Characteristics of Soil Phosphorus in Tree Island Hardwood Hammocks of the Southern Florida Everglades

The Florida Everglades is a P limited, freshwater wetland ecosystem. In many cases, soil P concentrations in tree islands in the Everglades greatly exceed concentrations in the surrounding marsh; however, little information is available regarding the characteristics of P in tree island soil. Surface soil samples from 26 tree islands were analyzed for total elements, distribution of soil P forms, and soil mineralogy. Total phosphorus (TP) concentrations of soil ranged from 0.764 to 88.1 g kg(-1). Most (>80%) of the TP in high P hammock soils was bound in an inorganic form (HCl-extractable), while organic P accounted for a relatively small (similar to 10%) proportion. Total P was positively correlated with non-carbonate inorganic soil matter (i.e., non-carbon matter, r = 0.98, p < 0.001), non-carbonate calcium (NCCa, r = 0.98, p < 0.001), and HCl-extractable phosphorus (HCl-P, r = 0.997, p < 0.001). Apatite was identified by X-ray diffraction (XRD) in soils with elevated P concentration. These soils also contained bone fragments. The high proportion of HCl-P observed in tree island soil coupled with a positive relationship between NCCa and P concentration is evidence for an exogenous P source. The presence of apatite and bone fragments in tree island soils indicates that deposition of biogenic apatite contributes to the soil P pool.