Session 7 : Stressor Analysis

1. Session 7:Stressor Analysis Virginia Tech Biological Systems Engineering Department DEQ TMDL Modeling Workshop; Richmond November 19-20, 2013

2. To illustrate the steps involved in conducting a stressor analysis for a benthic impairment. Objective

3. The SA Process

4. Define the scope of the investigation • Watershed outlet defined by: • Downstream extent of impaired stream segment • The monitoring point • Confined to available data, generally • Past exceptions: E. coli, toxicity tests, diurnal DO • Create a list of potential sources • Develop a conceptual model List Candidate Causes

5. Listing Station, Impaired Segment, and Contributing Watershed Little Otter River Linville Creek Buffalo Creek WWTP Outfall

6. Sources • EPA stressor ID guidance • Previous benthic TMDLs • Available physical data or observations • Conversations with stakeholders Potential stressors • Sediment • pH • Nutrients • Temperature • Organic matter • Toxics (metals, pesticides, ammonia, etc.) • Hydrologic modifications (channelization, channel hardening) Create a List of Potential Stressors

7. Insufficient stream buffers Barren areas Impervious Areas Industrial/ Commercial Transportation Sources: Residential Agriculture VPDES dischargers Unstable stream banks Sewer system overflows Stream bank trampling by livestock Construction Nutrient Enrichment Stressors: PAHs Organic Enrichment Erosion Increased TSS Increased high flows Increased sedimentation Removal of organisms by flushing or scouring Embeddedness; loss of in-stream habitat Loss of bank habitat Altered food source Aquatic mortality Causes: Shift in benthic macroinvertebrate community Effects: Develop a Conceptual Model

8. The SA Process

9. Between direct measurements of candidate causes (stressors) and effects (benthic impairment) Between measures of exposure in our watershed and measures of effects from lab studies (WQS, threshold values) Between site measurements with intermediate steps in the chain of causal processes Between experimental measurements of cause and effect in a controlled setting(published research) Analyze the Evidence

10. Co-occurrence (spatially and temporally) Biological gradient Consistency of association Complete exposure pathway Specificity of cause Plausible mechanism Experiments Analogies Causal Considerations

11. The SA Process

12. Relies on negative evidence, e.g. • there is either no data, meaning others thought it wasn’t important enough to monitor, or • available data shows no effect on biology. Eliminate Alternatives

13. Temperature • Class IV Waters maximum standard = 31°C • No exceedences Not a Stressor

14. Relies on positive cause-effect relationships In medicine, diagnostic protocols identify a disease by its signs and symptoms Use Diagnostic Protocols

15. Upstream of STP • Minnows – no reaction • Daphnids – decreased reproduction rates • Downstream of STP • Minnows – decreased growth rates • Daphnids – all dead in 24 hours • Specific toxic(s) not identified Toxicity Tests

16. Quail Run Example Probable Stressor

17. When neither Elimination nor Diagnosis indicate a clear, unambiguous stressor Determine which stressor(s) has the strongest evidence Weight of Evidence

18. TN: 31 out of 53 samples in optimum range used for reference watersheds TP: 161 / 213 in sub-optimal range; 4 / 61 exceeded “observed effects” threshold DO: no exceedences with 1 minor exception Nutrients Example: Upper Little Otter River Possible Stressor

19. Sediment Example: Upper Little Otter River • Evidence of stress: • Poor habitat metrics for bank stability, sediment deposition, and bank vegetative protection • Abundant disturbed acreage • Some livestock present with stream access • Some DEQ ambient samples with elevated TSS concentrations • LRBS siltation index = -1.2 (< -1 indicates excessive human impacts • Evidence of minimal impact: • Relatively stable population of haptobenthos • Suspected Source(s): • Sediment deposition in-stream from various upland sources, stream bank erosion, and loss of riparian vegetation Probable Stressor

20. The SA Process

21. Rank the potential stressors by strength of evidence Political / legal considerations Collective Best Professional Judgment Identify Probable Cause(s)

22. Suspected source identified, but no monitoring to isolate its effect, e.g. springs in Long Meadow Run Pollutant identified, but insufficient monitoring to isolate and target source(s), e.g. PAH in Moores Creek Spatial data not resolute enough to capture watershed characteristics, e.g. Long Meadow Run Poor correspondence in time and/or space between ambient and biological data Stressor analysis is inconclusive When might observed data be insufficient?

23. Stressor Analysis Exercise

24. Questions?