Selecting Comparator Sites for Ecological Causal Assessment Based on Expected Biological Similarity

Area of Science:

• Environmental Science
• Ecology
• Water Quality Assessment

Background:

• Ecological sites in poor condition necessitate causal assessments for effective management.
• Current site-specific causal assessments are often time-consuming.
• Identifying ecologically similar comparator sites is a critical but lengthy step.

Purpose of the Study:

• To develop and describe a quantitative method to expedite the identification of comparator sites for causal assessments.
• To streamline the process of comparing biological conditions and stressor exposures at impaired sites.
• To facilitate faster and more efficient environmental management decisions.

Main Methods:

• Utilized expected biological similarity, measured by Bray-Curtis dissimilarity (BC) of predicted benthic macroinvertebrate taxa, to select comparator sites.
• Generated comparator site sets for 15 demonstration sites in Southern California using a predictive biotic index.
• Evaluated four example stressors (total nitrogen, ammonia, specific conductivity, bifenthrin) using established causal assessment evidence types.

Main Results:

• Successfully selected over 100 comparator sites for most demonstration sites (BC < 0.1).
• Elevated specific conductivity was identified as the most frequent likely cause of poor biotic conditions.
• Total nitrogen and bifenthrin were also indicated as potential stressors at some sites.

Conclusions:

• The developed quantitative method effectively expedites comparator site selection for causal assessments.
• This approach can be adapted for various bioassessment programs with sufficient data and predictive indices.
• It provides a foundation for rapid, screening-level stressor evaluations to inform management actions.