the stressor identification process

The Stressor Identification Process

2

Define the Case

List Candidate Causes

Evaluate Data from the Case

Evaluate Data from Elsewhere

Identify Probable Cause

Detect or Suspect Biological Impairment

As Necessary: Acquire Data

and Iterate Process

Identify and Apportion Sources

Management Action: Eliminate or Control Sources, Monitor Results

Biological Condition Restored or Protected

Decision-maker and

Stakeholder Involvement

Stressor Identification

The causal analysis framework

3

Define the Case






and Iterate Process




Decision-maker and



Detect or suspect biological impairment

• Fish kills• Organismal anomalies• Changes in community

structure• Low biotic index values• Violation of biocriteria

4

• ‘98 303(d) List

• Public-Owned Treatment Works (POTW) main focus

• TMDLs target Cu, Pb, Zn

POTW

Willimantic River case study#

5

POTW

Willimantic River case study#

MR3

MR1

• Impaired site MR3 (↓ EPT taxa)

• Less impaired site (MR1) upstream of MR3

66

Triggering the causal analysis

Invertebrate Index Scores as % of reference site RB1

0

20

40

60

80

100

RB1 FB2 FB5 MR1 MR2 MR3 WL1 WL2 WL3 WL4 SR HR TR

moderately impaired

7

Step 1: Define the Case







and Iterate Process




Decision-maker and



• What biological effects are observed?

• Where are they occurring?• Where are comparable

reference sites?

88

Example: defining the biological impairment in the Willimantic case study

Biological effect

MR1 (reference)

MR3 (impaired) Change

Number of EPT taxa 17 9 decrease

Making the impairment specificThe more specific you can make—or the more narrowly you can define—the impairment, the better.

•Specific = better discrimination across candidate causes

•Can consider multiple impairments

Level of specificity Examples Utility in SI

LOW Failure to meet biocriteria Triggers SI

↓ sensitive taxa↓ EPT richness

Listing candidate causesDeveloping conceptual model

HIGH ↓ ParaleptophlebiaAbsence of brook trout

Grouping sitesDiagnosing causesEvaluating strength of evidence

10

Define the Case






and Iterate Process




Decision-maker and



Step 2: List Candidate Causes

• Make a map• Gather information on

potential sources, stressors, & exposures

• Develop a conceptual model

• Engage stakeholders

1111

• Focus on stressor(s) that may be causing biological impairment

• May have causal scenarios, with several stressors acting in combination

• Candidate causes may include:–Mechanisms or modes of action–Sources

Listing candidate causes

1212

MR3

MR1

POTW

Stafford Springs

woodsindustrial

facility farms

Example: the Willimantic River case study

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↑ other toxics

Example: using models for communication

↓ dissolved oxygen

↑ temperature

↓ EPT richness

POTWindustrial facility dams subdivisiondairy farm

↑ NH3↑ Zn

14

↑ other toxics



↑ temperature

↓ EPT richness

POTWindustrial facility dams subdivisiondairy farm

↑ NH3↑ Metals

Evidence?

Evidence?

Evidence?

15

Define the Case






and Iterate Process




Decision-maker and



Step 3: Evaluate Data from the Case

EVIDENCE FROM THE CASE• Co-occurrence• Exposure or mechanism• Causal pathway• Stressor-response

relationships from field• Manipulation• Lab tests of site media• Temporal sequence• Verified predictions• Symptoms

Supports

Weakens

Spatial/Temporal Co-Occurrence Upstream Downstream Comparison

Physical Interaction

Causal agents change an affected agent by physical interaction.

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Spatial/Temporal Co-Occurrence

Adverse change compared to references

1. Toxics

Upstream reference

Watershed reference

Impaired site

Upstream Watershed

Al 0.080 0.037 0.101 Yes Yes

a 8/28/00b 7/23/01

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Spatial/Temporal Co-Occurrence

Candidate Cause

Measurement Upstream reference

Watershed reference

Impaired site

Adverse change compared to references

1. Toxics

Total Metals and Ammonia (mg/L)

MR1 RB1 MR3 MR1 RB1

Al 0.080 0.037 0.101 Yes Yes

Cd 0 0 0 No No

Cr 0 0 0.005 Yes Yes

Cu 0.004 0.004 0.005 Yes Yes

Fe 0.395 0.208 0.695 Yes Yes

Ni 0 0.001 0 No No

Pb 0.001 0 0.001 No Yes

Zn 0.006 0.004 0.011 Yes Yes

NH3 0.1 0.1 0.1 No No

a 8/28/00b 7/23/01

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Spatial/Temporal Co-OccurrenceSpatial co-occurrence

