DISTRIBUTION OF ORGANIC AND INORGANIC PHOSPHORUS COMPOUNDS IN MARINE AND LACUSTRINE SEDIMENTS: A 31P NMR STUDY

Abstract

Solution 31P NMR spectroscopy has been used for the characterization of different classes of organic and inorganic phosphorus compounds in a number of different marine and lacustrine sediment environments. All samples contain orthophosphate mono- and di-esters of which the former is always the major constituent. Of possible orthophosphate mono-ester candidates, inositol phosphates may be of importance. The amount of orthophosphate di-esters is much higher in the reduced sediments from the Baltic Sea than in those areas with anoxic/suboxic conditions, indicating a more efficient decomposition of di-esters in oxic environments. The same situation was also observed in the lake sediment profiles. Pyro- and polyphosphate are found in the oxic sediments from the lakes whereas no sign of such compounds could be seen in the Baltic Sea sediment samples. Redox variations (lake samples) and cation strength variations between the sea water and the lacustrine water will most likely be the main explanation for the observed distribution patterns of pyro- and polyphosphate. Small but sharp peaks indicate the occurrence of phosphoric acids in a sediment from the southern Baltic Sea. Several other unidentified peaks were also observed, some of which could be assigned to aromatic di- and mono-esters.