Mitigation for the Construction and Operation of Libby Dam

We know that biological significance is not always the same as statistical
significance. Increases in the abundance of several sensitive taxa indicate that there may
have been subtle improvements in the biotic condition during 2003. Moreover, the
occurrence of these taxa as some of the most abundant (overall) taxa is important because it
underscores the presence of sensitive taxa in the stream. That is, to colonize the restoration
site, they must be able to live in Grave Creek in the first place. The causes of these subtle
improvements may—or may not—be related to the restoration. These small improvements
may be due to environmental differences between the two years—at the basin or regional
scale. The best way to assess the benefits of the restoration is to compare the restored site
to sites that have not been restored. This will allow changes associated with the restoration
to be distinguished from broader environmental variation in the region.
Figure 46. Minimal detectible difference for Taxa Richness for Libby Creek. This graph
assumes a= 0.05, and b=0.1. With three replicates, the taxa richness must increase from
33 to > 46 for the change to be statistically significant.
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