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

Abstract

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 À1 ) 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 À2 , 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.

The contribution of mineralization to grassland N uptake on peatland soils with anthropogenic A horizons

“…Drainage of peat soils results in mineralization, shrinkage and subsidence which also changes the bulk density. The observed bulk density of the topsoil in our study was found to be about twice as high compared with the 45-55 cm layer, a trend similar to the findings of Schothorst (1977) and Kluge et al (2008). This higher bulk density closer to the soil surface will be partly due to shrinkage and partly due to the anthropogenic addition of solid sand size particles.…”

“…This estimate approaches the observations of Kluge et al (2008) for extensively managed grasslands with shallow groundwater tables in East Germany. For recent decades, they reported a mean decrease in peat thickness of 2.7 mmyr −1 for peatland soils with groundwater levels fluctuating between 50 and 70 cm below the surface.…”

“…Long-term agricultural use of peatland soils may result in drastic subsidence of the land surface (Kluge et al 2008). Some peatland soils, such as those located in the lower reaches of the Rhine-Meuse Delta, contain large amounts of nitrogen (N) and peat decomposition is a substantial contributor to the mineral N supply of crops.…”

Can a bog drained for forestry be a stronger carbon sink than a natural bog forest?

“…A similar approach was used by Leifeld et al (2011a), who estimated mean carbon loss rates ranging from +140 to +490 g C m −2 a −1 for two drained pre-Alpine mountain bogs. Kluge et al (2008) modeled a larger mean annual peat-carbon loss of about +700 g C m −2 a −1 for an agricultural peatland in northeastern Germany. Reported soil emission rates of forested peatlands span a wide range, including our rough estimate.…”

Biogeochemische Stoffkreisläufe

“…Für ein flussnahes Niedermoor in Nordostdeutschland wurden durchschnittliche Abbauraten der organischen Bodenhorizonte von 0,7 cm Mächtigkeit pro Jahr über einen Zeitraum von 40 Jahren gemessen (Kluge et al 2008). Für ein zukünftiges Klima mit im Schnitt 2 °C höheren Temperaturen und 20 % ge-ringerem Niederschlag im Sommerhalbjahr sagt dieselbe Studie eine Zunahme der Abbaurate um ca.…”