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Abstract

Amazonia has been recently included in discussions on the role of tropical peatlands in the global carbon cycle owing to extensive peatlands up to 7.5 m thick, reported from Western Amazonia (Peru). The aim of this study was to explore peat accumulation in Central Amazonia (Brazil). Of seven field sites, six located in the Negro River basin and one close to the junction of the Negro River with the Amazon, four had a peat deposit from 0.10 to 2.10 m thick. Another two sites had other organic soil type which could not be called peat. Only one site did not have any organic deposit. The loss-on-ignition (LOI), carbon content and dry bulk density, measured for the four peatland sites, varied from 17.7 to 97.4 %, 11 to 59 %, and 0.0002 to 0.572 g cm−3, respectively. All sites were classified as minerotrophic based on pH and peat thickness. The study confirms that Amazonian peatlands are not limited to Western Amazonia but also exist in Central Amazonia. We could not find as thick and extensive peats as in Western Amazonia, which we suggest is due to differences in rainfall and hydrology, tectonic conditions, topography, subsoil type and frequency of fires.

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... Although these ecosystems cover 14% of the basin, there are two reasons why their vulnerability may have substantial cascading effects. First, floodplains in the western and central Amazon include peatlands that store enormous amounts of carbon (estimates of ∼3.14 Pg C, available only for western peatlands) (26,27), which could potentially be released to the atmosphere by fire. Second, our results imply that if the climate becomes drier, fire-prone savannas might expand through floodable areas toward the core of the Amazon forest and become sources of fires that may spread to large parts of that region. ...
... The acid and nutrient-poor black water that flows in countless streams and tributaries born in the forest has a major influence on half of Amazonian floodplains (46). Amazonian floodplains also include peatlands (26,27), swamps, palm forests, white-sand forests, and extensive islands of savanna (46). ...
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The massive forests of central Amazonia are often considered relatively resilient against climatic variation, but this view is challenged by the wildfires invoked by recent droughts. The impact of such fires that spread from pervasive sources of ignition may reveal where forests are less likely to persist in a drier future. Here we combine field observations with remotely sensed information for the whole Amazon to show that the annually inundated lowland forests that run through the heart of the system may be trapped relatively easily into a fire-dominated savanna state. This lower forest resilience on floodplains is suggested by patterns of tree cover distribution across the basin, and supported by our field and remote sensing studies showing that floodplain fires have a stronger and longer-lasting impact on forest structure as well as soil fertility. Although floodplains cover only 14% of the Amazon basin, their fires can have substantial cascading effects because forests and peatlands may release large amounts of carbon, and wildfires can spread to adjacent uplands. Floodplains are thus an Achilles' heel of the Amazon system when it comes to the risk of large-scale climate-driven transitions.
... Another worrying fact is the degradation of forest-associated ecosystem, such as the peatland ecosystems of the Amazon, concentrated in Western and Central Amazon, mainly in Peru and Brazil (Román-Cuesta et al. 2011, Lähteenoja et al. 2012, Lähteenoja et al. 2013, Draper et al. 2014). Increased deforestation due to land use make these wet ecosystems susceptible to fire (Adrianto et al. 2020). ...
... The peatlands in the Brazilian Amazon are distributed mainly in the Amazonas and Amapá states (Lähteenoja et al. 2013 (Figure 1). Both states are affected by fires and other anthropic impacts. ...
Article
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The Amazon rainforest has been the target of several attacks, such as the massive increase in deforestation and fire outbreaks. The Amazon biome is not only composed of forest ecosystems, but also of an important carbon stock system called Peatland, which contains ca. 1 to 8 billion tons of carbon in its plants and soil. If burned, this peculiar ecosystem is likely to release tons of greenhouse gases, which may aggravate global warming. Therefore, our objective is to alert and anticipate problems associated with deforestation and fires in Peatland that, if not contained, may difficult global warming controlling, and the achievement of goals set in the Paris Agreement (which Brazil is a signatory).
... Many peatlands in tropical region are minerotrophic having been formed from the lateral migration of rivers (Lähteenoja et al., 2012(Lähteenoja et al., , 2013Lähteenoja, Ruokolainen, Schulman, & Alvarez, 2009;Lähteenoja, Ruokolainen, Schulman, & Oinonen, 2009;Schumann & Joosten, 2008). Most of them are located in river deltas, floodplain areas, abandoned river channels and shallow oxbow lakes (dead arms; Baker et al., 2014;Craft & C.B.T.-C., 2016;Rebelo et al., 2009;Rieley et al., 2008). ...
... This new estimate is two to three The new estimates of total peat cover in the tropics represent a volume of about 3,850-7,268 km 3 (estimated using area from Gumbricht et al., 2017 andXu et al., 2018, and mean depth from Gumbricht et al., 2017), which is much higher than the previous es- Figure 2). It is important to note that in Indonesia there is a longer history of fieldwork and, therefore, a relatively large database of ground-truthing points (Jaenicke et al., 2008), whereas to date there are relatively few published field data from the Congo Basin (Dargie et al., 2017), and even fewer from Brazil (Lähteenoja et al., 2013). ...
Article
Peatlands are carbon‐rich ecosystems that cover 185‐423 million hectares of the earth’s surface. The majority of the world’s peatlands are in temperate and boreal zones, whereas tropical ones cover only a total area of 90‐170 million hectares. However, there are still considerable uncertainties in C stock estimates as well as a lack of information about depth, bulk density and carbon accumulation rates. The incomplete data is notable especially in tropical peatlands located in South America, which are estimated to have the largest area of peatlands in the tropical zone. This paper displays the current state of knowledge surrounding tropical peatlands and their biophysical characteristics, distribution and carbon stock, role in the global climate, the impacts of direct human disturbances on carbon accumulation rates and greenhouse gas emissions. Based on the new peat extension and depth data, we estimate that tropical peatlands store 152‐288 GtC, or about half of the global peatland emitted carbon. We discuss the knowledge gaps in research on distribution, depth, C stock and fluxes in these ecosystems which play an important role in the global carbon cycle and risk releasing large quantities of greenhouse gases into the atmosphere (CO2 and CH4) when subjected to anthropogenic interferences (e.g. drainage and deforestation). Recent studies show that although climate change has an impact on the carbon fluxes of these ecosystems, the direct anthropogenic disturbance may play a greater role. The future of these systems as carbon sinks will depend on advancing current scientific knowledge and incorporating local understanding to support policies geared toward managing and conserving peatlands in vulnerable regions, such as the Amazon where recent records show increased forest fires and deforestation.
... Hence, these forests are crucial for maintaining local fishery activities (Saint-Paul et al. 2000). This ecosystem also hosts extensive peatlands as a potential carbon source if burnt (L€ ahteenoja, Flores & Nelson 2013), yet despite their high natural flammability, most blackwater forests across the Amazon remain unprotected. ...
... atmosphere from burning forest biomass and peat deposits (L€ ahteenoja, Flores & Nelson 2013;Grace, Mitchard & Gloor 2014). Therefore, fire prevention in blackwater forests during drought events may be the most practical way to protect this ecosystem's unique biodiversity as well as its capacity to provide resources for local peoples. ...
Article
Climate change may increase the occurrence of droughts and fires in the Amazon. Most of our understanding on how fire affects tropical ecosystems is based on studies of non-flooded forest-savanna ecotones. Nonetheless, tropical floodplain forests in the Amazon can burn severely during extreme droughts. The mechanisms slowing down forest regeneration in these ecosystems remain poorly understood and have never been assessed in the field. We studied the recovery of Amazonian blackwater floodplain forests after one and two fire events. We used Landsat images to map fire history and conducted field surveys to measure forest structure, tree species richness, tree seed bank and post-fire invasion of herbaceous plants. Sites burnt once had on average 0% trees, 6% tree seed abundance, 23% tree seed species richness and 8% root mat thickness compared to unburnt forests. In contrast, herbaceous cover increased from 0 to 72%. Nonetheless, forest structure and diversity recovered slowly towards pre-burn levels, except for tree seed banks that remained depleted even 15 years after fire. Sites burnt twice had on average 0% trees, 1% tree seed abundance, 3% tree seed species richness and 1% root mat thickness compared to unburnt forests. Herbaceous cover increased to 100%. Mean recovery of tree basal area was 50% slower and of root mat thickness 93% slower compared to recovery in sites burnt once. Tree seed banks did not recover at all, and herbaceous cover persisted close to 100% for more than 20 years after the second fire. Synthesis and applications. Our results indicate that after a second fire event, Amazonian blackwater floodplain forests lose their recovery capacity, and persist in a non-forested state dominated by herbaceous vegetation. Such fragility implies that preventing human ignited fires during drought episodes is a particularly important conservation strategy for these ecosystems.
... In Peru, peatlands are found at both low (Lähteenoja et al. 2009b;Householder et al. 2012;Lähteenoja et al. 2013;Draper et al. 2014) and high altitudes (Hribljan et al. 2016;Hribljan et al. 2017) and can be ombrotrophic or minerotrophic (Lähteenoja et al. 2009a) which support the growth of different vegetation types (Roucoux et al. 2013;Draper et al. 2017). No difference in total ecosystem C stocks was observed between ombrotrophic or minerotrophic sites, even though areas that are less influenced by river systems may continue to accumulate organic matter and transform into elevated ombrotrophic bogs (Lähteenoja et al. 2009a;Lawson et al. 2014). ...
Article
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Tropical peat swamp forests (PSF) are characterized by high quantities of carbon (C) stored as organic soil deposits due to waterlogged conditions which slows down decomposition. Globally, Peru has one of the largest expanse of tropical peatlands, located primarily within the Pastaza-Marañón river basin in the Northwestern Peru. Peatland forests in Peru are dominated by a palm species—Mauritia flexuosa, and M. flexuosa-dominated forests cover ~ 80% of total peatland area and store ~ 2.3 Pg C. However, hydrologic alterations, land cover change, and anthropogenic disturbances could lead to PSF’s degradation and loss of valuable ecosystem services. Therefore, evaluation of degradation impacts on PSF’s structure, biomass, and overall C stocks could provide an estimate of potential C losses into the atmosphere as greenhouse gases (GHG) emissions. This study was carried out in three regions within Pastaza-Marañón river basin to quantify PSF’s floristic composition and degradation status and total ecosystem C stocks. There was a tremendous range in C stocks (Mg C ha⁻¹) in various ecosystem pools—vegetation (45.6–122.5), down woody debris (2.1–23.1), litter (2.3–7.8), and soil (top 1 m; 109–594). Mean ecosystem C stocks accounting for the top 1 m soil were 400, 570, and 330 Mg C ha⁻¹ in Itaya, Tigre, and Samiria river basins, respectively. Considering the entire soil depth, mean ecosystem C stocks were 670, 1160, and 330 Mg C ha⁻¹ in Itaya, Tigre, and Samiria river basins, respectively. Floristic composition and calcium to Magnesium (Ca/Mg) ratio of soil profile offered evidence of a site undergoing vegetational succession and transitioning from minerotrophic to ombrotrophic system. Degradation ranged from low to high levels of disturbance with no significant difference between regions. Increased degradation tended to decrease vegetation and forest floor C stocks and was significantly correlated to reduced M. flexuosa biomass C stocks. Long-term studies are needed to understand the linkages between M. flexuosa harvest and palm swamp forest C stocks; however, river dynamics are important natural drivers influencing forest succession and transition in this landscape.
