Factors influencing phosphorus levels delivered to Everglades National Park, Florida, USA.

Everglades restoration is dependent on constructed wetlands to treat agricultural phosphorus (P)-enriched runoff prior to delivery to the Everglades. Over the last 5 years, P concentrations delivered to the northern boundary of Everglades National Park (Park) have remained higher than the 8 μg L(-1)-target identified to be protective of flora and fauna. Historically, Everglades hydrology was driven by rainfall that would then sheetflow through the system. The system is now divided into a number of large impoundments. We use sodium-to-calcium ratios as a water source discriminator to assess the influence of management and environmental conditions to understand why P concentrations in Park inflows remain higher than that of the target. Runoff from Water Conservation Area 3A (Area 3A) and canal water from areas north of Area 3A are two major sources of water to the Park, and both have distinct Na:Ca ratios. The P concentrations of Park inflows have decreased since the 1980s, and from June 1994 through May 2000, concentrations were the lowest when Area 3A water depths were the deepest. Area 3A depths declined following this period and P concentrations subsequently increased. Further, some water sources for the Park are not treated and are impeding concentration reductions. Promoting sheetflow over channelized flow and treating untreated water sources can work in conjunction with constructed wetlands to further reduce nutrient loading to the sensitive Everglades ecosystem.