What are biological assessments?
Below are photographs of two wetlands. The one on the right has obviously
been damaged by human activities. The one on the left looks like it is
healthier. But is it really healthy? Some human activities can damage
a wetland without leaving clearly visible signs. For example, some herbicides
and pesticides kill tadpoles, dragonflies, and other wetland creatures.
How can we measure the health of a wetland and be sure that it really
is healthy?
To evaluate the biological integrity or "health" of wetlands, scientists
participating in BAWWG are developing biological assessment (bioassessment)
methods. To conduct a bioassessment, a scientist visits a wetland and
collects information about the number of different kinds of organisms
and what types of organisms are living there. The scientist also collects
information about the habitat quality, water level, and chemistry to support
the biological information. The scientist then analyzes the information
and compares the wetland's biological information to reference conditions.
This is similar to the way a human doctor would collect information about
a patient, such as blood pressure and temperature, and compare it to a
known range of condition. If the values are too high or too low, then
the doctor knows that the patient is sick. Similarly, the wetland scientist
can compare the biological information to a known range of conditions
and determine the health of the wetland.
Bioassessments are based on the premise that the community of plants
and animals living in a wetland will reflect the health of a wetland.
When a wetland is damaged, the diversity of animals and plants often decreases
and the composition of species changes. Typically, the organisms that
are intolerant to human disturbances die and organisms that are more tolerant
to the disturbance make up a larger proportion of the individuals. For
example, the farmed wetland shown above will most likely have fewer kinds
of plants and animals than the healthier wetland and will be dominated
by organisms that can tolerate poor environmental conditions. After examining
an assemblage of plants or animals in wetlands ranging from high quality
to poor quality, scientists can use this known range as a measuring stick
to estimate the relative health of other wetlands. The bioassessment results
will show if a wetland is damaged in any way.
  
Organism assemblages used in wetland bioassessment
What is biological integrity?
The goal of the Clean Water Act is to maintain and restore the chemical,
physical, and biological integrity of the Nation's waters, including wetlands.
But what is biological integrity?
Biological integrity is commonly defined as "the ability to support
and maintain a balanced, integrated, and adaptive community of organisms
having a species composition, diversity and functional organization comparable
to those of natural habitats within a region" (Karr, J. R. and D. R. Dudley.
1981. Ecological perspectives on water quality goals. Environmental Management
5: 55-68).
A more detailed discussion of biological integrity can be found on the
Key
Concepts for Using Watershed Biological Indicators page of the Biological
Indicators of Watershed Health site.
What is an Index of Biological Integrity (IBI)?
Most wetland biological assessment (bioassessment) projects use an index
of biological integrity (IBI) to evaluate the health of wetlands. An IBI
is somewhat similar to the economic indicators used to evaluate the condition
of our economy. An IBI combines multiple indicators of biological condition,
called metrics, into an easy-to-understand index value. The value can
be compared to reference values and help managers assess the relative
health of individual wetlands. The IBI concept was originally developed
by stream ecologists to assess the biological condition of streams (see
Key
Concepts for Using Watershed Biological Indicators). Although sampling
methods and metrics are different for wetlands than for streams, the general
IBI framework can be adapted for wetlands as well as lakes, estuaries,
and terrestrial systems.
Some states--Maine, for example--use multivariate statistics instead
of IBIs.
How is an IBI developed for wetlands?
The first step in creating an IBI is for researchers to classify wetlands
and select reference sites. Wetlands occur in many climatic, hydrologic,
and landscape conditions; as a result, the community composition and diversity
of an assemblage will naturally vary between wetland types. The goal is
to group wetlands such that the diversity and composition of an assemblage
within groups is minimized and the variation between groups is maximized.
Bioassessment projects typically group wetlands by using one or more
existing classification systems, such as ecoregions or hydrogeomorphic
(HGM) classes. Classification is an iterative process. Researchers often
start with one or more methods and then lump or split as needed to end
up with an appropriate number of groups of biologically distinct wetlands.
For example, when the Montana
Department of Environmental Quality 
developed its IBI, the state used ecoregions as a first tier and then
further separated wetlands by landscape position and other characteristics,
such as acidity and salinity. The state later found that it could lump
the wetlands of two ecoregions because of their biological similarity.
After classifying wetlands, researchers select sampling sites across
a gradient of human disturbance for each wetland group. Because no standard
gradient of human disturbance yet exists, some projects have tried to
quantify disturbance by using surrogates such as the percentage of impervious
surfaces or agriculture in a watershed. Other projects have tried using
qualitative indices of human disturbance that incorporate a combination
of watershed and wetland information. Regardless of the gradient used,
it is crucial to select wetlands that range from minimally impaired reference
sites to severely degraded wetlands, and everything in between. Hand picking
sites is most appropriate for developing bioassessment methods because
random samples often fail to provide sufficient range in condition.
