142-9 Solubility of Phosphate Minerals In the Pine Rockland's Calcareous Soils After Prescribed Fire.



Monday, October 17, 2011
Henry Gonzalez Convention Center, Hall C, Street Level

Chung Nguyen1, Yuncong Li1, James Snyder2, Rafael Munoz-Carpena1, Bruce Schaffer1 and Nicholas Comerford3, (1)University of Florida, Gainesville, FL
(2)Big Cypress National Preserve Field Station, USGS, Florida Integrated Science Center, Ochopee, FL
(3)North Florida Research and Education Center, University of Florida, Quincy, FL
Phosphorus is a limiting factor in the Pine Rockland slash pine forest (Pinus elliottii var. densa) because of high soil pH (average 7.5) and abundance of Ca, Mg, Fe, and Mn. Increase in available content of P after fire can result in alterations of P-mineral solubility in soils. The objective of this research was to assess impacts of fire on solubility of phosphate minerals by constructing activity diagrams between HPO42- versus with different pH values. Stability diagrams of phosphate within a presence of monocalcium-P, monetite, dicalcium-P, beta-tricalcium-P, octacalcium-P, hydroxyapatite, strengite, vivianite, Mg3(PO4)2, MgHPO4:3H2O, Mn3(PO4)2, and MnHPO4 were constructed basing on ionic activities simulated from the Minteq’s geochemical models at the atmospheric CO2 partial pressure of 0.00038 atm. The input data for the Minteq’s equilibrium speciation models included soil pH, ionic strength, and concentrations of PO4-P, Ca, Mg, K, Na, Fe, Mn, Zn, Cu, NH4+, and NO3- extracted from soil solution. Ionic strength was calculated from EC (electrical conductivity) by Marion-Babcock equation. Our result showed that monocalcium-P and strengite were not present in the diagram, vivianite mineral was at equilibrium in pre-fire while other selected phosphate minerals were under-saturated, the equilibrium shifted to MnHPO4 in 14-day postfire, both vivianite and MnHPO4 reached the equilibrium in 30-day postfire, and the equilibrium went back the pre-burn status in 180 days after fire. With these findings, we concluded that solubility of phosphate in the Pine Rockland forest ecosystem was primarily controlled by vivianite and MnHPO4.
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