High permeability explains the vulnerability of the carbon store in drained tropical peatlands

Baird, Andy J.; Low, Robert; Young, Dylan M.; Swindles, Graeme T.; López, Omar R.; Page, Susan

doi:10.1002/2016gl072245

Cited by 57 publications

(83 citation statements)

References 29 publications

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“…5C). Very high permeability near the peat surface is consistent with our observations of more void space higher in the peat profile and also with recent data from other tropical peatlands (30 …”

Section: Resultssupporting

confidence: 92%

How temporal patterns in rainfall determine the geomorphology and carbon fluxes of tropical peatlands

Cobb

Hoyt

Gandois

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

111

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Tropical peatlands now emit hundreds of megatons of carbon dioxide per year because of human disruption of the feedbacks that link peat accumulation and groundwater hydrology. However, no quantitative theory has existed for how patterns of carbon storage and release accompanying growth and subsidence of tropical peatlands are affected by climate and disturbance. Using comprehensive data from a pristine peatland in Brunei Darussalam, we show how rainfall and groundwater flow determine a shape parameter (the Laplacian of the peat surface elevation) that specifies, under a given rainfall regime, the ultimate, stable morphology, and hence carbon storage, of a tropical peatland within a network of rivers or canals. We find that peatlands reach their ultimate shape first at the edges of peat domes where they are bounded by rivers, so that the rate of carbon uptake accompanying their growth is proportional to the area of the still-growing dome interior. We use this model to study how tropical peatland carbon storage and fluxes are controlled by changes in climate, sea level, and drainage networks. We find that fluctuations in net precipitation on timescales from hours to years can reduce long-term peat accumulation. Our mathematical and numerical models can be used to predict long-term effects of changes in temporal rainfall patterns and drainage networks on tropical peatland geomorphology and carbon storage.tropical peatlands | peatland geomorphology | peatland hydrology | peatland carbon storage | climate-carbon cycle feedbacks T ropical peatlands store gigatons of carbon in peat domes, gently mounded land forms kilometers across and 10 or more meters high (1). The carbon stored as peat in these domes has been sequestered by photosynthesis of peat swamp trees (2) and preserved for thousands of years by waterlogging, which suppresses decomposition. Human disturbance of tropical peatlands by fire and drainage for agriculture is now causing reemission of that carbon at rates of hundreds of megatons per year (2-5): Emissions from Southeast Asian peatlands alone are equivalent to about 2% of global fossil fuel emissions or 20% of global land use and land cover change emissions (6, 7). Because peat is mostly organic carbon, a description of the growth and subsidence of tropical peatlands also quantifies fluxes of carbon dioxide (1,4,8). Evidence from a range of studies establishes that accumulation and loss of tropical peat are controlled by water table dynamics (4, 9). When the water table is low, aerobic decomposition occurs, releasing carbon dioxide; when the water table is high, aerobic decomposition is inhibited by lack of oxygen, production of peat exceeds its decay, and peat accumulates. In this way, the rate of peat accumulation is determined by the fraction of time that peat is exposed by a low water table (Fig. 1).The water table rises and falls in a peatland according to the balance between rainfall, evapotranspiration, and groundwater flow. Water flows downslope toward the edge of each peat dome, where it is bo...

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Section: Resultssupporting

confidence: 92%

How temporal patterns in rainfall determine the geomorphology and carbon fluxes of tropical peatlands

Cobb

Hoyt

Gandois

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

111

View full text Add to dashboard Cite

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“…Many other studies have shown how depth‐integrated decay of peat (usually the dominant component of R E ) increases as the water table deepens (see Baird et al., ). The combined P G and R E data from Hirano et al.…”

Section: Discussionmentioning

confidence: 98%

“…Hirano et al (2012) investigated the C balance of drained and near-natural ombrotrophic tropical peatlands using eddy correlation. For a near-natural site, they found that gross primary production (P G ) showed a quadratic relationship with water- Baird et al, 2017). The combined P G and R E data from Hirano et al (2012) show that net rates of peat accumulation are highest when a tropical peatland is at its wettest and lowest when it is at its driest.…”

