The ICI - Invertebrate Community Index - is
one of the measurements the Ohio EPA uses to determine stream
water quality. Other measurements include the IBI (Index of
Biological Integrity) which is based on fish samples, and the Iwb
(Index of Well-Being) which is also based on fish data. These
parameters can be combined and compared to values obtained at
reference sites, which are minimally impacted. The scores can
also be compared to various criteria for different levels of
water quality, as defined by the Ohio EPA.
Step 1 - Sampling: The first step in calculating the ICI is to take
the appropriate samples. Normally, this involves using a
Hester-Dendy type sample for a period of 6 weeks during the
summer. For classroom purposes, we will use samples obtained with
a Surber sampler. As a result, the results will not really
be comparable with the Ohio EPA reference sites and standards.
For details on how to obtain the samples see OEPA 1989a.
Step 2 - Identification: The next step is to identify all of the specimens
to the lowest possible taxonomic level. At this point, create a
table with all the taxa and the number of specimens for each
taxon. The Winmac program will generate a table useful for this
purpose. The other piece of information you need is the area of
the stream upstream from the sampling site.
Step 3 - Calculate
Individual Metrics: With the
data in hand, you are ready to calculate the ICI. The ICI is
composed of 10 different metrics. Each metric is scored either 0,
2, 4, or 6, depending on the data. Sometimes the scoring is
numerical; in most cases it is determined from a graph. The
graphs in this document have been color-coded so that the red zones correspond to an ICI score of 0; orange to 2, yellow to 4, and green to 6. It is important to note that the
metrics can only be calculated for watersheds over 10 square
miles. The procedure for calculating the ICI is
presented in Section 5 of OEPA 1987b; some of the figures for
determining individual metric scores were updated in OEPA 1989b.
The instructions below present a simplified overview of the
process.
Metric 1 -
Total number of Taxa:
The total number of taxa decreases
as river drainage increases over 100 square miles.
Metric
2 - Number of Mayfly Taxa
Mayflies are most common in
intermediate-sized streams.
Metric 3 - Number of Caddisfly Taxa:
The number of caddisfly taxa
increases as river drainage increases over 10 square
miles. . Note that a 0 score is assigned when no
caddisflies are found in streams under 600 square miles
or when 1 taxa is found from streams with drainages over
600 square miles.
Metric 4 - Number of Dipteran Taxa:
The number of dipteran taxa
decreases as river drainage increases over 100 square
miles.
Metric 5 - Percent Mayflies:
Again, mayflies are most common in
intermediate-sized streams. Note that this metric uses
the percent abundance of mayfly individuals. To obtain
the percentage, sum the percentages of all the mayfly
taxa. For instance, if there are 3 taxa of mayflies in a
sample, one representing 12% of the sample, one 3% of the
sample, and one 4% of the sample, the percent mayflies
would be 19%.
Metric 6 - Percent Caddisflies:
Again, caddisfly numbers increase
with drainage basin. Note that this metric uses the
percent abundance of caddisfly individuals in the sample.
Obtain the percentage in the same fashion as you did for
mayflies, above.
Metric 7 - Percent Tanytarsini midges:
Tanytarsini midges (Chironomidae)
are indicators of good water quality. Note that this
metric uses the percent abundance of tanytarsini
individuals. Use the same methods here as for mayflies
and caddisflies. Score 0 if there are no Tanytarsini
midges.
Metric 8 - Percent Other Diptera and
Non-Insects
This grouping includes all dipteran
taxa (except Tanytarsini) as well as all
non-insect invertebrates (worms, scuds, flatworms,
aquatic sow bugs, hydras, snails, etc.). The scale here
is reversed from most of the
other metrics, here, more of these species is a bad
sign.To obtain the percentage, divide the number of other
diptera and non-insect individuals by the total number of
specimens (or sum the percentages of all the other
diptera and non-insects). If no organisms are collected,
score a 0.
