Tampa Bay Estuary Program 

Technical Publication # 04-06 

Benthic Oxygen and Nutrient Fluxes in Tampa Bay: 

A Final Report to the Tampa Bay Estuary Program, 

Florida Department of Environmental Protection, 

and U.S. Environmental Protection Agency Gulf of 

Mexico Program 

FINAL REPORT 

August 2006 
BENTHIC OXYGEN AND NUTRIENT FLUXES IN TAMPA BAY: 

A FINAL REPORT TO THE TAMPA BAY ESTUARY PROGRAM, FLORIDA, 

DEPARTMENT OF ENVIRONMENTAL PROTECTION, AND U. S. ENVIRONMENTAL 

PROTECTION AGENCY GULF OF MEXICO PROGRAM 

Prepared by Paul Carlson and Laura Yarbro, 

Florida Fish and Wildlife Research Institute 

February 15, 2006 

Introduction: This project measured rates of nutrient fluxes between Tampa Bay 

sediments and the overlying water column. This information has been lacking from 

previous nitrogen budgets for Tampa Bay, potentially hampering their accuracy and 

effectiveness. At the beginning of this study and in previous nitrogen budgets for 

Tampa Bay, sediment fluxes were assumed to provide approximately 25% to 30% of 

"new" nitrogen entering the water column. Our measurements demonstrate that the 

actual role of sediments in the nitrogen cycle of Tampa Bay is more complex than we 

anticipated. Nutrient fluxes measured at eight sites in Tampa Bay indicate that 

sediments in different Bay segments can serve as sources or sinks for nitrogen as well 

as temporary storage pools. Furthermore, the role of sediments within a Bay segment 

can vary seasonally. Refined nitrogen budgets for Tampa Bay can now include 

sediment processes in the continued development of nitrogen loading targets to support 

habitat restoration. 

Background and Rationale: More than 80% of the seagrass habitat present in Tampa 

Bay in the late 1800’s has been lost, primarily as the result of water quality degradation 

(Lewis et al., 1985). Seagrasses are extremely sensitive to declines in water quality 

because they are shaded by phytoplankton in the water column and by epiphytic algae 

which proliferate when nutrients- nitrogen and phosphorus- in the water column are high 

(Tomasko and Lapointe, 1991; Dixon and Leverone, 1995). Phosphorus 

concentrations in Tampa Bay are naturally high because several rivers drain the Bone 

Valley phosphorite deposits in eastern Hillsborough and Polk Counties (Fanning and 

Bell, 1985). For this reason, Tampa Bay is nitrogen-limited, and efforts are being made 

to improve Tampa Bay water quality by limiting nitrogen inputs to the Bay (Johansson, 

1991; Janicki and Wade, 1996). 

Water quality in Tampa Bay reached its nadir in the mid-1970’s when almost 10,000 

tons of nitrogen entered the Bay from various sources- a number five times greater than 

historical estimates (Zarbock et al., 1994). Nitrogen loading to Tampa Bay dropped to 

less than 4000 tons/year in the 1985-1991 period, primarily as the result of declines in 

point-source loading and fugitive emissions. However, resource managers are 

concerned by future nitrogen loading rates which might rise to nearly 6000 tons per year 

in 2010, in response to increases in nonpoint-source and atmospheric nitrogen loading. 

If we hope to maintain and restore seagrass habitats and their fisheries resources in 

Tampa Bay, we need to control nitrogen inputs to the estuary. 

Efforts to manage nitrogen levels in Tampa Bay, in turn, depend on accurate estimates 

of nitrogen inputs, exports, and internal transformations for the Bay. However, existing 

nitrogen budgets for Tampa Bay have not included estimates of the rate of nitrogen 

exchange between sediments and the water column because those processes have not 
been measured in Tampa Bay. This omission is serious because Tampa Bay is a 

relatively shallow and well-mixed estuary, so exchanges between the water column and 

bottom sediments are potentially very large and might affect the entire water column 

(Fanning and Bell, 1985). In other estuaries, nitrogen is recycled between water column 

and sediments, effectively amplifying the effect of external nitrogen loads on estuarine 

water quality (Cowan et al., 1996; Fisher et al., 1982; Nixon 1981, Twilley et al., 1999). 

Other studies have shown that the sediment processes of denitrification and burial can 

enhance water quality by exporting or sequestering nitrogen from the water column 

(Seitzinger, 1987, 1988). 

Methods- We collected four replicate cores from each of eight sites in Tampa Bay in 

fall 2002 as well as winter, spring, summer, and fall 2003. We incubated cores in the 

dark in plexiglas core sleeves with approximately one liter of water overlying each core. 

We stirred and sampled the overlying water periodically over 48 hours and analyzed 

filtered supernatant samples for ammonia, nitrate/nitrite, total dissolved nitrogen, 

phosphate, total dissolved phosphorus and silicate. Dissolved organic nitrogen and 

dissolved organic phosphorus were estimated by difference. 

Site Selection: Within four regions of Tampa Bay (Old Tampa Bay, Hillsborough Bay, 

Middle Tampa Bay, and Lower Tampa Bay) we selected one site with fine-grained 

sediment and one site with coarse sediment. To locate coarse and fine sediment in 

each Bay region, we used sediment texture (sand, silt-clay) data collected by 

Hillsborough County Environmental Protection Commission. The data (in an Excel 

spreadsheet) were provided to us by Steve Grabe of HCEPC. We transferred the data 

to Arcview (Figure 1) and created contour maps of sediment texture using Spatial 

Analyst. From the contour map, we extracted the latitude and longitude of four to five 

sites in each Bay region which were likely to have either coarse or fine-grained 

sediment. 

Several sites in each bay region were visited, and the eight sites selected were chosen 

using two primary criteria. The first criterion was sediment texture because, in this pilot 

study, we want to constrain the highest and lowest rates of benthic metabolism and 

nutrient flux for each bay region. Previous studies, ours and those of other authors, 

have shown that fine-grained sediments typically have high microbial respiration rates 

and high nutrient flux rates. We verified sediment texture at each site using a Petit 

Ponar benthic grab. The scarcity of fine-grained sediment in Lower Tampa Bay forced 

us to sample in Little Bayou, an embayment on the west side of Lower Tampa Bay. The 

second criterion was to find coarse and fine-grained sites within each region which were 

close enough together to have similar salinity regimes. The eight sites selected are 

shown below in Figure 2. 

