analyzed by the Environmental Protection Commission of Hillsborough 
County. Experiments in "sandy" and "muddy" sediments were performed 
during a winter and a summer month. "Mud" and "sand" locations, as 
previously defined in phase I, contained 85% "mud" (mean phi 6.9) and 88 % 
"sand" (mean phi 3.1), respectively. The SOD and NER results in Table 2 
may be the best available for Hillsborough Bay, but due to the paucity of 
measurements, these results should be considered as initial estimates 
with room for refinement. The highest SOD rate occurred during the summer 
at the "muddy" high organic sediment location and that value was roughly 
twice the rates of all other season-sediment combinations. These 
preliminary results also indicate that sediment releases of inorganic 
phosphate and ammonia were greatest during the summer, and therefore may 
be a function of temperature. Nixon, Oviatt and Hale (1976) related 
benthic ammonia fluxes to bottom water temperatures between 0 and 25°C by 
the equation: 
(1) dc/dt (NH 4 ) = e o-16T+1.90 
where T = temperature in degrees Celcius. 
We calculated flux rates (uM m"^h“^) using this equation with Table 2 
data. The predicted (119) and measured (116) flux rates for winter data 
at 18°C were in close agreement. However, the average measured summer 
flux rate (485) was only half the predicted rate (880) at 30.5°C 
indicating that Nixon et al.’s (1976) function may not apply at 
temperatures above 25°C. 
Table 2. Sediment oxygen demand (SOD, mmoles O 2 m _ 2 h _1 ) and nutrient 
exchange rate (NER, umoles nT^h"*) estimates in Hillsborough 
Bay during 1986. The negative value indicates a decrease in 
water column concentration with time, consequently, a 
meaningful N:P ratio for mud during the winter could not be 
calculated. 
Parameter 
Sand 
WINTER 
Mud 
Sand 
SUMMER 
Mud 
SOD 
8.8 
5.6 
8.1 
14 
NER (PO 4 -P) 
10 
-23 
137 
104 
NER (NH 3 -N) 
111 
121 
396 
573 
N:P ratio 
11 
-- 
2.9 
5.5 
The relatively low N:P ratios of inorganic nutrient fluxes from 
the sediments (Table 2), particularly during the summer, may reflect the 
importance of bacterial dentrification in the sediments. Assuming that 
deposited organic material is mostly derived from phytoplankton, then the 
Redfield N:P ratio of 16:1 might be expected in the regenerated nutrient 
supply. Low N:P ratios measured in benthic nutrient fluxes to the water 
136 
