Middle St. Johns - Florida Department of Environmental Protection

Water Quality Assessment Report: Middle St. Johns
175
Table 4.4: Number of Listings for Each Parameter Exhibiting the
Impairment
Parameters under Concern
Number of
Impairments
Percent Total
Impairments
Nutrients 40 45%
DO 14 16%
Fecal Coliforms 11 13%
Total Coliforms 8 9%
Mercury 6 7%
Iron 5 6%
Lead 2 2%
Cadmium 1 1%
Unionized Ammonia 1 1%
Selenium 0 0%
units of the basin, 40 nutrient impairments are identified, which account
for about 45 percent of the total number of impairments. The number of
dissolved oxygen (DO) impairment ranked second among all the pollutants.
Totally 14 DO impairment are identified in 6 of the 9 planning units,
and account for about 16 percent of the total number of impairments in
the basin. This is followed by the number of fecal coliform bacteria, which
appear in 4 of the 9 planning units, and account for about 13 percent of the
total impairment.
There are 6 segments listed as being impaired by mercury in fish tissue
based on the fish consumption advisories issued by the Florida Department
of Health (DOH). Fish tissue mercury easurements taken by the Florida
Fish and Wildlife Commission (FWC) in the preceeding 7.5 years confirm
the impairment. Segments include Lake Margaret (WBID 2892, planning
unit: Lake George), Grasshopper Lake (WBID 2916B, planning unit:
Lake George), Wildcat Lake (WBID 2905C, planning unit: Lake Kerr),
Cowpen Pond (WBID 2934A, planning unit: Wekiva River), Lake Lucien
(WBID 3011C, planning unit: Wekiva River), and Lake Harney (WBID
2964A, planning unit: Deep Creek). Other metal pollutants within
the water column include iron, lead, selenium, and cadmium. Based on
Table 4.3, the Deep Creek planning unit appears to have the most types of
metal pollutions verified for the entire basin.
According to the IWR, to place a water segment on the Verified List for
nutrients, the Department must identify the limiting nutrient or nutrients
on the Verified List. The following method is used to identify the limiting
nutrient(s) in streams and lakes:
1. The ratios of total nitrogen (TN) to total phosphorus (TP) are
calculated for each paired value of TN and TP (per sampling event)
collected during the verified period.
2. The accumulative frequencies of the ratios below 10, in between
10 and 30, and above 30 are analyzed. If 100 percent of the ratios
fall in any 1 of these 3 ranges, the given water segment would be