PARAMETERS OF INTEREST 
Reports by the HCEPC allow the depiction of spatial and temporal 
patterns useful in comprehending the bay’s overall character, and 
relationship to other estuaries. Most of the following discussion is 
adapted from Boler (1986) for 1984 or 1985. Rainfall in 1984 was below 
average (32.3 inches) compared to 1985 (44.6 inches). 
Salinity 
Salinity ranges from nearly zero in tidal rivers to normal 
salinity of the Gulf of Mexico. Salinity less than 50 percent occurs in 
Old Tampa and Hillsborough Bays, and the tidal rivers. Runoff affects 
the upper bays more than the lower bay (Figure 5). The mid-bay area 
usually exhibits the greatest transitional salinities. 
Light 
The color, nutrient-enhanced plankton, and detritus associated 
with runoff reduce light penetration in approximately the same areas and 
times of salinity reduction (Figure 6). Seasonal variation in light 
climate is much more complicated than salinity, however, owing to the 
non-conservative nature of some light-controlling factors. Since 1974, 
mean Secchi depth for Lower Tampa Bay has exceeded 70 inches, where 
seagrasses are most abundant, whereas the middle bay area has had some 
years with less than 70 inches of effective light penetration. Upper bay 
areas have had the poorest light climate, especially Hillsborough Bay 
(Figure 7). 
Chlorophyll 
Chlorophyll a levels between 10.0-15.0 ug/1 are common throughout 
much of Tampa Bay inland of the Sunshine Skyway Bridge, and chlorophyll 
concentrations greater than 20 ug/1 are common in Hillsborough Bay 
(Figure 8). A slight increase in chlorophyll may be occurring through 
time over several bay areas although levels in Hillsborough Bay appear to 
be declining (Figure 9). In developing a water quality model for 
Hillsborough Bay, Ross, Ross and Jerkins (1984) included a self-shading 
factor to account for the inhibition of photosynthesis by very high 
concentrations of phytoplankton in surface waters, as reflected by 
chlorophyll level. 
Nutrients 
The exceptional levels of total phosphorus (TP) in Tampa Bay were 
introduced in an earlier section. In 1984, TP ranged from 1.55 mg/1 as P 
in Hillsborough Bay (at the Alafia River) to 0.08 mg/1 at Egmont Key 
(Figure 10). Phosphorus levels have been declining for more than a 
decade (Figure 11) owing to environmental regulations and production 
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