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Aquatic Life Use Support (ALUS)
Biocriteria Links
Additional Information
Index Period
The intent of a statewide bioassessment program is to evaluate overall biological conditions. The capacity of the aquatic community to reflect integrated environmental effects over time can be used as a foundation for developing bioassessment strategies. An index period is a time frame for sampling the condition of the community that is a cost-effective alternative to sampling on a year-round basis. Ideally, the optimal index period will correspond to recruitment cycles of the organisms (based on reproduction, emergence, and migration patterns). In some instances, an index period would be oriented to maximize impact of a particular pollutant source (e.g., high-temperature/low-flow period for point sources).
Sampling during an index period can
- (1) minimize between-year variability due to natural events,
- (2) optimize accessibility of the target assemblages, and
- (3) maximize efficiency of sampling gear.