Nitrous oxide emissions from drained organic forest soils -: an up-scaling based on C:N ratios (Reprinted)

Total emissions of N(2)O from drained organic forest soils in Sweden were estimated using an equation linking the C:N ratio of the soil to N(2)O emissions. Information on soil C:N ratios was derived from a national database. It was estimated that the emissions from Histosols amount to 2,820 tonnes N(2)O a(-1). This is almost five times the value calculated for the same soils using the method suggested by the Intergovernmental Panel on Climate Change: 580 tonnes N(2)O a(-1). The higher value in the present study can mainly be explained by improved accuracy of estimates of N(2)O emissions from nutrient-rich soils, including former agricultural soils. In Sweden, in addition to 0.94 Mha of drained Histosols, there are 0.55 Mha of other types of drained organic soils. The annual emissions from these soils were estimated to amount to 1,890 tonnes of N(2)O. The total emission value calculated for drained organic forest soils was thus 4,700 tonnes N(2)O a(-1), which, if added, would increase the current estimate of the Swedish anthropogenic N(2)O source strength by 18%. Of these emissions, 88% occur from sites with C:N ratios lower than 25. The exponential relationship between C:N ratio and N(2)O emissions, in combination with a scarcity of data, resulted in large confidence intervals around the estimates. However, by using the C:N ratio-based method, N(2)O emission estimates can be calculated from a variable that is readily available in databases. Also, the recent findings that there are exceptionally large emissions of N(2)O from the most nitrogen-rich drained organic forest soils are taken into account.