... Here we present a new multi-proxy dataset from a peat and sediment sequence from a palm 74 swamp at a site called Quistococha, in Amazonian Peru. Our detailed study of a single core, 75 supported by published pollen data from the same sequence (Roucoux et al. 2013), 76 complements more extensive but less detailed surveys of the carbon, nitrogen and selected 77 metal cation concentrations of cores and near-surface peat samples from several sites in the 78 same region of Amazonian Peru and western Brazil (including five samples from a separate 79 core at Quistococha: Lähteenoja et al. 2009a, b, 2013 Lähteenoja and Page 2011). 80 Our principal aim in this paper is to interpret the characteristics of our peat and sediment 81 sequence in terms of past and present environmental conditions and peatland processes. ...
Article
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The chemical, physical and palaeobotanical composition of peat can be used to infer the history of a peatland and the processes presently operating within it. Here we present new data on the geochemistry of a peat sequence from a lowland palm swamp, Quistococha, in Peruvian Amazonia. We show, through comparison with subfossil pollen data from the same sequence, that changes in the depositional environment cause changes in peat properties including lignin content, C/N ratios, and the abundance of several metal cations, but that these properties are altered by post-depositional processes to a large extent. An upward trend in the top 1.5 m of the sequence in the concentrations of N, K, Ca, Mg and Na probably reflects nutrient uptake and cycling by the standing biomass. Upward trends in Mn and Fe concentrations suggest that limited oxygenation of the peat may occur to a similar depth. Comparison with other published records suggests that such deep biological alteration may be characteristic of tropical forested peats.
... High rainfall, frequent flooding and low lying topography provide the waterlogged and anoxic conditions required for peat formation which, in this geological setting, have enabled significant thicknesses (up to 7.5 m) of peat to accumulate [9,17,18]. Much smaller peatlands have also been reported from Southern Peru (294 km 2 , 0.027 PgC [19]), central Amazonia (area and carbon stocks unknown [20]), and North of the Amazon basin in the Orinoco delta (7000 km 2 , 0.049 Pg C [21]). In contrast with the better-known but highly degraded and at-risk peatlands of SE Asia [22], those of the PMFB remain largely intact and the threat of destruction from direct human impacts is comparatively low. ...
Article
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Peatlands in Amazonian Peru are known to store large quantities of carbon, but there is high uncertainty in the spatial extent and total carbon stocks of these ecosystems. Here, we use a multi-sensor (Landsat, ALOS PALSAR and SRTM) remote sensing approach, together with field data including 24 forest census plots and 218 peat thickness measurements, to map the distribution of peatland vegetation types and calculate the combined above- and below-ground carbon stock of peatland ecosystems in the Pastaza-Marañon foreland basin in Peru. We find that peatlands cover 35 600 ± 2133 km2 and contain 3.14 (0.44–8.15) Pg C. Variation in peat thickness and bulk density are the most important sources of uncertainty in these values. One particular ecosystem type, peatland pole forest, is found to be the most carbon-dense ecosystem yet identified in Amazonia (1391 ± 710 Mg C ha−1). The novel approach of combining optical and radar remote sensing with above- and below-ground carbon inventories is recommended for developing regional carbon estimates for tropical peatlands globally. Finally, we suggest that Amazonian peatlands should be a priority for research and conservation before the developing regional infrastructure causes an acceleration in the exploitation and degradation of these ecosystems.
... The volume of the in situ peat sample is usually assumed to be identical to the internal volume of the corer. In reality, core recovery is often imperfect, especially in fibrous or woody peat that cannot be cut cleanly, or where the peat is structurally weak and is not retained within the corer, or (in the case of piston corers) it fails to fill the barrel (Wright 1991;Dommain et al. 2011;Lähteenoja et al. 2013). Thus, DBD measurements are probably often subject to large errors stemming from erroneous volume estimations. ...
Article
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Our limited knowledge of the size of the carbon pool and exchange fluxes in forested lowland tropical peatlands represents a major gap in our understanding of the global carbon cycle. Peat deposits in several regions (e.g. the Congo Basin, much of Amazonia) are only just beginning to be mapped and characterised. Here we consider the extent to which methodological improvements and improved coordination between researchers could help to fill this gap. We review the literature on measurement of the key parameters required to calculate carbon pools and fluxes, including peatland area, peat bulk density, carbon concentration, above-ground carbon stocks, litter inputs to the peat, gaseous carbon exchange, and waterborne carbon fluxes. We identify areas where further research and better coordination are particularly needed in order to reduce the uncertainties in estimates of tropical peatland carbon pools and fluxes, thereby facilitating better-informed management of these exceptionally carbon-rich ecosystems.
... Also accumulation of organic matter in these forested environments might be higher than in uncanopied systems and might be partially responsible for the formation of peatlands (Lahteenoja et al. 2013), with implications for the carbon budget and emission of greenhouse gases from the region (Wright et al. 2013). ...
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Rivers and floodplains on the Andean-Amazon interface have been much less studied but are clearly distinct in their hydrological regimes and thus the ecological roles that floodplain inundation plays in these ecosystems. Flooding occurs seasonally in multiple discrete events that control the water regime of floodplains, fish migration, plant phenology, and human activities associated with these processes. Yet at the outset of this research we lacked even a fundamental description of the hydrological features of these river systems, which are lined with vast floodplains. The Napo River is a major Amazon tributary that drains ~105 km2 and flows through the Andean foreland, a sparsely inhabited rainforest region of exceptional biodiversity. The Napo River corridor includes a diversity of floodplain and lacustrine ecosystems, many of which are hydrologically connected to the main stem of the river. Large-scale hydrological modifications have been proposed in the basin, including the Napo barge waterway along the lowland reaches of the river in Ecuador and Peru, the Mazán hydroelectric project near its confluence with the Amazon, and the Coca Codo Sinclair hydroelectric project in the Andean portion of the basin. These works would modify the geomorphology and hydrology of the river channels, and impacts may extend far inland where extensive floodplains exist, as well as far upriver and downstream, with unknown environmental consequences. A comprehensive assessment of the hydrology and ecology of these environments is required to predict and minimize impacts of these kinds of development projects. Thus, with this in mind I set off to improve our understanding of the ecohydrological relationships between the Napo River and its floodplains. To address this goal during nine field campaigns conducted from 2007 to 2013 I used a combination of field observations and water sampling, deployment of sensor networks (including unattended sensors and water collectors), and ground truthing of remotely sensed imagery. Study sites were reached by boat along ~800 km of river reaches in Ecuador and Peru. Floodplains and wetlands were explored on foot with guides from the local communities and a research assistant, during low water when they were accessible. More than 1000 water samples were collected for major solute analysis to determine the water sources (i.e., river overflow vs local rainfall or runoff) of inundation. Observations of the spatial distribution of inundation and associated vegetation were made to aid in interpretation of field and remote sensing data, and flood regimes (hydroperiod, depth of flooding) of more than 100 sites along the river were determined. Among the outcomes of this project are: 1) the development of a method to assess inundation in different environmental settings using the diel amplitude of temperature, 2) the identification of the main sources of flood waters in the floodplains using major solutes, and 3) the determination of the hydrological regimes of the Napo River floodplains using the approaches listed above. Results obtained through this work improved our understanding of the ecohydrology and diversity of tropical floodplains and wetlands, and serve as a basis for future studies on how hydrology determines the structure and composition of tropical floodplain communities and ecosystem processes, and provide information crucial for the assessment of potential negative impacts on these environments caused by proposed river development projects. This study will help natural resource managers and other decision makers set priorities for conservation and develop guidelines and strategies for the wise use of environments in the region.
... Peat-forming vegetation ranges from palm forests and herbaceous vegetation growing on thicker peat layers (5 to 10 m) (Aslan et al., 2003;Vegas-Vilarrúbia et al., 2010), to swamp forest and shrublands on thinner peats (≤150 cm) (Vegas-Vilarrúbia et al., 2010). Lähteenoja et al. (2013) have suggested that the lesser extent of reported peatlands in central Amazonia, compared with western Amazonia, could be explained by a number of factors, including rainfall and hydrology, tectonic conditions, topography, minerogenic subsoil type and the frequency of fires. ...
Article
The status of tropical peatlands, one of Earth’s most efficient natural carbon stores, is of increasing international concern as they experience rising threat from deforestation and drainage. Peatlands form over thousands of years, where waterlogged conditions result in accumulation of organic matter. Vast areas of Southeast Asian peatlands have been impacted by land use change and fires, whilst lowland tropical peatlands of Central Africa and South America remain largely hydrologically intact. To predict accurately how these peatlands may respond to potential future disturbances, an understanding of their long-term history is necessary. This paper reviews the palaeoecological literature on tropical peatlands of Southeast Asia, Central Africa and South America. It addresses the following questions: (i) what were the past ecological dynamics of peatlands before human activity?; (ii) how did they respond to anthropogenic and natural disturbances through the palaeoanthropocene, the period from whence evidence for human presence first appeared?; and, (iii) given their past ecological resilience and current exposure to accelerating human impacts, how might the peatlands respond to drivers of change prevalent in the anthropocene? Throughy synthesising palaeoecological records, this review demonstrates how tropical peatland ecosystems have responded dynamically, persisting through fire (both natural and anthropogenic), climatic and human-induced disturbances in the palaeoanthropocene. Ecosystem resilience does, however, appear to be compromised in the past c. 200 years in Southeast Asian peatlands, faced with transformative anthropogenic impacts. In combination, this review’s findings present a pantropical perspective on peatland ecosystem dynamics, providing useful insights for informing conservation and more responsible management.
... Large uncertainties stem from the sparseness of measurements and uncertainties in habitat areas. Particularly large data gaps exist for the Llanos de Moxos (Bolivia), peatlands in the Pastaza Marañon foreland basin (Peru, Lähteenoja et al. 2012) and central-west Amazon (Lähteenoja et al. 2013), coastal freshwater wetlands (Castello et al. 2013), riparian zones along streams throughout the basin (Junk et al. 2011), small reservoirs associated with agriculture (Macedo et al. 2013) and habitats above 500 m. Improved estimates also require incorporation of seasonal and interannual variations in inundation and habitat areas. ...
Chapter
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This Report provides a comprehensive, objective, open, transparent, systematic, and rigorous scientific assessment of the state of the Amazon’s ecosystems, current trends, and their implications for the long-term well-being of the region, as well as opportunities and policy relevant options for conservation and sustainable development.
... More recently, studies have begun to assess peatland carbon storage and distribution across central Africa (Dargie et al., 2017) and south America 148 (Lahteenoja et al., 2013, Kelly et al., 2017. Studies in Panama have thus far assessed variation in CO 2 and CH 4 fluxes along vegetation gradients with reference to the impacts of environmental factors , Wright et al., 2011, Wright et al., 2013a, Wright et al., 2013b, and decomposition processes (Hoyos-Santillan et al., 2015, Hoyos-Santillan et al., 2016a, Hoyos-Santillan et al., 2016b, Hoyos Santillan et al., 2018, Utpon et al., 2018 and microbial community structure (Troxler et al., 2012 and context, as well as next steps for elucidating plant influences on broader patterns of nutrient cycling. ...
