POLYPHOSPHATE IN LAKE-SEDIMENTS - P-31 NMR-SPECTROSCOPY AS A TOOL FOR ITS IDENTIFICATION

Variations in the nonreactive P content of lake sediments as a consequence of changing redox conditions suggest that microorganisms may contribute to uptake and release of P. In this study, 31-50% of the nonreactive P was identified as polyphosphate (poly-P) in NaOH extracts of sediments from eutrophic Lake Baldegg and oligo-mesotrophic Lake Lucerne by means of P-31 NMR spectroscopy. Poly-P was present in surface sediments but not in deeper sediment layers. In samples where poly-P was detected, analysis under a scanning transmission electron microscope equipped with energy-dispersive X-ray spectroscopy indicated the presence of sediment bacteria containing P-rich granules. Although poly-P is stable in pure NaOH solution, it partially hydrolyzes during and after sediment extraction with NaOH. Cracking of poly-P molecules to shorter fragments is, however, much slower if the sediment is pre-extracted with EDTA and NaOH is replaced by a mixture of NaOH/EDTA to extract nonreactive P from sediments.