Organic Soils

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Peat-containing drained organic soil with sediment interlayers in the Swiss Seeland.

Organic soils are important carbon stores. In bogs, they are formed by the incomplete (anaerobic) decomposition of plant matter in the water-saturated soil. When these soils are drained or damaged, they become a major and persistent CO2 source. 

The use of drained organic soils for arable farming or grazing therefore leads to emissions of this greenhouse gas. In Switzerland, some bogs have been intensively drained or mined for peat since the early 18th century. Organic soils, which today are for the most part used for agriculture and forestry, occupy a surface area of around 30,000 ha, with the agriculturally used organic soils having undergone more degradation than those under forest. 

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Surface areas of Swiss organic soils according to Wüst-Galley et al., 2015

Despite their previous use, around 30 million tonnes of carbon is still stored in organic soils. These soils continuously lose carbon, however, with those under agriculture losing approx. 600,000 tonnes  CO2-equivalent per year. Since 2018, at a site in the St. Gallen Rhine Valley, we have been studying whether the carbon stocks in organic soils can be preserved despite their agricultural use through cover fills with mineral soil, or whether the peat will continue to decompose. For this, the exchange of greenhouse gases CO2, methane and nitrous oxide is being measured over a period of several years.

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Micrometeorological measurement of CO2 and methane fluxes on a drained fen covered with mineral soil

In order to reduce the sometimes very high CO2 emissions from organic soils, areas are repeatedly rewetted, i.e. returned to an original state. Such measures are also worthwhile within the context of trading CO2 certificates. Rewetting may even yield new peat growth. Through the use of modern molecular and isotope-based methods, we study whether the accumulation of peat outweighs its degradation, and whether the organic soil is once again becoming a carbon sink.

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