Collection and Incubation of Core Samples: During each sampling interval (fall 2002 

and winter, spring, summer and fall 2003), cores from Old Tampa Bay and Hillsborough 

Bay sites were sampled on one date and Middle Tampa Bay and Lower Tampa Bay 

sites were sampled a week later. On each sampling date, divers collected four cores at 

each site, for a total of sixteen cores. 
Figure 1: Location of HCEPC sediment sampling sites 

Figure 2. Eight sites selected for benthic flux measurements in this study. The first letter of each 

site code refers to bay region, while the second letter refers to sediment texture (C=coarse; 

F=fine). 
To collect a core, divers inserted a Plexiglas core sleeve into the sediment to a predetermined depth. Visibility was often so poor that divers literally could not see their 

hands in front of their faces. In those cases, rubber bands on the outside of core 

sleeves served as a tactile reference for core insertion. The core was capped with an 

undisturbed column of water in the sleeve. The core sleeve was gently excavated, and 

a custom-made, dual O-ring, piston was inserted in the bottom of the core sleeve to seal 

the sediments in place and to prevent any disturbance of sediment or porewater nutrient 

profiles. The sealed core was gently transferred to the boat (see Figure 3 below) and 

transported to the lab at FWRI. 

Figure 3: Jitka Hyniova collects a core at the LTB fine site. 

In the laboratory, cores were transferred to two 20-gallon aquaria. The aquaria were 

filled with water from each bay region to prevent cores from heating or cooling during 

incubation. Incubations were carried out in a dark, temperature-regulated wet lab (see 

Figure 4, below). 

After collection and transfer to the wet lab, cores were held overnight in the dark 

while being bubbled with air to prevent hypoxia. In the morning after collection, the 

supernatant water was gently siphoned off the cores and replaced with low-nutrient 

seawater adjusted to ambient salinity for each site. Nutrient fluxes were measured over 

the next 48 hours by periodically withdrawing supernatant from each core. Supernatant 

samples were filtered and frozen prior to analysis for dissolved silicate, ammonia, 

nitrate+nitrite, phosphate, total dissolved phosphorus, and total dissolved nitrogen. 

Extrapolation of measured fluxes- Estimates of benthic nutrient supply (or uptake) 

for Bay segments were carried out in a series of steps. Supernatant water for each core 

was sampled every two hours on the first day of incubation, and filtered water samples 

were analyzed for silicate, phosphate, ammonia, nitrate+nitrite, total dissolved nitrogen 

and total dissolved phosphorus. Linear regression was then performed on nutrient 
concentration data to calculate flux rates, using only data from the first day of core 

incubation (see QA section below). Mean flux rates were calculated for each group of 

four replicate cores, and outliers were excluded. 

Figure 4. Cores on wet lab bench. Photos taken after incubations. 

Flux rates, expressed in millimoles oxygen, nitrogen, phosphorus, or silica per square 

meter per day (see Appendix A tables), were multiplied by the area of fine-grained and 

coarse sediment present in each Bay segment. Sediment texture was determined from 

the HCEPC sediment dataset noted earlier, and bottom area for each sediment type 

was calculated using ArcGIS 8.3. HCEPC water temperature data were also used to 

translate seasonal flux measurements into annual estimates. The annual estimates, in 

turn, were compared to external nitrogen and phosphorus loads calculated by Poe et al. 

(2005). Complete spreadsheets outlining calculations are included in the Appendix. 

Precautions for quality control and data analysis- At every step in the sampling, 

core incubation, and data analysis, precautions were taken to ensure data quality: 

1. Cores were collected by divers using methods to minimize disturbance of the 

sediment-water interface and the isolated column of sediment. Double O-ring pistons 

were inserted into the bottom of each core sleeve to minimize leakage. Core sleeves 

were completely filled with site water and capped to avoid disturbance during transport 

to the lab. 

2. In the lab, core sleeves were aerated continuously in the dark overnight to "reset" the 

status of benthic microalgae. Phytoplankton and benthic microalgae have 
demonstrated the capacity to fix nitrogen and phosphorus for up to 12 hours in the dark. 

Site water was replaced with low nutrient seawater adjusted to the salinity of each site. 

In our calculations of nutrient flux rates, we ignore the potential effect of a concentration 

gradient decreased by elevated water column nutrient concentrations. Replacing site 

water with filtered seawater also eliminated any potential influence of phytoplankon on 

core flux estimates. 

3. Estimates of nutrient fluxes in each core were based solely on fluxes measured 

during the first day of incubation. Although incubations were carried out for almost 72 

hours, concerns about longer incubation times were expressed at the Tampa Bay Basis 

4 Symposium. Fred Holland, in particular, was concerned that, based on sedimentwater exchange measurements in the Patuxent Estuary, artifacts increased with 

increasing duration of incubation. Artifacts that might affect flux estimates include 

development of microalgal or bacterial mats, decomposition of infauna killed by coring 

or by subsequent hypoxia. 

4. Core incubations and sampling were carried out in total darkness, so cores were 

examined and photographed at the end of the incubation period to identify incubation 

artifacts. Data were not used from cores which demonstrated leakage around piston Orings or contained dead infauna. 

Results and Discussion: Differences in sediment texture and redox state among sites 

were striking. For example, Figure 5 (below) illustrates visible redox discontinuities in 

the Middle Tampa Bay coarse sediment core and the Lower Tampa Bay coarse 

Figure 5: Fine and coarse texture sediment cores from Middle Tampa Bay and Lower Tampa 

Bay 
sediment core. Fine grained sediment cores from Middle Tampa Bay and Lower Tampa 

Bay are uniformly anoxic. Fine sediment cores from Hillsborough Bay had the highest 

silt-clay content, followed by Old Tampa Bay, Middle Tampa Bay, and Lower Tampa 

Bay. 

Bioturbation and irrigation of cores by infauna also might have had significant impacts 

on measured fluxes depending on the number, size, and activity of animals (Figure 6). 

Old Tampa Bay and Hillsborough Bay cores typically had brachiopod bivalves and small 

polychaetes in them. Many sites have numerous brittle stars, and the LTB coarse site 

has lots of sand dollars. With the exception of sand dollars, we allowed organisms to 

remain in the cores because it is too disruptive to remove them. 

. 

Figure 6. Effects of burrowing organisms on sediment cores. Core on left contains a large brittle star 

with its disk approximately 5 cm below the sediment surface and its arms stretched upward through 

the sediment into the overlying water. Core on right contains numerous small polychaetes which 

irrigate the sediment during incubations. 

Transformations among nitrogen species occurred during core incubations as shown 

in Figure 7. Core incubations remove phytoplankton from the overlying water, and they 

eliminate external sources and sinks. However, Tampa Bay sediments (and all 

estuarine sediments) contain a mixture of dissolved organic nitrogen (DON) as well as 

inorganic nitrogen species such as ammonium (NH4), nitrate (NO3), and nitrite (NO2). 

