Top PDF Root oxygen mitigates methane fluxes in tropical peatlands

Root oxygen mitigates methane fluxes in tropical peatlands

Root oxygen mitigates methane fluxes in tropical peatlands

Tropical peatlands are a globally important source of methane, a potent greenhouse gas. Vegetation is critical in regulating fluxes, providing a conduit for emissions and regular carbon inputs. However, plant roots also release oxygen, which might mitigate methane efflux through oxidation prior to emission from the peat surface. Here we show, using in situ mesocosms, that root exclusion can reduce methane fluxes by a maximum of 92% depending on species, likely driven by the significant decrease in root inputs of oxygen and changes in the balance of methane transport pathways. Methanotroph abundance decreased with reduced oxygen input, demonstrating a likely mechanism for the observed response. These first methane oxidation estimates for a tropical peatland demonstrate that although plants provide an important pathway for methane loss, this can be balanced by the influence of root oxygen inputs that mitigate peat surface methane emissions.
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Root oxygen mitigates methane fluxes in tropical peatlands

Root oxygen mitigates methane fluxes in tropical peatlands

ACCEPTED MANUSCRIPT • OPEN ACCESS Root oxygen mitigates methane fluxes in tropical peatlands To cite this article before publication: Nicholas Girkin et al 2020 Environ. Res. Lett. in press https://doi.org/10.1088/1748-9326/ab8495 Manuscript version: Accepted Manuscript

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Composition and concentration of root exudate analogues regulate greenhouse gas fluxes from tropical peat

Composition and concentration of root exudate analogues regulate greenhouse gas fluxes from tropical peat

A B S T R A C T Tropical peatlands are a signi ficant carbon store and source of carbon dioxide (CO 2 ) and methane (CH 4 ) to the atmosphere. Plants can contribute to these gas emissions through the release of root exudates, including sugars and organic acids amongst other biomolecules, but the roles of concentration and composition of exudates in regulating emissions remains poorly understood. We conducted a laboratory incubation to assess how the type and concentration of root exudate analogues regulate CO 2 and CH 4 production from tropical peats under anoxic conditions. For CO 2 production, substrate concentration was the more important driver, with increased CO 2 fluxes following higher addition rates of four out of the six exudate analogues. In contrast, exudate type was the more important driver of CH 4 production, with acetate addition associated with the greatest production, and inverse correlations between exudate concentration and CH 4 emission for the remaining five treatments. Root exudate analogues also altered pH and redox potential, dependent on the type of addition (organic acid or sugar) and the concentration. Overall, these findings demonstrate the contrasting roles of composition and con- centration of root exudate inputs in regulating greenhouse gas emissions from tropical peatlands. In turn this highlights how changes in plant communities will in fluence emissions through species specific inputs, and the possible impacts of increased root exudation driven by rising atmospheric CO 2 and warming.
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Statistical modelling of variability in sediment-water nutrient and oxygen fluxes

Statistical modelling of variability in sediment-water nutrient and oxygen fluxes

and water oxygen saturation was always high even in summer months. The decreased of TOU and ammonia and silicate fluxes at high levels of turbidity can be explained by the dilution of sediment organic material re-suspended in the water column particularly in winter time when water productivity is low and sediment organic matter is refractory (Tengberg et al., 2003). Hence, our results suggest that resuspension events can impact the sediment biogeochemistry in different ways depending on the sediment properties and the sources of organic matter. The effect of turbidity on sediment remineralisation is controversial in the literature. Turbidity is a measurement used to indicate the occurrence of resuspension due to physical processes such as weather conditions and tidal currents or anthropogenic perturbations such as trawling. Hydrodynamic forces can influence both cohesive sediment, changing the thickness of the diffusive boundary layer (e.g., Tengberg et al., 2003), and permeable sand, inducing advective pore water transport (Huettel and Gust, 1992). Resuspension can also impact the sediment biogeochemistry involving both organic matter and fine sediment particle transport in less turbulent zones (Creutzberg et al., 1984; Jenness and Duineveld, 1985; Jonsson et al., 1990) and playing an important role in unclogging or “re- setting” permeable sands (Cook et al., 2007; Glud, 2008; Zetsche et al., 2012). Almroth et al. (2009) showed a clear enhancement of oxygen consumption rates due to simulated resuspension events in chamber incubation experiments however, no effects on silicate fluxes were found. A decreasing in ammonia effluxes were also measured in 50% of the incubation replicates when the bottom water oxygen concentration was low (see also Rasmussen and Jørgensen, 1992) and between accumulating and dispersive
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Denial of long-term issues with agriculture on tropical peatlands will have devastating consequences

Denial of long-term issues with agriculture on tropical peatlands will have devastating consequences

However, recent encouraging developments towards better management of tropical peatlands have been undermined by misleading newspaper headlines and statements first published during the conference. Arti- cles in leading regional newspapers (‘Oil palm planting on peat soil handled well, says Uggah, 2016b; Cheng & Sibon, 2016; Nurbianto, 2016a,b; Wong, 2016) widely read across the region portrayed a general consensus, in summary of the conference, that current agricultural practices in peatland areas, such as oil palm planta- tions, do not have a negative impact on the environ- ment. This view is not shared by many scientists or supported by the weight of evidence that business-as- usual management is not sustainable for tropical peat- land agriculture.
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Environmental impacts as affected by different oil palm cropping systems in tropical peatlands

Environmental impacts as affected by different oil palm cropping systems in tropical peatlands

http://researchonline.ljmu.ac.uk/ Citation (please note it is advisable to refer to the publisher’s version if you intend to cite from this work) Dhandapani, S, Ritz, K, Evers, SL and Sjogersten, S (2019) Environmental impacts as affected by different oil palm cropping systems in tropical peatlands. Agriculture, Ecosystems and Environment, 276. pp. 8-20. ISSN 0167-8809

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Is intercropping an environmentally-wise alternative to established oil palm monoculture in tropical peatlands?

