title: Overestimation of organic phosphorus in wetland soils by alkaline extraction and molybdate colorimetry.
abstract: Accurate information on the chemical nature of soil phosphorus is essential for understanding its bioavailability and fate in wetland ecosystems. Solution phosphorus-31 nuclear magnetic resonance (31P NMR) spectroscopy was used to assess the conventional colorimetric procedure for phosphorus speciation in alkaline extracts of organic soils from the Florida Everglades. Molybdate colorimetry markedly overestimated organic phosphorus by between 30 and 54% compared to NMR spectroscopy. This was due in large part to the association of inorganic phosphate with organic matter, although the error was exacerbated in some samples by the presence of pyrophosphate, an inorganic polyphosphate that is not detected by colorimetry. The results have important implications for our understanding of phosphorus biogeochemistry in wetlands and suggest that alkaline extraction and solution 31p NMR spectroscopy is the only accurate method for quantifying organic phosphorus in wetland soils.
authors.affiliation: Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancón, Republic of Panama. turnerbl@si.edu
authors.forename: Benjamin L
authors.initials: BL
authors.lastname: Turner
authors.forename: Susan
authors.initials: S
authors.lastname: Newman
authors.forename: K Ramesh
authors.initials: KR
authors.lastname: Reddy
mesh_terms: D003124:Colorimetry / Q000379:methods; D004784:Environmental Monitoring; D006878:Hydroxides / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008982:Molybdenum / Q000737:chemistry*; D009943:Organophosphorus Compounds / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis*; D012680:Sensitivity and Specificity; D012989:Soil Pollutants / Q000032:analysis*
chemical_list: D006878:Hydroxides; D009943:Organophosphorus Compounds; D012989:Soil Pollutants; C044659:molybdate; D010758:Phosphorus; D008982:Molybdenum