different classes of
wetlands
More information on the tolerances and
sensitivities of invertebrates in wetlands
Consistent funding dedicated to staff to work
on invertebrate biological assessments
2 Biological assessment of wetlands using
macroinvertebrates will provide scientifically
sound data for States, Tribes, and organiza-
tions to gauge the degree of impairment to wet-
lands from a mix of stressors. This will enable
them to:
Develop invertebrate biocriteria for determining
aquatic life use support
Report on condition of wetlands in 305(b)
reports and in 303(d) (TMDL) lists and facilitate
prioritization
Understand the condition of watersheds using
carefully designed studies
Compare the results from biological condition
assessments with assessments from other
"rapid" physical assessment methods to validate
the latter
Provide a solid foundation for citizen
biomonitoring programs using protocols derived
from those used by States, Tribes, and
organizations
Provide a sound method to determine the
effectiveness and suitability of permitting
decisions
Provide a sound method to assess the results
of restorations and mitigations in wetland
replacements
23
-------
Appendix J shows an example of the metric scores
for a set of depress!onal wetlands in Minnesota.
The sites are sorted by the IBI scores, and tenta-
tive lines were drawn to indicate which of the sites
might be considered to be in excellent, moderate,
or poor condition. This was done by trisecting the
range of IBI scores (10 to 50 total points for 10
metrics). Although most of the sites that were con-
sidered to be reference, or least impaired, wetlands
had IBI scores in the excellent range, a few candi-
date reference sites scored as moderate. It is ex-
pected that some sites chosen to be reference sites
may not be in the highest condition, but will them-
selves have a range of conditions. Other approaches
may be used for determining the criteria lines.
24
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York: John Wiley, pp. 1043-1086.
Wright JF. 1995. Development and use of a system for
predicting the macroinvertebrate fauna in flowing
waters. AustralJEcol20:181-197.
WrubleskiDA. 1987. Chironomidae (Diptera) of
peatlands and marshes in Canada. In: Rosenberg DM,
Danks HV (eds). Aquatic Insects of Peatlands and
Marshes in Canada. Memoirs of the Entomological
Society of CanadaNo. 140. Ottawa, pp. 141-171.
YoderCO. 1991. Answering some questions about
biological criteria based on experiences in Ohio. In:
Flock GH (ed). Water Quality Standards for the 21st
Century, Proceedings of a National Conference in
Arlington, Virginia. U.S. Environmental Protection
Agency, Office of Water, Washington, DC. pp. 95-104.
EPA-440-5-91-005.
33
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APPENDIX A. ADVANTAGES AND DISADVANTAGES OF USING INVERTEBRATES FOR
BIOLOGICAL ANALYSIS OF WETLANDS
Advantages
Invertebrates can be expected to respond to a wide array of stresses to
wetlands, such as pollutants In water and bottom sediments, nutrient
enrichment, Increased turbidity, loss or simplification of vegetation,
slltatlon, rearing of bait or game fish, Input of stormwater or wastewater
runoff, Introductions of exotic species, or alterations of the landscape
around the wetland.
Life cycles of weeks to months allow Integrated responses to both
chronic and episodic pollution, whereas algae recover rapidly from acute
sources, and vertebrates and macrophytes may take longer to respond to
chronic pollution
Toxic ologlcal/lab oratory based Information Is extensive. Invertebrates are
used for a large variety of experimental approaches.
There Is an extensive history of analysis of aquatic Invertebrates In
biological monitoring approaches for streams.
Invertebrates are used for testing bloaccumulatlon of contaminants to
analyze effects of pollutants In food webs.
Invertebrates are Important In food webs offish, salamanders, birds,
waterfowl, and predatory Invertebrates.
Many Invertebrates are ubiquitous In standing water habitats.
Many Invertebrates are tightly linked to wetland conditions, completing
their life cycles within the wetlands. They are exposed to site-specific
conditions.
Many Invertebrates depend on diverse wetland vegetation, some depend
on particular types of vegetation for reproduction.
Invertebrates have short and long life cycles and they Integrate stresses to
wetlands often within a 1-year time frame.
Invertebrates can be easily sampled with standardized methods.
Invertebrates can be sampled once during the year, If the best Index
period Is selected for optimal development of Invertebrates.
