Step 5 Identifying probable causes Whats going on

Step 5: Identifying probable causes

What’s going on at Pretend Creek? TYPE OF EVIDENCE ↑ metals ↑ temp ↓ DO YES NO YES Data from the case Spatial co-occurrence Stressor-response relationships from the field YES (Zn) ? (Cu) Causal pathway Manipulation of exposure YES Data from elsewhere Stressor-response relationships from other field sites YES 2

Detect or Suspect Biological Impairment Stressor Identification Define the Case List Candidate Causes Decision-maker and Stakeholder Involvement Evaluate Data from the Case Evaluate Data from Elsewhere As Necessary: Acquire Data and Iterate Process Step 5: Identify Probable Cause Identify and Apportion Sources Management Action: Eliminate or Control Sources, Monitor Results Biological Condition Restored or Protected 3

How we identify probable causes • Eliminate when you can • Diagnose when you can • Otherwise, analyze strength of evidence HOW? Apply a scoring system to the available evidence under each type of evidence 4

The scoring system R refutes D diagnoses +++ convincingly supports (or weakens - - -) ++ strongly supports (or weakens - -) + somewhat supports (or weakens - ) 0 neither supports nor weakens NE no evidence 5

Scoring of spatial/temporal co-occurrence + 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. 0 It is uncertain whether the candidate cause and the effect co-occur. --- 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. R 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. 6

Scoring of laboratory tests of site media +++ Laboratory tests with site media show clear biological effects that are closely related to the observed impairment. + Laboratory tests with site media show ambiguous effects, OR clear effects that are not closely related to the observed impairment. 0 Laboratory tests with site media show uncertain effects. - Laboratory tests with site media show no toxic effects that can be related to the observed impairment. 7

Scoring of stressor-response from other field studies ++ The stressor-response relationship in the case agrees quantitatively with stressor-response relationships from other field studies. + The stressor-response relationship in the case agrees qualitatively with stressor-response relationships from other field studies. 0 Agreement between the stressor-response relationship in the case and stressor-response relationships from other field studies is ambiguous. - The stressor-response relationship in the case does not agree with stressor-response relationships from other field studies. -- There are large quantitative differences or clear qualitative differences between the stressor-response relationship in the case and the stressor-response relationships from other field studies. 8

Example: strength of evidence analysis Willimantic case study Metals NH 3 Flow Silt Low DO Temp Food Episodic Mix Types of Evidence that Use Data from the Case Spatial/Temporal Co-Occurrence + - Evidence of Biological Mechanism + + - Causal Pathway Stressor-Response from the Field + --- + + + - - + - + + Manipulation of Exposure +++ Verified Predictions +++ Types of Evidence that Use Data from Elsewhere Stressor-Response from Other Field -- + Stressor-Response from Laboratory ++ - - + 9

Weighing the evidence for each candidate cause • Evaluate the quantity & quality of evidence • Evaluate consistency & credibility • Summarize the compelling evidence 10

Evaluate quantity & quality of evidence • Quality & quantity of data influence scores • Lots of consistent evidence reduces quality concerns for any 1 type of evidence • Poor quality data may be discounted • Consider study designs, methods, relevance, variability, & other QA issues 11

Evaluate consistency & credibility • Prepare summary table of scores • Do not add up scores! • Evaluate consistency of evidence • Look for compelling evidence • If evidence is inconsistent, consider mechanistic explanations – e. g. , lab data not consistent with field conditions due to differing bioavailability 12

Scoring consistency & credibility Consistency of Evidence All available types of evidence support the case for the candidate cause. +++ All available types of evidence weaken the case for the candidate cause. --- All available types of evidence support the case for the candidate cause, but few types are available. + All available types of evidence weaken the case for the candidate cause, but few types are available. - The evidence is ambiguous or inadequate. 0 Some available types of evidence support and some weaken the case for the candidate cause. - There is a credible explanation for any negative inconsistencies or ambiguities in an otherwise positive body of evidence that could make the body of evidence consistently supporting. Explanation of the Evidence ++ There is no explanation for the inconsistencies or ambiguities in the evidence. 0 There is a credible explanation for any positive inconsistencies or ambiguities in an otherwise negative body of evidence that could make the body of evidence consistently weakening. 13

Willimantic case study Metals NH 3 Flow Silt Low DO Temp Food Episodic Mix Types of Evidence that Use Data from the Case Spatial/Temporal Co-Occurrence + - Evidence of Biological Mechanism + + - Causal Pathway Stressor-Response from the Field + + --- + + - - + - + Manipulation of Exposure +++ Verified Predictions +++ Types of Evidence that Use Data from Elsewhere Stressor-Response from Other Field -- + Stressor-Response from Laboratory ++ - - + Evaluating Multiple Types of Evidence Consistency of Evidence - - - +++ 14

