The Everglades, located in South Florida, accumulated organic soils (peats) for over 5000 years. The northern portion of the natural Everglades, called the Everglades Agricultural Area (EAA), has been drained since 1914 AD, and has experienced soil subsidence since then. Rates of soil subsidence in the EAA have been reduced from 2.5 cm yr-1 in the 1950s to 1.45 cm yr-1 in the 1990s due to changes in crop and water management. The purpose of this study was to adapt a model of peat dynamics to the EAA based on historic and current data to explore parameter estimation and to identify information/parameters that might be useful to model and predict soil subsidence in organic soils. The model was adapted to represent subsidence in the EAA by introducing an intermediate peat layer that experienced drainage and compaction in addition to two peat layers (drained and flooded). Historic data on peat accumulation and subsidence rates were used in an optimization procedure for parameter estimation, a sensitivity analysis was performed, and the model was used to predict subsidence under future management scenarios.
Results/Conclusions
Model optimization predicted a predrainage peat thickness of 2.57 m with nearly linear peat accumulation prior to drainage, and a current subsidence rate of 0.65 cm yr-1. Sensitivity analyzes indicate that initially soil subsidence was strongly influenced by compaction, and currently is influenced mostly by water tables. Model prediction of future scenarios indicate that increasing biomass input to the soils from the current dominant crop (sugarcane) has the greatest potential to reduce future subsidence, while increasing the water table depth and reducing the aerobic decomposition rate by improving cover crops could also help reduce subsidence. To decrease subsidence in the EAA and improve soil conservation, farm practices that increase biomass input and water table depth would need to be implemented. Adding a seasonal water table component to this model and improving estimates of biomass input to the soil are the next steps to improve predictions of soil subsidence in the EAA under alternative management scenarios. Additionally, future modeling of drained peatlands should focus on the influence of carbon pools at different stages of the subsidence process and subsidence caused by loss of dissolved organic carbon in drainage.