Question1: What controls the geographical distribution of peatlands in the tropics?
TroPeaCC is working to develop the peatland module in JULES (a land surface model) for tropical peatlands. Initially, JULES-peat has being run for 7 initial study sites across the tropics. We found the default configuration of JULES-peat for the tropical sites underestimated how much carbon is contained in these peatlands. Several improvements have been applied to try and capture the carbon cycling in tropical peatlands. A property of interest for improved hydrology modelling in JULES-Peat is the hydraulic conductivity. There is little data on hydraulic conductivity for tropical peatlands and PhD student Dehaen won a grant to travel to Colombia and measure this parameter on TroPeaCC sites.
Question2: How large is the tropical peatland CO2 sink and what are its main climatic drivers?
Work towards gathering a pan-tropical carbon accumulation dataset to fulfil the second objective of the project is on-going. This global compilation of sites includes data from a prior global compilation (Gallego-Sala et al., 2018) located between 30°N to 30°S. Additionally, all sites found in the literature have been added, plus a call for unpublished data from the CPEAT community was also put forward. Currently, the database counts 39 sites ranging from 5m elevation to 4570m with varying sampling and measurement resolutions. Data from the TroPeaCC project sites will be added to the database, peat cores from different regions in the tropics have been collected and are being analysed in the Exeter laboratories for carbon and nitrogent content, bulk density and sent for radiocarbon dating to Chrono, Queen's, Belfast.
Question3: How large is the methane flux in tropical peatlands? What are the main controls at the intercontinental scale?
3A. Eddy covariance method
Tropical peatland methane fluxes and carbon sink function is still poorly quantified, especially from ground measurements needed to calibrate airborne and top down approaches. Ecosystem scale measurements with the eddy covariance technique are particularly scarce, with the majority of existing sites located in South East Asia on disturbed or drained peatlands. TroPeaCC project addresses this knowledge gap by setting up two new eddy covariance sites in undisturbed tropical peatlands, one in papyrus swamp in Uganda and another in flooded forest in Colombian Amazon. The Ugandan site has been providing carbon dioxide and methane flux data since March 2023. For the Colombian site, the building of the infrastructure is underway. In the Colombian site, we have recorded data with a meteorological station in a nearby open area to determine the optimal orientation of the flux tower.
3B. Chamber measurements
Although plant methane (CH4) emissions can be regionally important in the tropics, in some cases contributing more than three quarters of total ecosystem level fluxes, they are neglected in global methane budgets. The large uncertainties in CH4 emissions mediated by plants in tropical peatlands occur due to i) insufficient long-term field experiments to capture seasonal and interannual variability in CH4 fluxes and ii) lack of information about plant species-specific emissions patterns and their drivers. To fill this gap, separate soil and plant fluxes are being taken within the scope of this project, aiming to unveil the contribution of plants as a source of CH4 at four sites. By identifying the magnitude and main drivers behind CH4 emissions through plants it will be possible to reduce uncertainties in modelling future emissions and hence future climate projections.
3c. Data from drained peatlands:
In SE Asia nearly 80% of natural peatlands have been deforested and drained, with the majority under plantations and agriculture. Within the scope of the project data from an EC tower in a mature oil palm plantation in Sarawak SE Asia was processed and analysed aiming to identify the drivers of CH4 emission from oil palm plantation. This information will be used in the model parameterization (see Q4).
Q4: What is the overall carbon balance of tropical peatlands and how will this change in the future?
The development of JULES encompasses the carbon accumulation (or carbon sink), see QUESTION 1, and the development of the methane component, described here. Both those advancements will allow to eventually answer this last TroPeaCC research question. JULES microbe is a global scale peatland microbial methane (CH4) model coupled with the JULES land surface model. JULES microbeWT is driven with simulated carbon accumulation in peat, soil temperature, and WTD. Although there is much progress in replicating these drivers in JULES, their development is ongoing for tropical peatlands. A sensitivity analysis of microbeWT for a tropical peatland has been performed to determine which parameters require calibration. Afterwards, microbeWT was calibrated to replicate daily CH4 flux from a tropical peatland that spans a wet and dry season. Finally, the transferability of the calibrated parameters to other tropical peatlands was assessed. The final objective of this research is to use JULES microbeWT to quantify CH4 emissions from peat across the tropics. Preliminary results are promising and indicate that a single microbeWT parameter set could be applied across all tropical peatlands, but more testing is needed at additional sites (e.g. TroPeaCC sites) and with longer time-series of CH4 observations.
