Middle St. Johns - Florida Department of Environmental Protection

178
Water Quality Assessment Report: Middle St. Johns
Table 4.5 (contnued)
WBID
Waterbody Segment
Waterbody
Type
Total Nitrogen and
Total Phosphorus
Median 1 (mg/L)
3004D Silver Lake Lake TN = 0.64 mg/L
TP = 0.03 mg/L
3004G Bay Lake Lake (TN = 1.21 mg/L)
TP =0.04 mg/L
Nitrogen to
Phosphorus Ratio
Median 2
Limiting Nutrient(s)
27 (118 values) N and P colimitation
31 (286 values) Colimitation based
on data of planning
period and P limitation
based on data of
verified period
3009 Bear Gulley Lake Lake TP = 0.04 mg/L 30 (66 values) P limitation
1
TN and TP medians are for the entire sets of TN and TP concentrations retrieved from IWR database.
2
TN to TP ratio medians are for the subset of TN and TP concentrations that paired TN and TP measurements
are available.
N = Nitrogen
P = Phosphorus
TN = Total nitrogen
TP = Total phosphorus
As required by the IWR, the Department must identify the pollutants
causing or contributing to DO exceedances to confirm impairment
and place the waterbody on the Verified List. If a water segment is on the
Verified List for both DO and nutrients, then nutrients is identified as a
pollutant contributing to DO exceedances. The Department also applies
the following analysis to identify the pollutant(s) contributing to DO
exceedances:
The water segment median values for biological oxygen demand
(BOD), TN, and TP are determined for the verified period (i.e.,
January 1995 to January 2002).
1. The median values are then compared with the screening levels
for the appropriate waterbody type. The screening levels represent
the 70th percentile value of data collected from streams, lakes, or
estuaries (Table 4.6).
2. If a water segment median value exceeds the screening level,
the parameter is identified as a pollutant contributing to the
exceedances.
Table 4.6: Screening Level Values (70th Percentile) Based on
STORET Data from 1970 to 1987
BOD (mg/L) TN (mg/L) TP (mg/L)
Streams 2.0 1.6 0.22
Lakes 2.9 1.7 0.11
Estuaries 2.1 1.0 0.19
Source: Friedemann, F., and J. Hand, 1989.