Calculating
the 10-Metric Genus-Level B-IBI for
(adapted from www.salmonweb.org)
A B-IBI is created by first
identifying and counting all benthic macroinvertebrates found from a stream
sampling event. Various metrics are then tabulated using these raw data. After
the metrics are calculated, they are each converted to a score of 1, 3, or 5 in
order to facilitate comparisons between areas both over time and space (i.e.,
between sampling site, watersheds, or regions). A value of "5" is
assigned for the range of expected results (i.e., for each metric) in an
UNDISTURBED SITE. A value of "3" is designated for results expected
from a SOMEWHAT DEGRADED SITE, and a value of "1" is assigned for
values expected in SEVERELY DEGRADED SITES.
The individual metric scores
are added together for a Total B-IBI score. In the genus-level ten-metric
B-IBI, a total score can range from 10 (i.e., 10 X 1) to 50 (i.e., 10 X 5). The
Total B-IBI score can then be assessed using a qualitative coding system (see “grading”
table near the end of this document.)
Genus-Level
10-Metric B-IBI Descriptions
Taxon means a single taxonomic
group such as family, genus, or species. Taxa is
plural. For genus-level scoring, aquatic insects are identified to the
genus level, with the exception of chironomids, which
are identified to the family level. Non-insects are identified to the order or
family level:
Here is the complete taxonomic
identification protocol that we use for the 10-metric genus-level B-IBI for the
Puget Sound Lowlands:
The following ten metrics are
calculated from the sample’s taxonomic identification:
Total
Taxa Richness
The total number of unique taxa is identified in each
replicate. The numbers from the three replicates are then averaged for this
metric.
Ephemeroptera Taxa Richness
The total number of unique mayfly (Ephemeroptera)
taxa is identified in each replicate. The numbers from the three replicates are
then averaged for this metric.
Plecoptera Taxa Richness
The total number of unique stonefly (Plecoptera)
taxa is identified in each replicate. The numbers from the three replicates are
then averaged for this metric.
Trichoptera Taxa Richness
The total number of unique caddisfly
(Tricoptera) taxa is identified in each replicate.
The numbers from the three replicates are then averaged for this metric.
Number
of Long-Lived Taxa
The cumulative number of unique long-lived taxa identified across all three
replicates.
Number
of Intolerant Taxa
The cumulative number of unique intolerant taxa identified across all three
replicates.
Percent
Tolerant Individuals
The total number of tolerant
individuals counted in each replicate, divided by the total number of
individuals in that replicate, multiplied by 100. The percentages from
the three replicates are then averaged for this metric.
Number
of Clinger Taxa
The total number of unique clinger taxa is identified in
each replicate. The numbers from the three replicates are then averaged for
this metric.
Percent
Predator Individuals
The total number of predator
individuals counted in each replicate, divided by the total number of
individuals in that replicate, multiplied by 100. The percentages from
the three replicates are then averaged for this metric.
Percent
Dominance
The sum of individuals in the three (3) most abundant
taxa in each replicate, divided by the total number of individuals in that
replicate, multiplied by 100. The percentages from the three replicates
are then averaged for this metric.
Percent
Dominance Example
|
Step
1 Calculate
taxa totals |
Step
2 Sum 3
Most numerous Taxa |
Step
3 Calculate
Percentage |
|
Taxon 1 = 10 organisms |
Pick Top 3: |
(# organisms in 3 dominant taxa /
Total # individuals) X 100 (21 / 22) X 100 |
|
Total = 22 organisms |
Total = 21 organisms |
Percent Dominance = 95% |
10 Metric
Genus Level Scoring Criteria
Square
braces indicate the value next to the brace is included in the range; rounded
parentheses indicate the value is not included.
