Biological Integrity and the Index of Biological Integrity

The following are brief descriptions of Biological Integrity, Biomonitoring, and the Index of Biological Integrity. For more indepth information, please refer to specific articles in the Publications section of this web site.

Biological Integrity and Biomonitoring -
what is it, why is it important, and how is it influenced by human activity?

Clean Water Act: "The objective of this Act is to restore and maintain the chemical, physical, and biological integrity of the nation's waters" - Clean Water Act (CWA) section 101 (a)

Integrity refers to an unimpaired condition, a state of being complete or undivided. Biological integrity has been defined as "[t]he ability to support and maintain a balanced, integrated adaptive assemblage of organisms having species composition, diversity, and functional organization comparable to that of natural habitat of the region." (Karr and Dudley 1981, Karr et al. 1986) As a result of evolution, each organism is adapted to the environmental conditions in its native biogeographic region. An environment that supports an assemblage of organisms similar to that produced by long-term evolutionary processes has high biological integrity. Changes that result from human activities cause a divergence from biological integrity, that is, a decline in biological condition.

A Word about Chemical vs. Biological Monitoring

The Clean Water Act stipulates that the chemical, physical and biological integrity of our waters are of value. Most monitoring activity over the past 25 years has focused on chemical monitoring with an emphasis of meeting human health goals. Unfortunately, the emphasis of chemical monitoring has not lead to clean water or to healthy streams. (Karr and Chu 1997). Chemical monitoring only provides a slice of the stream integrity picture - water quality as a value to humans.

Chemical monitoring can underestimate degradation in living systems. When biological condition is measured, the number of impaired river miles doubles from 25% as indicated by chemical monitoring to 50% (Karr and Chu 1998). As this statistic indicates, biological monitoring provides insight to a stream's ability to provide a healthy place to live for aquatic organisms.

Biological integrity, although specified in the Clean Water Act has been, until recently, largely ignored. Measuring the stream biota provides a direct assessment of resource condition because the characteristics of the biota reflect the influence of human activity in the surrounding watershed. If the biota is not present at the level expected, we have direct confirmation that human influences are degrading steams and the environments that they drain. Biological monitoring is a method for measuring biological condition. In aquatic environments, biological monitoring can be focused on a variety of assemblages (e.g., algae, invertebrates, fish, macroinvertebrates).

Measuring Human Influences

Biological monitoring allows us to understand more of the processes occurring in our watersheds by determining what organisms are found in a stream and comparing it to what organisms are expected to be present. Biological integrity of streams is directly influenced by human activity (forestry, agriculture, urban development, recreation, grazing, etc.) Measuring biological integrity provides an insight to the human impacts upon stream systems and provides clues regarding where we need to protect streams or where we can start helping to restore their integrity.

A biological integrity monitoring approach consists of five steps: 1) defining biological condition in a minimally disturbed area - what the natural condition in the area should be, 2) defining biological attributes that change along the gradient of human influence, 3) associating those changes with specific human impacts, 4) identifying management practices for improving biological integrity, and 5) communicating results to citizens and policy makers.

Biological Integrity and the Decline of Salmon

The loss of biological integrity within salmon spawning grounds equates to a loss of salmon. If a stream's biological condition is degraded (as reflected by the condition of the benthic macroinvertebrate population), it is safe to conclude that the stream will not support healthy salmon or other fish populations. The decline of healthy salmon spawning and rearing habitat has been identified as one major cause of the decline of wild salmon populations.

SalmonWeb focuses on monitoring the integrity of salmon habitat by monitoring benthic (bottom dwelling) macroinvertebrates (large organisms without backbones). These critters may consist of mayfly larvae, stonefly larvae, caddisfly larvae, worms, beetles, snails, dragonfly larvae, and many others. SalmonWeb has chosen to measure benthic macroinvertebrates because they are long-term inhabitants of streams, relatively immobile, easy to collect, and represent an assemblage that responds predictably to human induced stress. Conversely, salmon are harder to collect, are highly mobile, and migrate out of their spawning grounds.

