COMBINED CHEMICAL AND 31P-NMR SPECTROSCOPIC ANALYSIS OF PHOSPHORUS IN WETLAND ORGANIC SOILS1

Abstract

The organic P (Po) status of wetland soils has a large influence on the internal P cycling, and therefore on the biological productivity and water quality, of wetland ecosystems. Chemical extraction and solution-state 31 P-nuclear magnetic resonance (NMR) spectroscopy were used to identify and quantify the distribution of the major forms of P in organic soils of three created wetland sites-Apopka Marsh, Eustis Muck Farm, and Sunny Hill Farm (SHF). Spectra were obtained on 0.25 M NaOH-0.05 M EDTA extracts of soils with and without previous chemical removal of labile soil P. 31 P-NMR spectral analysis of the NaOH-EDTA extracts revealed the presence of inorganic ortho P (Pi), ortho-P monoesters, and ortho-P diesters. Chemically determined proportions of total P (TP) as Pi in the NaOH-EDTA extracts were similar to those obtained by 31 P-NMR. P monoester was the predominant P form in Apopka Marsh (51% TP) and SHF (59% TP) soils. The Eustis soil contained a high proportion of Pi (65% TP), and the SHF soil contained significant (10% TP) P diester. Chemical removal of labile Pi, using 1 M KCl and 0.5 M NaHCO 3 , enhanced the quality of all NMR signatures and demonstrated that not all P diesters are removed in the NaHCO 3 extract. NMR spectra were obtained with acquisition times ranging from 0.5 to 1.2 h, which represents a significant reduction in data acquisition times reported in the previous 31 P NMR studies of soil extracts.