Article
Tropical forested peatlands are a major carbon store and are a significant source of global carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emissions. While the role of environmental variables, including temperature and water table depth have been relatively well studied, uncertainty remains in the extent to which plant roots regulate greenhouse gas (GHG) fluxes and peat biogeochemistry. This study examined the role of roots, and root inputs of carbon and oxygen in regulating fluxes from peat under two dominant plant species, Campnosperma panamensis and Raphia taedigera, a broadleaved evergreen tree and canopy palm, in San San Pond Sak wetland, in Bocas del Toro Province, Panama. A combination of in situ and ex situ experiments were performed between February 2015 and August 2017. Small scale variation in GHG fluxes and peat biogeochemistry was measured at two distances within the rooting zones of C. panamensis and R. taedigera. Peat organic matter properties were assessed using Rock-Eval 6 pyrolysis. Results indicated significant variation in CH4 but not CO2 fluxes at different distances within the rooting zone, with CH4 fluxes subsequently linked to measures of the overall size of the available organic carbon pool (S2). Rock-Eval pyrolysis data was used to construct a three-pool model of organic matter thermostability which indicated significant differences in organic matter composition between peats derived from different botanical origins, in addition to a high level of heterogeneity within the rooting zone. Changes in GHG production and peat biogeochemical properties in response to the addition of root exudate analogues were assessed in an ex situ anoxic incubation experiment. A combination of organic acids and sugars, identified as common forest plant root exudate components, were added over a two week period to peats derived from C. panamensis and R. taedigera. GHG fluxes varied significantly between treatments but not by peat botanical origin, and were associated with significant changes in soil properties including, pH and redox potential, thereby demonstrating a link between plant root carbon inputs, peat properties and GHG fluxes. In situ mesocosms were used to assess the effects of root exclusion on peat biogeochemistry and GHG fluxes. Partial and full root exclusion significantly reduced dissolved oxygen concentrations and was associated with greater root necromass. Full root exclusion increased CH4 fluxes five-six fold compared to partial root exclusion, equivalent to an 86 – 90% reduction in CH4 oxidation, demonstrating the important role of root inputs of oxygen in mitigating CH4 efflux from tropical peat. A 13CO2 pulse labelling experiment was conducted using both R. taedigera, C. panamensis, and Symphonia globulifera, a second broadleaved evergreen tree species, to demonstrate a direct link between plant photosynthesis and CH4 fluxes, and identify aspects of the bacterial and fungal community associated with the turnover of labile carbon. The extent of 13C enrichment of CH4 differed significantly between plant types (palms vs broadleaved evergreen trees), as did the extent of net CH4 efflux. Phospholipid fatty acid (PLFA) biomarker analysis indicated both peat types were dominated by Gram negative bacteria. There was strong 13C enrichment of Gram negative bacteria, supporting their previously proposed role as important decomposers of labile carbon. Collectively, these results demonstrate that root inputs of carbon and oxygen can strongly regulate tropical peatland GHG fluxes, and that the extent of regulation can vary significantly between tropical wetland plant species from contrasting dominant plant types. This is particularly important in understanding regulatory processes in a globally significant carbon store and understanding possible consequences of land use change in the tropics.
... Although large and significant, the PMFB is just one of the basins in the Amazon that contains peat. Others have been classified in the eastern Amazon in Peru (Householder et al., 2012) and in the Brazilian Amazon (Lähteenoja, Flores and Nelson, 2013), and there are probably many more, currently "invisible" areas that need to be formally identified and classified and which are subject to various threats. Compared with the situation in Southeast Asia (Page and Hooijer, 2016), many of the Amazon's peatlands are relatively intact and under limited immediate threat of drainage or conversion. ...
... Elevation, by itself, does not guarantee low soil moisture, high levels of erosion, or sparse, droughtstricken vegetation (e.g., Fig. 5). Furthermore, as indicated unequivocally by blanket-peat distribution in temperate regions (e.g., Gorham, 1957;Bragg and Tallis, 2001;Evans and Warburton, 2011), or, similarly, by high elevation inland-upland peat accumulations in the modern tropics (Amazon - Lähteenoja et al., 2013;Malaysia -Wüst and Bustin, 2001;Africa -Dargie et al., 2017), uplands are not necessarily, and certainly not obligately, dry. Rather, elevated areas are subject to periodic drought if the prevailing climate is seasonally dry, but they may experience little or no drought if the regional climate is aseasonally humid. ...
Article
The Late Mississippian and Pennsylvanian have been referred to as the Coal Age due to enormous paleotropical peat accumulations (coal beds). Numerous fossil floras have been collected from these coals, and their associated seat-earth paleosols and roof-shales, over more than two centuries, leading to the inference of vast swampy wetlands covering the Pangean tropics during the Pennsylvanian. In contrast, the Permian tropics are characterized as more arid, with sparser and more heterogeneous vegetation than inferred for the Pennsylvanian. In the tropics, the Pennsylvanian to Permian transition has been described as a changeover from a pteridophytedominated “Paleophytic flora”, to a seed-plant dominated “Mesophytic flora. This view notwithstanding, floras dominated by xeromorphic seed plants also are well known from the Pennsylvanian tropics. Some authors have characterized these plants as being occupants of uplands, subsequently transported into basinal-lowland, preservational environments. In this model, uplands are well drained, causing areas of drought under otherwise everwet climates. In this paper, we present an alternative interpretation: that the apparent transition in Pennsylvanian-Permian tropical vegetation reflects two types of taphonomic megabias. First is a preservational megabias, strongly favoring the vegetation of humid climates over that of seasonally dry climates. Accordingly, tropical-plant preservational potential fluctuated in concert with Late Paleozoic Ice Age glacial-interglacial oscillations, and contemporaneous sea-level and climatic changes. Second is an analytical megabias, strongly favoring the discovery and collection of the wetland biome from Pennsylvanian strata, overlooking the less frequently and more poorly preserved drought-tolerant biome. By Permian times, vast wetlands, and their fossil record, had largely disappeared from central Pangea (although continuing in Cathaysia), making drought-tolerant vegetation more “visible” to searchers, without changing its preservational circumstances. We demonstrate that the upland model is untenable, being inconsistent with the principles of plant biogeography and with geological aspects of the fossil record.
... Although large and significant, the PMFB is just one of the basins in the Amazon that contains peat. Others have been classified in the eastern Amazon in Peru (Householder et al., 2012) and in the Brazilian Amazon (Lähteenoja, Flores and Nelson, 2013), and there are probably many more, currently "invisible" areas that need to be formally identified and classified and which are subject to various threats. Compared with the situation in Southeast Asia (Page and Hooijer, 2016), many of the Amazon's peatlands are relatively intact and under limited immediate threat of drainage or conversion. ...
Preprint
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Peatlands have long been unrecognized or ignored, but they will play a crucial role in climate change and water security and must be a focus of policy and research
... Although large and significant, the PMFB is just one of the basins in the Amazon that contains peat. Others have been classified in the eastern Amazon in Peru (Householder et al., 2012) and in the Brazilian Amazon (Lähteenoja, Flores and Nelson, 2013), and there are probably many more, currently "invisible" areas that need to be formally identified and classified and which are subject to various threats. Compared with the situation in Southeast Asia (Page and Hooijer, 2016), many of the Amazon's peatlands are relatively intact and under limited immediate threat of drainage or conversion. ...
Article
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More knowledge is needed urgently on how to implement effective management regimes for the forest–water nexus. In this article, we draw on our collective experience and the recent literature to highlight knowledge gaps in the integration of the forest–water nexus in science, policy and practice, including the climate-change discourse and the Sustainable Development Goals (SDGs).
... These approaches work better in peats formed from woody vegetation, such as the swamp forests of tropical climates today (Lähteenoja et al., 2013) and in the geological past (Naafs et al., 2018). As angiosperms contain syringyl phenols having two methoxy groups, angiosperm peats may have twice the methoxy of the vanillyl phenols dominating in gymnosperms (Weng and Chapple, 2010). ...
Article
Lignin is a major structural plant biochemical and biogeochemical compound present in peat and lignite. Its monomeric (phenolic) and polymeric structures include varying amounts of ether-bonded methyl groups (i.e., methoxy or OCH3). These methoxy groups are generally underused targets for both structural characterization and isotopic analyses. We analyzed the quantity and C and H isotopic composition of methoxy groups within a range of substrates including lignin phenols, lignin, wood, peat, lignite, and sub-bituminous and bituminous coal. We used the Zeisel method to cleave the ether bonds with hydroiodic acid to yield iodomethane which can be analyzed by gas chromatography (GC). Finding inconsistent transfer and isotope effects associated with room temperature headspace injections, we instead used isooctane as a solvent for the iodomethane analyte (the liquid method). Using the liquid method, we obtained a linear response by GC-flame ionization detection (GC-FID) for iodomethane and a linear calibration and 85 ± 6% recovery of methyl from methoxy groups from solid standards of phenolic compounds of known stoichiometry. We introduced quantification via lignin phenolic compounds to calibrate both analytical and experimental yield. Methyl yields provided structural information and confirmed that lignin oxidation products (LOPs) from copper oxide oxidation underestimate the number of methoxy-bearing phenols (yield < 0.3 of expected based on stoichiometry); in combination the two approaches provide structural information and quantification. We found that concentrations of methyl from methoxy groups in geologic sediments (lignite, sub-bituminous and bituminous coal) initially increase with diagenesis as lignin to cellulose ratio increases, and then decline to low concentrations during coalification, offering new possibilities for characterizing the transformation of peat and lignite. We assessed an array of plant biochemicals and established that natural and synthetic methoxy groups span a broad range of dual stable carbon and hydrogen isotopic compositions indicating scope for biogeochemical and forensic applications.
... Boreal and arctic peatlands cover the largest land area and have been the most extensively studied (i.e., Turunen et al., 2002;Gorham et al., 2003;Smith et al., 2004;MacDonald et al., 2006;Yu et al., 2009;Jones and Yu, 2010). Several studies have advanced understanding of long-term carbon dynamics in tropical peatlands in Indonesia (Neuzil, 1997;Page et al., 2004;Dommain et al., 2011;Page et al., 2011), Africa (Kivinen and Pakarinen, 1981;Joosten and Clarke, 2002;Page et al., 2011), and South America (Lähteenoja et al., 2009(Lähteenoja et al., , 2013, which collectively comprise 11% of the global peatland area (Page et al., 2011). The Florida Everglades is an expansive low-latitude peat accumulating system, but information on the long-term carbon dynamics, especially as it relates to climate, hydrology, and vegetation, is sparse. ...