Invertebrates can be Identified using available taxonomlc keys within labs
of the entitles doing the monitoring. Staff help develop blomonitorlng
programs.
High numbers of taxa and Individual counts permits the use of statistical
ordination techniques that might be more dlffucult with just a few
species, e.g. with amphibians.
Citizens can be trained to Identify wetlands Invertebrates and become
Interested and Involved In wetlands assessment. Citizens are excited to
see the richness of wetland Invertebrates.
Disadvantages/Comments
Because It Is likely that multiple stressors are present, It may not be
possible to pinpoint the precise cause of a negative change In the
composition of Invertebrates. However, data from major sources of
human disturbance, e.g., water and sediment chemistry, the nearby
wetland landscape features, sources of hydrologlc alteration, and other
disturbance factors cam be assessed In relation to the Invertebrate data
to see which factors have the greatest effects.
Information on short-term, pulse Impairments (using algae,
zooplankton) or more long-term Impairments (using macrophytes,
vertebrates) or more landscape-level (using birds, amphibians)
Impairment may be desired.
Toxlcologlcal response data may not be available for all Invertebrates;
data for some wetlands species are less extensive than for stream species.
Using Invertebrates to assess the condition of wetlands Is now under
development In several States and organizations.
Tissue contaminant analyses are always costly. This Is true for tissue
analysis of any group of organisms: vertebrate, Invertebrate, or plant.
Aquatic Invertebrates tend not to be valued by the public as much as
fish, amphibians, turtles, or birds. However, citizens do respond to
Invertebrates.
Invertebrate composition will differ In different wetland classes, as will
other groups of organisms (plants, birds) that might be used to assess
wetlands.
Some Invertebrates migrate In from other waterbodles, these taxa are not
as tightly linked to the conditions In the specific wetland.
Loss of Invertebrates may be a secondary effect from the loss of wetland
vegetation, e.g., from herbicide treatments. Vegetation loss Is an
impairment.
Many complete their life cycle within a year, they are not as "long-lived"
as birds, amphibians or perennial vegetation.
Picking Invertebrate samples Is labor-intensive.
Invertebrate composition of wetlands often varies within the seasons of
the yearly cycle. Invertebrates mature at different times. This necessitates
selecting an "Index period" for sampling once, or alternatively, sampling
more than once In the season.
Expertise Is required to perform Identifications of Invertebrates. Some
may choose to contract out some or all the Identifications. There Is a
cost Involved.
Large numbers of taxa and Individual counts make the sample
processing more labor Intensive than other groups. Adequate training
and staff time are required. More lab time Is needed than for some
other groups of organisms.
Citizen monitoring requires training to learn many Invertebrates In a
short time, a structured program, and a commitment by volunteers and
local governments; citizens may tend to underrate high quality wetlands.
34
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37
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APPENDIX E. ISSUES RELATED TO QUALITY ASSURANCE FOR INVERTEBRATE
BIOASSESSMENT WORK
Any biological monitoring program should have its own written Standard Operating Procedures
(SOP's) for each assemblage that is used, and for all field and laboratory protocols and data analysis
methods. Detailed guidance for developing a Quality Assurance Project Plan is available from the
U.S. Environmental Protection Agency, Guidance for the Data Quality Objectives Process (EPA
QA/G-4, EPA/600/R-96/055, ORD) andEPAs Content Requirements for Quality Assurance Proj ect
Plans for Water Division Programs (EPARegion V, Environmental Sciences Division, August 1994).
For examples of SOPs see Florida DEP SOP Draft 2000, North Carolina DWQ 1997 SOP.
The following text describes some considerations specific to biological assessment using
macroinvertebrates.
1. At least 10% of the samples should be checked and verified for the accuracy of taxonomic
identifications by a second taxonomist and/or by comparison to the reference collection. Changes in
taxonomy must be tracked and continuously updated, using current taxonomic references and re-
gional experts. At least 10% of the picked residuals of samples should be checked by the experi-
enced taxonomist to assure all the macroinvertebrates were picked out.
2. Samples should be stored carefully for a defined period of time, if not indefinitely, for later verifi-
cations or quality assurance, especially if the assessments are part of a regulatory decision. They
should not be disposed of right after the identifications are completed. Taxonomists are revising
certain groups of invertebrates as new information is gathered. Archived samples can be reanalyzed
for the group in question if necessary.
