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 Prot ection Agency Gulf of Mexico Program

FINAL REPORT

August 2006BENTHIC OXYGEN AND NUTRIENT FLUXES IN TAMPA BAY:
A FINAL REPORT TO THE TAMPA BAY ESTUARY PROGRAM, FLORIDA,
DEPARTMENT OF ENVIRONMENTAL PROT ECTION, 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 begi nning 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 cycl e of Tampa Bay is more complex than we anticipated. Nutrient fluxes measured at eight sites in Tampa Bay indicate that sediments in different Bay s egments can serve as sources or sinks for nitrogen as well as temporary storage pools. Furthermore, t he role of sediments within a Bay segment can vary seasonally. Refined nitrogen budg ets for Tampa Bay can now include sediment processes in the continued developm ent of nitrogen loading targets to support
habitat restoration.

Background and Rationale : More than 80% of the seagr ass 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). Seagra sses 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 nutrient s- 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 limit ing nitrogen inputs to the Bay (Johansson, 1991; Janicki and Wade, 1996).

Water quality in Tampa Bay reached its nadi r 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, pr imarily as the result of declines in point-source loading and fugitive emissi ons. However, resource managers are concerned by future nitrogen loading rates whic h 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 nitr ogen inputs to the estuary.

Efforts to manage nitrogen leve ls in Tampa Bay, in turn, depend on accurate estimates of nitrogen inputs, exports, and internal transformati ons for the Bay. However, existing nitrogen budgets for Tampa Bay have not incl uded estimates of the rate of nitrogen exchange between sediment s and the water column because those processes have notbeen 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 en tire 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 seques tering 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 approximat ely one liter of water overlying each core. We stirred and sampled the overlying wa ter periodically over 48 hours and analyzed filtered supernatant samples for ammonia, ni trate/nitrite, total dissolved nitrogen, phosphate, total dissolved phosphorus and s ilicate. 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 text ure (sand, silt-clay) data collected by Hillsborough County Environm ental 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 cr eated contour maps of sedim ent texture using Spatial Analyst. From the contour m ap, we extracted the latitude and longitude of four to five sites in each Bay region which were likel y 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 criteri on 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 se diments typically have high microbial respiration rates and high nutrient flux rates. We verified sediment textur e at each site using a Petit Ponar benthic grab. The sca rcity 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-gr ained sites within each region which were close enough together to have si milar salinity regimes. T he 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), co res 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 sa mpling 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 meas urements 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 Plexigla s core sleeve into the sediment to a predetermined depth. Visi bility was often so poor that dive rs 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 co re 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 di sturbance of sediment or porewater nutrient profiles. The sealed core was gently trans ferred to the boat (s ee 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 heat ing 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 mo rning after collection, the supernatant water was gently siphoned off t he cores and replaced with low-nutrient seawater adjusted to ambient sa linity for each site. Nutrient fluxes were measured over the next 48 hours by periodica lly withdrawing super natant from each core. Supernatant samples were filtered and frozen prior to anal ysis for dissolved silicate, ammonia, nitrate+nitrite, phosphate, total dissolv ed phosphorus, and total dissolved nitrogen.

Extrapolation of measured fluxes - Estimates of benthic nut rient 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 r egression was then performed on nutrientconcentration data to calculate flux rates, us ing only data from th e 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 oxy gen, 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 segm ent. Sediment textur e 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 measur ements into annual estimates. The annual estimates, in turn, were compared to external nitrogen an d phosphorus loads calculated by Poe et al. (2005). Complete spreadsheet s outlining calculations ar e included in the Appendix.

Precautions for quality control and data analysis - At every step in the sampling, core incubation, and data analysis, precauti ons were taken to ensure data quality:

1. Cores were collected by divers usi ng 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 c ontinuously in the dark ov ernight to "reset" the status of benthic microalgae. Ph ytoplankton and benthic microalgae havedemonstrated the capacity to fix nitrogen and phosphorus for up to 12 hours in the dark. Site water was replaced with low nutrient seawat er adjusted to the salinity of each site. In our calculations of nutrient flux rates, we ignore the potential effe ct of a concentration gradient decreased by elevated water column nutrient concentrations. Replacing site
water with filtered seawater al so eliminated any potential in fluence 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 particula r, was concerned that, based on sedimentwater exchange measurements in the Patuxent Estuary, artifacts increased with increasing duration of incubati on. Artifacts that might affect flux estimates include development of microalgal or bacterial ma ts, decomposition of infauna killed by coring or by subsequent hypoxia.

4. Core incubations and sampling were carr ied out in total darkness, so cores were examined and photographed at the end of the incubation pe riod to identify incubation
artifacts. Data were not used from co res which demonstrated leakage around piston Orings or contained dead infauna.

Results and Discussion: Differences in sediment text ure 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 Baysediment core. Fine grained sediment co res from Middle Tampa Bay and Lower Tampa Bay are uniformly anoxic. Fine sediment co res from Hillsborough Ba y had the highest silt-clay content, followed by Old Tampa Bay, Middle Tampa Bay, and Lower Tampa Bay.

