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Update on Development of a Method to Assess PIBI Goal Attainment

Update on Development of a Method to Assess PIBI Goal Attainment. Claire Buchanan (ICPRB) TMAW meeting October 5, 2006. PIBI Goal. Living Resources Subcommittee (LRSC) approved a PIBI interim goal of 4.0 on a 1.0 - 5.0 scale at its January 26, 2006 meeting

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Update on Development of a Method to Assess PIBI Goal Attainment

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  1. Update on Development of a Method to Assess PIBI Goal Attainment Claire Buchanan (ICPRB) TMAW meeting October 5, 2006

  2. PIBI Goal • Living Resources Subcommittee (LRSC) approved a PIBI interim goal of 4.0 on a 1.0 - 5.0 scale at its January 26, 2006 meeting • high level of biological integrity is certain • very low risk of harmful algal blooms • assoc. WQ meets SAV habitat requirements • commensurate with Ches Bay water clarity and DO criteria attainment • LRSC did not establish how attainment of a PIBI goal of 4.0 should be measured

  3. PIBI Goal Currently exploring options for measuring attainment of PIBI Goal Objectives: • Attainment of the PIBI goal should reflect attainment of a restored Bay and the WQ criteria • “Apples to apples” goals for Benthic, SAV and Phytoplankton

  4. The 2005 “Bay Health Index” (BHI)presently compares “apples to oranges” single multi- multi- metric metric metric

  5. Some Background • PIBI > 4.0 are not uncommon • 435 (9.4%) of 4647 records from CBP biomonitoring stations, 1984 - 2005 • Highest PIBI values are transient at this stage of Chesapeake Bay restoration • PIBIs in a segment can fluctuate two or more scale units in a year • slight declining trend is evident… • Highest PIBI are commensurate with water clarity and DO criteria attainment

  6. Measuring Attainment of PIBI Goal • Goal Option 1 “(all) PIBI scores at a Chesapeake Bay biomonitoring station must be between 4.0 and 5.0 for the station to pass.” • comparable to approaches used for SAV & original BIBI goals • PIBI > 4.0 more difficult to attain than BIBI > 3.0 • attainment reflects a very superior phytoplankton community and a fully restored Bay • each station (aka segment) passes or fails individually 2005 all segments fail

  7. Measuring Attainment of PIBI Goal • Goal Option 2 “the bay-wide area-weighted mean score must be > 4.0 for the entire Bay to pass.” • average the 6 monthly mean scores in each segment, weight by segment’s proportional area, and sum to obtain the bay-wide mean • annual bay-wide score is biased by largest segments • goal can be attained even when smaller segments regularly fail 2005 Bay mean = 2.94, or Fair

  8. Measuring Attainment of PIBI Goal • Goal Option 3 “the area-weighted frequency of PIBI values between 4.0 and 5.0 must be greater than some predetermined percentage for the entire Bay to pass.” • uses frequency rather than mean • weight each segment’s attainment frequency (n = 6-12) by segment’s proportional area, sum to obtain bay-wide attainment frequency • Bay score is biased by largest segments • method used in 2005 Health and Restoration Assessment because a single Bay # was requested 2005 Bay freq. of attain. = 9.8%

  9. Measuring Attainment of PIBI Goal • Goal Option 4 “the mean annual score of the station or stations within a CBP segment must be > 4.0 for the segment to pass." • uses mean rather than frequency • each segment passes or fails individually • removes area-weighting bias in annual score • more in line with how WQ criteria and SAV & BIBI goal attainment are measured 2005 …CB5 mean = 3.75

  10. Measuring Attainment of PIBI Goal • Goal Options 1 – 4 • propose either a threshold (1, 3) or a mean (2, 4) for evaluating PIBI values • Chesapeake Bay Aquatic Life Uses • sample values are compared to reference distributions (CFDs) or historic benchmarks to assess attainment • Phyto. reference communities (1984-2005) • PIBI distributions for least-impaired WQ conditions currently found in Chesapeake Bay, not PIBI distributions in fully restored Bay with long uninterrupted periods of good WQ & robust grazer populations • mean PIBI ≈ 3.4

  11. Measuring Attainment of PIBI Goal • Six segment-years in 1984-2005 phytoplankton monitoring data have segment annual mean of PIBI > 4.0 (Option 4) • N=39 • lowest PIBI was 3.0 • No sig. diff. betw. MH and PH Could be a reference curve, or baseline

  12. Measuring Attainment of PIBI Goal • Goal Option 5 “a segment passes if at least two of three criteria are met: • annual average of monthly mean PIBI scores is > 4.0, • none (or only one) of monthly mean PIBI scores is below 3.0, or • PIBI sample distribution is not significantly different from the baseline PIBI distribution (Kolmogorov-Smirnov test, p > 0.10).” 2005 17.6% of goal attained (CB5 is 17.6% of sampled segments)

  13. Percent Attainment of PIBI Goal ____Option 3 (avg. = 14.3%) in 2005 Report ____Option 5 (avg. = 25.6%)

  14. The 2005 “Bay Health Index” (BHI) Option 5 puts us closer to “apples to apples” • SAV Goal: segment acreage meets or exceeds historic baseline (minimum) • Benthos Goal(s): several methods that use BIBI > 3.0 or a reference distribution as criteria • Phytoplankton Option 5: segment meets at least two of three criteria (mean PIBI > 4.0, min PIBI > 3.0, sample distribution ≈ baseline distribution)

  15. single multi- multi- metric metric metric  DO? “Degraded Area Method” (303d)? (Llanso & Volstad 2006) ?  water clarity  DO  Chl a Option 5 Option 3 The 2005 “Bay Health Index” (BHI)  water clarity

  16. 2005

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