Long-term carbon loss and CO₂-C release of drained peatland soils in northeast Germany

Peatlands are common in many parts of the world. Draining and other changes in the use of peatlands increase atmospheric CO₂ concentration. If we are to make reliable quantitative predictions of that effect, we need good information on the CO₂ emission rates from peatlands. The present study uses two different methods for predicting CO₂-C release of peatland soils: (i) a 40-year field investigation of balancing organic carbon stocks and (ii) short-term CO₂-C release rates from laboratory experiments. To estimate long-term losses of peat, and its resulting C input to the atmosphere, we combined highly detailed maps of surface topography and its changes, and the organic C contents and bulk densities of a drained peatland from different years. Short-term CO₂-C release rates were measured in the laboratory by incubating soil samples from several soil horizons at various temperatures and soil moistures. We then derived nonlinear CO₂-C production functions, which we incorporated into a numerical simulation model (HYDRUS). Using HYDRUS, we calculated daily soil water components and CO₂-release for (i) real-climate data from 1950 to 2003 and (ii) a climate scenario extending to 2050, including an increase in temperature of 2°C and 20% less rainfall during the summer half year, i.e. from April to September inclusive. From our field measurements, we found a mean annual decrease of 0.7 cm in the thickness of the peat. Large losses (> 1.5 cm year⁻¹) occurred only during periods when groundwater levels were low (i.e. a deep water-table). The annual CO₂-C release results in a mean loss from the peat of about 700 g CO₂-C m⁻², mostly as a direct contribution to the atmosphere. Both methods produced very similar results. The model scenarios demonstrated that CO₂-C loss is mainly controlled by the groundwater (i.e. water-table) depth, which controls subsurface aeration. A local climate scenario estimated a c. 5% increase of CO₂-C losses within the next 50 years.