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Obtain Water Quality Score Results
Biological indicators have been used since EPA’s inception to establish water quality goals and to measure our progress in meeting these goals. For example, Indices of Biotic Integrity (IBIs) were developed by EPA ORD to describe the health of fish and macrobenthos inhabiting streams in the mid-Atlantic highlands. This was accomplished through a formalized step-wise process that included selection of candidate biological metrics, assessment of responsiveness to stress, consolidation of the metrics into a single index, and testing of the indices in relation to disturbance gradients.Two elements that are critical in all phases of index development and testing, and subsequently in estimation of biotic condition, are the selection of methods to define reference condition and the selection of meaningful thresholds of biotic response to represent water quality conditions (e.g., impaired/unimpaired, good/fair/poor, etc). This section presents best practices to consider when developing, testing, and implementing indices of biotic integrity. Evaluation Guidelines for Ecological Indicators also contains information regarding existing methods and recommendations for developing more credible indices of biotic integrity. All of the approaches described in this section are applicable to regional, state, or local geographic areas.
Sample Site Selection
Sample sites used to develop biological indices should be representative of the range of conditions for the geographic area of interest, including the best and worst conditions. This can be accomplished through a probabilistic, targeted, or combination of designs. Calibration sites will be used to develop the metrics and overall index, and the validation sites will be used to test the index with an independent data set. <more on sampling design> <more on data analysis>
Metric Selection: When conducting biological assessments, measurements are taken in the field or lab. Metrics for each assemblage sample are calculated from these measurements. Metrics are the fundamental units of the index. Each metric represents an ecologically important attribute of the biological community. Metrics are initially selected from a “pool” of existing metrics used by others along with potential metrics of regional interest. These metrics must be tested to ensure their precision and accuracy. Most IBIs contain between 8 and 12 metrics. The following tables present an example of representative metrics for each type of assemblage.
| Metric | Response to Stress |
|---|---|
| No. of Taxa | Reduced |
| No. of Sunfish Species | Reduced |
| No. of Sucker Species | Reduced |
| No. of Intolerant Species | Reduced |
| % tolerant individuals | Increased |
| % piscivores | Reduced |
| % omnivores | Increased |
| % invertivores | Reduced |
| % planktivores | Increased |
| Reproductive | Reduced |
| Composition | Reduced |
| Total Number of Individuals | Substantially different under stress |
Fish healthy (pathology)
|
Reduced under severe organic pollution or contamination |
| Tissue Contaminants | Elevated under contamination (eg mercury, organochlorines) |
| Metric | Response to Stress |
|---|---|
| No. of Taxa | Reduced |
| Mean number of individuals per taxon | Substantialy lower or higher |
| % contribution of dominant taxon | Elevated |
| Shanon - Wiener diversity | Reduced |
| % intolerant species | Reduced |
| % oligarchies | Elevated under organic enrichment |
| ETO taxa (ephemeroptera, tichoptera, odonates) | Reduced under enrichment, DO, stress |
| % non-insects | Reduced |
| Crustaceans + mollusc taxa | Reduced under acid stress |
| % crustaceans and molluscs | Reduced under acid stress |
| Tollerance indices (e.g. HBI [Hilsenhoff 1987]; Hulbert's Lake Condition Index [LCI] [Frydenborg et al. 1995]) |
Reduced |
| % enrichment feeders | Reduced |
| % shredders | Reduced under enrichment or in very large lakes |
| Metric | Response to Stress |
|---|---|
| Total vegetated area (% of littoral) | Substantially more or less than reference |
| % exotics or weedy species | More than reference |
| No. of exotic species | High |
| Density or biomass in vegetated areas | Substantially more or less than reference |
| No. of taxa | Low |
| % dominant species (by weight) | High |
| Maximum depth of plant growth | Reduced under enrichment, deeper under acidification |
| Periphtyon Metrics considered to be more diagnostic | Description |
|---|---|
| Species richness | An estimate of the number of algal species (diatoms, soft algae, or both) |
| Total Number of Genera (Generic richness) | Total number of genera (diatoms, soft algae, or both) |
| Total Number of Divisions | |
| Shannon Diversity (for diatoms) | A function of both the number of species in a sample and the distribution of individuals among those species (Klemm et al. 1990) |
| Percent Community Similarity (PSc) of Diatoms | Percent community similarity values range from 0 (no similarity) to 100%. |
| Pollution Tolerance Index for Diatoms | Species assigned a value of 1 for most tolerant taxa (e.g., Nitzschia palea or Gomphonema parvulum) to 3 for relatively sensitive species |
| Percent Sensitive Diatoms | Sum of the relative abundances of all intolerant species |
| Percent Achnanthes minutissima | Quartiles of this metric from a population of sites has been used to establish judgment criteria, e.g., 0-25% = no disturbance, 25-50% = minor disturbance, 50-75% = moderate disturbance, and 75-100% = severe disturbance |
| Percent live diatoms | Percent live diatoms was proposed by Hill (1997) as a metric to indicate the health of the diatom assemblage. |
For example, indicators of condition for the Mid-Atlantic Highlands (MAHA) study design were Fish community Structure (IBI), Macroinvertebrate Community Structure (EPT) and Periphyton Community Structure. To learn more about how each metric was selected, please view the PowerPoint presentation, which gives more detail.
Correcting for Watershed Size Influences: It is known that watershed size is a dominant influence for ecological communities, particularly for the different types of organisms known as “taxa richness." Metrics need to be corrected for this natural influence to ensure the best discriminatory ability of the final IBI. Several approaches have been developed, but many often have a “residual” correlation with watershed size. The approach developed for this study has great potential to reduce that residual correlation and increase the precision and accuracy of IBIs.
Results
Each metric is then assigned an ordinal score which is related to its deviation from the reference (or expected) site values. In more complicated studies, multimetric indices can be calculated, which is the sum of all the metric scores within each biological assemblage. <more on multimetric indices>
After each metric is calculated, the biological community results are presented in ecologically significant terms. Guidelines are developed which allow for easy interpretation of each macroinvertebrate fish score.
For example, to determine whether a stream or other waterbody is impaired, the Mid-Atlantic Integrated Assessment (MAIA) compares the index scores for that particular site to a range of scores for the chosen reference (healthiest) site. For instance, for MAIA, the fish IBI was calculated by summing the selected metric scores, dividing by the total number of metrics, and multiplying by 10 to yield a 0-100 scale.
Results are typically presented as a percentage of watershed resources (e.g. streams) that are considered to be good, fair, or poor based on a scoring system. Streams rated good or fair, are considered to be healthy, with good streams comparable to the highest quality reference streams and fair comparable to the rest of the reference sites. Poor sites are considered unhealthy in comparison to the chosen reference sites.