K-3 
2.0 OBJECTIVES 
1. Develop a new method for the assessment of Chesapeake Bay benthic commu¬ 
nity status for 303(d) impairment decisions. 
2. Produce an assessment for the 2006 303(d) report using both the new method 
and the Wilcoxon approach. 
3. Apply the benthic diagnostic tool and the insufficient/excessive abundance 
criteria to the 2006 assessment data. 
3.1. DATA 
3.0 METHODS 
Like the Wilcoxon (described in Llanso et al. 2003), the Degraded Area method 
compares reference data sets to assessment data sets. The reference data set 
consisted of the calibration and validation data used to develop the Chesapeake Bay 
benthic index of biotic integrity (B-IBI). The Chesapeake Bay B-IBI is described in 
Weisberg et al. (1997) and Alden et al. (2002). The B-IBI consists of benthic 
community metrics and scoring thresholds (metric values) that were developed sepa¬ 
rately for seven habitat types (Table 1). The numbers of reference samples in each 
habitat used to develop the B-IBI, the Wilcoxon approach, and the method described 
in this report are listed in Table 2. The reference samples were either “good” (=unde- 
graded, collected at sites known to have good sediment and water quality) or 
“degraded” (collected at sites with low dissolved oxygen, organic enrichment, or 
high sediment contaminant concentrations and toxicity). To develop the B-IBI, Weis¬ 
berg et al. (1997) used averages of three replicate samples per site for mesohaline 
and polyhaline habitats, while Alden et al. (2002) used single replicate samples for 
tidal fresh and oligohaline habitats. We used the same metrics values produced by 
these two studies, but re-calculated B-IBI scores from these metrics to be consistent 
with the latest B-IBI methodology. The methods for the calculation of the Chesa¬ 
peake B-IBI are described in the World Wide Web at: http://www.baybenthos. 
versar.com/ referenc.htm. 
The assessment data for the 2006 303(d) report consisted of random samples 
collected from 2000 to 2004 throughout the Chesapeake Bay. A total of 1,430 
samples (single replicates) were used, including 750 samples collected by the Mary¬ 
land Chesapeake Bay benthic monitoring program, 500 samples collected by the 
Virginia Chesapeake Bay benthic monitoring program, 150 samples collected by the 
Elizabeth River benthic biological monitoring program, and 10 samples collected for 
a gear comparison study in each of Mobjack Bay, the tidal fresh Mattaponi River, 
and the Nansemond River. All assessment samples were collected with a Young grab 
(440 cm 2 surface area, 0.5-mm screen). For sample collection methods, see the 
benthic monitoring program comprehensive reports posted at the World Wide Web 
address given above. 
appendix k 
2006 303(d) Assessment Methods for Chesapeake Bay Benthos 
