Greenhouse gas emissions from compacted peat soil

Abstract: Cultivated peat soils are a main driver for CO2 and N2O emissions, while the gas fluxes are dependent on intrinsic soil properties and land use. Sand addition into peat soils might reduce greenhouse gas (GHG) emissions and enhance soil strength, and thus the ability to tolerate soil compaction. Soil compaction due to vehicular traffic leads to a decrease in aeration and changes in water flow, which might alter microbial activity and gas flow. The goal of this thesis was to investigate how soil compaction with different stress levels and sand addition affect soil physical properties and GHG emissions of peat soils. Incubator measurements three days before and after compaction were used to analyze the effect of soil compaction, which was conducted in a uniaxial compression machine. Furthermore, a new method was developed to observe the dynamics of gas fluxes during compaction. Field measurements complemented the laboratory study to determine the effect of sand addition. The compressive behaviour of peat soils was examined using the compression (Cc) and recompression index (Cs) which are measures for soil compressibility and rebound after stress release. This study shows reduction of CO2 emissions after compaction. However, this effect might be due to the high initial water-filled pore space and at lower water contents, compaction might have the opposite effect on GHG emissions. Higher mechanical loading had an effect on CO2 fluxes, while the trend was unclear and seems to be dependent on water content. Methane fluxes were below the detection limit and compaction might lead to hot moments in N2O emission. Sand addition reduced CO2 emissions and influenced the compressive behaviour of peat soils by reducing soil compressibility but also rebound. Linear relationships between soil mechanical properties and initial void ratio were found, indicating the high dependency of mechanical behaviour on intrinsic soil properties. In conclusion, sand addition might be a good agricultural management practise for cultivated peat soils, while the impact of soil compaction on GHG emissions under different moisture regimes has to be further assessed. This pilot study, emphasizes a need of further research to improve understanding the influencing factors of vehicular traffic as well as sand addition on GHG emissions and soil mechanical properties of cultivated peat soils.