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 degrees 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.