Abstract
The most carbon (C)-dense ecosystems of Amazonia are areas characterized by the presence of peatlands. However, Amazonian peatland ecosystems are poorly understood and are threatened by human activities. Here, we present an investigation into long-term ecohydrological controls on C accumulation in an Amazonian peat dome. This site is the oldest peatland yet discovered in Amazonia (peat initiation ca. 8.9ka BP), and developed in three stages: (i) peat initiated in an abandoned river channel with open water and aquatic plants; (ii) inundated forest swamp; and (iii) raised peat dome (since ca. 3.9ka BP). Local burning occurred at least three times in the past 4,500years. Two phases of particularly rapid C accumulation (ca. 6.6-6.1 and ca. 4.9-3.9ka BP), potentially resulting from increased net primary productivity, were seemingly driven by drier conditions associated with widespread drought events. The association of drought phases with major ecosystem state shifts (open water wetland-forest swamp-peat dome) suggests a potential climatic control on the developmental trajectory of this tropical peatland. A third drought phase centred on ca. 1.8-1.1ka BP led to markedly reduced C accumulation and potentially a hiatus during the peat dome stage. Our results suggest that future droughts may lead to phases of rapid C accumulation in some inundated tropical peat swamps, although this can lead ultimately to a shift to ombrotrophy and a subsequent return to slower C accumulation. Conversely, in ombrotrophic peat domes, droughts may lead to reduced C accumulation or even net loss of peat. Increased surface wetness at our site in recent decades may reflect a shift towards a wetter climate in western Amazonia. Amazonian peatlands represent important carbon stores and habitats, and are important archives of past climatic and ecological information. They should form key foci for conservation efforts.
Highlights
Tropical peatlands are found in Southeast Asia, Central Africa, and Central and South America
Beginning at the river edge and working towards the peatland interior, the vegetation zones comprise: A1 dominated by Oxandra euneura, Parahancornia peruviana, Lacmellea oblongata and Eschweilera sp. 1; A2 dominated by Zygia sp. 1, Oxandra euneura, Mauritia flexuosa and Trichomanes pinnatum; A3 dominated by Iryanthera ulei, Zygia sp. 1, Alibertia sp. 1 and Oenocarpus mapora; A4 dominated by Iryanthera ulei, Zygia sp. 1 and Alibertia sp. 1; A5 dominated by Mauritia flexuosa, Zygia sp. 1, Virola pavonis and Iryanthera ulei; and A6 dominated by Iryanthera ulei, Brosimum sp. 1 and Euterpe precatoria
A multiproxy palaeoecological dataset shows that the oldest peat dome yet discovered in Amazonia developed in three distinct phases: (i) peat initiated in an abandoned river channel or backwater with standing open water and aquatic plants; (ii) inundated forest swamp; and (iii) raised peat dome
Summary
Tropical peatlands are found in Southeast Asia, Central Africa, and Central and South America. 98 99 much is known about the C dynamics of Amazonian vegetation, including the finding that its ability to store C is diminishing (Brienen et al, 2015), little is known about how Amazonian peatlands developed, including their ecohydrological dynamics through time, C accumulation, and their response to climatic changes. Potential threats to these intact peatlands include hydroelectricity (river damming) projects, road and railway construction, ore, gas and oil exploration, logging and clearance of land, and drainage for agriculture – in particular oil palm plantations (Roucoux et al., 2017). Multiproxy palaeoecological dataset to (i) determine the developmental trajectory of the peatland; and (ii) assess the peatland’s response to past climate change. 119 Materials and Methods
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