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Tropical and subtropical peatlands are considered a significant carbon sink. The Florida Everglades includes 6000-km2 of peat-accumulating wetland; however, detailed carbon dynamics from different environments within the Everglades have not been extensively studied or compared. Here we present carbon accumulation rates from 13 cores and 4 different environments, including sawgrass ridges and sloughs, tree islands, and marl prairies, whose hydroperiods and vegetation communities differ. We find that the lowest rates of C accumulation occur in sloughs in the southern Everglades. The highest rates are found where hydroperiods are generally shorter, including near-tails of tree islands and drier ridges. Long-term average rates of 100 to >200 g C m−2 yr−1 are as high, and in some cases, higher than rates recorded from the tropics and 10–20 times higher than boreal averages. C accumulation rates were impacted by both the Medieval Climate Anomaly and the Little Ice Age, but the largest impacts to C accumulation rates over the Holocene record have been the anthropogenic changes associated with expansion of agriculture and construction of canals and levees to control movement of surface water. Water management practices in the 20th century have altered the natural hydroperiods and fire regimes of the Everglades. The Florida Everglades as a whole has acted as a significant carbon sink over the mid- to late-Holocene, but reduction of the spatial extent of the original wetland area, as well as the alteration of natural hydrology in the late 19th and 20th centuries, have significantly reduced the carbon sink capacity of this subtropical wetland.
... Montane freshwater peatlands in the Tropics are useful for reconstruction of climate and ecosystem change owing to their relatively widespread distribution and their high organic matter (OM) content for measurement of organic geochemical proxies and radiocarbon. While the largest tropical peatlands occur in rainforest lowlands of Southeast Asia (Page et al., 2011), Africa (Dargie et al., 2017), and South American Amazonia (Lähteenoja et al., 2013), low-latitude peatland ecosystems can also be found in mountainous terrain, where waterlogged soils are maintained in locally flat areas of heavy rainfall. Such ecosystems and organic deposits are found, for example, in Papua New Guinea (Hope, 2014), West Kalimantan (Anshari et al., 2004), South American Andes (Benavides et al., 2013) and the Guyana Highlands (Zinck and Huber, 2011) and various Pacific Islands (Rieley and Page, 2015). ...
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The Hawaiian Islands are the only high land in a vast stretch of the North Pacific where past climatological and ecological processes can be reconstructed from terrestrial Earth system archives. We measured hydroclimatic proxies and carbon accumulation in an organic sediment core from the windward montane peatland Pēpē‘ōpae on the Island of Moloka‘i, Hawai‘i using radiocarbon, leaf wax geochemistry, and stable isotopes of carbon and hydrogen in addition to historical pollen records. Following a period of soil development, substantial carbon accumulation began around 10 ka BP (thousands of years before present) under wet conditions. Peat formation was continuous but variable throughout the Holocene, including maxima in carbon accumulation around 9 and 3 ka and a minimum around 1.5 ka that has resulted in a belowground carbon storage today of 144 kg C m-2. From this core we generated a new chronology for previously published pollen spectra from the study site and a Wetness Index that shows increases in dry-adapted taxa in upwind forests during periods of decreased carbon accumulation in the peatland. Shifts in the distribution of sedimentary n-alkane chain lengths in the context of 14 species of modern bog plant n-alkanes suggests litter inputs have been derived from a diverse plant community that changed in dominant species in response to climate. Hydrogen stable isotope ratios of sedimentary C29 n-alkanes show negative departures around 9 and 3 ka consistent with increases in storm-derived rainfall likely related to the position and strength of the northern jet stream. This study is the first to provide a continuous organic sedimentary record of links between hydroclimate, vegetation, and montane belowground carbon sequestration for this part of the North Pacific.
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A comparison is made between two strategies to characterise the Amazonian carbon budget: (i) the ‘bottom-up’ approach using plot data and remote sensing and (ii) the ‘top-down’ approach using aircraft-based measurements in the planetary boundary layer. Plot data provide insights into processes which aircraft data cannot provide, but upscaling plot data to the entire basin involves many assumptions and uncertainties: it is necessary to estimate the separate fluxes of carbon to represent rates of deforestation, degradation, timber harvests, and other terms and then add them together. As each term is uncertain, the overall uncertainty is considerable. We estimate the carbon budget to be near to zero, the deforestation fluxes being roughly balanced by the growth of old and successional forests in a normal year. Drought may tip the balance to make the basin a strong source of CO2. Aircraft flights have provided a more direct measurement over the Amazon basin area. Flights need to be made several times a year, and the profiles may be compared with concentrations measured in the incoming air from the Atlantic Ocean. Such measurements demonstrate that the vegetation itself is a sink in a normal year, but the basin is near neutral over 12 months because of carbon losses through burning. Overall, the results from aircraft profiles are not very different from the upscaled estimate.
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The peatland pole forests of the Pastaza-Marañón Foreland Basin (PMFB), Peru, are the most carbon-dense ecosystems known in Amazonia once below ground carbon stores are taken into account. Here we present the first multiproxy palaeoenvironmental record including pollen data from one of these peatlands, San Jorge in northern Peru, supported by an age model based on radiocarbon and 210Pb dating. The pollen data indicate that vegetation changes during the early phases of peat initiation resulted from autogenic succession in combination with fluvial influence. The overall pattern of vegetation change is not straightforward: the record does not reflect a process of unidirectional, progressive terrestrialization, but includes a reversal in the succession and vegetation transitions, which omit predicted successional phases. This complexity is similar to that seen in the only other existing pollen record from a PMFB peatland, at Quistococha, but contrasts with peat records from Panama and Southeast Asia where successional patterning appears more predictable. Our dating results provide the first evidence from a PMFB peatland that peat accumulation may have been discontinuous, with evidence for reduced rates of peat accumulation, or a possible hiatus, around 1300–400 cal yr BP. An ecological shift from open lake to palm swamp occurs at this time, possibly driven by climatic change. The pollen data indicate that the present pole forest vegetation at San Jorge began to assemble c. 200–150 cal yr BP. Given this young age, it is likely that the pole forest at this site remains in a state of transition. https://authors.elsevier.com/a/1UEOC73Nzmxnr
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Wetlands are important providers of ecosystem services and key regulators of climate change. They positively contribute to global warming through their greenhouse gas emissions, and negatively through the accumulation of organic material in histosols, particularly in peatlands. Our understanding of wetlands' services is currently constrained by limited knowledge on their distribution, extent, volume, inter-annual flood variability, and disturbance levels. We present an expert system approach to estimate wetland and peatland areas, depths and volumes, which relies on three biophysical indices related to wetland and peat formation: 1. Long-term water supply exceeding atmospheric water demand; 2. Annually or seasonally water-logged soils; 3. A geomorphological position where water is supplied and retained. Tropical and subtropical wetlands estimates reach 4.7 million km(2) . In line with current understanding, the American continent is the major contributor (45%) and Brazil, with its Amazonian inter-fluvial region, contains the largest tropical wetland area (800,720 km(2) ). Our model suggests, however, unprecedented extents and volumes of peatland in the tropics (1.7 million km(2) and 7,268 (6,076-7,368) km(3) ), which more than three-fold current estimates. Unlike current understanding, our estimates suggest that South America and not Asia contributes the most to tropical peatland area and volume (ca. 44% for both) partly related to some yet unaccounted extended deep deposits but mainly to extended but shallow peat in the Amazon Basin. Brazil leads the peatland area and volume contribution. Asia hosts 38% of both tropical peat area and volume with Indonesia as the main regional contributor and still the holder of the deepest and most extended peat areas in the tropics. Africa hosts more peat than previously reported but climatic and topographic contexts leave it as the least peat forming continent. Our results suggest large biases in our current understanding of the distribution, area, and volumes of tropical peat and their continental contributions. This article is protected by copyright. All rights reserved.
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Vegetation on sandy soils, ranging from open grasslands and shrublands to closed-canopy, thin-trunked forests, can be found in patches throughout the Amazon. Despite variation in names, appearance, ecological correlates, and suggested origins, these 'white-sand ecosystems' (WSE) share distinctive characteristics and biological communities. Here, in the first Amazon-wide review of WSE, we review the variation in WSE and the factors underlying this variation. We present the most comprehensive Amazon-wide map to date of WSE and calculate their total area. We find that WSE are still not completely mapped, and we use biological correlates as a proxy to indicate where white-sand vegetation patches likely occur. Through our synthesis of the literature, we find that key factors, such as geologic origin, soil characteristics, hydrology, and fire regimes, vary widely and have differing impacts in different regions on vegetation structure and on floral, faunal, and fungal species composition. Although studies of WSE have increased dramatically in recent years, WSE in many parts of the Amazon remain understudied, and there is little synthesis of the interaction of factors across different areas. In response, we suggest priorities for future research. Finally, we find that WSE are inadequately protected and, where accessible, are regularly mined for sand, logged, or burned and cleared for agriculture. We argue that due to their island-like distribution patterns and resultant complex metapopulation dynamics, their extremely slow recovery after disturbance, and their important contributions to basin-wide diversity patterns and ecosystem services, WSE should be given special consideration in conservation efforts to ensure their persistence in Amazonia.
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Tropical peatlands represent globally important carbon sinks with a unique biodiversity and are currently threatened by climate change and human activities. It is now imperative that proxy methods are developed to understand the ecohydrological dynamics of these systems and for testing peatland development models. Testate amoebae have been used as environmental indicators in ecological and palaeoecological studies of peatlands, primarily in ombrotrophic Sphagnum-dominated peatlands in the mid- and high-latitudes. We present the first ecological analysis of testate amoebae in a tropical peatland, a nutrient-poor domed bog in western (Peruvian) Amazonia. Litter samples were collected from different hydrological microforms (hummock to pool) along a transect from the edge to the interior of the peatland. We recorded 47 taxa from 21 genera. The most common taxa are Cryptodifflugia oviformis, Euglypha rotunda type, Phryganella acropodia, Pseudodifflugia fulva type and Trinema lineare. One species found only in the southern hemisphere, Argynnia spicata, is present. Arcella spp., Centropyxis aculeata and Lesqueresia spiralis are indicators of pools containing standing water. Canonical correspondence analysis and non-metric multidimensional scaling illustrate that water table depth is a significant control on the distribution of testate amoebae, similar to the results from mid- and high-latitude peatlands. A transfer function model for water table based on weighted averaging partial least-squares (WAPLS) regression is presented and performs well under cross-validation (r[Formula: see text]). The transfer function was applied to a 1-m peat core, and sample-specific reconstruction errors were generated using bootstrapping. The reconstruction generally suggests near-surface water tables over the last 3,000 years, with a shift to drier conditions at c. cal. 1218-1273 AD.
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In the tropics peat occurs mostly in sub-coastal lowlands and is formed from rainforest trees and associated higher plants. There are regional differences in the plant species involved and there are also changes with increase in altitude with a tendency to lower growing and more low temperature tolerant plants. The best estimate of the area of tropical peatland is 441,025 km2 which is about 11 % of the global peatland resource, although there is a wide range of estimate from 387,201 to 657, 430 km2 depending upon whether or not all Histosols and shallow organic soils are included. Current inventories of peatland area, peat thickness and carbon stores leave much to be desired and their accuracy varies not only from region to region but also country to country. The largest area of tropical peatland and peat carbon store is in Southeast Asia with 56 % of the former and 77 % of the latter owing to the large extent of peatlands and the considerable thickness of peat (regularly exceeding 10 m) in this region. Following Southeast Asia, South America contains the next largest area (24 %) of peatland but a smaller proportion of the global tropical peatland carbon store because of the thinner peat deposits. Africa contributes 13 % of the global area and 8 % of the carbon store, while Central America and the Caribbean, Mainland Asia and Australia and the Pacific contribute only 5 %, 1 % and <1 %, respectively and only 3 % of the carbon store, collectively. Tropical peatlands are now being subjected to intensive land use change and conversion to forms of agriculture including commercial plantations. This is well advanced in Southeast Asia, especially Indonesia and Malaysia where most of the peatland area has already been deforested, drained and converted often using fire as a land clearance tool. Apart from losses of biodiversity there have been immense emissions of greenhouse gases and large losses of carbon from the peat store, contributing to climate change processes. Other regions are further behind in these environmentally damaging impacts on the tropical peatland resource.