3. The lab should have defined rules for counting of taxa of each invertebrate group to be identified
at different levels of taxonomic resolution, for identifying immature specimens, and for when it is
acceptable to identify "morphospecies."
4. Taxonomic coding. In addition to having a lab list of taxa identified with unique codes, the
wetland invertebrates are coded in the database using the national Integrated Taxonomic Information
System (ITIS) codes (www.itis.usda.gov/). This is a partnership of Federal agencies in the United
States and Canada to improve and standardize biological nomenclature nationwide. The ITIS data-
base includes taxonomic information with authority, synonyms, common names, a unique taxonomic
serial number (the code), publications, experts, and data quality indicators. There should be a routine
procedure for checking the ITIS database to update and change any codes in the invertebrate data-
base.
One problem is that not all wetland invertebrates have received the codes or serial numbers in the
ITIS system. So the agency must, temporarily, create its own codes for uncoded taxa. Minnesota is
coding taxa not found in the ITIS database with unique negative numbers. These can be easily
flagged and have no possibility of interfering with ITIS codes. ITIS is requesting input from biolo-
gists, so states can notify them of uncoded taxa. The ITIS database should be searched periodically
38
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APPENDIX E. (CONTINUED)
to see if uncoded taxa have received codes so the in-house, temporary codes can be replaced with
ITIS codes.
5. Database and records management It is important to have a database management staff
person assigned to ongoing work with the biological data and the associated physical and chemical
wetlands data. This is especially true during the time of development of the biological database and
the selection of metrics and indexes. But the work is never static; changes occur and new directions
arise as the biological assessments are made and applied to reports and decisions. Taxonomy is
updated, and new needs arise in linking the biological data to other data sets and in making assess-
ments accessible to the public through agency web pages. Data should be backed up routinely.
6. Field data forms. Standardized field forms should be developed to ensure that methods and site
conditions are thoroughly recorded and all procedures are consistently documented. Backup photo-
copies should be stored separately from original data forms and field notebooks in case data are lost
or destroyed. It is important to reconcile issues of data comparability between old and new methods.
In addition to the standard locational, wetland habitat, and physical sampling information, the inverte-
brate sampling method, numbers of samples collected, and the depth and locations of sampling should
be included on a field sketch. GPS (Global Positioning System) locations of latitude and longitude of
sampling locations should be recorded.
7. Sample labeling and tracking. All sample containers should be clearly labeled with pencil or
India ink on labels of 100% cotton or alcohol-proof paper placed inside the jar and include the
following information: sampling method, sample number, station ID, date, collector, site name and
location (township, county), and sample j ar number (e.g., j ar 1 of 2, etc.) if more than one j ar is used
for a single sample. Standard procedures for sample tracking and chain of custody should be estab-
lished as part the monitoring program's quality assurance plan.
8. Laboratory Procedures.
a. Coding andrecordkeeping. In the laboratory, a unique identification code should be assigned to
each sample. This code should be included in all subsequent records associated with the sample (vial
or jar labels, tally sheets, databases, etc.). All laboratory data forms should be standardized and
should include the information described above (see Sample Labeling and Tracking) in addition to the
sample identification code and laboratory staff name(s). As with field data forms, backup photo-
copies should be made of all laboratory records.
b. Sample sorting. Macroinvertebrates should be sorted from detritus (picked) by trained personnel
working under the supervision of a professional biologist. Picking procedures should be included in
Standard Operating Procedures. It is recommended that a 10% random subset of all samples be
repicked by different experienced laboratory personnel working under the supervision of a profes-
sional biologist to determine sorting completeness. In all cases, initial sample sorting and quality
control repieking should be completed by different individuals.
c. The Standard Operating Procedures should clearly define which groups of macroinvertebrates
are to be picked, what if any methods can be used to subsample, and what level of taxonomic
resolution should be used for the identifications for each group of invertebrates.
39
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APPENDIX G. EXAMPLES OF INVERTEBRATE ATTRIBUTES USED AS METRICS IN
DIFFERENT STATES FOR BIOLOGICAL ANALYSIS OF WETLANDS. ATTRIBUTES BEING
TESTED ARE STARRED.
