Carbon loss estimates from cultivated peat soils in Norway: a comparison of three methods

Drainage and cultivation of peat soils stimulates soil organic matter (SOM) mineralization, which substantially increases CO₂ emissions from soils. Large uncertainties are associated with this CO₂ flux, and little data are available, especially in Norway. The objective of the present research was to estimate C losses from cultivated peatlands in West Norway by three independent methods: (1) long-term monitoring of subsidence rates, (2) changes in ash contents, and (3) soil CO₂ flux measurements. Subsidence of cultivated peat soils averaged about 2.5 cm year⁻¹. We estimated that peat loss and compaction were respectively responsible for 38% and 62% of the total subsidence during a 25-year period after drainage. Based on this estimate the corresponding C loss equals 0.80 kg C m⁻² year⁻¹. The observed increase in mineral concentration of the topsoil of cultivated peat is proportional to their C loss, providing no mineral particles other than lime and fertilizers are added to the soil. Using this novel approach across 11 sites, we estimated a mean C loss of 0.86 kg C m⁻² year⁻¹. Soil CO₂ flux measurements, corrected for autotrophic respiration, yielded a C loss estimate from cultivated peat soils of 0.60 kg C m⁻² year⁻¹. The three methods yielded fairly similar estimates of C losses from Norwegian cultivated peatlands. Cultivated peatlands in Norway cover an estimated 63,000 ha. Total annual C losses from peat degradation were estimated to range between 1.8 and 2 million tons CO₂ year⁻¹, which equals about 3–4% of total anthropogenic greenhouse gas emissions from Norway.