Ecosystem state shifts during long-term development of an Amazonian peatland
2018
The most carbon (C) dense ecosystems of Amazonia are areas characterised by the presence of peatlands. However,
Amazonianpeatland ecosystems are poorly understood and are threatened by human activities. Here we present an investigation into long-term
ecohydrologicalcontrols on C accumulation in an
Amazonian
peat
dome. This site is the oldest peatland yet discovered in Amazonia (
peatinitiation c. 8.9 ka BP), and developed in three stages; (i)
peatinitiated in an abandoned river channel with open water and
aquatic plants; (ii) inundated forest
swamp; and (iii) raised
peat
dome(since c. 3.9 ka BP). Local burning occurred at least three times in the past 4,500 years. Two phases of particularly rapid C accumulation (c. 6.6-6.1 and c. 4.9-3.9 ka 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 c. 1.8-1.1 ka BP led to markedly reduced C accumulation and potentially a
hiatusduring the
peat
domestage. 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.
Amazonianpeatlands represent important carbon stores and habitats, and are important archives of past climatic and ecological information. They should form key foci for conservation efforts.
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