Holocene limnologic evolution and river flood history from a multi-basin sinkhole lake in Washington County, Florida

Recent floods in northern Florida have had costly and devastating consequences. Intense rainfall causes extraordinary floods in the wide and flat floodplain of the Choctawhatchee River, often spanning several miles on either side of the river, destroying farm land, homes, and businesses despite the presence of engineered levee systems along portions of the river. The instrumental records of flood history and climate variations are too short to gauge how the frequency of floods varies on centennial and millennial timescales, which is necessary to identify the mechanisms that drive flooding across a variety of environmental and climatic conditions and to improve natural hazard prediction and mitigation. Reconstructing long climate records beyond the instrumental record is essential to our understanding of the cause and timing of such events. We present a new lacustrine sediment record of riverine flood deposits in NW Florida during the Holocene from Red Bug Pond. We identified flood deposits and determined the long-term depositional history of two depositional basins in Red Bug Pond using grain size variations, XRF elemental abundances, loss-on-ignition (LOI), and the C to N ratio of organic matter. ²¹⁰Pb and ¹⁴C chronologies indicate that sediment accumulated continually during the past 9000 years. LOI and C/N highlight a long-term transition in the depositional environment from dominantly peat to sapropel that coincides with a long-term trend in inorganic sediment accumulation from coarse sand to fine silt. Brief increases in coarse grain and Ti abundances superimposed on this long-term trend are interpreted as event-scale floods. Major flooding during the Holocene appears to be closely related to changes in regional water balance, suggesting that the water table depth plays a significant role in flood occurrence at the millennial timescale, similar to the historical relationships between flooding, water balance, and heavy rainfall.