B-IBI Recalibration Documents and Materials

This document describes our effort to modify taxa attribute lists used to calculate B-IBI using published literature and knowledge of local taxa, explore individual taxa response to factors of human disturbance, and correlate metrics derived from updated taxa attribute lists with an independent human disturbance measure within the Puget Sound watershed.

An essential step in watershed management is the identification of key natural and anthropogenic stressors influencing important biological indicators of watershed health, such as B-IBI. Relative risk analysis provides quantifiable associations between stressors of concern and biological response, making this a useful tool to identify potential risks to aquatic biota, complimenting monitoring programs, and supporting watershed management decisions. For this project, water quality, sediment chemistry, and physical habitat data (146 sites) from the Washington State Department of Ecology’s Status and Trends Monitoring for Watershed Health and Salmon Recovery program were used to determine the relative importance and strength of relationship between benthic macroinvertebrate metrics and environmental stressors in western Washington streams and small rivers.

Side-by-side macroinvertebrate samples were collected from 55 Puget Sound stream sites using both 3 and 8 sq. ft. sampling protocols to (1) determine if data collected from 3 and 8 sq. ft. are comparable, and (2) if they are not comparable develop a conversion algorithm or “cross-walk”. Analyses showed no significant difference in mean B-IBI or B-IBI metric scores and taxonomic composition between 3 and 8 sq. ft. sampling areas. A minimum 500-count subsample is critical to the comparability between sampling protocols. Thus, no adjustments to metrics or the B-IBI are needed to make samples from different surface areas comparable if a target 500-count subsample is used.

2013 sampling at 20 Puget Sound river sites was combined with existing data available on Puget Sound rivers in the PSSB to evaluate candidate metrics for larger Puget Sound streams and rivers.