Environmental controls over greenhouse gas production from the Central African peatland complex

The Cuvette Centrale peatland complex is one of the world’s most important carbon stores, and spans the Republic of Congo and Democratic Republic of Congo, storing approximately 30.6 Pg C. However, despite significant carbon storage, the role of environmental controls over the production and emission of greenhouse gases including carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) remain poorly understood, and in situ flux measurements were only undertaken for the first time in 2019. This hampers our ability to understand the likely responses of emissions to future environmental change.

We conducted an ex-situ incubation experiment to investigate the roles of inundation and oxygen availability (flooded aerobic, flooded anoxic, and mesic conditions), vegetation type (palm versus hardwood dominated peat swamp). We concurrently assessed the role of vegetation in regulating peat organic chemistry using a combination of Fourier Transformed Infrared Spectroscopy (FTIR) and Rock-Eval Pyrolysis, and used regression models to assess controls over potential greenhouse gas production.

We found that CO₂ fluxes were consistently highest across sites under mesic conditions, and flooded anoxic conditions were associated with lowest fluxes. CH₄ production were highest under anoxic conditions, followed by the flooded oxic and the mesic treatments. Inundation and oxygen availability had more variable impacts on N2O production. 

CO₂ fluxes were greatest from hardwood and mixed forest for the mesic and flooded oxic treatments, and the highest anoxic CO₂ fluxes were from the mixed forest. The were no significant differences in CH₄ fluxes among the three vegetation types for any of the treatments. N₂O fluxes were greatest from the hardwood sites under the mesic treatment but there were no significant differences among forest types for the flooded aerobic and anoxic treatments.

We used regression models to link a range of peat inorganic and organic chemical properties across flooding treatments to greenhouse gas production, highlighting important potential controls over emissions. We concurrently assessed changes in emissions with peat depth (0 – 1.7 m), identifying broad declines in potential production with peat depth, matched by concurrent changes in organic chemistry.

Taken together our results indicate that the inundation represents a key control over emissions, alongside peat organic chemistry, which in turn is closely related to dominant vegetation type which controls inputs. Collectively these findings imply that any changes in peatland inundation through future climate change or alterations in land management (for example drainage) will have significant implications for greenhouse gas fluxes. Moreover, changes in dominant vegetation or ecosystem productivity will alter the balance of plant inputs into the peat, with subsequent implications for greenhouse gas dynamics.