The Determination of Minimum Flows for Sulphur Springs, Tampa

DRAFT
the river do not penetrate the upper spring run. The upper spring run is not a true
freshwater zone in that salinity values generally fluctuate seasonally between 1 and 3
ppt, but salinity values do not experience any variation over the tidal cycle.
20
Hours of Continuous Exposure
16
12
8
4
Salinity > 5 ppt
Salinity > 10 ppt
0
Flow_Duration_1.grf
5 10 15 20 25 30
Flow (cfs)
Figure 5-7. Duration of salinity incursions greater than or equal to 5
ppt or 10 ppt at the data recorder in upper spring run for 1 cfs flow
classes from Sulphur Springs.
Many of the invertebrate taxa that inhabit the upper spring run are euryhaline, or able to
tolerant of a range of salinity. These species can flourish in either the spring run or in
nearby areas of the Lower Hillsborough River. Other invertebrate groups that have been
found in the run, however, are comprised of species that are found predominantly in
fresh water. The invertebrate community that was observed in the spring run in 1997
included many freshwater taxa that are tolerant of slightly elevated salinity. The high
salinity values that occurred as a result of large springflow diversions during the 2000-
2001 drought were a factor in the loss of these taxa from the spring run (Allen et al.
2001). As described in Section 3.3.7.3, some of these taxa reappeared in later samples
that were collected after periods of normal flow. The collection of December 2003,
which was preceded by sixteen months of normal flow from the spring, found that
species richness and the abundances of a number of taxa improved greatly, with the
appearance of many freshwater taxa that have some tolerance of low salinity. In
likelihood, the resumption of low, stable salinity values contributed to recovery.
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