# Presentation: 599896

## Spatial Distribution of 

**Different Forms of **
**Sedimentary Phosphorus **
**in Florida Bay: **
**sequential extraction approach**
** **
**Jia-Zhong Zhang  ****and**** Charles Fischer **
- Ocean Chemistry Division, AOML, NOAA, Miami, FL 33149

**Notes:**
ASLO 2002

## Florida Bay

**Notes:**
Florida Bay is a large (2200 km2), shallow lagoon at the southern end of Florida peninsula, with a mean water depth of approximately 1 m. 

## Bottom type

**Notes:**
Green – sea grass; Yellow – hard bottom; Brown – open mud; light brown - open sand

## Low phosphate concentration in Florida Bay water					Zhang & Chi, 2002

## Sediment sampling station

**Notes:**
Since the Bay is divided by mud banks to numerous sub-basins, a total of 40 sampling stations were occupied in this study in order to cover the bay with sufficient spatial resolution during 13-14, November 2000. 

## Sequential extraction procedure

## Percentage of CaCO3 in Florida Bay sediments

**Notes:**
CaCO3 is a dominant component of Florida Bay sediments, ranging 81.2% to 95.6% with an average of 89.2  4.3%. The lowest concentrations (81.2%) were found at northwest coastal stations 9 and 12. The second to the lowest concentration (82.36-82.79%) were found at stations 30 and 31 in Rabbit Key basin. Eastern Bay sediments contain high percentage (>92%) of calcium carbonate. Variations in calcium carbonate content in the sediment are mainly caused by dilution of CaCO3 by buried organic matter. Therefore the spatial distribution of CaCO3 should reflect the accumulation rate of organic matter, hence the productivity of benthic community and overlying water. The areas of relatively low percentage of calcium carbonate were found in northwest and north central bay, corresponding to areas of high productivity. 

## Total Sedimentary Phosphorus in Florida Bay

**Notes:**
Total sedimentary P showed a strong spatial gradient in Florida Bay. The highest concentration of total sedimentary P (9-14 mol/g) was found at the northwest bay, near Cape Sable. The lowest concentration was found in eastern bay where low chlorophyll concentrations are usually found. A strong gradient of decreasing sedimentary P concentration was observed from the west to east across the central Florida Bay. 

## Total exchangeable phosphorus by MgCl2 extraction

**Notes:**
The reactive P concentrations extracted by MgCl2 solution show a similar pattern as total sedimentary P. The highest concentration (1 mol/g) was found at the northwest bay, near Cape Sable. The second to the highest concentration (>0.8 mol/g) were found at stations 30 and 31 in Rabbit Key basin. The lowest concentration was found in eastern bay. This fraction of sedimentary P is exchangeable with water column and is generally considered as bioavailable. The organic P is about 60% of total P extracted by MgCl2 solution. 

## Exchangeable Inorganic phosphorus by MgCl2 extraction

## Exchangeable organic phosphorus by MgCl2 extraction

## Iron-bound Phosphorus by dithionite extraction

**Notes:**
The iron-bound P shows a similar pattern as exchangeable P with higher concentrations in the northwest bay and lower concentrations in eastern bay. The highest concentrations (> 2 mol/g) occur at station 9, 10, 12, 13 along the coast of north western bay. The second to the highest concentrations (>1.8 mol/g) occur at station 30 and 31 in Rabbit Key basin. 

## Reactive iron in Florida Bay sediments

**Notes:**
Reactive Fe concentrations from reduction of ferric oxide in sediment show a strong gradient of decreasing concentration away from the Florida mainland. The maximum concentrations were found in the northeastern bay and a second highest concentration at north central coast. Low concentrations were found in southern Bay. The distribution pattern of reactive iron indicates that fresh water runoff is a major pathway that transports the terrestrial iron, mainly as particulate and colloidal iron, into Florida Bay. 

## Salinity of Florida Bay water during sediment sampling					 By courtesy of Lee & John

**Notes:**
 The passage of fresh water runoff into the bay can readily be identified from the salinity distribution at the beginning of the wet season that was preceded by a prolonged dry season during summer of 2001. The distribution of reactive iron shows a good spatial correlation with that of salinity, indicating that freshwater input is the source of iron to the Bay. 

