Chapter 1 Minimum Flows and Levels - Southwest Florida Water ...

Water Chemistry
2.4.6 Water Quality Data
Although flow can affect water quality, it is not expected that the adoption and
achievement of minimum flows in the upper Braden River will necessarily lead to
substantial changes in water quality. However, as part of the MFLs development
process, available USGS water quality data for the Braden River were reviewed
for identification of potential relationships between flow and water chemistry.
For the following analyses, water quality data for the Braden River near Lorraine,
FL gage were retrieved from the USGS on-line database. While some data are
available on a number of water quality parameters, analysis was restricted to
those parameters for which trends have been evaluated on other rivers for which
MFLs have been developed. The USGS has long-term flow and water quality
data for a number of gage sites throughout the District. Flow records at many
sites exceed 50 to 60 years, and some of these have water quality records of 40
years or more. Except for special studies of relatively short duration, water
quality at most USGS sites was typically monitored on a quarterly basis at best.
Unfortunately, the water quality record for the Braden River is not as extensive as
that for many other rivers in the District.
Data for each parameter discussed in the following sections of this chapter are
typically presented in three plots, including two time-series plot and a plot of the
parameter versus flow. Unlike previous studies (e.g., Kelly et al. 2005a, 2005b,
and 2007), we have not presented plots of the residuals obtained from a
LOWESS regression of the parameter versus flow simply because the flow and
water quality record were not sufficient for such an analysis.
2.4.7 Phosphorus
Phosphorus has over the years been variously reported by the USGS as total
phosphorus, dissolved phosphate, and as ortho-phosphate. For our analyses, it
was assumed that dissolved phosphate and ortho-phosphate are essentially
equivalent. Although some of the older data were reported as mg/l phosphate,
all values were converted and expressed as mg/l phosphorus (P).
Friedemann and Hand (1989) determined the typical ranges of various
constituents found in Florida lakes, streams and estuaries. Based on their
finding, 90% of all Florida streams exhibited total phosphorus concentrations less
than 0.87 mg/l P. Although the record is not extensive, phosphorus
concentrations in the upper Braden River (Figure 2-17) appear comparable to
those observed in the upper Myakka River (see Table 2-8) and do not appear
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