Lake Panasoffkee SWIM Plan - Southwest Florida Water ...

system discharge and receives a large volume of continuous groundwater inflow. Sampling
results indicate that the relatively small nutrient load from the residential canal and shore
systems is quickly diluted as this discharge volume enters the lake proper; therefore, OSDS
are presently not considered a significant nutrient source.
Trophic State
Lakes can be classified according to many attributes, including physical, chemical, and
biological characteristics. The most frequently used classification scheme for lakes is based
on their degree of nutrient enrichment (i.e., trophic state); and the most widely used trophic
state classification system is a modification of the TSI proposed by Carlson (1 977) as modified
by Huber et al. (1982). The TSI can be calculated on the basis of chlorophyll a concentration,
Secchi disk transparency, or limiting nutrient concentrations. The limiting nutrient is
determined from the TN to TP ratio. Trophic State classification generally used for Florida
lakes begins with a determination of the ratio of TN to TP (Huber et al.). This ratio indicates
whether the water body is potentially nitrogen-limited, phosphorus-limited, or
nutrient-balanced. Bays and Crisman (1981) found a TN/TP ratio of 24 for Lake Panasoffkee,
while 1990 USGS data yielded a value of 27. The TNiTP ratio based upon the CH2MHill
study (1995) is 18.8. All three values indicate Lake Panasoffkee is nutrient-balanced,
meaning that the lake will respond to increases in either nitrogen or phosphorus.
The 1992-1993 water quality data yield a TSI of 47 which places Lake Panasornee in the
mesotrophic category. This value is essentially the same calculated by Bays and Crisman
(1981), 46, and from the USGS data taken from 1977 to 1990, 45. The TSI value for Lake
Panasoffkee was found to be average compared to other lakes included in a statewide study
by Huber et al., 1982 (as cited by CH2MHilll995). Since Lake Panasoffkee is a macrophyte
dominated lake, the TSI value may be understated.