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Inthis paper, water samples from 29 (twenty nine) tributaries of the Rio Negro went analysed and compared according to their physico-chemical qualities. The majority of the tributaries were very poor in dissolved minerals and highly acidic. Significant relationship were found between the level of colored organic substances ans several chemical parameters. The left bank afluents, originating form the mountains in the North, had higher nutrient levels. While the right bank afluents which, in their majority, originates in the "terras alagadiças" (swampy lands) and in "campinas" (podzol soils), were considered extremely poor. In general, physical, chemical, and biological conditions affect the nitrogen values. The recent fertilization of flooded areas and the appearance of aquatic macrophytes in the Lower Negro are discussed.
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This paper examines organic matter deposition in the avulsion-controlled floodplain of the Saskatchewan River at the Cumberland Marshes, east-central Saskatchewan. Organic-rich deposits were formed throughout the late Holocene in fen/bog (coarse brown peat) and lacustrine (fine dark-brown and black organic-rich mud) environments. The thicknesses of individual organic-rich layers reach 3.2 m but are typically less than 1 m thick. Lateral extents of these beds are limited by elevated alluvial ridges, but they may attain exceptional dimensions of 15 km in transverse and 50 km in longitudinal directions.Conditions for organic deposition on avulsion-controlled floodplains appear to be different from those on other floodplains. In addition to floods, terrigenous sediments are delivered by progradational avulsions into parts of the floodbasin previously accumulating organic-rich sediments. Elevated alluvial ridges resulting from former avulsions, however, block large parts of the floodplain from normal flooding and therefore prevent clastic deposition. Total organic content of floodplain sediments is inversely related to sediment grain size and sedimentation rate. The composition of organic-rich layers reflects a predominantly progradational avulsion style. The center portions of many organic-rich layers are commonly composed of brown fen/bog peat overlain successively by organic-rich and organic-poor lacustrine mud, eventually passing upwards into coarser deposits. The rate of avulsive progradation is roughly reflected in the vertical organic-content gradient within the alluvial sections. Rapid progradation, typical for most portions of the most recent (1870's) avulsion belt, results in relatively abrupt changes of organic content, whereas slower progradation is accompanied by more gradual decreases in organic content.
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We present results of research concerning the distribution, depth, volume, geomorphology, and habitat diversity of peatlands in the southern Peruvian Amazon. We identified 295 peatlands covering 294 km2 and ranging in size from 10 to 3,500 ha. Individual peatlands were mostly restricted to the meander belt of the Madre de Dios River. Mean peat depth was 2.54 ± 1.84 m (n = 429), however we encountered depths to 9 m and 10% of the measurements exceeded 5 m. We developed a calibration factor to calculate peat volume across the study area, estimating total peat volume within 295 peatlands at 657 ± 119 Mm3. An interpolated depth map of subsurface morphology of a single peatland showed that fluvial features were well-conserved beneath several meters of peat and three distinct subsurface geomophological units defined by peat depth could be identified: the Primary Basin, Secondary Basin, and Intrabasin flats. Subsurface geomorphology resulted in increased within-habitat heterogeneity and explained 35% of the variation of pixel values extracted from Landsat™ imagery. Representing a hydrological link from elevated uplands to the lower floodplains, peatlands in Madre de Dios are especially threatened on local scales by habitat alteration in the uplands and gold mining in the floodplains.
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Decomposition of leaf litter is an important process that releases energy and nutrients in both terrestrial and aquatic environments (Moore et al . 2004, Wallace et al . 1997); therefore, the physical, chemical and biological processes controlling leaf-litter decomposition rates can affect nutrient cycling and productivity in these systems (Cross et al . 2007, Wood et al . 2009). Several studies have shown that leaf decomposition is faster in aquatic than in terrestrial habitats due to relatively constant temperatures, continuous leaching and the physical breakdown of leaves by flowing water (Hutchens & Wallace 2002, Langhans & Tockner 2006, Langhans et al . 2008). Yet, comparatively few studies have examined these relationships in tropical systems with flooded forests. Flooding is a predominant feature of the upper Amazon Basin, but its occurrence and magnitude is complex and not strictly seasonal (Junk et al . 1989). To identify the dominant energy pathways and understand the nutrient dynamics of upper Amazon rain forests, it is imperative to investigate organic matter processing in the aquatic/terrestrial transition zones of these ecosystems.
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The Cumberland Marshes in east-central Saskatchewan, Canada, occupy over 5000 km 2 and contain a variety of active and abandoned fluvial features. In 1873, an avulsion of the Saskatchewan River diverted most of its flow into a portion of the Cumberland Marshes (locally termed the breakout area), and altered the alluvial terrain as the invaded wetlands adjusted to the influx of sediment and water. These adjustments continue today. The post-1873 record of deposition and terrain modification in the breakout area suggests four stages of floodplain evolution following avulsion. -from Authors
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A 9.5 m core from an inland peatland in Kalimantan, Indonesia, reveals organic matter accumulation started around 26 000 cal. yr BP, providing the oldest reported initiation date for lowland ombrotrophic peat formation in SE Asia. The core shows clear evidence for differential rates of peat formation and carbon storage. A short period of initial accumulation is followed by a slow rate during the LGM, with fastest accumulation during the Holocene. Between ∼13 000 and 8000 cal. yr BP, > 450 cm of peat were deposited, with highest rates of peat (> 2 mm yr−1) and carbon (> 90 g C m−2 yr−1) accumulation between 9530 and 8590 cal. yr BP. These data suggest that Kalimantan peatlands acted as a large sink of atmospheric CO2 at this time. Slower rates of peat (0.15–0.38 mm yr−1) and carbon (7.4–24.0 g C m−2 yr−1) accumulation between ∼8000 and 500 cal. yr BP coincide with rapid peat formation in coastal locations elsewhere in SE Asia. The average LORCA (long-term apparent carbon accumulation rate) for the 9.5 m core is 56 g C m−2 yr−1. These data suggest that studies of global carbon sources, sinks and their dynamics need to include information on the past and present sizeable peat deposits of the tropics. Copyright © 2004 John Wiley & Sons, Ltd.
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Recent studies on relict eolian dunes in the Rio Negro basin, northern Amazon, Brazil (00°35′N, 63°14′W), indicate a drier climate regime during the Late Pleistocene–Holocene transition that is different from the present humid climate. The eolian sands form long chains of linear dunes bordering the Rio Negro River and some tributaries. Here, we present thermoluminescence (TL) ages spanning the period 32,000–8000 yr B.P. The final dune stabilization took place after 8,000 yr B.P. and now the bases of the dunes are fixed by vegetation. Clustering of the TL dates suggests that the dry climate in the Amazon Basin occurred in distinct episodes and argues against current opinions that drastic ecological changes did not affect in the Amazon during the last global glaciation.
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A comparative analysis on the rate of fine litterfall and its associated nutrient fluxes was carried out in a mixed forest on Tierra Firme, a tall Amazon Caatinga and a Bana on podsolized sands near San Carlos de Rio Negro. There was seasonality in leaf fall and total litterfall in mixed forest and tall Amazon Caatinga forest but no definite trend in the Bana. Litterfall curves were significantly correlated among sites indicating common regulating factors in the three forests. Leaf litter from mixed forest on Tierra Firme was richer in N with extremely low Ca and Mg concentrations; tall Amazon Caatinga litter had higher P and Mg concentration, while Bana litter was low in N but K concentration was twice as high as in the other two forests. Annual fine litterfall in Tierra Firme mixed forest was nearly 4 times higher than in Bana, But N flux was 10 times higher, while Ca and Mg fluxes were similar. Tall Amazon Caatinga had Ca and Mg fluxes in litterfall 2–3 times higher than the other two forests. Within-stand efficiency of nitrogen, calcium and magnesium use, as measured by biomass/nutrient ratios, differentiates Tierra Firme from Caatinga and Bana forest: Tierra Firme has the lowest N, but the highest Ca and Mg use efficiencies. Higher P use efficiency was measured in Bana followed by Tierra Firme and Caatinga; while Tierra Firme and Caatinga showed similar higher K use efficiencies than Bana. N/P ratios indicates that Tierra Firme forest is limited by P availability, while low N availability predominates in Caatinga. Bana appears limited by both N and P. These differences probably relate to variations in degree of sclerophylly and leaf duration which determine leaf nutrient concentrations in the ecosystems studied.
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Amazonian floodplain forests are characterized by an annual flood pulse with changes of the water table that exceed 10 meters. Seedlings and adult trees are waterlogged or submerged for continuous periods lasting up to seven months per year. The monomodal flood pulse of the rivers causes drastic changes in the bioavailability of nutrients, oxygen levels, and concentrations of phytotoxins. The aquatic phase occurs during a period in which temperature and light conditions are optimal for plant growth and development, implying the need for adaptations. Not only do trees persist in a dormant state, they grow vigorously during most of the year, including the aquatic period. The regularity of flooding may have enhanced the evolution of specific traits, which partially are well known from floodplain trees in other tropical and in temperate regions. Different kinds of adaptations are found at the level of structural, physiological, and phenological traits. Combinations of adaptations regarding seed germination, seedling development, and traits of roots, shoots, and leaves result in a variety of growth strategies among trees. These lead to specific species distributions and zonations along the flooding gradient and within Amazonian floodplain systems (nutrient-rich white-water várzea and nutrient-poor black-water igapó).
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Leaf material was incubated in flasks containing streamwater in which the pH and the concentration of isolated fulvic acid were varied independently of one another. Decomposition of the leaf material was slower at pH 4 than at pH 5 or 7, but the concentration of fulvic acid had no effect when the pH was held constant. At pH 5, 20 mg Cl–1 humic acid also had no effect on decomposition. High concentrations of dissolved fulvic acids may contribute to the slow decomposition of plant litter characteristic of many wetlands through their contribution to hydrogen ion activity, but we could find no evidence for other properties of fulvic acid which inhibit leaf litter decomposition.
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Locally extensive pre-Columbian human occupation and modification occurred in the forests of the central and eastern Amazon Basin, but whether comparable impacts extend westward and into the vast terra firme (interfluvial) zones, remains unclear. We analyzed soils from 55 sites across central and western Amazonia to assess the history of human occupation. Sparse occurrences of charcoal and the lack of phytoliths from agricultural and disturbance species in the soils during pre-Columbian times indicated that human impacts on interfluvial forests were small, infrequent, and highly localized. No human artifacts or modified soils were found at any site surveyed. Riverine bluff areas also appeared less heavily occupied and disturbed than similar settings elsewhere. Our data indicate that human impacts on Amazonian forests were heterogeneous across this vast landscape.
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Hirota et al. (Reports, 14 October 2011, p. 232) used spatial data to show that grasslands, savannas, and forests represent opposing stable states. Reanalyzing their data and drawing from temporal studies, we argue that spatial analyses underestimate the bistability of grasslands and savannas due to limitations of substituting space for time. We propose that temporal and spatial data are needed to predict critical transitions between grasslands and savannas.