|
Scoring Criteria: |
1 |
3 |
5 |
|
|
Metrics: Taxa
richness and composition |
||||
|
|
Total
number of taxa |
[0,
14) |
[14,
28] |
>
28 |
|
|
Number
of Ephemeroptera (mayfly) taxa |
[0,
3.5) |
[3.5,
7] |
>
7 |
|
|
Number
of Plecoptera (stonefly) taxa |
[0,
2.7) |
[2.7,
5.3] |
>
5.3 |
|
|
Number
of Trichoptera (caddisfly)
taxa |
[0,
2.7) |
[2.7,
5.3] |
>5.3 |
|
|
Number
of long-lived taxa |
[0,
4) |
[4,
8] |
>
8 |
|
Tolerance |
||||
|
|
Number
of intolerant taxa |
[0,
2) |
[2,
4] |
>
4 |
|
|
% of
individuals in tolerant taxa |
>
44 |
[27,
44] |
<
27 |
|
Feeding
ecology |
||||
|
|
% of
predator individuals |
[0,
4.5) |
[4.5,
9] |
>
9 |
|
|
Number
of clinger taxa |
[0,
8) |
[8,
16] |
>
16 |
|
Population
attributes |
||||
|
|
%
dominance (top 3 taxa) |
> 75 |
[55,
75) |
[0,
55) |
|
|
||||
10 Metric
Genus Level B-IBI Worksheet
|
METRICS (averaged) |
Rep 1 |
Rep 2 |
Rep 3 |
Replicate Average |
Metric IBI Score |
|
(1,
3, or 5) |
|||||
|
Total
number of taxa |
|
|
|
|
|
|
Number
of Ephemeroptera (mayfly) taxa |
|
|
|
|
|
|
Number
of Plecoptera (stonefly) taxa |
|
|
|
|
|
|
Number
of Tricoptera (caddisfly)
taxa |
|
|
|
|
|
|
% of
individuals in tolerant taxa |
|
|
|
|
|
|
Number
of clinger taxa |
|
|
|
|
|
|
% of
predator individuals |
|
|
|
|
|
|
%
dominance (3 taxa) |
|
|
|
|
|
|
METRICS (cumulative) |
Rep 1 |
Rep 2 |
Rep 3 |
Cumulative Unique |
Metric IBI Score |
|
(1,
3, or 5) |
|||||
|
Number
of long-lived taxa |
|
|
|
|
|
|
Number
of intolerant taxa |
|
|
|
|
|
|
Total B-IBI Score (Add Metric B-IBI scores for
Total B-IBI score): |
|
||||
For the percentage metrics, remember to multiply the
final computation by 100 for each replicate, e.g., % predator individuals =
(total number predator individuals / total number individuals) X 100
Once you've calculated the
Puget Sound B-IBI, you have a number between 10 and 50. What does that number
mean?
The B-IBI is a measure of a
stream's biological condition (i.e., health). Each of the individual metrics reflect the condition of important biological components.
These components provide insight and clues about the types of degradation
responsible for changes within the biological community of benthic
macroinvertebrates.
A
value close to 50 indicates that the stream's biology is equivalent to what
would be found in a "natural" stream of that area. A value close to
10 indicates a poor biotic condition within the stream. Most scores will fall
somewhere in between these two extremes. Listed below are cut-off values for
the B-IBI scores and their qualitative interpretation.
“Grading” System For B-IBI For
|
Score |
Grade |
Definition |
|
50-46
|
Healthy |
Ecologically
intact, supporting the most sensitive life-forms. |
|
44-36
|
Compromised |
Showing
signs of ecological degradation. Impacts expected to one or more salmon
life-stages. |
|
34-28
|
Impaired |
Healthy
ecosystem functions demonstrably impaired.
Cannot support self-sustaining salmon populations. |
|
26-18
|
Highly
impaired |
Highly
adverse to salmon and various other life-forms. |
|
16-10
|
Critically
impaired |
Unable
to support a large proportion of once-native life-forms. |
It is
important to not only look at the final B-IBI score, but to look at the
individual metric scores for clues to the types of impacts affecting the final
score. For example: Did you have a high percentage of pollution tolerant taxa?
Were long lived taxa present? Were sediment tolerant taxa present? The
individual metrics, the original data set, and your notes on the land uses
surrounding the site will help you understand the processes occurring within
and around your sampling site.
Indices of Biological Integrity
do more than generate a final score - they provide the opportunity to
investigate the types of influences acting upon a watershed. However, keep in
mind that human disturbances act upon stream systems in complex ways and thus
the resulting IBI scores should be interpreted as a whole (Rossano,
1996). For example, a sampling site may possess high diversity (i.e., total
taxa richness) and thus indicate a high biological integrity score. However, if
the species contributing to a high diversity are pollution tolerant species,
the overall biological integrity of the system may be poor. Knowing the stream
ecology of the different taxa associated with streams in your region will aid
in the interpretation of your data and the resulting IBI.
Fore, L. S., K. Paulsen, & K. O'Laughlin. (In press) Assessing the performance of volunteers in monitoring streams. Freshwater Biology.
Karr, J.R. 1996a. Ecological integrity and
ecological health are not the same. Pp. 97-109 in P.C.
Schulze, ed. Engineering Within Ecological Constraints.
Karr, J.R. 1996b. Rivers as Sentinels: Using the
biology of rivers to guide landscape management. Pp in RJ.
Naiman and R.E. Bilby, eds. The Ecology and Management of
Streams and Rivers in the
Karr, J.R., and E.W. Chu.
1997. Biological Monitoring and Assessment: Using Multimetric Indexes
Effectively. EPA 235-R97-001.
Karr, J.R. 1999. Defining and measuring river health. Freshwater Biology, 41:221-234.
Karr, J.R. and E.W. Chu.
1998. Restoring Life in Running Waters: Better Biological Monitoring. Island Press,
Karr, J.R. and D.R. Dudley. 1981. Ecological perspective on water quality goals. Environmental Management, 5:55-68.
Karr, J.R., K.D. Fausch, P.L. Angermeier, P.R. Yant, and I.J.
Schlosser. 1986. Assessing biological integrity in running waters, a
method and its rational.
Rossano, E.M. 1996. Diagnosis of
Stream Environments with Index of Biological Integrity. Sankaido,