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TECHNICAL REPORTS

Ecological Risk Assessment

Development of Indices to Predict Phosphorus Release from Wetland Soils

^a Geological Sci. Dep., 241 Williamson Hall, P.O. Box 112120, College of Liberal Arts and Sciences, Gainesville, FL 32611-2120
^b Soil and Water Sci. Dep., 106 Newell Hall, P.O. Box 110510, Institute of Food and Agricultural Sciences, Gainesville, FL 32611-2120

^* Corresponding author (vdn{at}ufl.edu).

Received for publication May 14, 2008. The U.S. Environmental Protection Agency created the Clean Water Action Plan to develop nutrient criteria for four water body types: lakes and reservoirs, rivers and streams, estuaries, and wetlands. Significant progress has been made in open water systems. However, only areas in and around the Florida Everglades have had numeric nutrient criteria set, due to the complexity, heterogeneity, and limited information available for wetlands. Our objective was to evaluate various soil tests to predict significant P release potential of soil in wetlands. A total of 630 surface soil samples (0–10 cm) were collected for this study from four southeastern states: Florida, Alabama, Georgia, and South Carolina. Soil samples were collected from the center of wetlands, the edge of the wetlands, and from adjacent uplands. The phosphorus saturation ratios (PSR), calculated using P, Fe, and Al molar concentrations from Mehlich 1 (M1-PSR), Mehlich 3 (M3-PSR), and oxalate (Ox-PSR) extractions and the amount of P extracted by different extractants were used to predict P loss potential from a soil. Total phosphorus (TP) concentration in wetland soils, estimated as the 75th percentile of the distribution of least impacted wetland soils as an example, was approximately 550 mg kg^–1. Based on this reference background condition, procedures for obtaining threshold values for P release to the surrounding water bodies were developed and threshold values calculated: M1-P = 24 mg kg^–1, M3-P = 44 mg kg^–1, Ox-PSR = 0.079, M1-PSR = 0.101, and M3-PSR = 0.067.

Abbreviations: DPS, degree of phosphorus saturation • M1-Al, M1-Fe, and M1-P • Mehlich 1-extractable aluminum, iron, and phosphorus • M3-Al, M3-Fe, and M3-P, Mehlich 3-extractable aluminum, iron, and phosphorus • Ox-Al, Ox-Fe, and Ox-P, oxalate-extractable aluminum, iron, and phosphorus • PSR, phosphorus saturation ratio • M1-PSR, phosphorus saturation ratio calculated as M1-P/(M1-Fe + M1-Al) • M3-PSR, phosphorus saturation ratio calculated as M3-P/(M3-Fe + M3-Al) • Ox-PSR, phosphorus saturation ratio calculated as Ox-P/(Ox-Fe + Ox-Al) • STP, soil test phosphorus • TP, total phosphorus • WSP, water-soluble phosphorus