Modelling N2O Fluxes in Peatlands: From Process to Global Mapping

Peatlands cover a small portion of the Earth's land area, but their impact on the carbon (C) and nitrogen (N) cycles at both regional and global scales is significant. The water regime of peatlands (as an indicator of oxygen content) and temperature are the main factors in peatland greenhouse gas (GHG) fluxes. Under high water tables, as well as very dry conditions, emissions of both carbon dioxide (CO₂) and nitrous oxide (N₂O) are low, but excess moisture and anoxic conditions increase methane (CH₄) emissions. At moderate soil moisture and fluctuating water table, CO₂ and N₂O emissions are high. Peatland N₂O emissions also depend significantly on availability of total mineral nitrogen (TIN). Permanently wet (i.e., natural) peatlands act as CO₂ sinks, accumulating organic C in the soil. In drained peatlands, both gaseous and dissolved C losses are high. Artificial drainage and climatic drying induce approximately 70% of all N₂O emissions from organic soils.

Tropical regions are some of the most important terrestrial sources of N₂O. In drained tropical peatlands, N₂O emissions are the second most important contributor to the GHG budget after CO₂. Forests dominate tropical peatlands. These are more complex ecosystems than open peatlands, as the canopy (phyllosphere) may significantly influence GHG fluxes, especially during wet periods. Our studies show that large N₂O fluxes from the soil can be absorbed by the canopy, although the underlying mechanisms remain unclear.

In our empirical process-based PeatN2O model, which simulates monthly N₂O fluxes in peatlands, we integrate the following parameters: peat ammonium (NH₄⁺) and nitrate (NO₃^–) content, C/N ratio, soil moisture level, rate of change in soil moisture, N and C cycle microbiome ratios, source (NH₄⁺ and/or NO₃^–) partitioning based on N₂O isotopologue signatures, a plant traits factor, and a canopy factor. The results of this model can be used to refine the global N₂O estimates based on a combination of N₂O emission estimates from the Global Peatlands Initiative map (2022) and the Major Land Cover Units map (MODIS, 2022). The sources are from our working group's global studies, IPCC emission factors, and other published studies. The main challenge in scaling future GHG fluxes to global change scenarios is predicting the spatial and temporal variability in environmental conditions that create hot spots and hot moments of fluxes.