Candidate Cause MeasurementUpstream reference

Watershed reference

Impaired site

Advance change compared to references

2: High FlowNo Evidence

MR1 RB1 MR3 MR1 RB1

3: Embeddedness% Silt Covered

Substrate0-25% 0-25% 50-75% Yes Yes

4: Low Dissolved Oxygen

Minimum Dissolved

Oxygen (mg/L)

7.32b 10.17b 8.91b No Yes

5: Temperature Stress

Maximum Temperature

22.56oCb 17.28oCa 23.41oCb Yes Yes

6: Altered food resource

No Measurements

a 8/28/00b 7/23/01

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Loss of suitable habitat

Increased amount of

fine particles

Fine particles fill interstitial

spaces

Impoundment

Increased algae

Road Sanding

Loss of invertebrates

Bank Failure

Decreased inter-gravel dissolved

oxygen

Particle settling

Impoundment filling and

particle export

More EPT taxa atMR2 downstream from dam andupstream from MR3

Proportion of substrate composed of sand was half the amount observed at the upstream reference site

Bank stability score was unchanged from upstream; stream banks armored by riprap and granite walls

X X X

Sequential Dependence

All effects result of a prior sequence of cause effect events

loss of interstitial habitat due to settled particles

21

Define the Case






and Iterate Process




Decision-maker and



Step 4: Evaluate Data from Elsewhere

EVIDENCE FROM ELSEWHERE• Stressor-response

relationships (from lab, other field studies, or ecosystem models)

• Mechanistically plausible cause

• Manipulation at other sites• Analogous stressors

Stressor-Response Relationships from Laboratory Studies

Weakens Strengthens

Sufficiency The intensity or frequency of a cause is adequate to produce the observed magnitude of effect.

Supports

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Stressor-Response Relationships from Laboratory Studies

CT Values

(ug/L)

Daphnids (ug/L) Test EC20 MR1 Exceeded at

MR1

MR3 Exceeded at

MR3

Al None1 1900 540 82.2 No 107 No

Cd 0.62 0.15 0.75 0.4 Yes 0.5 Yes

Cr 100 <44 0.5 0.2 No 2 Yes

Cu 4.8 0.23 0.205 2.2 Yes 2.5 Yes

Fe None1 4380 - 522.8 No 532 No

Ni 88 <5 45 0.2 No 0.3 No

Pb 1.2 12.3 - 0 No 0.8 No

Zn 58.2 46.73 - 6.5 No 8.6 No

NH3 1430-2470 630 120 No 100 No

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•Impairment is so great, exposure to some agent at highly adverse levels must be occurring.

•Natural variability could not account for this.

Effect Impaired site

Number of EPT Taxa 9

Lacking Sufficiency from Analogous Situations

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Prediction from Analogous Situations

Experience suggests that highly toxic exposures are involved.

1. Bracket site, look for origination of impairment.

2. At the origination, there should be a point source, not non-point source.

3. The point source will intermittently release a highly toxic pollutant or precursor.

Effect Impaired site

Number of EPT Taxa 9

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Verified Predictions of Source

Illicit discharge observed upstream from impairment



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Manipulation of Source/Exposure

SUPPORTSImpairment occurs when stressor present and does not occur when stressor is removed

WEAKENSImpairment occurs when stressor present and when stressor is removed

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0

5

10

15

MR2 MR3 WL1

1999-2000

2001-2002

Mean number of EPT taxa before (1999-2000) & after (2001-2002) rerouting of illicit discharge



Manipulation of Source/Exposure

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Define the Case





and Iterate Process




Decision-maker and



Step 5: Identify Probable Cause

Evaluate Data from Elsewhere• Weigh strength of

evidence for each cause– eliminate if you can– diagnose if you can

• Compare strength of evidence across causes

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Willimantic case studyMetals NH3 Flow Silt Low

DOTemp 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 + + +

Verified Predictions + + +

Types of Evidence that Use Data from ElsewhereStressor-Response from Other Field - - +

Stressor-Response from Laboratory + + - - +

Example: strength of evidence analysis

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How to evaluate consistency of evidence

Candidate cause

Type of evidence NH3 Cu TSS

Co-occurrence + – +

Causal pathway + – –

Manipulation + – +

Stressor-response + – –

CONSISTENCY supports weakens weakens

Willimantic case study Metals NH3 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 Co-occurrence + + +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 - - - - - + - + + +

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↑ other toxics



↑ temperature

↓ EPT richness

POTW dams subdivisiondairy farm

↑ NH3↑ Cd

DO higher at impaired site vs. reference

industrial facility

after rerouting industrial discharge had decreased concentrations of Zn & other toxics, increased EPT taxa richness

NH3 same at impaired site and references.

Cd greater at impaired site vs. reference, but not at levels sufficient to cause impairment

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Define the Case







and Iterate Process




Decision-maker and



Causal analysis is one step in management process…

• After causes are identified, sources & management actions must be identified

• Biological monitoring verifies that actions are effective

the stressor identification process

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