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Histosols are potentially important in the global carbon cycle, since they show significant carbon accumulation. Variations in Histosol features may influence both vegetation types and carbon storage amounts and rates. In this paper, we compare Histosols of the Lower Orinoco River Delta by examining relationships among the vegetation communities they maintain and differences among organic and mineral layers. We preliminarily assess their potential organic carbon accumulation. Soil samples were collected from 227 sites and analyzed for soil texture, organic matter, pH, salinity, organic carbon, exchangeable cations, nutrients (P, N, K) and sulphate acid potential.
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A mosaic of JERS-1 L-band synthetic aperture radar (SAR) images was used to investigate the influence of tectonic faults on wetland distributions in ∼200,000 km2 of central Amazon lowland (0–4° Lat. S, 60–64° Long. W). The geographic distribution of flooded wetland was clearly evident on the mosaic due to the unique characteristics of L-band radar. Two distinct linear boundaries were encountered limiting the northern distribution of wetlands, one north of the Negro river main channel and west of the Branco river, oriented WNW–ESE, and one south of the Negro main channel and east of the Branco, oriented NW–SE. The orientations and positions of these boundaries were consistent with the prevailing tectonic fracture pattern in the region. Geophysical, pedological and geomorphological data supported the hypothesis that these boundaries are tectonically controlled. The ecological, economic and biogeochemical implications of the observed wetland distribution were considered. The distributions of wetland-dependent biota were expected to be severely limited north of the Negro main channel. Fish production, wetland timber yields and methane emissions were also predicted to be exceptionally low in this region.
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Theoretically, fire–tree cover feedbacks can maintain savanna and forest as alternative stable states. However, the global extent of fire-driven discontinuities in tree cover is unknown, especially accounting for seasonality and soils. We use tree cover, climate, fire, and soils data sets to show that tree cover is globally discontinuous. Climate influences tree cover globally but, at intermediate rainfall (1000 to 2500 millimeters) with mild seasonality (less than 7 months), tree cover is bimodal, and only fire differentiates between savanna and forest. These may be alternative states over large areas, including parts of Amazonia and the Congo. Changes in biome distributions, whether at the cost of savanna (due to fragmentation) or forest (due to climate), will be neither smooth nor easily reversible.
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Forested tropical peatlands in Southeast Asia store at least 42 000 Million metric tonnes (Mt) of soil carbon. Human activity and climate change threatens the stability of this large pool, which has been decreasing rapidly over the last few decades owing to deforestation, drainage and fire. In this paper we estimate the carbon dioxide (CO2) emissions resulting from drainage of lowland tropical peatland for agricultural and forestry development which dominates the perturbation of the carbon balance in the region. Present and future emissions from drained peatlands are quantified using data on peatland extent and peat thickness, present and projected land use, water management practices and decomposition rates. Of the 27.1 Million hectares (Mha) of peatland in Southeast Asia, 12.9 Mha had been deforested and mostly drained by 2006. This latter area is increasing rapidly because of increasing land development pressures. Carbon dioxide (CO2) emission caused by decomposition of drained peatlands was between 355 Mt y−1 and 855 Mt y−1 in 2006 of which 82% came from Indonesia, largely Sumatra and Kalimantan. At a global scale, CO2 emission from peatland drainage in Southeast Asia is contributing the equivalent of 1.3% to 3.1% of current global CO2 emissions from the combustion of fossil fuel. If current peatland development and management practices continue, these emissions are predicted to continue for decades. This warrants inclusion of tropical peatland CO2 emissions in global greenhouse gas emission calculations and climate mitigation policies. Uncertainties in emission calculations are discussed and research needs for improved estimates are identified.
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Forested tropical peatlands in Southeast Asia store at least 42 000 Million metric tonnes (Mt) of soil carbon. Human activity and climate change threatens the stability of this large pool, which has been decreasing rapidly over the last few decades owing to deforestation, drainage and fire. In this paper we estimate the carbon dioxide (CO<sub>2</sub>) emissions resulting from drainage of lowland tropical peatland for agricultural and forestry development which dominates the perturbation of the carbon balance in the region. Present and future emissions from drained peatlands are quantified using data on peatland extent and peat thickness, present and projected land use, water management practices and decomposition rates. Of the 27.1 Million hectares (Mha) of peatland in Southeast Asia, 12.9 Mha had been deforested and mostly drained by 2006. This latter area is increasing rapidly because of increasing land development pressures. Carbon dioxide (CO<sub>2</sub>) emission caused by decomposition of drained peatlands was between 355 Mt y<sup>−1</sup> and 855 Mt y<sup>−1</sup> in 2006 of which 82% came from Indonesia, largely Sumatra and Kalimantan. At a global scale, CO<sub>2</sub> emission from peatland drainage in Southeast Asia is contributing the equivalent of 1.3% to 3.1% of current global CO<sub>2</sub> emissions from the combustion of fossil fuel. If current peatland development and management practices continue, these emissions are predicted to continue for decades. This warrants inclusion of tropical peatland CO<sub>2</sub> emissions in global greenhouse gas emission calculations and climate mitigation policies. Uncertainties in emission calculations are discussed and research needs for improved estimates are identified.
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The visual uniformity of tropical peat swamp forest masks the considerable variation in forest structure that has evolved in response to di¡erences and changes in peat characteristics over many millennia. Details are presented of forest structure and tree composition of the principal peat swamp forest types in the upper catchment of Sungai Sebangau, Central Kalimantan, Indonesia, in relation to thickness and hydrology of the peat. Consideration is given to data on peat geochemistry and age of peat that provide evidence of the ombrotrophic nature of this vast peatland and its mode of formation. The future sustainability of this ecosystem is predicted from information available on climate change and human impact in this region.
Article
Accurate inventory of tropical peatland is important in order to (a) determine the magnitude of the carbon pool; (b) estimate the scale of transfers of peat-derived greenhouse gases to the atmosphere resulting from land use change; and (c) support carbon emissions reduction policies. We review available information on tropical peatland area and thickness and calculate peat volume and carbon content in order to determine their best estimates and ranges of variation. Our best estimate of tropical peatland area is 441 025 km 2 ($11% of global peatland area) of which 247 778 km 2 (56%) is in Southeast Asia. We estimate the volume of tropical peat to be 1758 Gm 3 ($ 18–25% of global peat volume) with 1359 Gm 3 in Southeast Asia (77% of all tropical peat). This new assessment reveals a larger tropical peatland carbon pool than previous estimates, with a best estimate of 88.6 Gt (range 81.7–91.9 Gt) equal to 15–19% of the global peat carbon pool. Of this, 68.5 Gt (77%) is in Southeast Asia, equal to 11–14% of global peat carbon. A single country, Indonesia, has the largest share of tropical peat carbon (57.4 Gt, 65%), followed by Malaysia (9.1 Gt, 10%). These data are used to provide revised estimates for Indonesian and Malaysian forest soil carbon pools of 77 and 15 Gt, respectively, and total forest carbon pools (biomass plus soil) of 97 and 19 Gt. Peat carbon contributes 60% to the total forest soil carbon pool in Malaysia and 74% in Indonesia. These results emphasize the prominent global and regional roles played by the tropical peat carbon pool and the importance of including this pool in national and regional assessments of terrestrial carbon stocks and the prediction of peat-derived greenhouse gas emissions.
Article
It has been claimed, on the basis of relatively short-term gage observations and the perceptions of riverbank dwellers, that height and duration of Amazon floods are increasing. The paper discusses these assertions and some of the processes that might lead to the predicated trends. Two such processes are: an increase in peak discharge and a decrease in channel cross-section. Both could be triggered or reinforced by human-induced changes in the environment. By altering the hydrologic relations of plant, soil and water, deforestation in the headwaters can enhance runoff. It can also increase the sediment load, which, if the carrying capacity of the river is exceeded, may be deposited in and aggrade the channel. That deforestation in the Amazon drainage, now affecting small affluents, will eventually bear upon the regime of major tributaries and of the main stem itself can hardly be disputed. However, given the vastness of the basin, and the proportionately small and concentrated areas impacted by settlement, reports that such effects are already perceptible thousands of kilometers from the cleared areas require careful scrutiny. A detailed statistical analysis, combining gage readings and adequate precipitation data, may, of course, reveal the existence, in one or more sections of the river, of long-term changes in flow that cannot be explained in terms of rainfall variability. Even then, one should not exclude the possibility that such trends might be elucidated without invoking human intervention. They might, indeed, be caused by stream adjustment to neotectonic influences. In relation to the testimony of riverine populations, major inundations are likely to polarize concerns and dim the memory of moderate floods.
Article
The spatial and temporal pattern of annual rainfall and the strength of the dry season within the Amazon region are poorly known. Existing rainfall maps are based on the data from full-scale, long-term meteorological stations, operated by national organizations linked to the World Meteorological Organisation, such as INMET in Brazil. Stations with 30 or more years of uninterrupted and reliable recordings are very few, considering the size of the region, and most of them are located along the major rivers. It has been suggested that rainfall conditions away from these rivers are substantially different. An analysis has been made of the records of a network of simple pluviometric sites in the Brazilian part of the region as maintained by the National Agency for Electric Energy (ANEEL) since 1970. The latter data sets were used to draw more detailed maps on annual rainfall, and on the strength of the dry season in particular; average number of consecutive months with less than 100 mm, 50 mm, and 10 mm, respectively. Also, some data were obtained on the spatial expression of El Niño events within the region. Sub-regional differences are large, and it is argued that they are important for the success or failure of agricultural settlements; for the hazard of large-scale fire damage of the still existing primary forest vegetation; for the functioning of this land cover as stock and sink of CO2, and for the likelihood that secondary forests on abandoned agricultural lands will have less biomass. The effects of past El Niño rainfall anomalies on the biodiversity of the natural savannahs within the forest region are discussed.
Article
We agree that the Terrestrial Ecosystem Model analyses by Tianet al. of carbon fluxes of Amazonian ecosystems represent a methodological improvement compared with extrapolation from site-specific estimates, especially with regard to spatial resolution. However, the resolution of a model cannot be finer than that of the input data, and Tian et al. disregard one important group of ecosystems: peatlands. This is understandable, as the literature grossly underestimates the extent of peatlands in Amazonia. Our estimate is 150,000 km2, ten times more than previously reported.
Article
Tianet al. have used their process-based ecosystem model to estimate the net CO2exchanges, also called net ecosystem productivity, for the years 1980-94. They deduced a large interannual variability ranging between -0.2 (from land to atmosphere) and +0.7 petagrams of carbon (Pg C) per year, the variability being mostly a function of soil moisture, which in turn is largely regulated by precipitation and temperature. These values were derived by including the modelled effects of increasing atmospheric levels of CO2. The above numbers are the differences between net primary productivity and heterotrophic respiration. Over the given time period for the CO2feedback case, these values were 5.0 (+/-0.3) and 4.8 (+/-0.1) Pg C per year, respectively. The calculated net ecosystem productivity was thus a small fraction, between -4% and +14%, of the net primary productivity, with an average over the 15-year period of +4%.
