Nitrous oxide emission hotspots from organic soils in Europe

Abstract

Abstract. Organic soils are a main source of direct nitrous oxide (N2O) emissions, 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, spatial explicit input driver maps to upscale N2O emissions on 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 included also 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 with up to 85% the major part of the inventory is induced by anthropogenic management, which shows the significant reduction potential by rewetting and extensivation of agricultural used peat soils.

High emissions of greenhouse gases from grasslands on peat and other organic soils

“…Leppelt et al . () calculated an ‘applied emission factor’ of 2.9 kg N 2 O‐N ha −1 yr −1 which is still slightly higher than our average N 2 O emissions.…”

“…The values are also lower than the European grassland average of 5.8 kg ha −1 yr −1 reported by Leppelt et al . () whose data set of 659 annual budgets contained a subset of our data. Leppelt et al .…”

“…Soil moisture (Estop‐Aragones et al ., ) or, as a proxy, water table depth (Moore & Knowles, ) is the main driver of CO 2 emissions as this parameter determines the oxygen concentration in the pore space and therefore the intensity of mineralization. Nitrogen fertilization may, additionally, cause high emissions of nitrous oxide (N 2 O) (Leppelt et al ., ), especially under intermediate soil moisture conditions (Linn & Doran, ; Jungkunst et al ., ). The GHG budgets of managed peatlands can be roughly estimated by land use, climate zone, soil nutrient status and drainage status (IPCC, ), but uncertainties remain relatively high.…”

“…Leppelt et al . () estimated that 25–44% of European peat soils are used as cropland or grassland. In Germany, more than 95% of peatlands are drained, mainly for grassland use (53%; UBA, ).…”

“…Large‐scale approaches to estimate GHG emissions from grasslands have been restricted to coarse classifications by climate, nutrient status and drainage (IPCC, ). Response functions have been developed for N 2 O (Leppelt et al ., ) and CH 4 (Turetsky et al ., ), but not for CO 2 . Such functions depending on site conditions and management, however, are required for an adequate representation of national conditions in GHG inventories and for designing effective mitigation strategies.…”