| The Everglades is P-limited, and receives P-enriched agricultural runoff. Because Fe-binding of P is redox sensitive, its role in P-storage in drained and flooded Everglades Histosols is a key area of inquiry. Three related questions are addressed: (1) Are techniques used for quantifying Fe-bound P in Everglades soils accurate? (2) Are Fe and P correlations in Everglades Histosols related to land use? (3) What conditions favor Eh reduction during flooding of an Everglades Histosol?; Question 1. Sequential extractions utilizing 0.1N NaOH to extract Fe-bound P, followed by 0.5N HCl for Ca-bound P, are commonly applied to quantify Fe-bound P in Everglades Histosols. I performed two experiments to test if Ca-resorption of P during the NaOH-extraction causes underestimation of Fe-bound P: (a) A mix of 40 mg synthetic Fe-bound P and 160 mg CaCO 3 was sequentially extracted. Only 6% of the Fe-bound P was recovered as Fe-bound P, with 55% recovered as Ca-bound P. (b) Fe-bound P was added to Everglades soil. Only 38% was recovered as Fe-bound P. An equal amount was recovered as Ca-bound P.; Question 2. I found strong positive correlations between total soil Fe and P in farmed soil (sugarcane cultivation), consistent with the hypothesis that as organic matter mineralizes, the potential for Fe to bind P increases. Negative correlations in P-enriched wetland soils (receiving 150 ug/L P water), concurrent in depth with the time nutrient enrichment began, are consistent with previous research indicating organic matter dominates P-storage in enriched areas.; Question 3. I found bioavailable carbon-limited soil reduction in an Everglades agricultural soil. Reduction response to added carbon was rapid (<48 hours to approximately −200 mv). Eh did not respond to P additions, even when carbon limitation was removed by addition of glucose. Plant material additions resulted in decreased Eh.; These results suggest that, in Everglades Histosols; (1) Fe-bound P is underestimated by sequential extractions. (2) Fe-bound P is most important in oxidized agricultural Histosols, and least important in enriched flooded soils. (3) Redox potentials low enough for Fe reduction can occur if agricultural soils are flooded with added available carbon (i.e. plant material). |