Article
Southeast Asia has the highest relative rate of deforestation of any major tropical region, and could lose three quarters of its original forests by 2100 and up to 42% of its biodiversity. Here, we report on the current state of its biota and highlight the primary drivers of the threat of extinction now faced by much of the unique and rich fauna and flora of the region. Furthermore, the known impacts on the biodiversity of Southeast Asia are likely to be just the tip of the iceberg, owing to the paucity of research data. The looming Southeast Asian biodiversity disaster demands immediate and definitive actions, yet such measures continue to be constrained by socioeconomic factors, including poverty and lack of infrastructure. Any realistic solution will need to involve a multidisciplinary strategy, including political, socioeconomic and scientific input, in which all major stakeholders (government, non-government, national and international organizations) must participate.
Article
Background: Large fire scars were detected in floodplain forests of the middle Rio Negro in dry years of the 1990s, using satellite data.Aim: Relate fire years and river level anomalies to the Tropical Pacific Southern Oscillation Index (SOI); measure fire damage and post-fire succession rate.Methods: We analysed the relationship between the SOI and water levels for 1968-2010. In Landsat images of the 1990s we determined fire scar ages. Using QuickBird images, we measured forest cover loss in 36 of these scars, covering 873 ha. This was validated by field measurements of tree mortality in 15 scars. As a metric of post-fire succession, we compared change in the Enhanced Vegetation Index (EVI) in 10 large floodplain fire scars and 12 terra firme slash-and-burn fallows.Results: SOI explained 32% of the variation in annual low water level. Forest cover loss in the 36 burn scars was 88% ± 8% (mean ± SD), range 67-98%. Post-fire tree mortality was 91%, ± 8%, range 75-100%. Correlation between cover loss and mortality was 73% (P < 0.002). Forest recovery was very slow. EVI values typical of bare soil were still present 13 years after the fires, indicating a successional stage similar to the first year in terra firme sites.Conclusions: Results suggest a very low resistance and resilience of blackwater floodplain forests to fire disturbance associated with drought during El Niño events.
Article
All is not well for biodiversity in the tropics. Despite recent debate over the extent of future tropical extinctions and the effectiveness of reserve systems, the continued disappearance of habitat, soaring human population, and loss of vital ecosystem services demand immediate action. This crisis is worrying, given that tropical regions support over two-thirds of all known species and are populated by some of the world's poorest people, who have little recourse to lower environmental-impact lifestyles. Recent evidence has shown that - in addition to unabated rates of forest loss - coastal development, overexploitation of wildlife, catchment modification, and habitat conversion are threatening human well-being. We argue that the recent technical debate about likely extinctions masks the real issue - that, to prevent further loss of irreplaceable tropical biodiversity, we must err on the side of caution. We need to avoid inadvertently supporting political agendas that assume low future extinction rates, because this will result in further destruction of tropical biodiversity.
Article
A peat sampler is described which eliminates the more serious faults of the Hiller type. The samples obtained are free from distortion, readily accessible for measurement and examination and may easily be removed intact for transport to the laboratory.
Article
Still active Sub-Andean foreland deformation is suggested to have syndepositionally modified the fluvial depositional environments in the Peruvian Amazonian foreland basin throughout Neogene-Quaternary time. Modern fluvial aggradation continues to proceed on a large scale ( c . 120 000 km ² ) in two differing depositional systems. Firstly, various multistoried floodbasin deposits are derived from the meandering and anastomosing rivers within the subsiding intraforeland basins. Secondly, in the northern part of the Pastaza-Marañon basin the largest known Holocene alluvial fan-like formation ( c . 60 000 km ² ) composed of reworked, volcaniclastic debris derived from active Ecuadorian volcanoes, has been identified. The widespread, poorly known, dissected surface alluvium ( terra firme ) which covers the main part of the Peruvian Amazonian foreland basin shows further evidence of long-term foreland deformation, and terraces indicate both the effects of tectonism and Pleistocene climatic oscillations. In northern Peru, the surface alluvium was deposited by a Tertiary fluvial system with palaeocurrents to the west and northwest into the Andean foreland basin. In southern Peru, the respective surficial alluvium was part of a post-Miocene fluvial system flowing northeast into the main Amazon basin. Both systems were gradually abandoned when the eastward migrating Andean foreland deformation led to the more distinctive partitioning of the intraforeland basins, and the modern drainage system was created.
Article
Tianet al. have used their process-based ecosystem model to estimate the net CO2exchanges, also called net ecosystem productivity, for the years 1980-94. They deduced a large interannual variability ranging between -0.2 (from land to atmosphere) and +0.7 petagrams of carbon (Pg C) per year, the variability being mostly a function of soil moisture, which in turn is largely regulated by precipitation and temperature. These values were derived by including the modelled effects of increasing atmospheric levels of CO2. The above numbers are the differences between net primary productivity and heterotrophic respiration. Over the given time period for the CO2feedback case, these values were 5.0 (+/-0.3) and 4.8 (+/-0.1) Pg C per year, respectively. The calculated net ecosystem productivity was thus a small fraction, between -4% and +14%, of the net primary productivity, with an average over the 15-year period of +4%.
Article
The carbon (C) dynamics of tropical peatlands can be of global importance, because, particularly in Southeast Asia, they are the source of considerable amounts of C released to the atmosphere as a result of land-use change and fire. In contrast, the existence of tropical peatlands in Amazonia has been documented only recently. According to a recent study, the 120 000 km2 subsiding Pastaza-Marañón foreland basin in Peruvian Amazonia harbours previously unstudied and up to 7.5 m thick peat deposits. We studied the role of these peat deposits as a C reserve and sink by measuring peat depth, radiocarbon age and peat and C accumulation rates at 5–13 sites. The basal ages varied from 1975 to 8870 cal yr bp, peat accumulation rates from 0.46 to 9.31 mm yr−1 and C accumulation rates from 28 to 108 g m−2 yr−1. The total peatland area and current peat C stock within the area of two studied satellite images were 21 929 km2 and 3.116 Gt (with a range of 0.837–9.461 Gt). The C stock is 32% (with a range of 8.7–98%) of the best estimate of the South American tropical peatland C stock and 3.5% (with a range of 0.9–10.7%) of the best estimate of the global tropical peatland C stock. The whole Pastaza-Marañón basin probably supports about twice this peatland area and peat C stock. In addition to their contemporary geographical extent, these peatlands probably also have a large historical (vertical) extension because of their location in a foreland basin characterized by extensive river sedimentation, peat burial and subsidence for most of the Quaternary period. Burial of peat layers in deposits of up to 1 km thick Quaternary river sediments removes C from the short-term C cycle between the biosphere and atmosphere, generating a long-term C sink.
Article
The congruency in the depositional origin and age of the uppermost sedimentary strata forming non-flooded rainforest ground (terra firme) in the western and central Amazon lowlands is a much debated subject. Here we conclude from the study of remote sensing imagery that active Andean foreland dynamics have played a major role in the evolution of the Plio-Pleistocene fluvial landscape in the western Amazon. Foreland dynamics have resulted in a terra firme composed of late Tertiary alluvium and younger alluvial terraces and plains. In Peru, thermoluminescence and 14C dating show local aggradation of this younger alluvium between 180 and 30 ka. The documented high age heterogeneity of the terra firme has implications for considerations of the biogeography of the Amazon forest.
Article
In tropical lowlands, peatlands are commonly reported from Southeast Asia, and especially Indonesian tropical peatlands are known as considerable C sinks and sources. In contrast, Amazonia has been clearly understudied in this context. In this study, based on field observations from 17 wetland sites in Peruvian lowland Amazonia, we report 0–5.9 m thick peat deposits from 16 sites. Only one of the studied sites did not contain any kind of peat deposit (considering pure peat and clayey peat). Historic yearly peat and C accumulation rates, based on radiocarbon dating of peat samples from five sites, varied from 0.94 ± 0.99 to 4.88 ± 1.65 mm, and from 26 ± 3 to 195 ± 70 g C m−2, respectively. The long-term apparent peat and C accumulation rates varied from 1.69 ± 0.03 to 2.56 ± 0.12 mm yr−1, and from 39 ± 10 to 85 ± 30 g C m−2 yr−1, respectively. These accumulation rates are comparable to those determined in the Indonesian tropical peatlands. Under altered conditions, Indonesian peatlands can release globally relevant amounts of C to the atmosphere. Considering the estimated total area of Amazonian peatlands (150 000 km2) close to that of the Indonesian ones (200 728 km2) as well as several factors threatening the Amazonian peatlands, we suggest that the total C stocks and fluxes associated with Amazonian peatlands may be of global significance.
Article
Accurate inventory of tropical peatland is important in order to (a) determine the magnitude of the carbon pool; (b) estimate the scale of transfers of peat-derived greenhouse gases to the atmosphere resulting from land use change; and (c) support carbon emissions reduction policies. We review available information on tropical peatland area and thickness and calculate peat volume and carbon content in order to determine their best estimates and ranges of variation. Our best estimate of tropical peatland area is 441 025 km2 (∼11% of global peatland area) of which 247 778 km2 (56%) is in Southeast Asia. We estimate the volume of tropical peat to be 1758 Gm3 (∼18–25% of global peat volume) with 1359 Gm3 in Southeast Asia (77% of all tropical peat). This new assessment reveals a larger tropical peatland carbon pool than previous estimates, with a best estimate of 88.6 Gt (range 81.7–91.9 Gt) equal to 15–19% of the global peat carbon pool. Of this, 68.5 Gt (77%) is in Southeast Asia, equal to 11–14% of global peat carbon. A single country, Indonesia, has the largest share of tropical peat carbon (57.4 Gt, 65%), followed by Malaysia (9.1 Gt, 10%). These data are used to provide revised estimates for Indonesian and Malaysian forest soil carbon pools of 77 and 15 Gt, respectively, and total forest carbon pools (biomass plus soil) of 97 and 19 Gt. Peat carbon contributes 60% to the total forest soil carbon pool in Malaysia and 74% in Indonesia. These results emphasize the prominent global and regional roles played by the tropical peat carbon pool and the importance of including this pool in national and regional assessments of terrestrial carbon stocks and the prediction of peat-derived greenhouse gas emissions.
Article
A tropical ombrotrophic peatland ecosystem is one of the largest terrestrial carbon stores. Flux rates of carbon dioxide (CO2) and methane (CH4) were studied at various peat water table depths in a mixed-type peat swamp forest floor in Central Kalimantan, Indonesia. Temporary gas fluxes on microtopographically differing hummock and hollow peat surfaces were combined with peat water table data to produce annual cumulative flux estimates. Hummocks formed mainly from living and dead tree roots and decaying debris maintained a relatively steady CO2 emission rate regardless of the water table position in peat. In nearly vegetation-free hollows, CO2 emission rates were progressively smaller as the water table rose towards the peat surface. Methane emissions from the peat surface remained small and were detected only in water-saturated peat. By applying long-term peat water table data, annual gas emissions from the peat swamp forest floor were estimated to be 3493±316 g CO2 m−2 and less than 1.36±0.57 g CH4 m−2. On the basis of the carbon emitted, CO2 is clearly a more important greenhouse gas than CH4. CO2 emissions from peat are the highest during the dry season, when the oxic peat layer is at its thickest because of water table lowering.
