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O/E: a standardized way to make site-specific assessments of biological condition

O/E: a standardized way to make site-specific assessments of biological condition. Chuck Hawkins Western Center for Monitoring and Assessment of Freshwater Ecosystems Utah State University.

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O/E: a standardized way to make site-specific assessments of biological condition

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  1. O/E:a standardized way to make site-specific assessments of biological condition Chuck Hawkins Western Center for Monitoring and Assessment of Freshwater Ecosystems Utah State University

  2. What is O/E? O/E is a measure of the taxonomic completeness of the biological community observed at a site O/E 0.38 E = 8 taxa O = 3 taxa

  3. Why Site-Specific Assessments are Important:The world is variable and assessments should lead to biologically meaningful, legally defensible, and fair assessments that minimize both false positives and false negatives.

  4. Why Standardized Assessments are Important:They allow uniform criteria and standards to be developed that apply to all waterbodies(uniform ≠ fixed)

  5. How can we achieve both site-specific and standardized assessments? • Recognize that natural ecosystems vary considerably in their expected biota. • Develop ways of describing the expected biota for individual sites (site-specific). • Assess the degree to which observed biota equal that expected for the site. • Develop criteria and standards based on the relative degree of departure from the expected biota (standardized).

  6. The Technical Challenge:Accurately and precisely describing the biota expected in different waterbodies in a State.

  7. The O/E Approach • Select a set of high-quality reference sites that fully characterize the natural biological variation and potential that occurs within a state. • Develop predictive models that relate variation in biota to easily measured predictor variables. • Quantify model error. • Compare the biota observed at a site to that predicted (expected) to occur for that site ‘type’. • Develop biological criteria and standards that incorporate measures of error and are consistent with the designated uses of different waterbodies.

  8. Reference Site Selection Criteria • Minimal chemical contaminants • Minimal flow alteration • Natural riparian vegetation • Natural mixture of habitat types

  9. Reference Criteria • Used comparable reference criteria • Based on: • EMAP reference criteria • Neighboring state reference criteria • Colorado water quality standards

  10. Taxonomic Data • Resolved ambiguous taxonomic information within and among sites • Both approaches used comparable taxonomic resolution

  11. Modeling and Assessments • Classify reference sites into groups based on their biological composition. • Estimate the frequencies of occurrence (fo) of different taxa in each reference site group. • Develop a statistical model that predicts the probabilities that an assessed site belongs to each group (pg) . • Weight fo by pg to refine estimates of the probabilities of capturing (pc) every taxon in the state at an assessed site. • Compute O/E from estimates of pc derived from sample data (O) and predictions (E). • Assess site condition in the context of model error.

  12. How O/E is Calculated: Sum of taxa pc’s estimates the number of taxa (E) that should be observed at the site given standard sampling. O/E = 3 / 4.01 = 0.75

  13. Describing Model Error O 1 E O/E

  14. Assessing Biotic Condition Criterion defining high biological integrity Reference Sites Number of Observations Decreasing biological integrity 0 1 O/E

  15. Initial Results for Colorado • No time to go into technical details of modeling. • Will focus on: • The biological classification of reference sites. • The predictors of biotic variability. • Error of the model.

  16. Foothills? Low elevation sites Plains High elevation sites

  17. Spatial Distribution of Different Classes of Reference Sites

  18. What group does a site with log WSA = 2.9 belong to? Temperature, stream size, and geography were the best predictors of what class a site belonged to.

  19. There was no evidence that the model was biased by biotic class or ecoregion. SD of 0.17 is ~ 2/3 of possible precision.

  20. Summary • The CO model is similar in performance to models developed for OR, WA, CA, and WY. • Initial results suggest that site-specific assessments can be made with acceptable error and expressed in standardized units that allow direct comparisons across stream types. • Assessments are easy to generate and have an intuitive biological meaning interpretable by all stakeholders.

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