J-2 
Phase 1 
Phase II 
Phase III 
Sample Size 
Evaluation 
Impairment Assessment 
Segment Characterization 
(Identify Probable Causes) 
N < 10 
Yes — 
Insufficient sample size 
— 
Optional use of 
B-IBI scores and diagnostic analyses 
in conjunction with other available 
data for305b/303d Integrated Report 
] No 
N> 10 
Yet - 
Apply Degraded Area 
Statistical method 
i 
Segment declared 
'nut impaired* for bcnlbic 
aquatic life communities 
in 305b/303d Integrated 
Report 
Yes — 
Optional ase of 
B-IBI scores and diagnostic analyses 
in conjunction with other available 
data for305b/303d Integrated Report 
1 No 
Segment declared 
'impaired* for benthic 
aquatic life communities in 
30$b/303d Integrated 
Report 
Ye* —» 
Apply diagnostic analyses for 
assignment of suspected causefs) of 
degradation in 305b/3fl3d Integrated 
Report 
Figure J-1. Overall Chesapeake Bay benthic index of biotic integrity assessment decision 
protocol. 
applied to override (reverse) the outcome of the formal statistical analysis results, but 
such reversals must be justified and documented. 
Phase III consists of the identification of probable causes of benthic impairment of the 
waterbody segment based upon benthic stressor diagnostic analyses. It is a two-step 
procedure that involves (1) Site Classification, and (2) Segment Characterization. 
1. Site classification: The first step is to assign probable cause of benthic degra¬ 
dation to each individual “degraded” benthic sample. For purposed of these 
diagnostic analyses, a sample is considered degraded if the B-IBI score is less 
than 2.7. 
Site Classification—Step la: The application of a formal statistical linear 
discriminant function calculates the ‘inclusion probability’ of each degraded 
site belonging to a ‘contaminant caused’ group or an ‘other causes’ group, 
based upon its B-IBI score and associated metrics. If a site is assigned to the 
‘Contaminant’ Group with a probability > 0.9, this site is considered impacted 
by contaminated sediment and no further classification is required. 
Site Classification—Step lb: If a site is classified as degraded due to ‘other 
causes (i.e., not contaminant-related), an evaluation of the relative abundance 
(and/or biomass) of the benthos is examined. Scores for both abundance and 
biomass are considered to be bipolar for the Chesapeake Bay Benthic IBI. For 
either metric; a high score of 5, indicating desirable conditions, falls in the mid¬ 
range of the abundance/biomass distributions, while a low score of 1, 
indicating undesirable conditions, can result either from insufficient abun- 
appendix j • Bay Estuarine Benthic Communities Assessment Protocol for Maryland and Virginia 