Article
An igap forest near the confluence of Rio Tarum Mirim (Tarumzinho) and Rio Negro has been studied. It is a typical ectotroph forest with a raw humus layer and suppressed litter decomposing activity by Higher (i.e., carpophore-producing) Fungi. The number of the latter is about one-fifth of that observed in the (anectotrophic) terra firme forest. All ectotrophically mycorrhizal fungi observed belonged in three families:Amanitaceae, Boletaceae, Russulaceae. Leguminosae are dominant, and of theseAldina latifolia andSwartzia cf.polyphylla were demonstrably ectomycorrhizal. The scarcity of mineral nutrients in the soils of igap, campinarana and campina is overcome by direct cycling through ectomycorrhizae. This is in contrast to other black- and white-water inundated forest communities in Amazonia.
Article
Rivers in Central Amazonia show annual water level fluctuations of up to 14m; the flooding period ranges from 50 to 270 days between the rising and falling phases. Differences in duration and type of flood in Amazonian floodplain forests result in a mosaic of habitats which include lakes, grasslands, forests, streams etc. To study the floristic composition, structure, variation on number of species and diversity in a forest that is seasonally flooded by a black-water river in Brazilian Amazonia, 200km NE of Manaus, I surveyed three hectares in habitats which included lake, river margin, and stream. The number of species per hectare ranged from 44 to 137. The number of trees varied from 796 to 1130. Total basal area ranged from 22.3m2 to 41.8m2. Leguminosae was the most abundant and dominant family in the river margin and stream plot, while Euphorbiaceae and Leguminosae were, respectively the most abundant and dominant families in the lake plot. The most dominant species in the river margin and stream plots was Aldina latifolia (Leguminosae), while Amanoa oblongifolia (Euphorbiaceae) was the most abundant and dominant species in the lake plot. Mean water level and flooding period decreased significantly from lake to the river margin to the stream. The mean number of species and the Shannon diversity increase significantly from the lake to the river margin to the stream habitats plots. Similarity indexes varied from 0.3 to 0.55% between the three plots sampled in this study.
Article
Studies were carried out in Central-Amazonian inundation forests having seasonal inundations during the emersion phase (e.p.) and the submersion phase (s.p.). Two várzea forests (white water areas), one in the Amazon valley on Ilha de Curarí and one at Lago Janauarí, and an igapó (black water area) situated in the Rio Negro valley at Rio Tarumã Mirím were investigated. A community analysis consisting of the species diversity and species similarity of the aquatic and terrestrial soil fauna was executed in these forests. Each forest is differentiated into an inner, middle, and outer part. The annual development of the soil invertebrates is dictated by the periodic changes in water level. Data on species diversity indicate an alternate occurrence of the soil- and trunk-dwelling carabids and staphylinids (Coleoptera). Low species diversity is obtained for the aquatic soil fauna during the high water period. This is correlated with both oxygen concentration and relative abundance of a few specialized species. A function model approach was tried. Investigations showed that both the phytophages and the saprophages consumed about 9.4% and 13% respectively of the yearly litter fall. Litter decomposition is retarded during the inundation period (170 g·m-2·s.p.-1 is decomposed) but is accelerated during the emersion phase (420 g·m-2·e.p.-1 is decomposed). Nearly 14% of the yearly litter fall is presumed to be exported by the current from the inundation forest during the inundation phase, probably into the surrounding rivers and lakes. A rough estimation of a nutrient budget containing some selected elements was given. The estimation allowed us to suppose, that in the igapó the loss of some elements cannot be compensated for by the input from the river water and the precipitation. Unlike the igapó, the várzea forest may compensate for this loss of litter through input of nutrients from the inflowing white water. The igapó may thus be considered as a source of nutrients while the várzea forest is a nutrient sink.
Article
Rivers in central Amazonia experience annual water-level fluctuations of up to 14m, flooding vast areas of adjacent forest for periods ranging from a few to 270 days per year. At different sites, variation in the duration and type of flooding results in a mosaic of habitats that includes lakes, grasslands, forests, and streams. To study the effects of flood duration on plant species richness and floristic composition, two river margin sites were surveyed on the rivers Ja and Tarum-Mirim. Both areas are seasonally flooded by blackwaters, and plots were made at different topographic levels (lower, middle and upper slopes). All woody plants with DBH>5cm were inventoried in five 10 40m plots in each of the three topographic levels, which varied in length of flood duration and mean water level. Plant species richness did not vary significantly between topographic levels, but species composition varied substantially. At both study sites, the species composition exhibited distinctive distribution patterns with respect to the three topographic levels and river site. Differences in the distribution of dominant species in both sites probably relate to the ability of species to withstand seasonal flooding, although other edaphic factors associated with the topographic levels may also be important, especially for less-dominant, locally rare, and habitat generalist species. Species composition overlap among topographic levels at the two sites was highly variable ranging from 15% to 43%. Knowledge about the complex pattern of species composition and distributions between and among topographic levels and river sites is important for the preservation of the diverse flora of the blackwater forests and for the creation of future conservation management plans and design of protected areas in this ecosystem that will maintain the biodiversity.
Article
The Rio Negro has responded significantly in the Late Pleistocene and Holocene to lagged environmental changes largely associated with activity during the last glacial in the Amazon basin. On the basis of geological structure, the Rio Negro can be divided into six distinct reaches that each reflects very marked differential processes and geomorphological styles. No deposits of the Upper Pleniglacial were recognized in the field. The oldest recognizable Late Pleistocene alluvial unit is the Upper Terrace of Middle Pleniglacial age (ca. 65–25 ka) (reach I), tentatively correlated with the oldest terrace identified on the left bank of reach III. At that time, the river was mainly an aggradational bed load system carrying abundant quartz sand, a product of more seasonal conditions in the upper catchment. The late glacial (14–10 ka) is represented by a lower finer-grained terrace along the upper basin (reach I), which was recognized in the Tiquié, Curicuriarí, and Vaupes rivers. At that time, the river carried abundant suspended load as a response to climatic changes associated with deglaciation.
Article
In tropical lowlands, ecosystems with peat strata are commonly reported from Southeast Asia, but hardly at all from Amazonia. In this paper, we quantify the horizontal distribution of four important plant nutrients (Ca, Mg, K and P) in five peatland sites located in Peruvian Amazonia and the vertical distribution of these nutrients in one of the sites. With this data as well as topography measurements of the peat deposit from one of the sites, we showed that minerotrophic and ombrotrophic peatlands can be detected in Amazonian floodplains. The nutrient-poor ombrotrophic bogs receive nutrients only from atmospheric deposition because of their thick peat layer and convex topography, while the minerotrophic swamps are periodically covered by nutrient-rich floodwater and/or receive nutrient input from surface waters or from groundwater with capillary rise. The existence of such peatlands in the Amazonian lowlands increases the regional habitat diversity and availability of palaeoecological information and probably has implications also for the hydrological dynamics, water quality, and carbon dynamics of the area.
Article
The Upper Rio Negro basin, under a constantly humid equatorial climate, is a low-altitude peneplain of more than 165,000 km2. Prevailing soils are Oxisols and Spodosols, and their distribution is usually related to the lithology of the parent materials; Spodosols being generally associated with sandy deposits. After exploratory surveys in this extensive region, six major soil-geomorphic units have been identified in which selected toposequences have been studied by means of micromorphological, chemical and mineralogical analyses. Detailed field analysis of the horizonation of the soil mantle has been carried out in three sequences consisting of Oxisols, Ultisols and Spodosols. Results show that sharp transitions, within distances of less than one hundred meters, separate the Oxisols from the Spodosols. However, the arrangement of the horizons in the soil mantle and similarities in micromorphological features, chemical composition and mineral components between the adjacent horizons are evidences that genetic relationships link contiguous profiles. The authors propose an alternative explanation for this soil distribution, based on the lateral transformation of Oxisols and Ultisols into Spodosols, and on the lateral evolution of the giant Spodosols into Histosols (peat) and waterlogged Ultisols. Interpretative models of landscape evolution as consequence of soil evolution are thus proposed.
Article
Although many of the current hypotheses to explain the origin and distribution of the Amazon biodiversity has been based directly or indirectly on geological data, the reconstruction of the geological history of the Amazon region is still inadequate to analyze its relationship with the biodiversity. This work has the main goal to characterize the sedimentary successions formed in the Brazilian Amazon in the Neogene-Quaternary discussing the evolution of the depositional systems through time and analyzing their main controlling mechanisms in order to fill up this gap. Radar image interpretation, sedimentological studies, and radiocarbon dating allowed the mapping of Plio-Pleistocene to Holocene units along the Solimões-Amazonas River, Brazil. This integrated work led to the characterization of five sedimentary successions overlying Miocene deposits of the Solimões/Pebas Formation, which include the following: Içá Formation (Plio-Pleistocene), deposits Q1 (37,400–43,700 14C yr B.P.), deposits Q2 (27,200 14C yr B.P.), deposits Q3 (6730–2480 14C yr B.P.), and deposits Q4 (280–130 14C yr B.P.). These deposits occur mostly to the west of Manaus, forming NW–SE elongated belts that are progressively younger from SW to NE, indicating a subsiding basin with a depocenter that migrated to the NE. The reconstruction of the depositional history is consistent with significant changes in the landscapes. Hence, the closure of a large lake system at the end of the Miocene gave rise to the development of a Plio-Pleistocene fluvial system. This was yet very distinct from the modern drainage, with shallow, energetic, highly migrating, braided to anastomosed channels having an overall northeast outlet. This fluvial system formed probably under climatic conditions relatively drier than today's. During the early Pleistocene, there was pronounced erosion, followed by a renewed depositional phase ca. 40,000 14C yr B.P., with the development of prograding lobes and/or crevasse splays associated with a lake system (i.e., fan-delta) and/or fluvial flood plain areas. After a period of erosion, a fluvial system with eastward draining channels started to develop at around 27,000 14C yr B.P. The fluvial channels were overflooded in mid-Holocene time. This flooding is attributed to an increased period of humidity, with a peak between 5000 and 2500 14C yr B.P. The data presented herein support that, rather than being a monotonous area, the Amazonia was a place with frequent changes in landscape throughout the Neogene-Quaternary, probably as a result of climatic and tectonic factors. We hypothesize that these changes in the physical environment stressed the biota, resulting in speciation and thus had a great impact on modern biodiversity.
Article
It has been suggested that tropical forest and savanna could represent alternative stable states, implying critical transitions at tipping points in response to altered climate or other drivers. So far, evidence for this idea has remained elusive, and integrated climate models assume smooth vegetation responses. We analyzed data on the distribution of tree cover in Africa, Australia, and South America to reveal strong evidence for the existence of three distinct attractors: forest, savanna, and a treeless state. Empirical reconstruction of the basins of attraction indicates that the resilience of the states varies in a universal way with precipitation. These results allow the identification of regions where forest or savanna may most easily tip into an alternative state, and they pave the way to a new generation of coupled climate models.
Article
Climate change, deforestation and the fate of Amazon. Understanding and mitigation the impact of the increasing population and global economic activities on tropical forests is one of the greatest challenges for scientists and policy makers. A summary of some of the latest findings and thinking on this topic has been reported by Malhi and colleagues in a recent paper published on Science. An overview and comments on this paper is herein proposed.