Hydroclimatic vulnerability of peat carbon in the central Congo Basin

Abstract

The forested swamps of the central Congo Basin store approximately 30 billion metric tonnes of carbon in peat1,2. Little is known about the vulnerability of these carbon stocks. Here we investigate this vulnerability using peat cores from a large interfluvial basin in the Republic of the Congo and palaeoenvironmental methods. We find that peat accumulation began at least at 17,500 calibrated years before present (cal. yr bp; taken as ad 1950). Our data show that the peat that accumulated between around 7,500 to around 2,000 cal. yr bp is much more decomposed compared with older and younger peat. Hydrogen isotopes of plant waxes indicate a drying trend, starting at approximately 5,000 cal. yr bp and culminating at approximately 2,000 cal. yr bp, coeval with a decline in dominant swamp forest taxa. The data imply that the drying climate probably resulted in a regional drop in the water table, which triggered peat decomposition, including the loss of peat carbon accumulated prior to the onset of the drier conditions. After approximately 2,000 cal. yr bp, our data show that the drying trend ceased, hydrologic conditions stabilized and peat accumulation resumed. This reversible accumulation–loss–accumulation pattern is consistent with other peat cores across the region, indicating that the carbon stocks of the central Congo peatlands may lie close to a climatically driven drought threshold. Further research should quantify the combination of peatland threshold behaviour and droughts driven by anthropogenic carbon emissions that may trigger this positive carbon cycle feedback in the Earth system.

Net greenhouse gas balance of fibre wood plantation on peat in Indonesia

“…There was clearly a strong association during the study period between C loss, subsidence and droughts driven by regional climate extremes 26 . Our results indicate that even low-level or indirect human disturbance (for example, by means of climate change) can lead to C loss, highlighting the hydroclimatic vulnerability of C in forested tropical peatlands [13][14][15][16] .…”

“…Tropical peatlands cycle and store large amounts of carbon in their soil and biomass [1][2][3][4][5] . Climate and land-use change alters greenhouse gas (GHG) fluxes of tropical peatlands, but the magnitude of these changes remains highly uncertain [6][7][8][9][10][11][12][13][14][15][16][17][18][19] . Here we measure net ecosystem exchanges of carbon dioxide, methane and soil nitrous oxide fluxes between October 2016 and May 2022 from Acacia crassicarpa plantation, degraded forest and intact forest within the same peat landscape, representing land-cover-change trajectories in Sumatra, Indonesia.…”

“…A fine balance between hydrology, ecology and landscape morphology has resulted in this long-term C store [6][7][8] . Climate and other environmental changes are, however, affecting this C store as a result of warming, drying conditions and change in disturbance rates [9][10][11][12][13][14][15][16][17] . Particularly, decreased rainfall, increased seasonality and frequent days without rainfall are resulting in GWL drawdowns 7,12,13 , which cause C loss [14][15][16][17] .…”

Deglacial export of pre-aged terrigenous carbon to the Bay of Biscay

“…In high northern latitudes wetlands, it has been shown that permafrost degradation leads to wetland shrinkage (Avis et al, 2011). In the tropics the situation is also critical, with anthropogenic (Moore et al, 2013) and natural (Schefuß et al, 2016;Garcin et al, 2022) factors contributing to the remobilization of pre-aged C from peatlands. Therefore, the release of large amounts of peat-derived OM described here for deglacial Europe has analogues in the present day and may be useful to inform future projections of permafrost peatland loss (e.g., Fewster et al, 2022), with our results advocating for the importance of better constraining the C cycle in wetlands.…”

Tropical peatlands in the Anthropocene: The present and the future

“…The main threat climate change poses to peatlands comes from the increased duration or greater severity of drought, which drives rapid degradation of peat through oxidation, or increased likelihood of fire events (Loisel et al, 2020). This can result in substantial peat carbon loss, or prolonged periods when peat is not accumulating, as evidenced in the Central African peatland complex (Garcin et al, 2022). Under most future climate change scenarios, there will be strong increases in rainfall seasonality and intensity (IPCC, 2013;Li et al, 2007), but precise effects on peatlands will differ between regions.…”