Metrics
Richness
Composition
Tolerance/
intolerance
Trophic structure
Individual health
Other metrics
Maine
Total genera
richness*
EOT genera*
Odonata genera*
Ephemeroptera
genera*
Trichoptera
genera*
Chironomid
genera*
% of total count
for:
EOT*
Odonata*
Ephemeroptera*
Trichoptera*
Gastropoda*
Isopoda*
Oligochaeta*
Amphipoda*
Minnesota
Total taxa
Chironomid genera
Leech taxa
Odonata genera
Snail taxa
ETSD metric
# of intolerant taxa
Tolerants % of total
count
Erpobdella % of total
count
Dominant 3 % of total
count
Corixidae % beetles +
bugs
Chironomid
malformations*
Montana
Total taxa
Chironomidae taxa
Leech, sponge and clam taxa
POET taxa
Mollusca+Crustacea taxa
Odonata + Trichoptera taxa*
%Chironomidae*
%Mollusca+Crustacean taxa*
%Orthocladiinae to total
Chironomidae*
%Diptera*
%Tanytarsini*
%Trichoptera*
%Odonata*
Ratio POET to POET and
Chironomidae*
%Pelycypoda*
%1, 2, 5 dominant taxa
% shredders
Ohio
Total taxa*
Chironomid taxa*
Mollusca taxa*
# Intolerant taxa*
% dominant 3 taxa of total count
Physella snail abundance
% Tanypodlnae and Tanytarsini of
Chironomidae
Patuxent
Total taxa*
# Snail genera*
# Odonata genera*
# Ephemeroptera and Trichoptera
gen.+ presence of Sphaeriidae and
dragonflles*
Corixidae % beetles + bugs*
% Total indiv as scrapers*
% total indiv as shredders*
% total abundance of 3 most
abundant taxa*
Ratio Ephemeroptera +
Odonata+Trichoptera abundance to
chironomids*
Shannon-Weaver Index*
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APPENDIX I. INVERTEBRATE INDEX OF BIOLOGICAL INTEGRITY FOR DEPRESSIONAL
WETLANDS IN MINNESOTA.
Ten metrics with scoring criteria and data ranges for large depressions. The numbers of reference sites (ref) and
agriculture- (ag) and urban stormwater-influenced (urb) sites scoring in each range are given, n is # of sites
scoring in the ranges. Codes are given for each metric. These codes are used in Appendix J.
Metric
1. Total invertebrate taxa
Code: TaxaTotal
2. Odonata
Code: Odonata
3. Chironomid taxa
Code: ChirTaxa
4. Leech taxa
Code: LeechTaxa
5. Snail taxa
Code: SnailTaxa
6. ETSD*
Code: ETSD
7. Number of intolerant taxa
Code: IntolTaxa
8. Tolerant taxa proportion of
sample count
Code: Toler%
9. Leech erpobdella
Code: Erpo%
10. Corixidae proportion of beetles
and bugs in activity traps
Code: Corix%
Metric data range
23-29 taxa
1-7 general
0-21 general
0-9 taxa
1-9 taxa
1-10
0-7 taxa
13-92%
0-14%
14-87%
Ranges
>59-79
>41-59
<23-41
5-6
3-4
0-2
14->20
7-13
0-6
6-9
3-5
0-2
7-9
4-6
0-3
7-10
4-6
0-3
5-7
3-4
0-2
13-39%
>39-65%
>65%
0-<1%
1-5%
>5%
<33%
33-67%
>67%
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10
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17
19
11
21
12
11
21
12
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16
20
10
16
18
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3
6
25
11
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*ETSD metric is total of number of genera of mayflies (Ephemeroptera), caddisflies (Trichoptera) plus the
presence of fingernail clams (Sphaeriidae) and dragonflies.
43
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APPENDIX K
CASE STUDY FLOW CHART FOR DEVELOPING INVERTEBRATE IBI IN MINNESOTA FOR LARGE DEPRESSIONAL
WETLANDS (SEE TEXT, HELGEN AND GERNES IN PRESS, GERNES AND HELGEN 1 999).