Because Tampa Bay sediments are generally anaerobic, porewater nitrate and nitrite 

concentrations are frequently very low, and DON and ammonium comprise most of the 

nitrogen dissolved in sediment porewaters. 
Figure 7. A conceptual model of nitrogen cycling and transformation in Tampa Bay, Florida. 

 Drawing by Lindsay Cross.

As DON and ammonium move from the sediment to the overlying water, bacteria on the 

sediment surface or in the overlying water can convert DON to ammonium or vice 

versa. In the process of nitrification, ammonium is oxidized to nitrite and nitrate. 

Anaerobic sediment bacteria can use nitrate as a terminal electron receptor for 

respiration, causing nitrate concentrations to decline in the overlying water. This 

process, denitrification, converts nitrate to nitrogen gas which then diffuses out of the 

sediment and overlying water. Because DON and ammonium concentrations are 

generally much higher in sediments than in overlying water, flux of these two nitrogen 

species from the overlying water to the sediments is generally negligible. 

Because nitrogen can be transformed in a number of different ways, the movement of 

total dissolved nitrogen is the most important parameter describing the nitrogen 

“processing” capability of sediments from different regions of Tampa Bay. The behavior 

of individual nitrogen species in core incubations represents the potential magnitude of 

fluxes and dominant microbial pathways. Potential losses from the system as the result 

of denitrification are particularly interesting, because they reduce the “fuel” for 

phytoplankton blooms. 
Seasonal and Spatial Patterns of Sediment Nitrogen Fluxes- Fluxes of the three 

principal nitrogen species varied seasonally among Bay segments and between fine 

and coarse sediment sites within Bay segments (Table 1). Net ammonia fluxes were 

positive (moving from sediment to overlying water) for most sites and most seasons. 

However, uptake by benthic microorganisms or nitrification caused ammonia 

concentrations to decline in Lower Tampa Bay coarse sediment cores collected in May 

and August. Elsewhere, lowest positive fluxes were observed in February when 

temperatures were lowest. Highest release from the sediments was measured in coarse 

sediments from Hillsborough Bay in August. Releases of ammonia were also elevated 

from coarse and fine sediments in Old and Middle Tampa Bay regions In May. 

The direction and magnitude of fluxes of the oxidized inorganic nitrogen species, nitrate 

and nitrite (NOX), varied seasonally and among sites. Moderate and positive NOX 

fluxes (increasing concentrations during core incubations) were observed in fine and 

coarse sediments of Hillsborough Bay for all seasons. Because Hillsborough Bay 

sediments are anaerobic, the observed increases in NOX species during core 

incubations probably resulted from nitrification of sediment ammonia at the sediment 

surface or in the overlying water. Old Tampa Bay sediments had mixed NOX fluxes, but 

Middle and Lower Tampa Bay sediments had small, negative NOX fluxes during most 

incubations, indicating denitrification occurred for much of the year. Small, positive 

fluxes (nitrification) occurred during November at Middle and Lower Tampa Bay sites. 

Table 1: Seasonal and Spatial Variation in Measured Nitrogen Fluxes. Data are mol/ha/d. 

 

 Hillsborough Bay Old Tampa Bay 

Middle Tampa 

Bay 

Lower Tampa 

Bay 

 Fine Coarse Fine Coarse Fine Coarse Fine Coarse 

Ammonia 

 Feb-03 1.94 5.53 7.78 3.27 7.89 0.20 8.42 0.47

 May-03 9.76 19.1 20.6 24.3 22.7 19.8 7.64 -2.48

 Aug-03 12.8 33.7 19.9 4.70 18.0 8.05 18.6 -1.27

 Nov-03 12.5 12.5 20.5 7.06 14.5 1.96 18.8 0.97

Nitrate+Nitrite 

 Feb-03 1.47 1.61 5.70 1.78 -0.59 -0.25 -0.25 0.09

 May-03 6.91 2.34 3.18 -0.81 -0.73 -1.39 0.16 -1.34

 Aug-03 5.54 1.01 -0.23 0.17 -0.60 -0.32 -1.09 -0.86

 Nov-03 4.63 1.64 -0.84 0.39 0.33 0.44 0.74 0.29

Dissolved Organic Nitrogen 

 Feb-03 11.9 8.00 9.27 5.26 9.39 -1.87 8.32 -0.23

 May-03 14.2 -19.7 -32.9 -18.2 15.0 24.2 8.44 -14.2

 Aug-03 -27.4 42.3 -39.2 -19.0 33.4 12.5 17.7 -20.9

 Nov-03 22.8 23.7 26.1 -13.6 31.8 7.57 41.8 -24.8

Total Nitrogen (by summation) 

 Feb-03 15.3 15.1 22.8 10.3 16.7 -1.92 16.5 0.34

 May-03 30.9 1.81 -9.20 5.30 37.0 42.6 16.2 -18.0

 Aug-03 -9.04 77.1 -19.5 -14.1 50.8 20.2 35.3 -23.0

 Nov-03 39.9 37.9 45.7 -6.10 46.6 9.97 61.3 -23.5
Dissolved organic nitrogen fluxes exhibited a complex spatial and temporal pattern, and 

their overall magnitude was slightly greater than to several times higher than ammonia 

fluxes. Negative DON fluxes occurred in the fine sediments of Hillsborough Bay in 

August and Old Tampa Bay in May and August. Negative DON fluxes occurred in 

Lower Tampa Bay coarse sediments in all seasons. 

Net total nitrogen fluxes were positive for most sites and most seasons, but there were 

some exceptions. Lower Tampa Bay coarse sediments were negative (net sediment 

uptake or denitrification) in May, August, and November. Small positive fluxes occurred 

at Lower Tampa Bay coarse sites only in February. Net positive fluxes occurred for all 

sampling dates in coarse sediments of Hillsborough Bay, and in fine sediments of 

Middle and Lower Tampa Bay. 

Comparison with other estuaries- Benthic fluxes of nutrients have been measured in 

a wide variety of estuaries in North America, and Twilley et al. (1999) summarized this 

information with an emphasis on fluxes in estuaries along the Gulf of Mexico. Ammonia 

releases from sediments from Ochlockonee Bay, Appalachicola Bay and Mobile Bay 

along the northern Gulf coast averaged from 4.5 to 15 mol ha-1 day-1, close to the range 

of our measurements. The range of average fluxes reported for Chesapeake Bay, 

Narragansett Bay, the Patuxent estuary, and the Neuse River estuary (-8 to 121 mol ha1

 day-1) is much greater than the range we observed in Tampa Bay (Twilley et al., 1999, 

this study). Average benthic fluxes of nitrate-nitrite in Ochlockonee Bay and Mobile Bay 

were greater than our measurements for Tampa Bay sediments and ranged from an 

uptake of -8.9 to release of 3.4 mol ha-1 day-1(Twilley et al., 1999). DON fluxes, which 

are a large part of the total nitrogen exchange between Tampa Bay sediments and the 

water column, were not reported in Twilley et al. (1999). 