Furthermore, a benthic macroinvertebrate monitoring program can provide insight to the biological integrity of a stream even if it has never carried a salmon within its banks. Using benthic macroinvertebrates has the additional advantage of being able to detect human influence upstream of any sampling site. In other words, what happens upstream is reflected in the biotic communities downstream - benthic macroinvertebrates are historical markers for upstream impacts.

Measuring Integrity: The Benthic Index of Biological Integrity (B-IBI)

"Our ability to protect biological resources depends on our ability to identify and predict the effects of human actions on biological systems, especially our ability to distinguish between natural and human-induced variability in biological condition" (Karr and Chu 1998).

An Index of Biological Integrity (IBI) is a synthesis of diverse biological information which numerically depicts associations between human influence and biological attributes. It is composed of several biological attributes or 'metrics' that are sensitive to changes in biological integrity caused by human activities. The multi-metric (a compilation of metrics) approach compares what is found at a monitoring site to what is expected using a regional baseline condition that reflects little or no human impact (Karr 1996b). Just as doctors use data from a check-up (e.g., blood samples, temperature, weight, blood pressure, etc.) to compare against what is considered healthy in humans, multimetric indexes utilize a variety of measurements to assess the biological condition, or health, of streams.

Multi-metric biological indexes include the following benthic macroinvertebrate information:

Measuring Human Influence with the Index of Biological Integrity

As human influence and impact increase along a gradient from high to low, indices of biological integrity mirror this gradient. One method for measuring the gradient of human influence is the percent of impervious surface (e.g., roads, parking lots, sidewalks, houses etc). As humans pave roads, develop rural areas into suburbs and cities, the impacts upon streams increase. These impacts create noticeable and measurable changes in the biotic community.


Still from the Fresh Waters Flowing Video of gradient of human disturbance.

An Index of Biological Integrity monitoring approach provides the following four types of stream condition descriptors of the condition of a stream as reflected by the biota:

Furthermore, monitors can understand the processes driving the final IBI score by analyzing how each metric contributed to the final score.

How IBI's Work

Indices of Biological Integrity are developed for specific geographic areas and for specific sampling methodologies. It is important to use an IBI calibrated for your sampling region and for your sampling methodology.

The Benthic Index of Biological Integrity (B-IBI) is one such benthic macroinvertebrate multimetric index designed and calibrated for use in Puget Sound Lowlands using the SalmonWeb monitoring protocol. Each of the metrics have been chosen because of their consistency in responding to several types of human disturbance: urbanization, forestry, agriculture, grazing, and recreation. The metrics are listed below with predicted response to human impact.

Metric Predicted Response due to Human Impact
  • Total number of taxa;
  • Decrease
  • Number of Mayfly taxa;
  • Decrease
  • Number of Stonefly taxa;
  • Decrease
  • Number of Caddisfly taxa;
  • Decrease
  • Number of long-lived taxa;
  • Decrease
  • Number of intolerant taxa*
  • Decrease
  • % of tolerant individuals*
  • Increase
  • % of predator individuals
  • Decrease
  • Number of clinger taxa
  • Decrease
  • % dominance (3 taxa)
  • Increase
    * Refers to organic pollution tolerances

    Level of Identification

    Macroinvertebrate identification is a key component of the benthic index of biological integrity (B-IBI) calculation. Identification may be completed to the taxonomic level of family or may be taken further to the genus or even species level for many aquatic insects. Volunteers may complete identification to family using pictorial keys. More specific identification to genus or species is completed by professionals using dichotomous keys. Dichotomous keys have not been created for all aquatic organisms to the species level because scientists are still learning how to distinguish among those that are very similar. The phrase "lowest practical taxonomic level" is typically used to indicate that organisms have been keyed as specifically as possible, given the present body of knowledge. Nearly all insects can be keyed down to at least the genus level, and most can be keyed to species. However, some non-insect macroinvertebrates, such as roundworms, leeches, and freshwater sponges, are typically keyed only to phylum, order, class, or sub-class level.