STEP 1 :
SELECT STUDY
SITES
STEP 2:
PLAN INVERTEBRATE
SAMPLING
STEP 3:
FIELD SAMPLING
STEP 4:
LABORATORY
PROCESSING
STEP 5:
METRIC ANALYSIS
Ecoregion: North Central Hardwood Forest (has abundant wetlands, is
central to the state, includes Twin Cities metro area)
Wetland class: large depressions
Range of disturbances: 15 least impaired , 15 agriculture-affected, 16
urban-affected wetlands
Attribute selection: 10 attributes tested based on previous work,
additional attributes were tested (see Appendix J)
Sampling strata: sampling to take place in near shore emergent vegeta-
tion zone from edge to less than 1 m deep (vegetated zone contains
greatest richness of invertebrates; nearshore area may be more exposed
to disturbances from the near wetland landscape)
Sampling methods: two standardized dip netting procedures plus 10
activity traps; all samples taken within approx. 40-50 m distance along
shoreline
Seasonal index period in June for optimal invertebrate development
Sampling methods had been pretested in previous projects
Samples were preserved in field and processed in lab; vegetation from
dip netting procedure was left at the site
Water and sediment chemistry samples were collected (for total N, total
P, conductivity, chloride, chlorophyll a, metals)
Entire sample was picked for macroinvertebrates (not for Ostracoda or
zooplankton); Neopleia was counted on a grid over lightbox and not
picked; chironomid identifications were contracted out, all others
identified at MPCA lab
Most taxa were identified to genus with exceptions: snails to species
where possible; fingernail clams at family level
SOP is written and reference collections made for verifcation
Data were entered into ACCESS database using ITIS coding and MPCA
coding where necessary.
Sites were analyzed for a human disturbance gradient composed of
estimates of disturbance in 50 m buffer and in near wetland landscape,
estimates of hydrologic alteration and rankings of water and sediment
chemistry data as compared to reference condition; each disturbance
was scored and summed to one score for human disturbances
Attribute data was plotted against scores for human disturbance
gradient for all the sites, and against water and sediment chemistry data
(see Figure 6 and 7) for all sites
Attribute data that showed a response to the human disturbance
gradient or to the chemistry data was trisected for a 1, 3 5 scoring as
metrics (see Appendix I)
10 metric scores were summed to IBI score and IBI scores were plotted
against the human disturbance gradient and chemistry data (see Figure 1)
IBI scoring range (10 - 50) was trisected for a hypothetical ranking of
best, moderate and poor condition (see Appendix J)
45
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GLOSSARY
Abundance The number or count of all individu-
als of one taxon or all taxa in a sample. When ex-
pressed per unit area or unit volume, it is called
density.
Activity trap (AT) A passive sampler, usually
containing a funnel-shaped opening and a container
that is enclosed, either as a bottle or j ar, or with a
mesh screen. The organisms swim into the funnel
and are trapped in the container. The size of the
funnel opening determines the size of organisms that
can swim into the trap.
Aquatic life use support The ability of a
waterbody to support the native aquatic life that it
is capable of supporting when there is little or no
human disturbance, or the ability of the waterbody
to support aquatic life as designated for that type of
water in Water Quality Rules.
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 (insects, crayfish, clams, snails,
etc.), and vascular plants
Attribute A measurable component of a biologi-
cal system. In the context of biological assessments,
attributes include the ecological processes or char-
acteristics of an individual or assemblage of species
that are expected, but not empirically shown, to
respond to a gradient of human influence.
Benthic invertebrates Invertebrates that inhabit
the bottom or benthic area of a waterbody.
Benthos All the organisms that inhabit the bot-
tom (benthic) area of a waterbody.
Biological assessment Using biomonitoring data
of samples of living organisms to evaluate the
condition or health of a place (e.g., a stream, wet-
land, orwoodlot).
Biological integrity "The ability of an aquatic
ecosystem to support and maintain a balanced,
adaptive community of organisms having a species
composition, diversity, and functional organization
comparable to that of natural habitats within a re-
gion" (Karr and Dudley 1981).
Biological monitoring Sampling the biota of a
place (e.g., a stream, a woodlot, or a wetland).
Biota All the plants and animals inhabiting an
area.
Bottletraps A kind of activity trap that is con-
structed from a bottle with a funnel opening.
Box-and-whisker plots Plots of data values
made for individual attributes with percentile "boxes"
around the median value, e.g., 25% and 75% boxes.
