In this study, molecular compositions of cyanobacteria, suspended matter, and surface sediments in the Dianchi Lake, a highly eutrophic lake, were investigated by solution and solid-state 31P nuclear magnetic resonance (NMR) spectroscopy. A solution-state 31P NMR spectral analysis of NaOH-EDTA-extracted samples revealed the presence of orthophosphate (ortho-P, 48.5%-91.2% of the total extracted phosphate), orthophosphate monoester (mono-P, 7.3%-43.9%), orthophosphate diester (diester-P, 0.9%-3.9%), and pyrophosphate (pyro-P, 0.7%-5.5%). The organic phosphorus (Po) distribution in suspended matters and cyanobacteria was relatively similar but different from surface sediments. The inorganic phosphorus (Pi) distribution in suspended matters and surface sediments was slightly similar. Results of the solid-state 31P NMR spectral analysis of non-extractable residue showed that cyanobacteria and suspended matter contain a large proportion of Po and poly-P. For surface sediment, only metal-bonded pyro-P and a high proportion of ortho-P were detected. The solid-state 31P NMR spectra results of extracted residual indicated that several of the pyro-P bound to metals and other Pi or Po compounds associated with mineral phases in suspended matter and surface sediment are non-extractable. This result revealed that a high proportion of biogenic phosphorus is bioavailable. These results verify the process of biogenic poly-P regeneration in the Dianchi Lake given that Po, poly-P, and pyro-P are predominant in cyanobacteria and can be released into lake water through chemical and biological degradation, thus further worsening eutrophication.
Keywords: Eutrophication; Molecular composition; Nuclear magnetic resonance; Nutrients; Phosphorus; Solid-state (31)P.
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