    A B-IBI can be calculated whether aquatic insects are identified to the family, genus, or lowest practical taxonomic level. Decisions about the appropriate level of macroinvertebrate identification typically depend on the purpose of the study, other potential uses for the data, the expertise of the taxonomist, and the funding available for the study. When samples are identified to genus or the lowest practical taxonomic level, a ten metric scoring system is used. When samples are identified to the family level, a five metric scoring system is used.

    B-IBI scores calculated from samples identified to the genus or lowest practical taxonomic level will reflect the ecological condition of a site with more statistical precision than samples identified to the family level only. In other words, smaller differences in site condition will be detected with genus or species level scoring than with family level scoring. The statistical precision improves because more metrics are included in the final scoring calculation and because more information is obtained for each metric at more specific levels of identification. Family level scoring is a useful tool for a "first cut" at site condition. Scientists completing research or resource managers who need to make land-use decisions often identify samples to genus or lowest practical taxonomic level. It has not yet been determined whether B-IBI scores calculated from lowest practical taxonomic level data are more statistically precise than B-IBI scores calculated from genus-level information.

    One group of aquatic insects that is particularly difficult to identify is Chironomidae, or midges, a family of the true flies. These flies have tiny heads and few easily identifiable characteristics, making their identification to lowest practical taxonomic level rather time consuming, even for professionals. Therefore some organizations may choose to have most of the organisms in their samples keyed to the genus level or lowest practical taxonomic level, but will leave Chironomidae only identified to family.

    B-IBI metric scores can be entered into the Salmonweb website at three taxonomic levels:

    These three methods all use the same ten metrics. The values assigned to the metrics are adjusted for each taxonomic level so that the final scores will still fall within the same ranges identifying the relative health of the stream. Scoring criteria for family-level identification, which uses five metrics, has different scoring ranges identifying the relative health of the stream. Family-level metric scoring cannot be entered onto the website at this time.


    Generating B-IBI Summary Metrics from Raw Data

    Ten summary metrics are used to calculate the B-IBI value of a stream. Each metric described below must be calculated for your field sample for submission to the SalmonWeb web site.

    The descriptions below assume that all taxa have been sorted, identified, and counted. Use the specie list designation (search the Northwest Taxa Database to find designations) to determine the metric scores (e.g., whether the taxa are long-lived, clingers, pollution tolerant, etc). Taxon means a single taxonomic group such as family, genus, or species. Taxa is plural.

    Species Level Summary Metrics

    The following species level metric descriptions are used for both the Species and Species/Family taxonomic identification methods.

    Species Level 10 Metric B-IBI

    Criteria are for species-level identification of most insects, rhyacophilids to subgroup, and chironomids to genus. See Species Level 10 Metric B-IBI for details and the Scoring Criteria for this level of taxonomic identification.

    Species/Family Level 10 Metric B-IBI

    Adjustments to are made to the species-level scoring criteria when chironomids are identified at the family rather than genus level. Criteria require species level identification for most insects. See Species/Family Level 10 Metric B-IBI for details and the Scoring Criteria for this level of taxonomic identification.

    Total Taxa Richness
    The total number of unique taxa 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 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 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 identified in each replicate. The numbers from the three replicates are then averaged for this metric.
     
    Number of Long-Lived Taxa
    The total number of unique long-lived taxa identified in each replicate. The numbers from the three replicates are then averaged for this metric.
     
    Number of Intolerant Taxa
    The total number of unique intolerant taxa identified in each replicate. Chironomids are not included in this metric. The numbers from the three replicates are then averaged for this metric.
     
    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. Chironomids are not included in this metric. The numbers from the three replicates are then averaged for this metric.
     
    Number of Clinger Taxa
    The total number of unique clinger taxa 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 numbers 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 numbers from the three replicates are then averaged for this metric.

    Genus Level Summary Metrics

    The following genus level metric descriptions are used for both the Genus and Genus (pre 1999) taxonomic identification methods.

