Lake Panasoffkee SWIM Plan - Southwest Florida Water ...

Paleolimnological analysis was performed based on diatom identifications and TSI
reconstruction techniques. Based on their analysis of sediment cores, Belanger et al. (1993)
concluded that very few changes have taken place in and around the lake since 1855. In fact,
analysis suggests that the trophic state of the lake was once eutrophic during this period and
has moved toward a mesotrophic state since about 1970. Patches of plant growth correspond
to the various pH readings; the highest pH values, which further accelerate the formation of
a calcium carbonate precipitate, were found in areas of dense vegetation. Removal of carbon
dioxide due to dense macrophyte growth and photosynthesis causes precipitation of calcium
carbonate (CaCO,). The precipitate on eelgrass was found to be 61 percent carbonate and
32 percent organic. The eelgrass plant itself exhibited a carbonate content of 17 percent.
The sediment mapping effort revealed sediment depths greater than 20 feet over 75 percent
of the lake bottom (Figure A-3). Despite deep sediment deposits, PB-210
---
dating (a dating
method that is based on the
measurement of the radioactive
-
decay of an isotope of lead) results
indicate that sedimentation rates m m
= nhw-wmm
have historically been low: 0.04 to T e U U N M
0.06 grams dry weight per cm2 per
year (approximately equivalent to
0.06 to 0.09 inches per year).
Sediments accumulate approximately
1 inch in 12 to 13 years. At this rate,
it would take at least 2880 years to
accumulate a 20 foot layer of
sediment.
Watershed and Hydrology
The USGS estimates Lake
Panasoffkee's drainage basin to be
approximately 420 square miles
forming a large portion of the
Withlacoochee River basin east of
the Withlacoochee River (Taylor
1977). Much of this watershed drains
to localized depressions that exist
due to the karst geology of the
region. As a result, only 62.2 mi2
(39,800 acres) drain directly to the
lake. The Lake Panasoflkee
drainage basin makes up 27.5
percent of the Withlacoochee River
watershed. However, the volume of
flow contributed by the lake to the
river can account for 50 percent to 70