Benthic fluxes of phosphorus and silicate- Fluxes of phosphate were highly variable 

throughout the study (Table 2) and ranged from uptake in Lower Tampa Bay coarse 

sediments during May, August, and November to large releases from coarse sediments 

in Hillsborough Bay during August and from fine sediments in Middle Tampa Bay in 

November. Phosphate was released from all Hillsborough Bay and Middle Tampa Bay 

cores, but showed a mixture of uptake and release in cores from Old Tampa Bay and 

Lower Tampa Bay. 

Fluxes of total dissolved phosphorus (TDP--phosphate and dissolved organic 

phosphorus) were similar in magnitude to fluxes of phosphate but generally did not 

show as strong a seasonal variation as was observed for phosphate fluxes. TDP was 

released from all Hillsborough Bay cores. Other sites showed a mixture of uptake and 

release, and fluxes tended to be smaller in February when temperatures were lowest. 

In Lower Tampa Bay coarse sediments, TDP was removed from the water column in 

February, August, and November. 

Silicate fluxes were much greater in magnitude than fluxes of any other measured 

nutrient, and were especially high in Hillsborough Bay. Except for coarse sediments 

from Lower Tampa Bay in May, silicate was released from all sediment cores. Overall, 

releases tended to be smaller in February, and to decrease seaward in the bay. Fluxes 
from coarse sediments in Lower Tampa Bay were an order of magnitude less than 

silicate fluxes observed elsewhere in the bay. 

Table 2: Seasonal and Spatial Variation in Measured Dissolved Phosphorus and Silicate 

Fluxes. 

 Data are mol/ha/day. 

 Hillsborough Bay Old Tampa Bay Middle Tampa Bay Lower Tampa Bay 

 Fine Coarse Fine Coarse Fine Coarse Fine Coarse 

Phosphate 

 Feb-03 1.44 0.77 2.59 0.98 3.54 1.38 1.74 1.13

 May-03 5.58 4.92 4.83 3.99 1.61 6.86 0.34 -0.05

 Aug-03 10.70 21.65 -3.37 -2.22 18.75 4.43 3.69 -2.29

 Nov-03 7.03 7.79 12.10 2.09 24.58 0.75 7.99 -1.16

Total Dissolved 

Phosphorus 

 Feb-03 4.89 2.46 0.67 2.91 1.78 -0.54 2.22 -0.25

 May-03 5.34 8.97 5.97 4.42 2.63 5.87 2.36 0.66

 Aug-03 8.54 8.10 -0.99 -1.42 10.45 4.76 5.44 -1.74

 Nov-03 8.17 6.93 6.63 1.62 21.59 0.22 6.25 -12.57

Silicate 

 Feb-03 36.25 17.60 52.26 35.05 71.41 4.78 21.22 2.36

 May-03 90.09 87.07 89.10 79.59 122.8 45.86 52.19 -4.35

 Aug-03 104.5 125.8 66.79 44.59 91.39 91.58 60.31 6.60

 Nov-03 73.64 37.20 68.27 16.78 45.60 16.92 63.24 0.16

 

Oxygen uptake by sediments showed a strong seasonal variation with lowest 

uptake in winter (-8.8 to 25 mmol m-2 day-1) and highest uptake (33 to 71 mmol m-2

day-1) in spring or summer (Table 3). Highest oxygen uptake rates were measured in 

coarse Hillsborough Bay sediments and fine Old Tampa Bay sediments in August. 

Lowest rates overall were observed in cores from coarse sediments in Lower Tampa 

Bay. 

Oxygen uptake was significantly and negatively correlated with ammonia and silicate 

fluxes (Figure 8) for all sites and seasons, but correlations of oxygen fluxes with 

nutrient fluxes were not significant for any other nutrient for all sites. 
 

Table 3. Benthic Uptake of Dissolved Oxygen by Tampa Bay Sediments: 

 

 Hillsborough Bay Old Tampa Bay Middle Tampa Bay Lower Tampa Bay 

Sediment 

Type: Fine Coarse Fine Coarse Fine Coarse Fine Coarse 

Areal fluxes based on core incubations (mmol/m2/day): 

 

 Feb-03 Mean -8.77 -9.22 -18.71 -25.00 -10.57 -15.34 -12.13 -10.63

 Std. Dev. 0.65 0.30 2.81 1.69 0.18 1.54 1.25 0.32

 May-03 Mean -43.19 -44.20 -47.78 -51.08 -38.75 -49.19 -50.60 -31.82

 Std. Dev. 5.40 3.58 7.26 5.42 0.90 7.82 8.75 5.12

 Aug-03 Mean -55.00 -70.64 -70.01 -49.88 -37.15 -42.31 -43.02 -33.23

 Std. Dev. 0.86 12.85 3.79 3.50 3.09 4.02 5.71 2.96

 Nov-03 Mean -41.20 -41.53 -41.39 -34.92 -44.21 -38.17 -56.34 -35.37

 Std. Dev. 0.75 3.93 6.83 2.92 10.1 5.26 9.89 8.45

Figure 8. Scatter plot of oxygen uptake versus ammonia and silicate release in Tampa Bay 

sediments. Data includes all sites and dates. 

Nitrogen Fluxes by Bay Segment- Seasonal flux data were extrapolated to annual 

fluxes for each site, and flux rates measured in coarse and fine sediments were 

multiplied by their respective Bay bottom areas for each Bay segment (Table 4). Total 

annual ammonia fluxes were positive in Hillsborough Bay, Old Tampa Bay and Middle 

Tampa Bay segments, but negative in Lower Tampa Bay. Annual nitrate/nitrite fluxes 

were positive for Hillsborough Bay and Old Tampa Bay and negative for Middle Tampa 

Bay and Lower Tampa Bay. DON fluxes were negative for Old Tampa Bay and Lower 

Tampa Bay but positive for the other two Bay segments. Sediments removed all 

nitrogen fractions in Lower Tampa Bay. For Tampa Bay as a whole, sediment releases 

of ammonia contributed the most nitrogen to estuarine waters; overall there was a small 

net release of NOX to the system, and a substantial net uptake of DON by the 

sediments. Overall, the sediments contributed about 2900 tons of nitrogen per year to 

Tampa Bay 

Oxygen Uptake vs Ammonia Release in Tampa Bay

-1

0

1

2

3

4

5

6

-90 -80 -70 -60 -50 -40 -30 -20 -10 0

Oxygen Uptake (mmol/m2/day)

Ammonia Release (mmol/m2/day)

Hillsborough Bay

Old Tampa Bay

Middle Tampa Bay

Lower Tampa Bay

R2

 = 0.49; P < 0.0001

Silicate Release vs Oxygen Uptake

-2

0

2

4

6

8

10

12

14

16

-80 -70 -60 -50 -40 -30 -20 -10 0

Oxygen Uptake (mmol/m2/day)

Silicate Flux (mmol/m2/day)

Hillsborough Bay

Old Tampa Bay

Middle Tampa Bay

Lower Tampa Bay

R2

 = 0.268; P < 0.0001
Table 4. Total Annual Nitrogen Flux Estimates by Bay Segment. 

