|
Data:
Data downstream from the Site A were used to characterize the stressor-response relationship. Dissolved oxygen was measured continuously at each location over a 3-d period with Datasonde continuous monitors.
Analysis:
Observed minimum DO were plotted against the three specific variables. Where appropriate a curve was fit to the observations as a visualization aid. The point corresponding to observed minimum DO and the biological response at Site A was overlaid on the plot (shown in red).
Figure W1-10. Comparisons of site conditions to stressor-response curves.
Discussion:
The observed proportion of mayflies and DELT seem reasonably consistent with the trends exhibited across the observed range of minimum DO values. However, uncertainty in the position of the fitted curve is large, given that only six data points were available. The observed value of relative weight is much larger than observed at other sites, and falls in the middle of the observed range of DO values.
Evidence Scoring Table:
| Finding |
Interpretation |
Score |
| A strong effect gradient is observed relative to exposure to the candidate cause, at spatially linked sites, and the gradient is in the expected direction. |
This finding strongly supports the case for the candidate cause, but is not convincing due to potential confounding. |
++ |
| A weak effect gradient is observed relative to expsoure to the candidate cause, at spatially linked sites, OR a strong effect gradient is observed relative to exposure to the candidate cause, at non-spatially linked sites, and the gradient is in the expected direction. |
This finding somewhat supports the case for the candidate cause, but is not strongly supportive due to potential confounding or random error. |
+ |
| An uncertain effect gradient is observed relative to exposure to the candidate cause. |
This finding neither supports nor weakens the case for the candidate cause, because the evidence is ambiguous. |
0 |
| An inconsistent effect gradient is observed relative to exposure to the candidate cause, at spatially linked sites, OR a strong effect gradient is observed relative to exposure to the candidate cause, at non-spatially linked sites, but the gradient is not in the expected direction. |
This finding somewhat weakens the case for the candidate cause, but is not strongly weakening due to potential confounding or random error. |
- |
| A strong effect gradient is observed relative to exposure to the candidate cause, at spatially linked sites, but the relationship is not in the expected direction. |
This finding strongly weakens the case for the candidate cause, but is not convincing due to potential confounding. |
-- |
Table W1-14. Stressor-response(field) scores for candidate causes.
| Candidate Cause |
Specific Effect |
Result |
Score |
| Dissolved oxygen |
Relative weight |
No apparent gradient |
0 |
| Proportion DELT |
Consistent with gradient |
+ |
| Proportion mayflies |
Consistent with gradient |
+ |
|