Table 6.

Weight of evidence (WoE) for each consideration and summary WoE for the hypothesis that the background specific conductivity (SC) is not different in Ohio.

Consideration	Summary WoE
Regional properties	The geology, climate, and physiography are similar throughout Ecoregion70. A geophysical model gave SC results that were similar for the two areas. Therefore, the geophysical processes that determine natural background are shared throughout the ecoregion. (+)
Empirically estimated background	The minima in the two areas are very similar, and 19% of sites in the new area are within the background level for the original area based on reference sites. However, the estimated natural background (25th centile) is 31% higher in the new area than the original area. Because the sampling designs and timing are different, these results are ambiguous. (0)
Distribution of low SC sites	The spatial distribution of low SC sites is consistent with residual natural background for the area. However, the data set is not optimal in either coverage or sampling of smaller streams. (+)
Biological properties	Ninety percent of the genera in the original area occur in the new area. Salt intolerant genera are present; therefore, some places are believed to have low SC. However, species within some genera in the new area could have different salt tolerance from species in the rest of the ecoregion, so results are supportive but not conclusive. (+)
Relevance and reliability of evidence	The reliability in terms of data quantity and QA procedures of the Ohio Ecoregion 70 SC data set was judged to be very good, but relevance in terms of similarity of sampling is questionable. The most prominent differences in Ohio are the uneven spatial distribution of sampling, the high proportion of July–August sampling, and deployed substrate versus kick-net biological sampling. (0) However, both the biological data and the regional property information were judged to be highly relevant and reliable. (+ +)
Summary for the body of evidence	Based on SC sampling, background stream SC in the new area appears to be higher than in the original area, but the geophysical model indicates that the difference in natural background is small. Potential natural causes of the difference are not supported by regional properties and the biota similarities imply similar background SC. (+)