![[logo] US EPA](http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
Aquatic Life Use Support (ALUS)
Biocriteria Links
Additional Information
Multimetric Approach to Bioassessments
The accurate assessment of biological integrity requires a method that integrates biotic responses through an examination of patterns and processes from individual to ecosystem levels. The early conventional approach to using individual population measures has been to select some biological parameter that refers to a narrow range of changes or conditions and evaluate that parameter (e.g., species distributions, abundance trends, standing crop, or production estimates). Parameters are interpreted separately with a summary statement about the overall health. This approach is limited in that the key parameters emphasized may not be reflective of overall ecological health. The preferred approach is to define an array of metrics that individually provide information on each biological parameter and, when integrated, function as an overall indicator of biological condition.
The strength of such a multimetric approach, when the component metrics are calibrated for a particular stream class, is its ability to integrate information from individual, population, assemblage, and zoogeographic levels into a single, ecologically-based index of water resource quality. The development of metrics for use in the biocriteria process can be partitioned into two phases. First, an evaluation of candidate metrics is necessary to eliminate nonresponsive metrics and to address various technical issues (i.e., associated with methods, sampling habitat and frequency, etc.). Second, calibration of the metrics determines the discriminatory power of each metric and identifies thresholds for discriminating between "good" and"poor" sites. Known impaired sites are used to provide a test of discriminatory power. This process defines a suite of metrics that are optimal candidates for inclusion in bioassessments. Subsequently, a procedure for aggregating metrics to provide an integrative index is needed.
For a metric to be useful, it must be
(1) relevant to the biological community under study and to the specified program objectives;
(2) sensitive to stressors;
(3) able to provide a response that can be discriminated from natural variation;
(4) environmentally benign to measure in the aquatic environment; and
(5) cost-effective to sample. A number of metrics have been developed and subsequently tested in field surveys of benthic macroinvertebrate and fish assemblage.