OBSERVATIONS ON THE PETROGRAPHIC AND CHEMICAL EFFECTS OF THE DROUGHTS AND FIRES OF 2007 AND 2011 ON THE PEAT DEPOSITS AND PEAT-FORMING ECOSYSTEMS OF THE OKEFENOKEE SWAMP

Recent prolonged droughts in the southeastern US and subsequent widespread fires in 2007 and again in 2011 caused loss of much of the emergent vegetation over large portions of the Okefenokee Swamp. Changes in surface vegetation, peat surface morphology, peat thickness, and petrographic and chemical composition were investigated by comparisons of data from sites studied here in the 1980’s with those revisited after these fires. Preliminary results reveal that, except in marginal portions of the deposit, significant losses of peat were generally small and primarily restricted to localized areas where the peat was previously mounded or domed. However, in some very limited areas, as much as 62 cm of peat were lost to ground burns, sometimes resulting in massive toppling of trees by root burn. Evidence is also provided for severe ubiquitous “deflation” of peat surfaces prior to and independent of burning, causing many domed root-supported mounds to protrude above the surrounding depressed peat surface, making them more prone to burning. In some of these same areas, pockets of ash composed predominantly of biogenic silica (freshwater sponge spicules) and clays were found on top of autochthonous charcoal, followed by a sharp contact with unburned peat beneath. An unusual petrographic phenomenon was sometimes observed just at this contact. Here many of the tissues were transformed to an orange color (vitrinized?), presumably by the oven effect of the overlying denser ash or by vaporization of the moisture at the contact. Sponge spicules from two of these ash sites are being investigated microscopically as “paleothermometers” to determine the temperatures of these peat burns. Preliminary results reveal that these ash layers reached temperatures of at least 700-800^o C. Additional trace element studies reveal that, nearly all trace elements increased initially at these intensely burned sites causing ephemeral algal blooms and potential increases in aliphatic hydrocarbons.