Bioturbation and irrigation of cores by inf auna 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 typi cally had brachiopod bivalves and small polychaetes in them. Many si tes have numerous brittle star s, and the LTB coarse site has lots of sand dollars. With the except ion of sand dollars, we allowed organisms to
remain in the cores because it is too disruptive to remove them.

.

Figure 6. Effects of burrowing orga nisms on sediment cores. Core on left contains a large brittle star with its disk approximately 5 cm below the sedim ent 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 phyt oplankton 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 sediment s are generally anaer obic, porewater nitrate and nitrite concentrations are frequently very low, and DON and ammoni um comprise most of the nitrogen dissolved in sedim ent 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 wate r can convert DON to ammonium or vice versa. In the process of ni trification, ammonium is oxid ized to nitrite and nitrate.
Anaerobic sediment bacteria can use nitr ate as a terminal electron receptor for respiration, causing nitrate concentrations to decline in the overlying water. This process, denitrification, conv erts nitrate to nitrogen gas which then diffuses out of the sediment and overlying water. Because DON and ammonium concentrations are generally much higher in sedi ments than in overlying water, flux of these two nitrogen species from the overlying water to the sediments is generally negligible.

Because nitrogen can be transform ed in a number of different ways, the movement of total dissolved nitrogen is the most impor tant parameter describing the nitrogen “processing” capability of sediments from diffe rent regions of Tampa Bay. The behavior of individual nitrogen species in core incubations represent s the potential magnitude of
fluxes and dominant microbial pathways. Potential losses fr om the system as the result of denitrification are particularly interest ing, because they reduce the “fuel” for phytoplankton blooms.Seasonal and Spatial Patterns of Sediment Nitrogen Fluxes- Fluxes of the three principal nitrogen species varied seas onally among Bay segments and between fine
and coarse sediment sites wit hin 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 microorganism s or nitrification caused ammonia concentrations to decline in Lower Tampa Bay coarse sediment core s collected in May and August. Elsewhere, lowest positive fluxes were observed in February when temperatures were lowest. Highest release fr om 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 in creases 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 occurr ed for much of the year. Small, positive fluxes (nitrification) occurred during Nove mber 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 -23.5Dissolved organic nitrogen fluxes exhibited a co mplex spatial and te mporal 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 Augus t. Negative DON fluxes occurred in Lower Tampa Bay coarse sediments in all seasons.

Net total nitrogen fluxes were positive for mo st sites and most s easons, but there were some exceptions. Lower Tampa Bay coarse sediments were negative (net sediment uptake or denitrification) in May, August, an d November. Small positive fluxes occurred at Lower Tampa Bay coarse sites only in Febr uary. Net positive fluxes occurred for all sampling dates in coarse sediments of Hil lsborough 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 Americ a, and Twilley et al. (1999) summarized this information with an emphasis on fluxes in est uaries along the Gulf of Mexico. Ammonia
releases from sediments from Ochlockone e 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 aver age fluxes reported for Chesapeake Bay, Narragansett Bay, the Patuxent estuary, and the Neuse River estuary (-8 to 121 mol ha 1 day -1 ) is much greater than the range we ob served in Tampa Bay (Twilley et al., 1999, this study). Average benthic fluxes of nitrat e-nitrite in Ochlockonee Bay and Mobile Bay were greater than our meas urements for Tampa Bay s ediments 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 tota l nitrogen exchange between Tampa Bay sediments and the water column, were not report ed in Twilley et al. (1999).

Benthic fluxes of phosphorus and silicate- Fluxes of phosphate were highly variable throughout the study (Table 2) and ranged fr om 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 a ll 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 phosphor us (TDP--phosphate and dissolved organic phosphorus) were similar in magnitude to fl uxes 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. Ot her sites showed a mi xture of uptake and release, and fluxes tended to be smaller in February when temperatures were lowest. In Lower Tampa Bay coarse sediments, TD P 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 Hills borough Bay. Except for coarse sediments from Lower Tampa Bay in May, silicate was re leased from all sediment cores. Overall, releases tended to be smaller in February, and to decrease seaward in the bay. Fluxesfrom 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 s easonal 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 Ol d Tampa Bay sediments in August.
Lowest rates overall were observed in core s from coarse sediments in Lower Tampa Bay.

Oxygen uptake was significantly and negativel y 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 we re extrapolated to annual fluxes for each site, and flux rates meas ured in coarse and fine sediments were multiplied by their respective Bay bottom ar eas for each Bay segment (Table 4). Total annual ammonia fluxes were positive in Hil lsborough Bay, Old Tampa Bay and Middle Tampa Bay segments, but negative in Lower Ta mpa 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 we re negative for Old Tampa Bay and Lower Tampa Bay but positive for the other tw o Bay segments. Sediments removed all nitrogen fractions in Lower Tampa Bay. For Ta mpa Bay as a whole, sediment releases of ammonia contributed the most nitrogen to es tuarine waters; overall there was a small
net release of NOX to t he system, and a substantial net uptake of DON by the sediments. Overall, the sediments cont ributed 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 R 2 = 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) Hillsbor ough Bay