The "whiskers" are lines extending beyond the per-
centile boxes for data value ranges that extend out-
side the percentile. These are used to compare the
amount of overlap in the data range for an attribute
between reference and impaired sites.
Community All the groups of organisms living
together in the same area, usually interacting or de-
pending on each other for existence.
Detritivores Organisms that consume decom-
posed organic particulate matter.
Dipnet A sturdy, long-handled aquatic net for
sampling aquatic habitats, also called sweep net.
Mesh sizes range from 500 to 1000 microns.
Disturbance "Any discrete event in time that
disrupts ecosystems, communities, or population
structure and changes resources, substrate avail-
46
-------
ability or the physical environment" (Picket and
White 1985). Examples of natural disturbances are
fire, drought, and floods. Human-caused distur-
bances can be referred to as "human influence" and
tend to be more persistent over time, e.g., plowing,
clearcutting of forests, conducting urban stormwater
into wetlands.
Dominance The relative increase in the abundance
of one or more species in relation to the abundance
of other species in samples from a habitat.
Dose-response In toxicology, a graded response
by test organisms to increasing concentrations of a
toxicant. In biological assessment, dose response
indicates a graded response (up or down) of an
attribute to a gradient of human disturbance.
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.
Epiphytic A layer of periphyton located on or
attached to the surfaces of stems of macrophytes.
See periphyton.
Family A taxonomic category compri sing one or
more genera or tribes of common evolutionary ori-
gin, and often clearly separated from other families.
Family is between the categories of order and tribe
(or genus).
Functional feeding groups (FFGs) Groupings
of different invertebrates based upon the mode of
food acquisition rather than the category of food
eaten. The groupings relate to the morphological
structures, behaviors and life history attributes that
determine the mode of feeding by invertebrates.
Examples 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).
Funnel trap See Activity trap.
Genus (plural genera) A taxonomic category
of organisms composed of one or more species that
are related morphologically and evolutionarily, the
principal category between family and species.
Gradient A regularly increasing or decreasing
change in a factor (e.g., a single chemical) or com-
bination of factors (as in theHuman disturbance
gradient).
Gradient of human influence The relative rank-
ing of sample sites within a regional wetland class
based on the estimation of degree of human influ-
ence (e.g., pollution and physical alteration of habi-
tats).
Habitat The sum of the physical, chemical, and
biological environment occupied by individuals of a
particular species, population, or community.
Herbivore An organism that consumes plant or
algal material.
Human disturbance gradient A gradient or
range of perturbations or impairments (or human-
caused disturbances) that alter the physical, chemi-
cal, or biological integrity of ecosystems or habi-
tats. The effects may persist over periods of time.
Examples pertaining to wetlands are alterations in
the natural hydrology, in the near wetland landscape,
or in the wetland buffer; or chemical pollution, silt-
ation, removal of aquatic vegetation, exotic species
introductions, cattle, fish-rearing, conducting of ur-
ban stormwater, or agricultural runoff. Compare
human disturbances with discrete events of natural
disturbances.
Impairment Adverse changes occurring to an
ecosystem or habitat. An impaired wetland has
some degree of human influence affecting it.
47
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Index of biologic integrity (IBI) An integrative
expression of the biological condition that is com-
posed of multiple metrics. Similar to economic in-
dexes used for expressing the condition of the
economy.
Index period A defined interval of the season
that serves as the sampling period for biological
assessments. For invertebrates the index period
would be the interval of time when there would be
optimal development of invertebrates and optimal
presence of resident taxa that developed in the
waterbody
Intolerant taxa Taxa that tend to decrease in wet-
lands or other habitats that have higher levels of
human disturbances, such as chemical pollution
or siltation.
ITIS The national Integrated Taxonomic Infor-
mation System (ITIS) coding system for organisms
in the United States and Canada. The database
includes information on each organism with author-
ity, synonyms, common names, and a unique taxo-
nomic serial number (the ITIS code) for all taxo-
nomic levels. It lists publications, experts, and data
quality indicators. ITIS accepts input from investi-
gators regarding uncoded taxa. The database is
update periodically. Website: www.itis.usda.gov/
Macroinvertebrates Animals without backbones
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.
Macrophytes The visible aquatic plants that are
emergent, floating, or submersed under water. They
may be attached to the bottom or not. Distinguished
from algae, most of which are microscopic.