Section: Allogenic and Autogenic Controls On Peatland Developmentmentioning

confidence: 99%

Ecosystem state shifts during long‐term development of an Amazonian peatland

Swindles

Morris

Whitney

et al. 2017

Global Change Biology

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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. 8.9 ka 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. 3.9 ka BP). Local burning occurred at least three times in the past 4,500 years. Two phases of particularly rapid C accumulation (ca. 6.6-6.1 and ca. 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 ca. 1.8-1.1 ka 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. Here, we present an investigation into the long-term controls on C accumulation in the oldest peatland reported in the Amazon basin.We develop a comprehensive, multiproxy palaeoecological dataset to (i) determine the developmental trajectory of the peatland and (ii) assess the peatland's response to past climate change. A hole was augered at each sampling point and water level measured at regular intervals until it equalized to determine depth to water Approximately one half of each surface litter sample was weighed, oven dried, burnt in a muffle furnace, and reweighed to determine moisture content and loss-on-ignition. The other half was used for analysis of contemporary testate amoebae (see Swindles et al., 2014). | MATERIALS AND METHODS | Study site

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“…al., ; Ingram, ; Leifeld et al, ; Morris et. al., ], the development of pipes [ Cunliffe et al, ; Holden and Burt, ; Holden, , ], changes in column height due to mechanical compaction [ Baird et al, ; Hooijer et al, ; Williamson et al, ; Wösten et al, ], and the development of bare peat [ Tallis, ; Parry et al, ] (all are discussed in supporting information, Text S2). While these processes could be developed in a future version of the model, our aim at this stage was to simulate the development of plausible peatlands and to explore the effects of artificial drainage in space as well as time; which is different from previous studies that use 1‐D models [e.g., Frolking et al ., ; Kurnianto et al ., ].…”

Section: Methodsmentioning

confidence: 99%

Simulating the long‐term impacts of drainage and restoration on the ecohydrology of peatlands

Young

Baird

Morris

et al. 2017

Water Resources Research

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Drainage alters the carbon storage and accumulation functions of peatlands, but the long‐term effects of drainage ditches, and their restoration, on peatland development are poorly understood. Timescales of monitoring studies in ditch‐drained and restored peatlands are typically limited to a few years, and occasionally decades. In addition, experimental studies seldom monitor spatial changes in peat structure caused by ditches, despite such changes affecting water flow and water retention in peat. Ecosystem models offer an alternative to experimental studies and can help explain how complex systems such as peatlands may respond to external disturbances. Here we report on a 2‐D application of a peatland development model (DigiBog) to explore how contour‐parallel ditches, and their damming, affect the ecohydrology of peatlands over decades to centuries, using blanket peatlands as a case study. Drainage resulted in the rapid loss of peat due to increased oxic decay. The majority of these losses occurred in the first 100 years after the ditch was created, but water table dynamics were altered even centuries later. Restoration halted the loss of peat and encouraged net peat accumulation, although the amount lost in 100 years of drainage had not been replaced 200 years after the ditch was dammed. Restoration of ditches in sloping peatlands brought about more peat regrowth downslope of the restored ditch than further upslope. Our study demonstrates the potential for spatially distributed ecosystem‐scale models as tools to explore complex spatiotemporal responses to disturbance, and to support land managers in making decisions about peatland drainage and restoration.

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High permeability explains the vulnerability of the carbon store in drained tropical peatlands

Cited by 57 publications

References 29 publications

How temporal patterns in rainfall determine the geomorphology and carbon fluxes of tropical peatlands

How temporal patterns in rainfall determine the geomorphology and carbon fluxes of tropical peatlands

Ecosystem state shifts during long‐term development of an Amazonian peatland

Simulating the long‐term impacts of drainage and restoration on the ecohydrology of peatlands

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