 Values are tons per year. 

 

 

Hillsborough 

Bay 

Old Tampa 

Bay 

Middle Tampa 

Bay 

Lower Tampa 

Bay 

Bay 

Total 

 

Ammonia 786 1110 1290 -44.3 3140

NO3&NO2 133 92 -70 -58.9 96

DON 541 -1030 1730 -1580 -339

TDN 1460 172 2950 -1680 2900

 

Comparison of Benthic Fluxes with External Nitrogen Load Estimates- Poe et al 

(2005) found that annual external nitrogen loads to Tampa Bay varied as the result of 

variations in rainfall. To provide a context for our measured flux rates, we compared 

benthic nitrogen fluxes to external load estimates for 2000, a dry year, and 2003, a wet 

year. In a dry year, total benthic nitrogen flux is approximately 200% of external 

nitrogen loads for Hillsborough Bay, 40% for Old Tampa Bay, 590% for Middle Tampa 

Bay, and -780% for Lower Tampa Bay (indicating net uptake by the sediments), 

respectively (Table 5). In a wet year, the magnitude of benthic fluxes diminishes in 

comparison to external inputs. For Tampa Bay overall, benthic fluxes of nitrogen 

contribute 156% of external loads in a dry year and 55% of external loads in a wet year. 

Ammonia fluxes range from a net uptake of 20% of external loads in Lower Tampa Bay 

to releases that were 280% of external nitrogen loads to Tampa Bay segments in a dry 

year. Acknowledging that there are errors associated both with external load estimates 

and those introduced by extrapolating core flux measurements, these flux estimates still 

suggest that sediments produce, store, and recycle considerable amounts of nitrogen in 

Tampa Bay (see Figure 7 above). Large differences in the magnitude and direction of 

fluxes among the four regions of Tampa Bay also indicate that nitrogen processing as 

well as loading vary significantly as a function of bay location. The upper bay is a source 

of remineralized inorganic nitrogen (ammonia and NOX) while the lower bay removes 

inorganic nitrogen from the water column. Cycling of DON is much more complex with 

Old Tampa Bay and Lower Tampa Bay sediments removing DON and Hillsborough Bay 

and Middle Tampa Bay sediments releasing DON to the water column. 

Negative fluxes of nitrate/nitrite and DON also indicate that sediments and associated 

microorganisms have the capacity to transform significant amounts of nitrogen in 

Tampa Bay. For example, DON processing by contact with sediments can account for 

up to 1030 tons of nitrogen in Old Tampa Bay each year, a number very similar to the 

positive ammonia flux measured for this Bay segment. 

How significant are benthic nitrogen fluxes to the Tampa Bay nitrogen budget? 

Our answer at this point is that benthic processing is very important. However, the 

assessment is more qualitative than quantitative, and our research indicates that 

several processes should be investigated further. For example, our flux estimates are 
based on diffusive fluxes. Mass flux driven by tidal pumping of porewaters or by 

groundwater discharge might increase flux estimates. 

We have also measured large, positive fluxes of ammonia in Old Tampa Bay, 

Hillsborough Bay, and Middle Tampa Bay. Additional research should determine 

whether the ammonia is “new” nitrogen entering the system from runoff or atmospheric 

deposition. 

Large, positive fluxes of dissolved organic nitrogen out of the sediments are also worthy 

of additional study because we don’t know how labile DON is in Tampa Bay. If it is 

easily broken down to ammonia, it can be a significant source of nitrogen for 

phytoplankton. 

Finally, large, negative fluxes of nitrogen into sediments of Lower Tampa Bay indicate 

this Bay region can remove large amounts of nitrogen from the water column. The fate 

of this nitrogen- denitrification or uptake by benthic algae- should be determined. 

 To better quantify the role of sediment/water exchange processes, we still need to 

answer the following questions: 

1. What is the storage capacity and turnover time of nitrogen in Tampa Bay 

sediments? How old is the nitrogen fluxing from sediments? Days, weeks, months, or 

years? 

2. What is the ultimate source of nitrogen in Tampa Bay sediments? Do sediments add 

new nitrogen to the system or recycle external nitrogen loads? 

References: 

Cowan, J. L. W., J. R. Pennock, and W. R. Boynton. 1996. Seasonal and interannual 

patterns of sediment-water nutrient and oxygen fluxes in Mobile Bay, Alabama (USA): 

Regulating factors and ecological significance. Mar. Ecol. Progr. Ser. 141: 229-245. 

Dixon, L. K. and J. R. Leverone. 1995. Light requirements of Thalassia testudinum in 

Tampa Bay, Florida. Mote Marine Laboratory Tech. Rept. No. 425, Sarasota, FL. 

Fanning, K.A.and L. M. Bell. 1985. Nutrients in Tampa Bay. pp. 109-129, in S.F. Treat, 

J.L. Simon. R.R. Lewis III, R. L. Whitman (eds.) Proceedings of the Tampa Bay Area 

Scientific Information Symposium, Report 65 of the Florida Sea Grant Program, 

Gainesville, FL. 

Fisher, T. R, P. R. Carlson, and R. T. Barber. 1982. Sediment nutrient regeneration in 

three North Carolina estuaries. Est. Coastal Shelf Sci. 14:101-116. 

Janicki, A. and D. Wade. 1996. Estimating critical external nitrogen loads for the 

Tampa Bay estuary: an empirically based approach for setting management targets. 

Tampa Bay National Estuary Program Technical Publ. #06-96, St. Petersburg, FL. 
Johannson, J. O. R. 1991. Long-term trends of nitrogen loading, water quality, and 

biological indicators in Hillsborough Bay, Florida. Pp. 151-176 in S.F. Treat and P A. 

Clark, eds. BASIS II: Tampa Bay Area Scientific Information Symposium 2. 

 Lewis, R. R. III, M. J. Durako, M. D. Moffler, and R. C. Phillips. 1985. Seagrass 

meadows of Tampa Bay: A review. Pp. 210-246 in Treat, S. F., J. L. Simon, R. R. 