Metric An attribute with empirical change in the
value along a gradient of human influence. See^-
tribute. Metrics are scored individually, and each
score composes the total score for the IBI.
Morphology The structure and form of an or-
ganism, both external and internal. Taxonomic iden-
tifications are mostly derived from the examination
of external morphologies, with exceptions.
Morphospecies A taxon that has distinct mor-
phologies from other similar taxa and is identified
as a distinct taxon based solely on the morphologi-
cal differences (see Oliver and Beattie 1996). The
biologist must determine that the differences are not
from developmental stages or change in features
within the same taxon before the taxon can be
counted in the overall taxa richness.
Multihabitat method A sampling method in
which the sampling effort attempts to sample most
of the habitats with the zone of study. The effort is
variously distributed among the habitats; in some
methods it is distributed in proportion to the repre-
sentation of the habitat in the zone of study, in other
methods it is distributed by giving greater effort to
habitats more likely to have the desired organisms.
Multivariate analysis Mathematical analysis
that examines numerous variables simultaneously.
Data from communities of organisms are multivari-
ate because there are several species with differing
abundances responding to numerous environmen-
tal factors. Various statistical methods are used,
e.g., ordination or discriminant analysis, to analyze
several variables at once.
Omnivores Are organisms that consume both
plant and animal material.
Periphyton The layer of algae that coats sub-
strates in aquatic systems such as plant stems, rocks,
logs, and benthic muds. This layer of algae coating
is often also colonized by bacteria, protozoans, and
rotifers and other microorganisms.
Population A group of individual organisms of
the same species living in the same area.
48
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Predators Organisms that consume animals.
Proportion The mathematical relation of one
part to the whole, expressed as magnitude or de-
gree, e.g., percent. An example of proportion at-
tributes are the percent of tolerant individuals of the
whole sample count or the proportion of the abun-
dance of the top two dominant taxa to the sample
abundance.
QA or QAPP The written plan for quality assur-
ance, or the quality assurance program plan, that
provides written detail for quality assurance plans
for quality assurance checks for all aspects of field
and laboratory procedures.
Ratio The numerical quotient of two variables or
quantities. An example of an attribute that is a ratio
is the ratio of scrapers/collector-filterers (seepro-
portion).
Reference site A minimally impaired site that is
representative of the expected ecological conditions
and integrity of other sites of the same type and
region.
Relative abundance Is the abundance of one
group or taxon of organisms in relation to the total
abundance of the sample.
Replicate A term usually reserved for the rep-
etition of an experiment to obtain information for
estimating experimental error. It is sometimes used
informally to describe repeated consistent samples
taken at a site with the same method, in the same
strata and habitat, and on the same date.
Species A taxonomic category below genus, the
fundamental biological unit, a population of organ-
isms that share a gene pool and are able to repro-
duce successfully and produce young that are able
to reproduce.
Stress (or stressor) Any environmental factor
that impedes normal growth, reproduction, or sur-
vivorship of organisms, or causes adverse changes
in populations of organisms or in ecosystems.
Sweep net Another term forDipnet.
Taxon (singular, taxa plural) A distinct taxo-
nomic group of any level (e.g., family, genus or spe-
cies); includes all subordinate groups. Taxon is any
group of organisms that is distinct enough from other
groups to be treated as a separate unit.
Taxonomic system
tion of organisms.
The hierarchy of classifica-
Taxonomist A biologist who specializes in the
identification of organisms.
Taxonomy The practice of describing, naming,
and classifying organisms.
Tolerance The biological ability of different spe-
cies or populations to survive successfully within a
certain range of environmental conditions.
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.
Sample A representative part of a larger unit
used to study the properties of the whole.
SOP Acronym for Standard Operating Proce-
dure. This is the detailed, written description of all
the methods to be used for field and laboratory pro-
cedures.
Trisecting The division into three parts of a
range of data for scoring a metric.
Trophic Feeding, thus pertaining to energy trans-
fers.
49
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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.ER.§ 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 sur-
face 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 predomi-
nantly hydrophytes, (b) the substrate is predomi-
nantly 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 sea-
son 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 fre-
quency and duration sufficient to support a preva-
lence of hydrophyte 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 agri-
cultural development which have a predominance
of permafrost soils [Food Security Act, 16 U.S.C.
50
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