Isolated Wetlands within the Lake Okeechobee Drainage Basin of Florida: Source and Sink of Phosphorus(pp.1-52)
Authors: (Jehangir H. Bhadha, Everglades Research and Education Center, University of Florida)
Abstract: Deteriorating water quality of Lake Okeechobee due to excess phosphorus (P) from beef cattle and dairy operations from surrounding basins have been an environmental concern for many decades within the state of Florida, USA. During this period, isolated wetlands within these basins have been extensively ditched and drained to improve farmlands and facilitate agriculture. Restoring the wetlands has been proposed as one of the strategies to reduce overland P loss by retaining it in the soils, and/or sequestered by aquatic vegetation. Phosphorus fluxes associated with soils and shallow pore water from agricultural lands can contribute to internal loading, which could undermine the effective use of these wetlands. Soil properties of deeper horizons within impacted isolated wetlands are rarely investigated due to the assumption that these wetlands are flooded, and that biogeochemical interactions occur at the soil-water interface. However, prolonged droughts and periodic draining can leave the wetlands dried for most of the year, and water tables can drop over a meter below the ground surface. In which case, characterizing the soils from deeper horizons can be useful especially if subsurface lateral groundwater flows are dominant within the region.
External loading of P from agricultural areas has been addressed through the implementation of best management practices, and interception strategies that involve the restoration of isolated wetlands in the state of Florida. However, internal loading through impacted soils, has prevented the rapid improvement of water quality within the basin. In addition, wetlands that are exposed to less than 100% hydroperiods can also be affected by drawdown events that increase soil oxidation and subsequent mobilization of P during reflooding. It is hypothesized that under fluctuating water table conditions, the internal load of P associated to advection may be significant compared to diffusion.
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