Bone Phosphorus Dominates Fixed Tree Island Soil in the Everglades WCA3

1. Bone Phosphorus Dominates Fixed Tree IslandSoil in the Everglades WCA3 John M. Galbraith Charles L. Coultas Margo Schwadron Nina E. O’Malley

2. Fig. 1. Study Area - Southern Everglades (Schwadron, 2006). Gumbo Limbo Island (red star). Miami

3. Fixed Tree Island Soil P • The amount of phosphorus (P) in fixed tree island soils is higher than in the surrounding waters and subaqueous soils (Sklar and van der Valk, 2002). • Possible sources of P include: • Guano • Windblown particles • Bones in the soil • Upwelling groundwater

4. Sources of P (Wetzel, 2002) Problem: slide has poor resolution, cannot be stretched this big.

5. Purpose for the Study • Problem: Dominant P source is still under debate • Solution: Measure or estimate P contribution from all four possible sources, relate those to observed soil properties

6. Hypotheses The bones of animals cooked and eaten by humans weathered and released high amounts of Ca and P where it was sequestered as secondary mineral precipitates of apatite (Ca5(PO4)3OH) (Graf, 2009) and calcite (CaCO3). The seasonally high water table and transpiration losses from the subsoil concentrated calcium in a layer that became cemented over time.

7. Soil P on Gumbo Limbo Island:Steps for Testing our Hypothesis • The soil on the island summit is an alkaline kitchen midden soil (Petrocalcic Hapludoll) made of char, shells, animal bones, and artifacts. • The soil has a petrocalcic horizon (calcrete) at less than 50 cm. • The soil has a fluctuating water table above limestone at ~2 m. • In 2009, we measured soil properties on Gumbo Limbo Island along with the soil water, slough water, and guano.

8. Soil Profile ^Au1 ^Au2 ^Au3 ^Bku ^Bkum ^BCku ^Cku1 • The soil is a series of former surface deposits of charcoal fires and cooking scraps, with some pottery and tools included. • The water table is at 110 cm this day. • The middle subsoil is cemented with secondary calcium carbonate and calcium phosphate.

9. Soil Closeup • Soil texture, bone and shell content are nearly identical above, in, and below the petrocalcic horizon. • Roots stop at the top of the petrocalcic.

10. Methods • Soluble P was measured by ICP directly in soil and offshore water and in bird guano droppings taken off plant leaves. • Total Pwas measured by HCl digestion in bulk unwashed soil (sieved to < 2 mm but not ground) and also in the water-washed sand fraction.

11. Results and Discussion • Bones > 2 mm made up 4 to 44% by volume but decreased sharply in the horizon just above the limestone and in the subaqueous soil offshore. • The reduced amount of very small bones just above the petrocalcic where roots and rainwater are concentrated indicate weathering and uptake by plants is taking place. The low amount offshore is due to absence of human activity and cooking.

12. Results Table 1. Particle Size of Lowest Three Horizons Hor. Sand Silt Clay Gravel Modifier Texture Class Name % weight % vol. ------------- < 2mm --------------- > 2mm   ^Cku2 64 32 4 19 Gravelly Sandy Loam ^2Cku3 82 15 3 19 Gravelly Loamy Fine Sand 3Ab 34 31 35 5 Clay Loam 4R ---------------- LIMESTONE ------------------------------------------------------ The sand is mainly bone and shell fragments except in the ^2Cku3 horizon. The gravel was mostly bones and shells, with some pottery and limestone. There were few bones and no artifacts in the lowest horizon.

13. Example 1: > 8mm Fragments in Horizon 2 (weathered) Bones Vertebrae Land Snail Pottery

14. Example 2: > 8 mm Fragments in Horizon 7 (coated by CaCO3) Vertebrae Land Snail Gar Scales Bones CaCO3

15. Table 2. Carbon and CaCO3 Hor. Org. C CaCO3 ---- % Soil < 2mm ----- 1 11.4 28 2 7.3 22 3 4.7 39 4 2.8 59CaCO3 accumulates just above the 5 1.4 34 petrocalcic where water is 6 0.0 41 extracted by plant uptake 7 0.0 32 8 0.4 30 9 0.6 27 10 7.460CaCO3is high in the older soil just above limestone R ----------------------------------------------------------------------- Organic carbon decreased with depth above the older buried soil. This slide should be converted into a histogram!!!

16. Table 3. Other P Sources P ppm Soil-Water 0.1 Open-Water Tr Guano 34 Elements by direct ICP analysis, no extraction used (Mullins and Heckendorn, 2005).

17. cm depth Total P in individually-measured fractions 50 100 150 200 0 % (wt) P in > 2 mm bones % (wt) P in < 2 mm soil Petrocalcic Horizon Fluctuating Water Table 0 10 20 30 40 50 percent P

18. Soil P Distribution # 1 • Soil water percolates through the rooted surface layers and may perch above the petrocalcic where roots concentrate. Large soft masses of CaCO3 reinforce this concept. • Organic acids and rainwater cause weathering of bone and allow uptake of P by plants above the petrocalcic. Underneath the petrocalcic there are no roots for plant uptake.

19. Soil P Distribution # 2 • The alkaline soil water causes precipitation of weathered phosphorus as apatite and prevents movement of P in the soil in soluble forms. • Bone content explains total P distribution and content. P movement to island tails may occur as plant leaves take up P from the soil if leaf litter is moved to the tails by wind, water or animals. Guano and dustfall may contribute small amounts of P to island heads and tails.

20. P Source or Sink? or Both? • The island soil is a large sink for P because it is a sink for bones brought in by humans and possibly animals. Now, only animals bring in bones. • The island soil is also a sink for guano P and windborne P, but they occur in trace amounts. • P in the upwelling groundwater is not a source because P is not mobile in the soil. Besides, the level of P in slough water is a trace amount. • The island plant leaf litter may be a source of P to island tails and nearby subaqueous soils.

21. Conclusions • P in bone fragments sufficiently explains the source, quantity and distribution of total phosphorus throughout the soil, although trace additions from the other sources are possible. • P cannot move in soil solution because of the high pH and excess free calcium. However, P and soil water can be taken up by plants, and weathering of sand-sized bone can occur just above the petrocalcic horizon. • Soil testing combined with archaeological evidence have preserved a record of island-building, soil weathering and secondary mineral precipitation.

22. Our Conclusion Following the Study Trace P from Plant Litter, Sediment moves High P in bones is not mobile in soil, but is taken up by plants

23. Acknowledgements • The South Florida Water Management District conducted some field work, provided air boat transportation, and funded the project. • Dr. Willie Harris at the University of Florida conducted some of the Total P lab analysis. • Doctoral candidate Maria-Theresa Grafconducted some field work and provided data, under direction of her advisor Dr. Gail Chmura of McGill University in Canada.