Once sites are selected, sampling can begin. Typically, researchers
sample at least two assemblages—commonly this can include algae, amphibians,
birds, fish, macroinvertebrates, and vascular plants. An IBI is developed
independently for each assemblage. Researchers then measure many biological
attributes of each assemblage (e.g., number of individuals, number of
taxa) in search of attributes that show clear patterns of response to
human disturbance. Most attributes will form scatter plots when plotted
against a human disturbance gradient. For example, abundance, density,
and production attributes typically form shotgun patterns because they
are naturally variable. However, some attributes will show clear patterns,
these are the metrics. Figures 1 through 3 are examples of attributes
that Ohio EPA might use as metrics (see the Case
Study for Ohio Environmental Protection Agency). Richness metrics
(e.g., number of taxa) and relative abundance metrics (e.g., number of
tolerant individual/total number of individuals) are often the most dependable.
Ratios or sums of attributes (e.g., number of midges/number of dragonflies;
mayflies + caddisflies + dragonflies) can hide valuable signals, be difficult
to interpret, and are often more variable than the individual attributes
(Karr, J.R., and E.W. Chu. 1999. Restoring Life in Running Waters:
Better Biological Monitoring. Island Press, Washington, D.C.).
After graphically and statistically analyzing the data, researchers
select 8–12 metrics that show empirical and predictable changes along
a gradient of human disturbance. A well-constructed IBI will contain a
number of metrics sensitive to chemical alterations, such as nutrient
enrichment, and others sensitive to physical or biological alterations,
such as the introduction of exotic species.
One approach of combining metrics into an IBI is to assign scores of
1, 3, and 5. For example, a metric with a low score would indicate degraded
condition and a metric with a high score would indicate more pristine
condition. If ten metrics are scored in this manner and then added together,
then the resulting IBI would range from 10 (severely impaired) to 50 (minimally
impaired). The IBI score should form a relatively straight line when plotted
against a gradient of human disturbance. Wetlands that fall far from the
line should be investigated. These outliers are often the result of either:
(1) misclassifying the wetland, or (2) a stressor, such as acid mine drainage,
that is damaging the wetland biota and was not captured by the gradient
of human disturbance.
Perhaps the greatest benefit of an IBI is that it summarizes and presents
complex biological information in a format that is easily communicated
to managers and the public. Most people can relate more easily with plant
and animal IBIs than with complex statistical calculations or some of
the more abstract chemical and physical wetland functions. While an IBI
score is helpful for quickly communicating the overall condition of a
wetland, most of the valuable information lies in the individual metrics.
When reporting bioassessment results, the IBI score should be accompanied
by (1) a narrative description of overall biotic condition in comparison
to reference wetlands of the same region and wetland type, (2) numeric
values of each metric, and (3) narrative descriptions of each metric in
comparison to reference conditions of the same region and wetland type.
What other methods are used in biological assessments?
In addition to IBIs, some states are using advanced statistics in the
biological assessments. Maine DEP uses multivariate statistics to evaluate
the condition of the state's streams and rivers. Maine DEP recently started
a pilot project in the Casco
Bay Watershed to develop biological assessment methods utilizing multivariate
statistics. In addition, advanced statistics have been commonly used to
evaluate algal communities. Maine
DEP and Montana
Department of Environmental Quality
both use statistical methods to examine the algal assemblage in their
wetlands.
What is the difference between biological assessments and functional
assessments?
Functional assessments, such as the Hydrogeomorphic
Approach
(HGMA), are designed to estimate the functions that wetlands provide,
such as water storage, nutrient cycling, and wildlife habitat. While bioassessments
are designed to evaluate wetland health, functional assessments are primarily
designed to inform management decisions involving the dredge and fill
of wetlands and restoring wetlands to compensate for wetland losses. Functional
assessments tend to focus on the physical structure and habitat features
of a wetland.
Used independently, functional assessments are not appropriate for estimating
wetland health because they do not adequately evaluate the condition of
wetland biological communities. In addition, functional assessments will
not detect damage to wetlands caused by many subtle stressors, such as
toxic chemicals. Some bioassessment projects, however, use some form of
functional assessments to gather habitat information. This information
is very valuable to confirm that a wetland is classified properly and
to help identify potential stressors damaging wetlands. Wetland
Bioassessment Fact Sheet 6, compares
bioassessments and HGM.
Additional information about wetland bioassessment methods is found on
the Bioassessment Methods
page.
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