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CADDIS Volume 3: Examples & Applications

Worksheets: Little Scioto River, OH

Spatial/Temporal Co-occurrence

Consider whether measurements of particular stressors (sediment, riffles/pools, dissolved oxygen, ammonia, metals, and PAHs) co-occur with observed biological impairment.

Data

Single observations of habitat quality were collected from the upstream site and the impaired site in 1992. PAH and metal concentrations were determined from fine sediments up to a depth of 15cm at each site. Dissolved oxygen and ammonia were measured in the water column.

Analysis

Table 7. Comparison of stressor measurements at the site and at an upstream site.
Candidate Cause Measurement Upstream site Site A Exposure increased at Site A?
Increased fine
sediments
Substrate embeddedness 2 1 Yes
Silt 2 1 Yes
Altered riffles Pool score 11 8 Yes
Riffle score 6 0 Yes
Dissolved oxygen
(mg/L)
Dissolved oxygen 8.8 5.7 Yes
Metals
(mg/kg)
Chromium 7.34 13.6 Yes
Copper 7.44 17.2 Yes
Lead 12.1 19.2 Yes
Zinc 3.06 79 Yes
PAHs
(mg/kg)
Anthracene ND ND No
Benzo[a]anthracene ND ND No
Benzo[ghi]perylene ND ND No
Chrysene ND ND No
Fluoranthene ND ND No

Discussion

PAHs were not detected at the site, so PAH toxicity was refuted as a potential cause. Ammonia was not detected at the site, but water column measurements of ammonia are highly variable. Spatial co-occurrence for all other stressors was compatible with the stressor being the cause.

Evidence scoring table:
Finding Interpretation Score
The effect occurs where or when the candidate cause occurs, OR the effect does not occur where or when the candidate cause does not occur. This finding somewhat supports the case for the candidate cause, but is not strongly supportive because the assocation could be coincidental. +
It is uncertain whether the candidate cause and the effect co-occur. This finding neither supports nor weakens the case for the candidate cause, because the evidence is ambiguous. 0
The effect does not occur where or when the candidate cause occurs, OR the effect occurs where or when the candidate cause does not occur. This finding convincingly weakens the case for the candidate cause, because causes must co-occur with their effects. ---
The effect does not occur where or when the candidate cause occurs, OR the effect occurs where or when the candidate cause does not occur, and the evidence is indisputable. This finding refutes the case for the candidate cause, because causes must co-occur with their effects. R

Table 8. Spatial/temporal co-occurrence scores for candidate causes.
Candidate Cause Result Score
Sediment Elevated sediment co-occurs with impairment +
Pool/riffle Poor pool/riffle condition co-occurs with impairment +
Dissolved oxygen Reduced DO co-occurs with impairment +
Ammonia Elevated ammonia not detected at site ---
Metals Elevated metals concentrations observed at impairment +
PAHs Elevated PAHs not detected at site R

View results in: Summary of Scores from the Case.

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