Middle St. Johns - Florida Department of Environmental Protection

Water Quality Assessment Report: Middle St. Johns 251
100(B/A) where A = the 95 percentile of the reference population and B = observed
value
For percent Diptera, the following formula was used:
100 (100-B)/(100-A) where A = the 95 percentile of the reference population and B
= observed value
An average LCI score was calculated by averaging the scores of the six metrics in
the method: total number of taxa; total number of taxa belonging to the orders
Ephemeroptera, Odonata, and Trichoptera (EOT taxa); percent EOT taxa; Shannon-
Wiener Diversity Index score; Hulbert Index score; and percent Dipteran individuals.
LCI calculations were only provided for clear lakes (< 20 platinum cobalt units [PCUs]).
As macroinvertebrate-based indices have not been shown to assess colored lakes in
Florida accurately (> 20 PCUs), they have been excluded from bioassessments. A poor
or very poor rating based on the average score constituted a failed bioassessment, based
on the Impaired Surface Waters Rule.
STREAM CONDITION INDEX
A total Stream Condition Index (SCI) score was calculated by adding the scores of
the seven metrics in the method, i.e., total number of taxa; total number of taxa belonging
to the orders Ephemeroptera, Plecoptera, and Trichoptera (EPT taxa); percent
Chironomid taxa; percent dominant taxa; percent Diptera; percent filter feeders; and
Florida Index. A poor or very poor rating based on the total score constituted a failed
bioassessment, based on the Impaired Surface Waters Rule. The Basin Status Reports
contain definitions and specific methods for the generation and analysis of bioassessment
data.
BIORECON
To establish an impairment rating based on BioRecon data, three metrics were used:
the Florida Index score, total number of taxa, and total number of EPT taxa. If all three
metrics failed to meet thresholds, the water was deemed “impaired” based on the
Impaired Surface Waters Rule.
BIOLOGICAL INTEGRITY STANDARD
Quantitative data, generated through the use of Hester-Dendy artificial substrate
samplers, were used to calculate Shannon-Wiener Diversity Index scores for paired
background and test sites, as specified in the Biological Integrity Standard of Subsection
62-302.530(11), F.A.C. One failure of the standard meant that a waterbody segment was
listed as potentially impaired.