TRANSFORMATION OF PHOSPHORUS SPECIES IN SETTLING SESTON AND DURING EARLY SEDIMENT DIAGENESIS

Sequential P extraction was combined with electron microscop and X-ray spectroscopy to characterise various P species and to study their tra nsformation in settling seston and in recent sediment. During early di agenesis most of the particulate P formed in the water was redissolved . No net transformation into species that would resist dissolution was observed. It was shown that the phosphorus (P) content and the P flux of settling particles varied seasonally over one order of magnitude p articles became enriched with reductant soluble P (BD-P) while settlin g through the hypolimnion changes in BD-P were highly significantly co rrelated with changes in reductant soluble iron (BD-Fe) bacteria oxidi sing Fe and Mn seemed to be mainly responsible for this increase in P concentration other fractions including organic P did not change durin g sedimentation most of the organic P and of the Fe bound P and 70 % o f TP was released from the sediment during early diagenesis the sedime nt surface did not act as a trap for P migrating upwards from deeper s ediment layers CaCO3 sedimentation contributed little to P sedimentati on but significantly to the permanent burial of P.