Xerces Guide to Pacific Northwest Macroinvertebrate Monitoring

STREAM BUGS AS BIOMONITORS
Guide to Pacific Northwest Macroinvertebrate Monitoring and Identification
Jeff Adams
with Mace Vaughan and Scott Hoffman Black - The Xerces Society (www.xerces.org)

> Interpret data

Interpret Data - Make Sense of the Macroinvertebrates You've Collected
Multimetric analysis (B-IBI) * Multivariate analysis (WOWSA)

The primary goal of interpreting or analyzing macroinvertebrate data is to translate the data into applicable information or sound management of your watershed. Two types of tools are regularly used in the Pacific Northwest for interpreting macroinvertebrate data: multimetric indices (primarily the Benthic Index of Biological Integrity or B-IBI) and multivariate statistics and models (particularly the Western Oregon and Washington Stream Assessment model or WOWSA). Even though the names sound rather intimidating, using these tools to analyze your data is fairly easy. Knowing how these tools are created and why, will help you better understand what your results mean for your streams and watershed.

Quick Comparison of Analysis tools

The image to the right (click to enlarge) describes some of the major characteristics of each analysis tool. Both tools use reference streams to determine what the biological condition of a stream would be in the absence of human influence. Reference streams are streams with watersheds have been the least affected by human activities (closest to natural conditions). Both generate a single score that indicates the biological condition of your stream, and also generate additional data that allow you to further interpret causes of degradation.

Multimetric analysis is relatively easy to communicate to others and to understand how a single score is obtained. Multivariate analysis is very straightforward, in that it is based on the basic idea of comparing what you found to what you might expect at reference sites. It is also slightly more powerful than multimetric analysis. However, the development of a multivariate analysis tool is highly complex and difficult to communicate to others. Both have advantages and disadvantages and are most effectively used together, since the information each produces complements the other nicely.

Advantages

Disadvantages

Multimetric analysis (B-IBI)

relatively easy to understand how scoring criteria are derived
results can be easily calculated by hand
allows you to think about how particular groups and types of macros respond to increasing human disturbance
easier to incorporate reference streams in future years into the index

metrics and scoring criteria should be reevaluated before using in a new area or different type of stream (e.g., valley vs. mountain)
does not directly incorporate habitat characteristics
requires judgment-based assignment of scoring criteria that may skew the results if several metrics happen to fall just to one side of the criterion

Multivariate analysis (WOWSA)

a single model covers an entire region and all the different types of streams in that region
slightly better at discriminating between levels of impact
provides information on taxa that were expected but absent, or not expected but present
incorporates habitat characteristics of the stream

model development is difficult to understand and more difficult to do
must rely on someone else to run your data through the model
updating the model with recent reference information that represents natural variability

Multimetric analysis (B-IBI) * Multivariate analysis (WOWSA)

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