Summarize compelling evidence • • Make an overall evaluation of strength of evidence for each candidate cause – what evidence compels belief that candidate cause induced effect? – what evidence strongly casts doubt? Consider the principle characteristics of causal relationships – these are what you’re trying to show – they summarize the 15 types of evidence 15

There is no magic formula… All candidate causes must be compared to determine: – if there is more than 1 probable cause – your level of confidence in the results 16

Comparing evidence among causes: best-case scenario You have compelling evidence for 1 candidate cause; others are weak or refuted. . . CANDIDATE CAUSE TYPE OF EVIDENCE 1 2 3 A ++ - R B + -- C + - Consistency + - …celebrate, then remediate for Candidate Cause 1 17

Comparing evidence among causes: more (likely) scenarios You have uneven evidence across candidate causes. . . CANDIDATE CAUSE TYPE OF EVIDENCE 1 2 A ++ – B + C + + Consistency + – 3 – • Strong evidence for one candidate cause may be sufficient • Consider if weakness is due to lack of data – and try to fill holes 18

You have unsatisfying evidence across all candidate causes… CANDIDATE CAUSE TYPE OF EVIDENCE 1 2 A + – B – – C Consistency + – Reconsider the impairment • Consider additional candidate causes • 3 – – Consider episodic events • Consider gathering more data • 19

You have evidence suggesting multiple causes… CANDIDATE CAUSE TYPE OF EVIDENCE 1 2 3 A ++ + + B + + ++ C ++ ++ + Consistency + + + • Consider disaggregating indices or metrics • Combine causes if they share causal pathways, modes of action, sources and routes of exposure, or if they interact • Remediate dominant cause • Design remediation to address multiple causes 20

You have insufficient data… CANDIDATE CAUSE TYPE OF EVIDENCE 1 2 3 A NE NE – B + NE NE C NE NE NE Consistency 0 0 0 Gather data if possible • Consider other bases for remediation (e. g. , BMPs, chemical criteria) and monitor biological responses • Use professional judgment as last resort • 21

Next: let’s try it out! Scoring the evidence exercise 22

What’s going on at Pretend Creek? TYPE OF EVIDENCE Spatial co-occurrence ↑ metals ↓ DO NE NE NE Stressor-response relationships from the field (data from case) Stressor-response relationships from other field sites (data from elsewhere) NE Causal pathway NE Manipulation of exposure ↑ temp NE NE NE Consistency of evidence Explanation of evidence 23

Things to keep in mind when scoring… • Be consistent across candidate causes • Don’t double-count data • Think about the quality & quantity of the data you’re using • Document your thought process 24

How do I communicate results? • Make your logic clear • Present the critical evidence • Reveal uncertainties • Fit communication to your audience • For technical reviewers, include text & tables • For decision makers, may be helpful to use annotated conceptual model 25

Using models for communication: Pretend Creek industrial facility ↑ metals urbanization dam ↑ temperature dairy farm subdivision ↓ dissolved oxygen ↓ EPT richness 26

Using models for communication: Pretend Creek industrial facility urbanization dam dairy farm subdivision DO higher at impaired site vs. reference ↑ metals ↑ temperature ↓ dissolved oxygen ↓ EPT richness 27

Using models for communication: Pretend Creek industrial facility urbanization dam dairy farm subdivision DO higher at impaired site vs. reference ↑ metals after rerouting industrial discharge had decreased metal concentrations & increased EPT taxa richness ↑ temperature ↓ dissolved oxygen ↓ EPT richness 28

Using models for communication: Pretend Creek industrial facility urbanization dam dairy farm subdivision DO higher at impaired site vs. reference ↑ metals after rerouting industrial discharge had decreased metal concentrations & increased EPT taxa richness ↑ temperature ↓ EPT richness ↓ dissolved oxygen temperature higher at impaired site vs. reference; negatively correlated with EPT taxa richness 29

What comes after causal analysis? • • If confidence in results is low… – plan studies to obtain critical evidence – experimental studies most likely to be convincing If confidence in results is high… – identify sources – take action – monitor results 30

Example: fish kills in Virginia & West Virginia There was no “smoking fish”… 1. Low dissolved oxygen in water 2. Gill damage from ammonia, high p. H, or other mechanism prevents uptake of oxygen 3. Altered blood chemistry from nitrite exposure prevents fish from using oxygen 4. Viral, bacterial, parasitic, or fungal infections Causal analysis resulted in: • Narrowed list of candidate causes • List of priority data needs 5. Mortality from high p. H 6. Mortality from p. H fluctuations 7. Mortality from ammonia toxicity 8. Toxicity of unspecified substances 9. Starvation due to inadequate food resources 31