Influence of Carbon Lability and Flooding Treatment in Potential Oxidation of Histosols in the Everglades Agricultural Area.

Drainage of the Everglades Agricultural Area (EAA) soils has resulted in soil subsidence. Subsidence rates have been reduced compared to previously reported rates. Increases in mineral content, recalcitrant carbon, and higher water tables attributed to best management practices, are considered possible causes for this reduction. The purpose of this research is to determine how soil C lability and water management affect subsidence rates. To determine the influence of these factors in soil subsidence, oxidation rates (CO₂ efflux) of shallow and deep EAA soils exposed to four water management treatments are being evaluated along with measurements of NO₃-N, NH₄-N, soluble organic nitrogen (SON), and dissolved organic carbon (DOC) performed on leachate. Additionally, a C fractionation procedure is being used to determine the size of the labile and recalcitrant C pools in these soils. Preliminary results indicate that soils exposed to 2 days flooding – 12 days draining cycles during the summer season have the highest CO₂ efflux rates (52 - 157 mg of CO₂ C m^-2 h^-1). The NH₄-N in leachates is highest in flooded soils (0.46 to 0.86 mg L^-1) compared to drained soils, whereas NO₃-N is highest in drained soils with concentrations as high as 395 mg L^-1. Similarly, the SON and DOC have the highest concentrations in drained soils, in the case of DOC, deep soils appear to have higher concentrations (54 - 74 mg C L^-1) compared to shallow soils (35- 39 mg C L^-1). Organic matter and the hot water extracted C (the most labile C pool) are higher in deep soils compared to shallow soils and decrease with soil depth. Preliminary results indicate that water management is of great importance controlling C and N cycling in subsiding histosols. Results also show that the distribution of soil C pools varies with depth in these soils.