Lewis III, and R. L. Whitman, Jr., eds., Proceedings Tampa Bay Area Scientific 

Information Symposium. Florida Sea Grant College Report No. 65, Gainesville, FL. 

Nixon, S. W. 1981. Remineralization and nutrient cycling in coastal marine ecosystems, 

pp. 111-138 in Neilson, B. J. and L. E. Cronin, eds. Estuaries and Nutrients, Humana 

Press. 

Poe, A., K. Hackett, S. Janicki, R. Pribble, and A. Janicki. 2005. Estimates of total 

nitrogen, total phosphorus, total suspended solids, and biochemical oxygen demand 

loadings to Tampa Bay, Florida: 1999—2003, Tampa Bay Estuary Program Technical 

Publication No. 02-05. 

Seitzinger, S. P. 1987. Nitrogen biogeochemistry in an unpolluted estuary: The 

importance of benthic denitrification. Mar. Ecol. Progr. Ser. 41: 177-188. 

Seitzinger, S. P. 1988. Denitrification in freshwater and coastal marine ecosystems: 

Ecological and geochemical significance. Limnol. Oceanogr. 33: 702-724. 

Tomasko, D.A., and B. E. Lapointe. 1991. Productivity and biomass of Thalassia 

testudinum as related to water column nutrient availability and epiphyte levels: field 

observations and experimental studies. Mar. Ecol. Progr. Ser. 75: 9-17. 

Twilley, R.R., J. Cowan, T. Miller-Way, P.A Montagna, and B. Mortazavi. 1999. Benthic 

nutrient fluxes in selected estuaries in the Gulf of Mexico, pp. 163-209 in T.S. Bianchi, 

J.R. Pennock, and R.R. Twilley (eds.) Biogeochemistry of Gulf of Mexico Estuaries, 

John Wiley and Sons, Inc., 

Zarbock, P. E., A. Janicki, D. Wade, D. Heimbuch, and H. Wilson. 1994. Estimates of 

total nitrogen, total phosphorus, and total suspended solids loadings to Tampa Bay, 

Florida. Tampa Bay National Estuary Program Technical Publ. #04-94, St. Petersburg, 

FL. 
Appendix : Estimates of Benthic Nutrient Fluxes 

Table A-1: Benthic Ammonia Flux Estimates 

 Hillsborough Bay Old Tampa Bay Middle Tampa Bay Lower Tampa Bay 

Sediment 

Type: Fine Coarse Fine Coarse Fine Coarse Fine Coarse 

 Areal fluxes based on core incubations (mmol/m2/day): 

 

Feb03 Mean 0.194 0.553 0.778 0.327 0.789 0.020 0.842 0.047

 

Std. 

Dev. 0.150 0.297 0.419 0.012 0.162 0.101 0.299 0.033

May03 Mean 0.976 1.91 2.06 2.43 2.27 1.98 0.764 -0.248

 

Std. 

Dev. 0.431 0.707 1.02 0.330 0.972 1.04 0.340 0.046

Aug03 Mean 1.28 3.37 1.99 0.470 1.80 0.805 1.86 -0.127

 

Std. 

Dev. 0.791 1.80 0.614 0.192 0.346 0.440 0.890 0.130

Nov03 Mean 1.25 1.25 2.05 0.706 1.45 0.196 1.88 0.097

 

Std. 

Dev. 0.605 0.311 0.798 0.349 1.06 0.142 0.604 0.046

 

Area (ha): 3160 7374 4013 16054 3099 27892 493 24165 

 AMMONIA FLUXES (MOL/HA/DAY) 

Feb03 1.94 5.53 7.78 3.27 7.89 0.202 8.42 0.475

May03 9.76 19.14 20.56 24.30 22.66 19.82 7.64 -2.48

Aug03 12.79 33.73 19.91 4.70 18.00 8.05 18.62 -1.27

Nov03 12.49 12.55 20.46 7.06 14.46 1.96 18.76 0.973

 

Days FLUXES (mol/subsegment/season) 

121 Winter 743100 4934000 3780000 6349000 2957000 682500 502200 1389000 

91 Spring 2806000 12840000 7508000 35500000 6390000 50290000 342700 -5460000 

92 Summer 3719000 22880000 7349000 6939000 5133000 20660000 844700 -2815000 

62 Fall 2447000 5736000 5091000 7028000 2778000 3391000 573500 1458000 

 

 FLUXES (mt/subsegment/season) 

 Winter 10.40 69.08 52.92 88.89 41.40 9.56 7.03 19.45 

 Spring 39.28 180.0 105.1 497.0 89.46 704.1 4.80 -76.44 

 Summer 52.07 320.3 102.9 97.15 71.86 289.2 11.83 -39.41 

 Fall 34.26 80.30 71.27 98.39 38.89 47.47 8.03 20.41 

 

ANNUAL FLUX BY SEDIMENT TYPE (mt/subsegment/yr): 

 136.0 649.7 332.2 781.4 241.6 1050 31.68 -75.99 

ANNUAL FLUX BY BAY SEGMENT (mt/segment/yr): 

 786 1114 1292 -44.3 

TOTAL ANNUAL FLUX FOR THE WHOLE BAY (mt/yr): 

 3147 
 Table A-2: Nitrate+Nitrite Fluxes from Tampa Bay Sediments 

 Hillsborough Bay Old Tampa Bay Middle Tampa Bay Lower Tampa Bay 

Sediment Type: Fine Coarse Fine Coarse Fine Coarse Fine Coarse 

 

Areal fluxes based on core incubations (mmol/m2/day): 

 

Feb-03 Mean 0.147 0.161 0.570 0.178 -0.059 -0.025 -0.025 0.009

Std. 

Dev. 0.058 0.115 0.130 0.108 0.022 0.019 0.047 0.039

May-03 Mean 0.691 0.234 0.318 -0.081 -0.073 -0.139 0.016 -0.134

Std. 

Dev. 0.641 0.071 0.151 0.046 0.011 0.034 0.027 0.076

Aug-03 Mean 0.554 0.101 -0.023 0.017 -0.060 -0.032 -0.109 -0.086

Std. 

Dev. 0.237 0.099 0.048 0.006 0.048 0.053 0.028 0.041

Nov-03 Mean 0.463 0.164 -0.084 0.039 0.033 0.044 0.074 0.029

Std. 

