Browsing by Author "Lewis, Simon L."

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    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.
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    Measuring, modeling and mapping ecosystem services in the Eastern Arc Mountains of Tanzania
    (V.H. Winston & Son, Inc., 2011-10-31T00:00:00Z) Fisher, Brendan; Turner, R. Kerry; Burgess, Neil D.; Swetnam, Ruth D.; Green, Jonathan; Green, Rhys; Kajembe, George; Kulindwa, Kassim; Lewis, Simon L.; Marchant, Rob; Marshall, Andrew R.; Madoffe, Seif; Munishi, P. K. T.; Morse-Jones, Sian; Mwakalila, Shadrack; Paavola, Jouni; Naidoo, Robin; Ricketts, Taylor; Rouget, Rouget; Willcock, Simon; White, Sue; Balmford, Andrew
    In light of the significance that ecosystem service research is likely to play in linking conservation activities and human welfare, systematic approaches to measuring, modeling and mapping ecosystem services (and their value to society) are sorely needed. In this paper we outline one such approach, which we developed in order to understand the links between the functioning of the ecosystems of Tanzania's Eastern Arc Mountains and their impact on human welfare at local, regional and global scales. The essence of our approach is the creation of a series of maps created using field-based or remotely sourced data, data-driven models, and socio-economic scenarios coupled with rule-based assumptions. Here we describe the construction of this spatial information and how it can help to shed light on the complex relationships between ecological and social systems. There are obvious difficulties in operationalizing this approach, but by highlighting those which we have encountered in our own case-study work, we have also been able to suggest some routes to overcoming these impediments
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    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.