    Genus Level 10 Metric B-IBI Criteria

    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. See Genus Level 10 Metric B-IBI for details and the Scoring Criteria for this level of taxonomic identification.

    Genus Level (pre 1999) 10 Metric B-IBI Criteria

    Criteria for genus level scoring used prior to 1999. 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. See Genus Level (pre 1999) 10 Metric B-IBI for details and the Scoring Criteria for this level of 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.

    Family Level Summary Metrics

    The 5-metric Family B-IBI will not give you as much qualitative information as the 10-metric B-IBI, but it will provide you with a relative integrity score. Researchers continue to evaluate the effectiveness of the 5 metric B-IBI.

    Family Level 5 Metric B-IBI Criteria

    Criteria are for family-level identification of all taxa. See Family Level 5 Metric B-IBI for details and the Scoring Criteria for this level of taxonomic identification.
    Total Taxa Richness
    The total number of unique taxa 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 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 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 identified in each replicate. The numbers from the three replicates are then averaged for this metric.
     
    Percent Dominance
    The sum of individuals in the single most abundant taxa in each replicate, divided by the total number of individuals in that replicate, multiplied by 100. The numbers from the three replicates are then averaged for this metric.

    Calculating an IBI and Interpreting the Results

    This section gives an overview of calculating an IBI. See Generating B-IBI Summary Metrics from Raw Data for a detailed description.

    An IBI is created by first identifying and counting all benthic macroinvertebrates found from a stream sampling event. Each metric is then tabulated using these raw data. After the metrics are calculated, they are then converted to a 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 DEGRATED SITE, and a value of "1" is assigned for values expected in SEVERLEY DEGRATED SITES.

    The individual 1, 3, and 5 metric scores are added together for a Total B-IBI score. Since there are ten metrics, a Total B-IBI 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 Interpreting Stream Health Scores table.)

    Interpreting your IBI Score

    Once you've calculated the Puget Sound B-IBI, you have a number between 10 and 50 (or between 5 and 25 for the 5-metric B-IBI). 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 (or 25) indicates you the stream's biology is equivalent to what would be found in a "natural" stream of that area. A value close to 10 (or 5) indicates a poor biotic condition within the stream. Most likely, however, you will achieve a score somewhere in between these two extremes. Listed below are cut off values for the B-IBI scores and the qualitative interpretation.

    Interpreting Stream Health Scores

    10 Metric B-IBI Score 5 Metric B-IBI Score Stream Condition
    SpeciesSpecies/FamilyGenusGenus
    (pre 1999)
    Family
    46-50 23-25 Excellent
    38-44 19-22 Good
    28-36 14-18 Fair
    18-26 9-13 Poor
    10-16 5-8 Very Poor

    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.

    Graphing Your Results

    Stream surveys of the surrounding land uses can help interpret the metric results. A useful way of interpreting IBI scores is to plot the final IBI score against a gradient of human influence expected. Scores lower than the general plotted trend may occur when surrounding or upstream human impacts (e.g., new development, leaking septic systems, new clearcuts, etc.) are present. Conversely, monitoring sites may plot higher than the trend in the presence of wetlands, protected riparian corridors, and other biological conducive conditions.

    References

    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. National Academy Press, Washington, DC.

    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 Pacific Northwest Coastal Ecoregion. Springer-Verlag, New York.

    Karr, J.R., and E.W. Chu. 1997. Biological Monitoring and Assessment: Using Multimetric Indexes Effectively. EPA 235-R97-001. Seattle: University of Washington.

    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, Washington, DC.

    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. Illinois Natural History Survey, Special Publication 5.

    Morley, S.A. (2000) Effects of urbanization on the biological integity of Puget Sound lowland streams: Restoration with a biological focus, Washington, USA. Thesis, University of Washington, Seattle, WA.

    Rossano, E.M. 1996. Diagnosis of Stream Environments with Index of Biological Integrity. Sankaido, Tokyo, Japan


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