The influence of degree of peat decomposition on phosphorus binding forms in fens

Re-wetting of drained fens can release phosphorus, introducing a eutrophication risk for associated aquatic ecosystems. Characterisation of the different forms of organic and inorganic bound phosphorus in the peat is an important step towards the development of tools for assessing the level of risk attached to individual re-wetting projects. In the work reported here, a sequential extraction (fractionation) method was used to distinguish the following P binding forms:1. labile P, detected by NH4Cl extraction;2. redox-sensitive P, detected by Na2S2O4/NaHCO3 extraction;3. P adsorbed to metal oxides, detected by HCl extraction;4. P bound to humic substances, detected by NaOH extraction; and5. organic and refractory bound P, detected using H2SO4 and H2O2.Special attention was paid to the degree of decomposition (DPD) of the peat, and metal concentrations were measured in selected fractions. Higher P concentrations were found in completely humified than in little humified peat for all fractions except the NH4Cl (labile P) fraction, where P content increased as DPD decreased. As only 1% of total phosphorus (TP) was present as labile P, the results indicate that the decisive horizons for nutrient release after re-wetting are those that are completely humified due to pedogenetic changes. The principal metal sorption partner for P was Fe.