Land use-driven historical soil carbon losses in Swiss peatlands

Context Globally, the intensive use of peatlands contributes substantially to greenhouse gas emissions. The intensification of peatland use has led to increasing carbon (C) losses over the last centuries, but without historical emissions data, these increases and cumulative emissions are difficult to quantify. Objectives To understand the magnitude and development of soil C losses through peatland drainage in Switzerland through time, and to relate the situation of peatlands today to this historical development. Methods Historical records and a published estimate of the peatland extent are used to estimate peatlands' original extent and C stocks, and to understand trends in the historical use of peatlands. Land use-specific emission factors are applied to estimate the C emission through drainage over the last 300 years. Results Ca. 15 to 55 Mt C have been lost through peatland drainage in Switzerland. Despite a decrease in the area of organic soils, annual C emissions have increased considerably especially since the mid-twentieth century due to intensification of their use, particularly for agriculture. This C loss is a magnitude greater than that lost through extracted peat. Remaining C stocks approximate those lost over the last 300 years. Conclusions The rate of peatland surface loss in Switzerland is typical of European wetlands. Uncertainties in emission factors remain high and should be refined to justify any mitigation strategies. Although peat is no longer mined in Switzerland, future C emissions from peatlands will remain high as long as the effects of drainage networks and their current intensity of use persist.