Sea level rise and climate change acting as interactive stressors on development and dynamics of tropical peatlands in coastal Sumatra and South Borneo since the Last Glacial Maximum

Abstract

Southeast Asian peatlands, along with their various important ecosystem services, are mainly distributed in the coastal areas of Sumatra and Borneo. These ecosystems are threatened by coastal development, global warming and sea level rise (SLR). Despite receiving growing attention for their biodiversity and as massive carbon stores, there is still a lack of knowledge on how they initiated and evolved over time, and how they responded to past environmental change, that is, precipitation, sea level and early anthropogenic activities. To improve our understanding thereof, we conducted multiproxy paleoecological studies in the Kampar Peninsula and Katingan peatlands in the coastal area of Riau and Central Kalimantan, Indonesia. The results indicate that the initiation timing and environment of both peatlands are very distinct, suggesting that peat could form under various vegetation as soon as there is sufficient moisture to limit organic matter decomposition. The past dynamics of both peatlands were mainly attributable to natural drivers, while anthropogenic activities were hardly relevant.Changes in precipitation and sea level led to shifts in peat swamp forest vegetation, peat accumulation rates and fire regimes at both sites. We infer that the simultaneous occurrence of El Niño-Southern Oscillation (ENSO) events and SLR resulted in synergistic effects which led to the occurrence of severe fires in a pristine coastal peatland ecosystem; however, it did not interrupt peat accretion. In the future, SLR, combined with the projected increase in frequency and intensity of ENSO, can potentially amplify the negative effects of anthropogenic peatland fires. This prospectively stimulates massive carbon release, thus could, in turn, contribute to worsening the global climate crisis especially once an as yet unknown threshold is crossed and peat accretion is halted, that is, peatlands lose their carbon sink function. Given the current rapid SLR, coastal peatland managements should start develop fire risk reduction or mitigation strategies.

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

“…Over a 5-year measurement period, the annual NEE-CO 2 ranged from 9.1 ± 3.7 to 25.6 ± 4.1 tCO 2 ha −1 year −1 , with an average value of 15.3 ± 3.7 tCO 2 ha −1 year −1 (Extended Data Table 3 ). The CO 2 emissions owing to GWL drawdown are consistent with previous studies in tropical peatlands in which reduced peat accumulation rates 8 , 15 , a hiatus in peat genesis 33 or even C loss 14 – 17 have been reported in response to droughts driven by intense and frequent El Niño–Southern Oscillation activity.…”

“…2 and Extended Data Table 5 ). The measured CO 2 emissions in this study indicate that the long-term rate of C accumulation of 2.8 tCO 2 ha −1 year −1 in the Kampar Peninsula 8 may no longer be occurring. If we take the measured GHG balance of the intact forest site as a reference, and treat our data from the fourth Acacia rotation as representative of longer-term conditions, then the conversion of intact site to Acacia plantation results in a long-term net increase in GHG emissions of 18.1 ± 6.0 tCO 2 -eq ha −1 year −1 (Fig.…”

“…This study was conducted in the Kampar Peninsula (Sumatra, Indonesia), an ombrogenous tropical peatland of around 700,000 ha that largely formed within the past 5,100 years (ref. 8 ). The base of the peatland is grey marine clays, over which peat varies from approximately 3 m deep near the river boundaries to over 11 m in the centre of the approximately 60-km-wide and more than 100-km-long peat dome (Fig.…”

“…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.…”

“…Over the Holocene, tropical peatlands have accumulated at least 75 Gt of carbon (C) in partially decomposed debris (wood, roots, litter, leaves) under waterlogged anoxic environments [1][2][3][4][5] . 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] .…”