Phosphorus Concentrations in a Florida Everglades Water Conservation Area Before and After El Niño Events in the Dry Season

The Florida Everglades depends on both seasonal hydroperiods and low nutrient loading. This study investigated phosphorus concentrations in a 237,000-ha wetland complex in the Greater Florida Everglades known as Water Conservation Area 3A (WCA-3A). WCA-3A is south and downstream of Lake Okeechobee and most of the agricultural activity in the Everglades region, but immediately north and upstream of the Everglades National Park. The original goal of the study was to investigate if this water conservation area was serving as a phosphorus sink during a 9-month period (October 2015 to June 2016) that normally would have bracketed the dry winter season of south Florida. The beginning of 2016 brought several unexpected polar fronts with high rainfall, an unusual weather pattern in subtropical Florida later confirmed to have been caused by an El Niño condition in the Pacific Ocean. Samples taken at the beginning of the dry season (October through December 2015 during pre-El Niño conditions) showed low phosphorus concentrations. In April and June 2016 during post-El Niño conditions, monthly average total phosphorus concentrations averaged 7.1–7.2 ppb total phosphorus in inflow region of WCA-3A, significantly higher (P = 0.030 and 0.045) than 3.0 and to 2.6 ppb in the wetland’s outflow region. The wetland was found to be a sink of phosphorus with a 47% decrease in total phosphorus from north to south during this post- El Niño time. If future additional wetlands and water quality strategies are not in place to mitigate fluxes of phosphorus during future climate variations such as this El Niño condition, this wetland complex may take on an even greater role of protecting the water quality of the downstream Everglades National Park