## CaCO3-bound total phosphorus by HAc (pH 4) extraction

**Notes:**
The concentrations of authigenic carbonate fluorapatite and biogenic apatite as well CaCO3 associated phosphorus show a similar pattern as total sedimentary P. The high inorganic phosphorus concentration (>4 mol/g) was found in the northwest bay, with the highest concentration of 5.5 mol/g at station 9 near Flamingo. The lowest concentration of inorganic phosphorus was found in eastern bay and its concentration gradually increases across central bay. 

## CaCO3-bound inorganic phosphorus

## CaCO3-bound organic phosphorus	

**Notes:**
The organic P concentration varied with location from less than 0.1 in station 1, 2, 3 4, 5, 26 and 40 to about 2.3 in station 13 and 14. The origin of organic P seems related to west shelf current. Although the sharp contract between eastern and western bay is similar, detail distribution, particularly the maximum region is different between inorganic and organic P extract in this step. The percentage of organic P relative to the total P in this step varies greatly from 2% to 40% with average of 19.4 ± 11%. The high percentage of organic P (>30%) was found in productive water of western and central bay while low values (2-5%) was found in less productive eastern bay. 

## Detrital phosphorus by HCl extraction

**Notes:**
Detrital apatite phosphorus of igneous or metamorphic origin shows a similar distribution pattern as total sedimentary P but its maximum concentration is <1 mole/g. Detrital apatite phosphorus of igneous or metamorphic origin represents the smallest fraction, only 4.6 ± 2.2% of total sedimentary P. 

## Residual refractory organic phosphorus by ashing

**Notes:**
This refractory organic P concentration, on average, constitutes 24.3 ± 4.3% of total sedimentary P and is the second largest pools of sedimentary P. Its concentrations vary from 0.3 to 3.4 mol/g in the Florida Bay. The low concentrations (< 1mol/g) of refractory organic phosphorus were found in entire eastern bay and its concentration increases rapidly across central bay from 1 to 2 mol/g. The high concentrations (> 2 mol/g) of refractory organic phosphorus were found in western bay. The maximum concentrations (>3 mol/g) were found in northern coastal stations (8 and 9) and central bay station 31 and 32. The spatial distribution of refractory organic P is similar to that of the content of organic matter in sediment as revealed from percentage of CaCO3 in the sediment. 

## comparison

**Notes:**
Comparison of direct determination of total sedimentary phosphorus by the high temperature combustion method and the sum of phosphorus pools determined from each sequential extraction steps in Florida Bay sediment samples. The sum of the five-pool phosphorus obtained by sequential extraction is in good agreement with an independent determination of total sedimentary phosphorus in the same samples by the high temperature combustion method with a correlation coefficient of 0.9724, demonstrating a good recovery of our sequential extraction technique. 

## Slide 21

## Percentage of Different Forms of Sedimentary Phosphorus

**Notes:**
eastern bay (1-3 mole/g TSP)
central bay (3-9 mole/g TSP) 
western bay (9-14mole/g TSP)

## Summary

- Strong W-E spatial gradient in TSP and every forms of sedimentary P
- CaCO3-bound P accounts 44% of TSP
- Refractory organic P constitutes 24% of TSP
- Iron-bound P accounts 19% of TSP
- Exchangeable P accounts 8% of TSP

## Sunset

- Acknowledgements:

- This research was supported by NOAA’s South Florida
- Ecosystem Restoration, Prediction and Modeling Program

- Recent Publications:

- Zhang, Jia-Zhong, Charles J. Fischer, and Peter B. Ortner, (2004) Potential availability of sedimentary phosphorus to sediment resuspension in Florida Bay*, **Global Biogeochemical Cycles**.** *18, GB4008, doi: 10.1029/2004GB002255, 2004*.*
- Zhang, J.-Z., J. Chi (2002) Automated analysis of nanomolar concentrations of phosphate in natural waters with liquid waveguide, *Environmental Science & Technology*, **36**(5): 1048-1053.