column in several shallow marine environments have been attributed to a 
loss of nitrogen as N 2 from the system by bacterial denitrification 
(Nixon 1981). Natural assemblages of Hillsborough Bay phytoplankton grown 
in chemostat cultures were often found to be nitrogen limited (COT 1983). 
Consequently, the rate of denitrification could influence the supply of 
nitrogen available to support primary productivity. 
The rate of organic matter consumption by Hillsborough Bay 
sediments, in terms of SOD rates, are within the range of rates measured 
in other Tampa Bay embayments as well as other U.S. east coast estuaries 
(Table 3). Annual benthic ammonia flux from Hillsborough Bay sediments 
into the water column were slightly higher relative to other U.S. east 
coast estuarine sediment releases (Table 4). As a growing number of in 
situ benthic flux measurements are generated, there appears to be a 
relationship between the amount of organic matter consumed and inorganic 
matter released by the benthos in terms of ammonia. Nixon (1981) found a 
positive relationship between summer rates of sediment oxygen uptake and 
ammonia release for temperate coastal marine systems with widely ranging 
phytoplankton productivity levels. Rate measurements of those marine 
systems ranged from about 2 to 8 mmoles 02m‘ 2 h" 1 uptake and 25 to 500 
umoles m _2 h _1 ammonia released. Hillsborough Bay falls in the upper 
ranges of those rates (11 0?; 485 ammonia) when the summer data (COT 
1986b) are averaged. The relatively high rates in Hillsborough Bay, a 
subtropical estuary, may simply be due to higher temperature. 
Table 3. In situ sediment oxygen demand (SOD) rate measurements (mmoles 
O 2 m 2 h"f) and water temperatures (°C) during experiments from 
selected U.S. east coast estuaries and Tampa Bay area estuarine 
embayments. 
Water Body 
Patuxent River Estuary 
Patuxent River Estuary 
Narragansett Bay 
Chesapeake Bay 
N. Carolina Estuaries 
Tampa Bay Area: 
Hillsborough Bay 
Hillsborough Bay 
Tampa Bay 
Sarasota Bay 
Temp 
SOD 
24-31 
11.8-19.3 
3-29 
1.3-10.7 
3-21 
0.6-9.4 
Aug-May 
3.9-8.1 
1-22 
0.8-3.2 
17-31 
5.6-14.4 
16-30 
2.1-8.2 
31 
6.9-12.7 
20-30 
4.8-14.2 
Source 
Boynton et al., 1981 
Boynton et al., 1980 
Nixon et al., 1976 
Boynton & Kemp, 1985 
Fisher et al., 1982 
COT, 1986b 
Murphy & Hicks, 1985 
Murphy & Hicks, 1985 
Murphy & Hicks, 1985 
137 
