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Development of a Method for Deriving Pollution Tolerance Values
Objective:
Identify and develop a defendable, repeatable, objective, and accurate method for the creation of pollution tolerance values to strengthen their use in regulatory decisions.
Approach:
- Demonstrate the need for the development of a method by characterizing the variation in current methods and resulting values.
- Evaluate and compare all known methods used to derive tolerance values using a variety of abiotic and benthic data collections.
- Use the identified method to analyze regional variability in tolerance values and the effect of collection method used to gather input data.
- Evaluate the identified method for creating stressor-specific tolerance values and for use with other taxonomic groups (i.e., fish, diatoms).
Why This Research Is Needed:
Tolerance-based indices for macroinvertebrates are a staple of stream biotic evaluation. The utility of these indices hinges upon the tolerance values that are assigned to each organism and there is limited information available to support the methods used to derive them. The values assigned to a group often disagree and some values currently used by Region 3 States differ by eight points on the traditional eleven point scale. For continued use of the HBI and other tolerance-based indices, the available methods must be scrutinized and a best available method identified, supported, and presented in a usable format to possible users.
EERD Experience:
- EERD is comparing and characterizing each of the empirical methods that are used for creating tolerance values.
- Tolerance values are being developed for each method using multiple datasets so that the repeatability and accuracy of each method can be determined.
Expected Outputs/Outcomes:
- States, regions, and tribes will be able to create their own tolerance values from their existing data using a verified and defended method. These values will better reflect the true optima of the taxa than best-professional-judgment values.
- States, regions, and tribes will have enhanced ability to determine stream condition and make robust regulatory decisions.
EPA Report
The Evaluation of Methods for Creating Defensible, Repeatable, Objective and Accurate Tolerance Values for Aquatic Taxa (PDF) (68 pp., 4 MB) - EPA 600/R-06/045 May 2006. In the field of bioassessment, tolerance has traditionally referred to the degree to which organisms can withstand environmental degradation. This concept has been around for many years and its use is widespread. In numerous cases, tolerance values (TVs) have been assigned to individual taxa or groups of taxa to represent their tolerance to pollution. The TVs are then often combined into metrics which describe characteristics of aquatic communities. Perhaps the most familiar example is the Hilsenhoff Biotic Index (HBI) (Hilsenhoff, 1977), an index that has been incorporated into many bioassessment programs. The HBI is typically very useful in distinguishing among sites of higher and lower water quality. To calculate the HBI, each environmental agency or organization typically uses its own set of tolerance values. However, the origins of these values, and rationales for their selection, are often obscure and unverifiable. Available methods for deriving TVs more objectively vary substantially in approach and complexity. Therefore, this study conducted systematic comparisons of existing lists of macroinvertebrate TVs and their resulting HBI scores. It also compared several objective TV derivation approaches, as well as bioassessment metrics derived from each, to determine their repeatability and sensitivity to disturbance. All analyses were run at the family and genus levels.
Contact: Karen Blocksom (blocksom.karen@epa.gov) (Cincinnati, OH)