Browsing by Author "Mbemba, Mackline"

Now showing 1 - 4 of 4
  • Thumbnail Image
    ItemOpen Access
    Current knowledge on the Cuvette Centrale peatland complex and future research directions
    (C I R A D, 2021-12-01) Biddulph, George Elliot; Bocko, Yannick Enock; Bola, Pierre; Crezee, Bart; Dargie, Greta C.; Emba, Ovide; Georgiou, Selena; Girkin, Nicholas T.; Hawthorne, Donna; Jovani-Sancho, A. Jonay; Kanyama, Joseph; Mampouya, Wenina Emmanuel; Mbemba, Mackline; Sciumbata, Matteo; Tyrrell, Genevieve
    The Cuvette Centrale is the largest tropical peatland complex in the world, covering approximately 145,000 km2 across the Republic of Congo and the Democratic Republic of Congo. It stores ca. 30.6 Pg C, the equivalent of three years of global carbon dioxide emissions and is now the first trans-national Ramsar site. Despite its size and importance as a global carbon store, relatively little is known about key aspects of its ecology and history, including its formation, the scale of greenhouse gas flows, its biodiversity and its history of human activity. Here, we synthesise available knowledge on the Cuvette Centrale, identifying key areas for further research. Finally, we review the potential of mathematical models to assess future trajectories for the peatlands in terms of the potential impacts of resource extraction or climate change.
  • Thumbnail Image
    ItemOpen Access
    Mapping water levels across a region of the Cuvette Centrale peatland complex
    (MDPI, 2023-06-13) Georgiou, Selena; Mitchard, Edward T. A.; Crezee, Bart; Dargie, Greta C.; Young, Dylan M.; Jovani-Sancho, Antonio J.; Kitambo, Benjamin; Papa, Fabrice; Bocko, Yannick E.; Bola, Pierre; Crabtree, Dafydd E.; Emba, Ovide B.; Ewango, Corneille E. N.; Girkin, Nicholas T.; Ifo, Suspense A.; Kanyama, Joseph T.; Mampouya, Yeto Emmanuel Wenina; Mbemba, Mackline; Ndjango, Jean-Bosco N.; Palmer, Paul I.; Sjögersten, Sofie; Lewis, Simon L.
    Inundation dynamics are the primary control on greenhouse gas emissions from peatlands. Situated in the central Congo Basin, the Cuvette Centrale is the largest tropical peatland complex. However, our knowledge of the spatial and temporal variations in its water levels is limited. By addressing this gap, we can quantify the relationship between the Cuvette Centrale’s water levels and greenhouse gas emissions, and further provide a baseline from which deviations caused by climate or land-use change can be observed, and their impacts understood. We present here a novel approach that combines satellite-derived rainfall, evapotranspiration and L-band Synthetic Aperture Radar (SAR) data to estimate spatial and temporal changes in water level across a sub-region of the Cuvette Centrale. Our key outputs are a map showing the spatial distribution of rainfed and flood-prone locations and a daily, 100 m resolution map of peatland water levels. This map is validated using satellite altimetry data and in situ water table data from water loggers. We determine that 50% of peatlands within our study area are largely rainfed, and a further 22.5% are somewhat rainfed, receiving hydrological input mostly from rainfall (directly and via surface/sub-surface inputs in sloped areas). The remaining 27.5% of peatlands are mainly situated in riverine floodplain areas to the east of the Congo River and between the Ubangui and Congo rivers. The mean amplitude of the water level across our study area and over a 20-month period is 22.8 ± 10.1 cm to 1 standard deviation. Maximum temporal variations in water levels occur in the riverine floodplain areas and in the inter-fluvial region between the Ubangui and Congo rivers. Our results show that spatial and temporal changes in water levels can be successfully mapped over tropical peatlands using the pattern of net water input (rainfall minus evapotranspiration, not accounting for run-off) and L-band SAR data.
  • Thumbnail Image
    ItemOpen Access
    Simulating carbon accumulation and loss in the central Congo peatlands
    (Wiley, 2023-10-10) Young, Dylan M.; Baird, Andy J.; Morris, Paul J.; Dargie, Greta C.; Mampouya Wenina, Y. Emmanuel; Mbemba, Mackline; Boom, Arnoud; Cook, Peter; Betts, Richard; Burke, Eleanor; Bocko, Yannick E.; Chadburn, Sarah; Crabtree, Dafydd E.; Crezee, Bart; Ewango, Corneille E. N.; Garcin, Yannick; Georgiou, Selena; Girkin, Nicholas T.; Gulliver, Pauline; Jovani-Sancho, A. Jonay; Schefuß, Enno; Sciumbata, Matteo; Sjögersten, Sofie; Lewis, Simon L.
