Drivers of CO2 emission from Danish agricultural peat soils

Peatlands store a significant proportion of global carbon, but their drainage and conversion to agricultural land have resulted in substantial CO₂ emissions, intensifying climate change. This study investigates the relationship between CO₂ emissions and soil bio-physical-chemical properties. The work is a step toward identifying priority areas of organic-rich soils most suitable for rewetting to support Denmark’s goal to cut agricultural GHG emissions by 2030. By understanding the driving factors for high CO₂ emissions, the study aims to support the development of targeted and efficient rewetting strategies.

A systematic soil sampling campaign was conducted across Denmark, where a total of 120 soil samples were collected from agricultural peatlands. The samples were analyzed for e.g., soil organic carbon content, pH, electrical conductivity, soil water retention, air diffusivity, eDNA, water repellency, and soil organic matter quality (temperature-controlled pyrolysis, Rock-EVAL). Relative CO₂ emissions were assessed through laboratory incubation experiments using undisturbed soil cores (100 cm³) equilibrated to -100 cm H₂O of soil-water matric potential (pF2).

Machine learning regression analysis, coupled with interpretation of feature importance via Shapley values, highlighted that organic matter quality (Rock-Eval indices), total nitrogen content, pH, and depth to the groundwater table at sampling were the primary drivers of CO₂ emission rates, while vegetation and microbial alpha diversity had little predictive value.

These findings advance the understanding of the key drivers of CO₂ emissions from peatlands. Modelling approaches will further explore these relationships and provide insights for developing more effective rewetting strategies to improve carbon sequestration and mitigate climate change.

Keywords: peatlands, CO₂ emissions, soil properties, rewetting, climate change mitigation