Nitrous oxide emission budgets and land-use-driven hotspots for organic soils in Europe

Abstract. Organic soils are a main source of direct emissions of nitrous oxide (N₂O), an important greenhouse gas (GHG). Observed N₂O emissions from organic soils are highly variable in space and time, which causes high uncertainties in national emission inventories. Those uncertainties could be reduced when relating the upscaling process to a priori-identified key drivers by using available N₂O observations from plot scale in empirical approaches. We used the empirical fuzzy modelling approach MODE to identify main drivers for N₂O and utilize them to predict the spatial emission pattern of European organic soils. We conducted a meta-study with a total amount of 659 annual N₂O measurements, which was used to derive separate models for different land use types. We applied our models to available, spatially explicit input driver maps to upscale N₂O emissions at European level and compared the inventory with recently published IPCC emission factors. The final statistical models explained up to 60% of the N₂O variance. Our study results showed that cropland and grasslands emitted the highest N₂O fluxes 0.98 ± 1.08 and 0.58 ± 1.03 g N₂O-N m⁻² a⁻¹, respectively. High fluxes from cropland sites were mainly controlled by low soil pH value and deep-drained groundwater tables. Grassland hotspot emissions were strongly related to high amount of N-fertilizer inputs and warmer winter temperatures. In contrast, N₂O fluxes from natural peatlands were predominantly low (0.07 ± 0.27 g N₂O-N m⁻² a⁻¹) and we found no relationship with the tested drivers. The total inventory for direct N₂O emissions from organic soils in Europe amount up to 149.5 Gg N₂O-N a⁻¹, which also included fluxes from forest and peat extraction sites and exceeds the inventory calculated by IPCC emission factors of 87.4 Gg N₂O-N a⁻¹. N₂O emissions from organic soils represent up to 13% of total European N₂O emissions reported in the European Union (EU) greenhouse gas inventory of 2011 from only 7% of the EU area. Thereby the model demonstrated that the major part (85%) of the inventory is induced by anthropogenic management, which shows the significant reduction potential by rewetting and extensification of agriculturally used peat soils.