Old Tampa Bay

Middle Tampa Bay

Lower Tampa Bay R 2 = 0.268; P < 0.0001Table 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 Ex ternal 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 contex t for our measured flux rates, we compared benthic nitrogen fluxes to external load esti mates for 2000, a dry year, and 2003, a wet year. In a dry year, tota l benthic nitrogen flux is approx imately 200% of external nitrogen loads for Hillsborough Bay, 40% for Old Tampa Bay, 590% for Middle Tampa Bay, and -780% for Lower Tampa Bay (indi cating net uptake by the sediments), respectively (Table 5). In a wet year, the magnitude of benthic fluxes diminishes in comparison to external inputs. For Tam pa Bay overall, benthic fluxes of nitrogen contribute 156% of external loads in a dry y ear 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 ni trogen loads to Tampa Bay segments in a dry year. Acknowledging that there are errors associated both with exte rnal load estimates and those introduced by extrapolating core flux measurements, these flux estimates still suggest that sediments produce, store, and re cycle considerable amount s of nitrogen in Tampa Bay (see Figure 7 above). Large differ ences in the magnitude and direction of fluxes among the four regions of Tampa Bay also indi cate that nitrogen processing as well as loading vary significantly as a functi on 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. C ycling of DON is much more complex with Old Tampa Bay and Lower Tampa Bay sedi ments removing DON and Hillsborough Bay and Middle Tampa Bay sediments releasing DON to the water column.

Negative fluxes of nitrate/ni trite 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 flu xes to the Tampa Bay nitrogen budget? Our answer at this point is that benthic pr ocessing is very important. However, the assessment is more qualitative than quantitat ive, and our research indicates that several processes should be investigated further . For example, our flux estimates arebased on diffusive fluxes. Mass flux driv en by tidal pumping of porewaters or by groundwater discharge might incr ease flux estimates.

We have also measured large, positive fl uxes of ammonia in Old Tampa Bay, Hillsborough Bay, and Middle Ta mpa 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 ni trogen out of the sedim ents are also worthy of additional study because we don’t know how labile DON is in Tam pa 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 upt ake by benthic algae- should be determined.

To better quantify the role of sediment/w ater exchange processes, we still need to answer the following questions:

1. What is the storag e 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. P ennock, and W. R. Boynton. 1996. Seasonal and interannual patterns of sediment-water nutrient and oxygen fluxes in Mobile Bay, Alabama (USA): Regulating factors and ecologica l significance. Mar. Ecol. Progr. Ser. 141: 229-245.

Dixon, L. K. and J. R. Lever one. 1995. Light requirements of Thalassia testudinum in Tampa Bay, Florida. Mote Marine Laborat ory 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. Whit man (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. Sedi ment nutrient regeneration in
three North Carolina estuaries. Es t. Coastal Shelf Sci. 14:101-116.

Janicki, A. and D. Wade. 1996. Estimating critical external ni trogen loads for the Tampa Bay estuary: an empirically bas ed approach for setting management targets. Tampa Bay National Estuary Program Techni cal 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, Flor ida. Pp. 151-176 in S.F. Treat and P A. Clark, eds. BASIS II: Tampa Bay Area Scie ntific 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. Cr onin, eds. Estuaries and Nutrients, Humana
Press.

Poe, A., K. Hackett, S. Janicki , R. Pribble, and A. Jani cki. 2005. Estimates of total nitrogen, total phosphorus, total suspended solids, and biochemical oxygen demand loadings to Tampa Bay, Florida: 1999—20 03, Tampa Bay Estuary Program Technical
Publication No. 02-05.

Seitzinger, S. P. 1987. Nitrogen biogeochemistry in an unpolluted estuary: The importance of benthic denitrif ication. Mar. Ecol. Progr. Ser. 41: 177-188.

Seitzinger, S. P. 1988. Deni trification in freshwater and coastal marine ecosystems: Ecological and geochemical signific ance. Limnol. Oceanogr. 33: 702-724.

Tomasko, D.A., and B. E. Lapointe. 1991. Productivity and biomass of Thalassia
testudinum as related to water column nutri ent 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 Mont agna, and B. Mortazavi. 1999. Benthic
nutrient fluxes in selected est uaries in the Gulf of Mexico, pp. 163-209 in T.S. Bianchi, J.R. Pennock, and R.R. Twilley (eds.) Biogeoc hemistry 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 su spended 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 0.033May03 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 0.046Aug03 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 0.475May03 9.76 19.14 20.56 24.30 22.66 19.82 7.64 -2.48Aug03 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):

3147Table A-2: Nitrate+Nitrite Fl uxes 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 T YPE (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):

96Table 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 0.052May03 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 0.141Aug03 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 -0.226May03 14.22 -19.67 -32.94 -18. 19 15.05 24.17 8.44 -14.21Aug03 -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 T YPE (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):

-332Table A-4 Phosphate Flux Estima tes 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 T YPE (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):

1176Table 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 T YPE (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):

738Table 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 (10 6 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 T YPE (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