Dev. 0.034 0.016 0.051 0.023 0.019 0.015 0.016 0.024

 

Area 

(ha): 3160 7374 4013 16054 3099 27892 493 24165

 

 NOX FLUXES (mol/ha/day) 

Feb-03 1.47 1.61 5.70 1.78 -0.59 -0.25 -0.25 0.09

May-03 6.91 2.34 3.18 -0.81 -0.73 -1.39 0.16 -1.34

Aug-03 5.54 1.01 -0.23 0.17 -0.60 -0.32 -1.09 -0.86

Nov-03 4.63 1.64 -0.84 0.39 0.33 0.44 0.74 0.29

 

Days FLUXES (mol/subsegment/season) 

121 Winter 563700 1435000 2766000 3453000 -222200 -833300 -14730 257800

 

91 Spring 1987000 1569000 1162000 -1185000 -206900 -3536000 6962 -2955000

92 Summer 1610000 685900 -85940 257000 -170900 -832700 -49270 -1913000

62 Fall 906600 748200 -208300 388500 63700 756300 22570 436800

 FLUXES (mt/subsegment/season) 

 Winter 7.89 20.09 38.72 48.34 -3.11 -11.67 -0.21 3.61

 Spring 27.82 21.97 16.27 -16.59 -2.90 -49.50 0.10 -41.37

 Summer 22.54 9.60 -1.20 3.60 -2.39 -11.66 -0.69 -26.78

 Fall 12.69 10.47 -2.92 5.44 0.89 10.59 0.32 6.12

 ANNUAL FLUX BY SEDIMENT TYPE (mt/subsegment/yr): 

 70.94 62.13 50.87 40.79 -7.51 -62.24 -0.48 -58.43

 ANNUAL FLUX BY BAY SEGMENT (mt/segment/yr) 

 133 92 -70 -58.9 

 TOTAL ANNUAL FLUX FOR THE WHOLE BAY (mt/yr): 

 96 
Table A-3. Dissolved Organic Nitrogen Flux Estimates for Tampa Bay Sediments. 

 Hillsborough Bay Old Tampa Bay Middle Tampa Bay Lower Tampa Bay 

Sediment Type: Fine Coarse Fine Coarse Fine Coarse Fine Coarse 

 

Areal fluxes based on core incubations (mmol/m2/day): 

Feb-03 Mean 1.19 0.800 0.927 0.526 0.939 -0.187 0.832 -0.023

Std. 

Dev. 0.369 0.202 0.118 0.088 0.151 0.683 0.222 0.052

May03 Mean 1.42 -1.97 -3.29 -1.82 1.50 2.42 0.844 -1.42

Std. 

Dev. 0.076 0.026 0.707 1.15 1.20 2.13 0.137 0.141

Aug03 Mean -2.74 4.23 -3.92 -1.90 3.34 1.25 1.77 -2.09

Std. 

Dev. 1.08 0.639 0.914 0.335 1.81 0.485 0.889 0.755

Nov03 Mean 2.28 2.37 2.61 -1.36 3.18 0.757 4.18 -2.48

Std. 

Dev. 0.018 1.12 0.648 0.568 1.63 0.148 2.09 0.677

 

Area (ha): 3160 7374 4013 16054 3099 27892 493 24165

 

 DON FLUXES (mol/ha/day) 

Feb-03 11.87 8.00 9.27 5.26 9.39 -1.87 8.32 -0.226

May03 14.22 -19.67 -32.94 -18.19 15.05 24.17 8.44 -14.21

Aug03 -27.37 42.33 -39.17 -19.01 33.36 12.50 17.75 -20.91

Nov03 22.76 23.74 26.10 -13.55 31.81 7.57 41.76 -24.76

 

Days FLUXES (mol/subsegment/season) 

121 Winter 4537000 7142000 4503000 10210000 3520000 -6317000 496100 -660000

91 Spring 4089000 -13200000 -12030000 -26570000 4243000 61340000 378800 -31260000

92 Summer -7957000 28720000 -14460000 -28080000 9512000 32090000 805000 -46480000

62 Fall 4458000 10850000 6494000 -13490000 6112000 13090000 1277000 -37090000

 FLUXES (mt/subsegment/season) 

 Winter 63.52 99.99 63.04 142.9 49.28 -88.44 6.95 -9.24

 Spring 57.25 -184.8 -168.4 -372.0 59.40 858.8 5.30 -437.6

 Summer -111.4 402.1 -202.4 -393.1 133.2 449.3 11.27 -650.7

 Fall 62.41 151.9 90.92 -188.9 85.57 183.3 17.88 -519.3

 ANNUAL FLUX BY SEDIMENT TYPE (mt/subsegment/yr): 

 71.78 469.2 -216.9 -811.0 327.4 1403 41.40 -1617

 ANNUAL FLUX BY BAY SEGMENT (mt/segment/yr): 

 541 -1028 1730 -1575 

 TOTAL ANNUAL FLUX FOR THE WHOLE BAY (mt/yr): 

 -332 
Table A-4 Phosphate Flux Estimates for Tampa Bay Sediments. 

 Hillsborough Bay Old Tampa Bay Middle Tampa Bay Lower Tampa Bay 

Sediment Type: Fine Coarse Fine Coarse Fine Coarse Fine Coarse 

 

Areal fluxes based on core incubations (mmol/m2/day): 

 

Feb-03 Mean 0.144 0.077 0.259 0.098 0.354 0.138 0.174 0.113

Std. 

Dev. 0.091 0.059 0.094 0.028 0.218 0.024 0.104

May-03 Mean 0.558 0.492 0.483 0.399 0.161 0.686 0.034 -0.005

Std. 

Dev. 0.421 0.411 0.265 0.165 0.077 0.424 0.012 0.218

Aug-03 Mean 1.07 2.17 -0.337 -0.222 1.88 0.443 0.369 -0.229

Std. 

Dev. 0.163 1.07 0.172 0.121 1.63 0.437 0.042 0.084

Nov-03 Mean 0.703 0.779 1.21 0.209 2.46 0.075 0.799 -0.116

Std. 

Dev. 0.410 0.468 0.637 0.184 0.624 0.253 0.455 0.025

 

Area (ha): 3160 7374 4013 16054 3099 27892 493 24165

 

 PO4 FLUXES (mol/ha/day) 

Feb-03 1.44 0.77 2.59 0.98 3.54 1.38 1.74 1.13

May-03 5.58 4.92 4.83 3.99 1.61 6.86 0.34 -0.05

Aug-03 10.70 21.65 -3.37 -2.22 18.75 4.43 3.69 -2.29

Nov-03 7.03 7.79 12.10 2.09 24.58 0.75 7.99 -1.16

 

Days FLUXES (mol/subsegment/season) 

121 Winter 551600 689200 1556000 1912000 1329000 4666000 104100 3300000

 

91 Spring 1605000 3301000 1765000 5833000 454900 17400000 15190 -100800

92 Summer 3110000 14690000 -1243000 -3282000 5347000 11360000 167400 -5089000

62 Fall 1376000 3564000 3011000 2083000 4723000 1293000 244400 -1744000

 FLUXES (mt/subsegment/season) 