    Peatlands of the central Congo Basin have accumulated carbon over millennia. They currently store some 29 billion tonnes of carbon in peat. However, our understanding of the controls on peat carbon accumulation and loss and the vulnerability of this stored carbon to climate change is in its infancy. Here we present a new model of tropical peatland development, DigiBog_Congo, that we use to simulate peat carbon accumulation and loss in a rain-fed interfluvial peatland that began forming ~20,000 calendar years Before Present (cal. yr BP, where ‘present’ is 1950 CE). Overall, the simulated age-depth curve is in good agreement with palaeoenvironmental reconstructions derived from a peat core at the same location as our model simulation. We find two key controls on long-term peat accumulation: water at the peat surface (surface wetness) and the very slow anoxic decay of recalcitrant material. Our main simulation shows that between the Late Glacial and early Holocene there were several multidecadal periods where net peat and carbon gain alternated with net loss. Later, a climatic dry phase beginning ~5200 cal. yr BP caused the peatland to become a long-term carbon source from ~3975 to 900 cal. yr BP. Peat as old as ~7000 cal. yr BP was decomposed before the peatland's surface became wetter again, suggesting that changes in rainfall alone were sufficient to cause a catastrophic loss of peat carbon lasting thousands of years. During this time, 6.4 m of the column of peat was lost, resulting in 57% of the simulated carbon stock being released. Our study provides an approach to understanding the future impact of climate change and potential land-use change on this vulnerable store of carbon.
  • Thumbnail Image
    ItemOpen Access
    The temperature dependence of greenhouse gas production from Central African savannah soils
    (Elsevier, 2025-03-01) Girkin, Nicholas T.; Cooper, Hannah V.; Johnston, Alice S.; Ledger, Martha; Niamba, G. R. Mouanda; Vane, Christopher H.; Moss-Hayes, Vicky; Crabtree, Dafydd; Dargie, Greta C.; Vasquez, Saul; Bocko, Yannick; Mampouya Wenina, Emmanuel; Mbemba, Mackline; Boom, Arnoud; Ifo, Suspense Averti; Lewis, Simon L.; Sjögersten, Sofie
    Savannahs cover 20 % of the global land surface, but there have been few studies of greenhouse gas (GHG) dynamics from savannah soils. Here, we assess potential turnover of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from surface (0–10 cm) and subsurface (20–30 cm) soils from two contrasting tropical savannah sites in the Republic of Congo, Central Africa, under dry (40 % water-filled-pore-space, WFPS) and wet (70 % WFPS) conditions. Under baseline conditions (25 °C), we found soils were sources of CO2 and N2O, but a sink for CH4. Assessment of the temperature response of GHG fluxes between 20 and 35 °C revealed variable temperature dependences. That is, CO2 fluxes showed a strong temperature response, whereas the temperature response of N2O fluxes was only significant under dry conditions, and no significant temperature response of CH4 fluxes was observed. The temperature quotient (Q10) of soil respiration increased from 1.58 ± 0.004 to 1.92 ± 0.006 at sites with lower soil organic carbon contents. The relative increase in N2O with CO2 fluxes across temperatures was significantly influenced by moisture conditions at both sites. No temperature or soil moisture response was observed for CH4 fluxes, collectively implying divergent GHG responses to changing climatic conditions. Using Rock-Eval pyrolysis we assessed the organic chemistry of all soil types, which indicated contrasting degrees of stability of carbon sources between sites and with depth which, alongside significant differences in a range of other soil parameters (including organic matter content, total carbon, total nitrogen, electrical conductivity, and pH), may account for site-specific differences in baseline GHG emissions. Taken together, our results are amongst the first measures of GHG temperature sensitivity of tropical savannah soils, and demonstrate that soil CO2 emissions are more sensitive to warming and changes in moisture than the emissions of other GHGs, although relatively low compared to responses reported for soils from other tropical ecosystems. This implies that GHG fluxes form savannah soils in the region may be at least partially resilient to climate-induced soil warming compared to other ecosystems.