Little Scioto River, OH, USA Worksheet Example Spatial/Temporal Co-occurrence

Example Worksheet : Spatial/Temporal Co-occurrence	Little Scioto River, OH, USA
Step 3: Evaluate Data from the Case
Candidate causes considered on this worksheet:	Sediment Riffles/Pools Dissolved oxygen Ammonia Metals PAHs

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 W1-7. 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
Increased fine sediments	Silt	2	1	Yes
Altered riffles	Pool score	11	8	Yes
Altered riffles	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 W1-8. 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