Little Scioto River, OH, USA Worksheet Example Causal Pathway

Example Worksheet : Causal Pathway	Little Scioto River, OH, USA
Step 3: Evaluate Data from the Case
Candidate causes considered on this worksheet:	Dissolved oxygen

Data:
Total phosphorus (TP) and biochemical oxygen demand (BOD) were measured at the site

Analysis:

Table W1-10. Steps in the causal pathway leading from increased nutrients to decreased DO.
	Data confirmed at site?
Increased nutrients (N and/or P)	Yes
Increased algae	No data
Increased BOD	No

Table W1-11. Steps in the causal pathway leading from channel modification to decreased DO.
	Data confirmed at site?
Channel modified	Yes
Decreased woody debris	No data
Increased BOD	No

Discussion:
Pathway linking nutrients to DO requires elevated BOD. Since BOD is not elevated, this causal pathway seems unlikely. Pathway linking channel modification to DO requires data on woody debris. Since data are missing, evidence is ambiguous.

Evidence Scoring Table:
Finding	Interpretation	Score
Data show that all steps in at least one causal pathway are present.	This finding strongly supports the case for the candidate cause, because it is improbable that all steps occurred by chance; it is not convincing because these steps may not be sufficient to generate sufficient levels of the cause.	+ +
Data show that some steps in at least one causal pathway are present.	This finding somewhat supports the case for the candidate cause.	+
Data show that the presence of all steps in the causal pathway is uncertain.	This finding neither supports nor weakens the case for the candidate cause.	0
Data show that there is at least one missing step in each causal pathway.	This finding somewhat weakens the case for the candidate cause, but is not strongly weakening because it may be due to temporal variability, problems in sampling or analysis, or unidentified alternative pathways.	-
Data show, with a high degree of certainty, that there is at least one missing step in each causal pathway.	This finding convincingly weakens the case for the candidate cause, assuming critical steps in each pathway are known, and are not found at the impaired site after a well-designed, well-performed, and sensitive study.	- - -

Table W1-12. Causal pathway scores for candidate causes.
Candidate Cause	Result	Score
Dissolved oxygen	Evidence of some steps are present for one pathway.	+