 Winter 7.72 9.65 21.78 26.77 18.61 65.32 1.46 46.20

 Spring 22.47 46.21 24.71 81.66 6.37 243.6 0.21 -1.41

 Summer 43.54 205.7 -17.40 -45.95 74.86 159.0 2.34 -71.25

 Fall 19.26 49.90 42.15 29.16 66.12 18.10 3.42 -24.42

 ANNUAL FLUX BY SEDIMENT TYPE (mt/subsegment/yr): 

 93.00 311.4 71.25 91.64 166.0 486.1 7.44 -50.87

 ANNUAL FLUX BY BAY SEGMENT (mt/segment/yr) 

 404 163 652 -43.4 

 TOTAL ANNUAL FLUX FOR THE WHOLE BAY (mt/yr): 

 1176 
Table A-5 Total Dissolved Phosphorus Flux Estimates for Tampa Bay Sediments. 

 Hillsborough Bay Old Tampa Bay Middle Tampa Bay Lower Tampa Bay 

Sediment Type: Fine Coarse Fine Coarse Fine Coarse Fine Coarse 

 

 Areal fluxes based on core incubations (mmol/m2/day): 

 Feb-03 Mean 0.489 0.246 0.067 0.291 0.178 -0.054 0.222 -0.025

 Std. Dev. 0.089 0.112 0.017 0.041 0.085 0.024 0.059 0.120

 May-03 Mean 0.534 0.897 0.597 0.442 0.263 0.587 0.236 0.066

 Std. Dev. 0.243 0.409 0.287 0.192 0.189 0.261 0.043 0.236

 Aug-03 Mean 0.854 0.810 -0.099 -0.142 1.04 0.476 0.544 -0.174

 Std. Dev. 0.129 0.432 0.523 0.043 0.488 0.433 0.127 0.092

 Nov-03 Mean 0.817 0.693 0.663 0.162 2.16 0.022 0.625 -1.26

 Std. Dev. 0.435 0.426 0.082 0.144 0.535 0.311 0.090 0.407

 

Area 

(ha) 3160 7374 4013 16054 3099 27892 493 24165

 

 TDP FLUXES (mol/ha/day) 

 Feb-03 4.89 2.46 0.67 2.91 1.78 -0.54 2.22 -0.25

 May-03 5.34 8.97 5.97 4.42 2.63 5.87 2.36 0.66

 Aug-03 8.54 8.10 -0.99 -1.42 10.45 4.76 5.44 -1.74

 Nov-03 8.17 6.93 6.63 1.62 21.59 0.22 6.25 -12.57

 

Days FLUXES (mol/subsegment/season) 

121 Winter 1870000 2199000 324300 5659000 666600 -1809000 132300 -742500

91 Spring 1535000 6018000 2179000 6462000 742000 14910000 106000 1450000

92 Summer 2484000 5497000 -364600 -2094000 2979000 12210000 246800 -3866000

62 Fall 1600000 3170000 1650000 1615000 4147000 378200 191000 -18830000

 FLUXES (mt/subsegment/season) 

 Winter 26.18 30.79 4.54 79.23 9.33 -25.33 1.85 -10.40

 Spring 21.49 84.25 30.51 90.47 10.39 208.7 1.48 20.30

 Summer 34.78 76.96 -5.10 -29.32 41.71 170.9 3.46 -54.12

 Fall 22.40 44.38 23.10 22.61 58.06 5.29 2.67 -263.6

 ANNUAL FLUX BY SEDIMENT TYPE (mt/subsegment/yr): 

 104.8 236.4 53.04 163.0 119.5 359.6 9.47 -307.8

 ANNUAL FLUX BY BAY SEGMENT (mt/segment/yr) 

 341 216 479 -298.4 

 TOTAL ANNUAL FLUX FOR THE WHOLE BAY (mt/yr): 

 738 
Table A-6. Silicate Flux Estimates for Tampa Bay Sediments. 

 Hillsborough Bay Old Tampa Bay Middle Tampa Bay Lower Tampa Bay 

Sediment Type: Fine Coarse Fine Coarse Fine Coarse Fine Coarse 

 

Areal fluxes based on core incubations (mmol/m2/day): 

 

Feb-03 Mean 3.62 1.76 5.23 3.50 7.14 0.478 2.12 0.236

 Std. Dev. 1.70 0.211 1.01 1.24 1.08 0.157 0.030

May-03 Mean 9.01 8.71 8.91 7.96 12.28 4.59 5.22 -0.435

 Std. Dev. 1.66 1.13 0.609 2.00 1.60 3.80 3.27 0.151

Aug-03 Mean 10.45 12.58 6.68 4.46 9.14 9.16 6.03 0.660

 Std. Dev. 1.37 0.712 1.85 0.433 0.115 3.19 2.38 0.337

Nov-03 Mean 7.36 3.72 6.83 1.68 4.56 1.69 6.32 0.016

 Std. Dev. 1.81 1.56 2.28 0.244 0.941 2.02 0.310

 

Area (ha): 3160 7374 4013 16054 3099 27892 493 24165

 

 SIO4 FLUXES (mol/ha/day) 

Feb-03 36.25 17.60 52.26 35.05 71.41 4.78 21.22 2.36

May-03 90.09 87.07 89.10 79.59 122.8 45.86 52.19 -4.35

Aug-03 104.5 125.8 66.79 44.59 91.39 91.58 60.31 6.60

Nov-03 73.64 37.20 68.27 16.78 45.60 16.92 63.24 0.16

 

Days FLUXES (106

 mol/subsegment/season) 

121 Winter 13.86 15.71 25.38 68.08 26.78 16.14 1.266 6.889

 

91 Spring 25.91 58.43 32.54 116.3 34.63 116.4 2.342 -9.571

 

92 Summer 30.39 85.33 24.66 65.85 26.06 235 2.735 14.67

62 Fall 14.43 17.01 16.98 16.7 8.761 29.26 1.933 0.2396

 FLUXES (mt/subsegment/season) 

 Winter 194.0 219.9 355.3 953.1 374.9 226.0 17.72 96.45

 Spring 362.7 818.0 455.6 1628 484.8 1630 32.79 -134.0

 Summer 425.5 1195 345.2 921.9 364.8 3290 38.29 205.4

 Fall 202.0 238.1 237.7 233.8 122.7 409.6 27.06 3.35

 ANNUAL FLUX BY SEDIMENT TYPE (mt/subsegment/yr): 

 1184 2471 1394 3737 1347 5555 115.9 171.2

 ANNUAL FLUX BY BAY SEGMENT (mt/segment/yr) 

 3655 5131 6902 287.1 

 TOTAL ANNUAL FLUX FOR THE WHOLE BAY (mt/yr): 

 15970