Method for Assigning Emission Factors to Mapping Units Based on Modelling the Spatial Structure and Functions of Peatland Ecosystems

The assignment of emission factors (EFs) to land classes is vital for evaluating and reporting the effectiveness of rewetting drained peatlands in mitigation projects. This process currently relies on developing land class catalogues with assigned EFs based on extensive datasets, known as GEST catalogues. However, the GEST method, which assigns EFs based on vegetation types, often fails to provide satisfactory results in heterogeneous sites or in projects aimed at reducing emissions from multiple sources beyond drainage.

We propose to assign EFs to mapping units by modelling the spatial structure and functions of peatland ecosystems. This method was tested in several peatland restoration projects conducted in Russia (2011-2022), Peru (2023-2024), and Mongolia (2023-2024).

Our spatial modelling approach is founded on the observation that most chamber emission measurements typically occur at the microform level (10-4 to 10-2 ha). However, microforms are too small for practical mapping at the project scale (from 102 ha). To overcome this limitation, we employed a hierarchical landscape classification to upscale chamber measurement outcomes. Landscape units at the facies level comprise various combinations of elementary microform units, represented by phytocoenoses or complexes thereof. These facies collectively define peatland areas (10-1 to 102 ha), making them suitable mapping units for typical peatland restoration projects. Notably, GEST does not clearly define spatial boundaries; it may refer to either facies or peatland areas, according to different authors.

 

To derive the EFs at the facies level, the area of each microform type is multiplied by its corresponding EF. The cumulative value theoretically yields the desired emission factor for the facies. This procedure can similarly be applied to calculate EFs for the spatial scale of peatland areas, aligning with classes identified in the IPCC guidelines.

Like many methods for calculating EFs, our proposed approach includes inherent uncertainties. A key question remains regarding the relationship between ecosystem function quantification (in this case, greenhouse gas emission factors) and the proportional area of the land cover class for which specific assessed values have been derived.

At the Orshinski Mokh peatland (Tver, Russia), we validated our calculated fluxes against direct measurements from an Eddy-Covariance tower. Preliminary calculations incorporating the area fractions of each facies resulted in net ecosystem exchange (NEE) values of 4.8 tCO2/ha and methane emissions of 7.8 kg CH4/ha over 157 days, while initial readings from the Eddy Covariance method indicated 4.6 tCO2/ha and 18.4 kg CH4/ha for the same duration. Further detailed calculations will refine these values.

In 2024, we set up a similar experiment in Mongolia's Khurkh peatland, with expectations for preliminary results in 2026.

Another methodological challenge encountered in assigning EFs for restoration projects in Mongolia and Peru involved factors and processes that complement drainage, notably nitrification and carbonisation, which significantly increase emissions. We propose to investigate these processes' impacts on peat under various conditions by summing up the outcomes of ex-situ published laboratory experiments. The resulting fluxes will be averaged over the duration in the nature of the conditions studied and incorporated into the GEST or calculated EFs for the drainage-rewetting process.