Metric 9 - Percent Tolerant Organisms:
This grouping includes the taxa
listed below. The scale here is reversed
from most of the other metrics, here, more individuals of
these species is a bad sign.To obtain the percentage, sum
up the percentages of each of the taxa listed below which
occur in your sample. If no organisms in these taxa are
collected, score a 0.
Common Name
Scientific Name
Aquatic Segmented Worms
Annelida: Oligochaeta
Midges
Diptera: Chironomidae
Psectrotanypus dyari
Cricotopus (C.) bicinctus
Cricotopus (Isocladius) sylvestris
group
Nanocladius (Nanocladius) distinctus
Chironomus (Chironomus) spp.
Dicrotendipes simpsoni
Glyptotendipes prob. barbipes
Parachironomus hirtalatus
Polypedilum (Polypedilum) fallax group
Polypedilum (Polypedilum) illinoense
Mollusca
Limpets
Ferrissia spp.
Pond Snails
Physella spp.
Metric 10 - Qualitative EPT Taxa
This is the only component metric
of the ICI that is based on a qualitative sample. All of
the other metrics are based on artificial substrate
(Hester-Dendy) samples. As such, this is really the only
metric that can be used with the type of samples we
normally take in class. EPT refers to Ephemeroptera, Plecoptera, and Trichoptera.
To calculate the metric, add up the number of taxa for
each of these 3 orders and refer to the graph above.
Step 4 - Calculate ICI: The next step is to calculate the overall ICI. This
is done by simply summing up all of the individual metrics to
obtain a number between 0 and 60. The larger the number, the
"better".
Step 5 - Interpret the Results: There are
several ways to interpret the ICI results. The figure below,
taken from the 1996 Ohio Water Resource Inventory (Rankin, Yoder
and Mishne, 1996) gives the ICI standards for attainment of
certain "uses". WWH refers to Warm Water Habitats,
MWH-C refers to Modified Warmwater Habitats with modified
Channels, MWH-A refers to non-acidic mine runoff affected
habitats, and MWH-I refers to extensively impounded modified
warmwater habitats (Rankin et al., 1996). In the figure below, H
refers to headwater streams (<20 square miles), W to wading
sites, and B to sites where boats were used to sample.
Other graphics (below) show the basic
criteria for the warmwater habitat as well as the criteria for
exceptional habitats (EWH):
Finally, you can compare your sample to
others taken by the Ohio EPA:
For help in interpreting these
graphs, see the appropriate OEPA documents. Remember that your
data was not taken in the summer and did not utilize the
Hester-Dendy sampler. Additional guides to interpretation of the
ICI can be found in Ohio EPA (1987b).
Literature Cited
Ohio Environmental Protection Agency.
1987a. Biological criteria for the protection of aquatic life:
Volume I. The role of biological data in water quality
assessment. Division of Water Quality Monitoring and Assessment,
Columbus, Ohio.
Ohio Environmental Protection Agency.
1987b. Biological criteria for the protection of aquatic life:
Volume II. Users manual for biological field assessment of Ohio
surface waters. Division of Water Quality Monitoring and
Assessment, Columbus, Ohio.
Ohio Environmental Protection Agency.
1989a. Biological criteria for the protection of aquatic life:
Volume III. Standardized biological field sampling and laboratory
methods for assessing fish and macroinvertebrate communities.
Division of Water Quality Monitoring and Assessment, Columbus,
Ohio.
Ohio Environmental Protection Agency.
1989b. Addendum to biological criteria for the protection of
aquatic life: Volume II. Users manual for biological field
assessment of Ohio surface waters. Division of Water Quality
Monitoring and Assessment, Columbus, Ohio.
Rankin, Edward T., C.O. Yoder, and D.
Mishne. 1996. Ohio Water Resource Inventory: Volume I. Summary,
Status and Trends. Division of Surface Water Monitoring and
Assessment Section, Ohio EPA, Columbus, Ohio.
