Long‐term carbon loss and CO ₂ ‐C release of drained peatland soils in northeast Germany

Summary Peatlands are common in many parts of the world. Draining and other changes in the use of peatlands increase atmospheric CO 2 concentration. If we are to make reliable quantitative predictions of that effect, we need good information on the CO 2 emission rates from peatlands. The present study uses two different methods for predicting CO 2 ‐C release of peatland soils: (i) a 40‐year field investigation of balancing organic carbon stocks and (ii) short‐term CO 2 ‐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 CO 2 ‐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 CO 2 ‐C production functions, which we incorporated into a numerical simulation model (HYDRUS). Using HYDRUS, we calculated daily soil water components and CO 2 ‐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 CO 2 ‐C release results in a mean loss from the peat of about 700 g CO 2 ‐C m −2 , mostly as a direct contribution to the atmosphere. Both methods produced very similar results. The model scenarios demonstrated that CO 2 ‐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 CO 2 ‐C losses within the next 50 years.