Age, extent and carbon storage of the central Congo Basin peatland complex

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From: Nature(Vol. 542, Issue 7639)
Publisher: Nature Publishing Group
Document Type: Report
Length: 8,426 words
Lexile Measure: 1520L

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Author(s): Greta C. Dargie (corresponding author) [1, 2]; Simon L. Lewis [1, 2]; Ian T. Lawson [3]; Edward T. A. Mitchard [4]; Susan E. Page [5]; Yannick E. Bocko [6]; Suspense A. Ifo [6]

Peatlands are carbon-rich ecosystems that cover just three per cent of Earths land surface [1], but store one-third of soil carbon [2]. Peat soils are formed by the build-up of partially decomposed organic matter under waterlogged anoxic conditions. Most peat is found in cool climatic regions where unimpeded decomposition is slower, but deposits are also found under some tropical swamp forests [2, 3]. Here we present field measurements from one of the worlds most extensive regions of swamp forest, the Cuvette Centrale depression in the central Congo Basin [4]. We find extensive peat deposits beneath the swamp forest vegetation (peat defined as material with an organic matter content of at least 65 per cent to a depth of at least 0.3metres). Radiocarbon dates indicate that peat began accumulating from about 10,600 years ago, coincident with the onset of more humid conditions in central Africa at the beginning of the Holocene [5]. The peatlands occupy large interfluvial basins, and seem to be largely rain-fed and ombrotrophic-like (of low nutrient status) systems. Although the peat layer is relatively shallow (with a maximum depth of 5.9metres and a median depth of 2.0metres), by combining in situ and remotely sensed data, we estimate the area of peat to be approximately 145,500 square kilometres (95 per cent confidence interval of 131,900156,400 square kilometres), making the Cuvette Centrale the most extensive peatland complex in the tropics. This area is more than five times the maximum possible area reported for the Congo Basin in a recent synthesis of pantropical peat extent [2]. We estimate that the peatlands store approximately 30.6 petagrams (30.61015 grams) of carbon belowground (95 per cent confidence interval of 6.346.8 petagrams of carbon)a quantity that is similar to the above-ground carbon stocks of the tropical forests of the entire Congo Basin [6]. Our result for the Cuvette Centrale increases the best estimate of global tropical peatland carbon stocks by 36 per cent, to 104.7 petagrams of carbon (minimum estimate of 69.6 petagrams of carbon; maximum estimate of 129.8 petagrams of carbon [2]). This stored carbon is vulnerable to land-use change and any future reduction in precipitation [7, 8].

The Congo Basin drains an area of approximately 3.7106 km2 , within which lies a central shallow depression overlaid by swamp forest, known as the Cuvette Centrale [9]. Over this region, the Congo River drops just 115m over 1,740km, with year-round waterlogging [9]; we therefore hypothesized that this wetlandthe second largest in the tropicsmight contain extensive peat deposits. A few grey literature sources since the 1950s briefly mention peat occurring in the central Congo Basin, but geolocations or other details were not reported [10, 11, 12, 13]. Recently published estimates of tropical peatland area and carbon storage still rely on this scant, unverifiable information [2, 14]. Therefore, here we first...

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Gale Document Number: GALE|A479710366