Peat bog restoration by floating raft formation: the effects of groundwater and peat quality.
1. A prerequisite for the restoration of desiccated bog remnants is rewetting the peat surface. Frequently in Europe, extensive areas are flooded in order to maximize water retention, and growth of peat mosses is often observed in the shallow zones. In deeper waters, regeneration appears to depend on whether residual peat will become buoyant and form floating rafts. 2. In order to study the initial stages of peat bog regeneration, conditions required for peat buoyancy were studied on peat monoliths collected from three cut-over bog remnants in the Netherlands. The effects of different peat quality and water chemistry on buoyancy of the monoliths, as well as growth of Sphagnum cuspidatum and nutrient availability, were followed in a glasshouse experiment. 3. Both groundwater and peat quality affected the buoyancy of the monoliths and the growth of S. cuspidatum. When groundwater containing bicarbonate (1 mmol l-1 HCO3-, pH 6.0) was applied, the pH of peat monoliths increased from c. 3.5 to c. 4.5 due to acid buffering. As a result, two of the peat types became more buoyant and the concentration, production and emissions of methane (CH4) increased. It was concluded that the increase in CH4 production, induced by the increased pH, was responsible for the buoyancy. 4. When groundwater contained both HCO3- (1 mmol l-1) and sulphate (1 mmol l-1), pH was further increased to approximately pH 5.0 due to alkalinity generated by the SO42- reduction process. CH4 production, however, decreased because of interference from the SO42-, as confirmed in additional incubation experiments. Phosphate concentrations, however, greatly increased in the HCO3-/SO42- addition treatment due to the interaction between sulphide and iron phosphate precipitates. 5. In one of the peat types, treatments did not influence CH4 production and buoyancy, most probably because of its low decomposability. The chemical characteristics of the peat, notably the concentrations of lignin and soluble phenolics as well as C:N, C:P and C:K ratios, were all higher than in the other two peat types. 6. The increase of S. cuspidatum biomass during the experiment appeared to be strongly related to the N:P ratios of the capitula, which differed considerably among the three peat types. 7. We conclude that when bog remnants are inundated the prospects for bog regeneration are largely determined by peat quality and water chemistry. Peat mats with low concentration of lignin and phenolics and low C:N ratios are most likely to become buoyant in water with a higher pH, so providing suitable environments for Sphagnum species. When peat quality is inadequate, either shallow inundation or the addition of suitable peat from elsewhere is indicated.