Leaching Potentials of Nitrogen and Phosphorus in Substrates of Soil Disposal Mounds in Florida's Everglades*

Hole-In-The-Donut (HID) is one of the most important restoration sites in the unique ecosystem of the Florida Everglades. The undertaking restoration project in HID is to reestablish native vegetation that is only supported by the original nutrient-poor soils and involves excavation and the permanent disposal of the exotic plants and the rock-plowed substrates. Currently, the excavated substrates are being stockpiled in HID areas. Nutrient leaching, particularly nitrogen (N) and phosphorus (P), from the soil disposal mounds and its potential subsequent transport to surrounding wetlands are among environmental concerns because the rock-plowed substrates had been farmed intensively and fertilized for more than 30 years. The primary goal of this study was to assess the leaching potentials of N and P in the soil disposal mounds and provide a guideline for the development of management strategies. Results derived from the column leaching study showed that the average peak concentrations were 9.8 and 13.9 mg L^?1 for NO₃-N and NH₄-N, respectively, and 26.2 and 100.7 μg L^?1 for PO₄-P and total P, respectively. Potential leaching rates per year ranged from 1.3% to 4.4% for NO₃-N, 6.2% to 11.2% for NH₄-N, 4.5% to 7.3% for inorganic N, and 0.005 to 0.006% for total P. Although the heterogeneous nature of the substrates in the soil disposal mounds resulted in high variation among the sampling sites studied, the results demonstrated that the storage of the abandoned agricultural soil mixed with shredded Brazilian pepper in mounds appears to be a viable method of disposal.