Is intercropping an environmentally-wise alternative to established oil palm monoculture in tropical peatlands?

REMAINING RESEARCH QUESTIONS This work indicates several future areas for research, First, paludiculture is widely discussed as a sustainable alternative to other drainage based agriculture in peatlands ( Tata, 2019 ). Even though there are several native crops suitable for paludiculture, the environmental, economical and social impacts, and viability of transforming oil palm agriculture to paludiculture is yet to be fully researched. Second, oil palm in intercropping sites in the reported studies were below 3 years of age ( Dhandapani et al., 2019a,b ). Intercropping may not be possible when oil palm plants mature, the canopy closes, and light becomes restricted for the understorey. These intercropping systems should be assessed further if they are converted from intercropping to oil palm monocropping to understand whether intercropping at initial stages of oil palm is beneficial to peat properties and the environment in the longer term. Third, while the impacts of intercropping on CO 2 and CH 4 fluxes have been observed,
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Denial of long term issues with agriculture on tropical peatlands will have devastating consequences

Denial of long term issues with agriculture on tropical peatlands will have devastating consequences

BirdLife International, The David Attenborough Building, 1st Floor, Pembroke Street, Cambridge CB2 3QZ, UK, 46 Centre for Tropical Environmental and Sustainability Science (TESS) & College of Science and Engineering, James Cook University, PO Box 6811, Cairns, Queensland 4870, Australia, 47 Partner in the Greifswald Mire Centre, Ernst Moritz Arndt University of Greifswald, c/o Michael Succow Stiftung, Ellernholzstr. 1/3, 17489 Greifswald, Germany, 48 Deltares, Boussinesqweg 1, 2629 HV Delft, Netherlands, 49 Cerulogy, The International Council on Clean Transportation, 11 Belgrave Road, London SW1V 1RB, UK,
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Investigation of Oxygen Exchange and Methane Combustion Kinetics for CaMnO3-based Oxygen Carriers.

Investigation of Oxygen Exchange and Methane Combustion Kinetics for CaMnO3-based Oxygen Carriers.

The second is gradual reduction of the OC surface over the duration of the run due to the reducing atmosphere in which the OC operates. If this reduction is the cause, a monotonic decrease in the reaction rate would be expected over time, as the surface is further reduced and activity decreases, but the 11 April 2017 runs do not provide enough evidence to confirm or refute this explanation. Additionally, the active site was initially hypothesized to occur at an oxygen vacancy on the surface of the OC. If this hypothesis were true, a more reduced surface would increase the number of active sites and therefore the rate of reaction, which is the opposite of the trend seen here.
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Zooplankton-Mediated Fluxes in the Eastern Tropical North Atlantic

Zooplankton-Mediated Fluxes in the Eastern Tropical North Atlantic

particularly interesting regarding biogeochemical processes in the North Atlantic. Very limited zooplankton data are available for the ETNA. A study by Chahsavar-Archard and Razouls (1982) provided a faunistic evaluation for several stations, with two net catches conducted down to 600 m depth, but no quantitative data on zooplankton abundance or biomass. Quantitative sampling efforts such as those undertaken routinely during the Atlantic Meridional Transect (AMT) cruises and the extensive collections of researchers from the former Soviet Union were mostly restricted to the upper 200 m of the water column (Piontkovski and Castellani, 2009). This hampers the estimation of zooplankton-mediated fluxes out of the surface layer and into the OMZ as net avoidance during daytime might occur at the surface (Ianson et al., 2004) and the organisms that take refuge at depth during daytime might do so at different depth levels. In a recent study, Hauss et al. (2016) observed the impact of an individual mesoscale eddy near Cape Verde on the distribution and vertical migration of zooplankton and Christiansen et al. (2018) investigated the distribution of a holopelagic polychaete in relation to particle abundance and mesoscale eddy dynamics across the tropical Atlantic, demonstrating that hypoxia tolerance is variable between species. For a migrating euphausiid (Euphausia gibboides) and a migrating copepod (Pleuromamma abdominalis), we have experimentally determined the critical oxygen partial pressure p crit at which aerobic metabolism can no longer be maintained independently of the environmental pO 2 (Kiko et al., 2016). A companion paper in this research topic (Hernández-León et al., 2019) conducted five day-night stations between 2 and 20 ◦ N. 1.4. Target Regions of Our Work
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High permeability explains the vulnerability of the carbon store in drained tropical peatlands

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

higher than values recently recorded for three Peruvian Amazonian fl oodplain peatlands [Kelly et al., 2014] — two fl at and one shallowly domed — that are likely to be different from the widespread ombrotrophic domes found elsewhere in the tropics because they are (or have been until the last few hundred years (T. J. Kelly, personal communication)) regularly overtopped by river fl oodwaters which will affect their bio- geochemistry and therefore peat properties. As shown in Figure 1, our median values are between two and more than 30 times higher than found in these Peruvian Amazonian fl oodplain peatlands [Kelly et al., 2014]. As noted by Kelly et al. [2014] [see also Dommain et al., 2010] very few other studies exist on the K of tropical peat. Takahashi and Yonetani [1997] measured K at depths of 1 to 1.7 m in an Indonesian forest swamp by using piezometers but published only a rounded value (K ≥ 1 × 10 4 m s 1 ) for depths < 1 m. Hoekman [2007] suggests a much higher value of 2.3 × 10 3 m s 1 but provides no information on how it was obtained. Nugroho et al. [1997] provide a more detailed data set for an Indonesian peatland, with a K range (n = 28) of 3.5 × 10 5 to 1.9 × 10 3 m s 1 but do not indicate how measurements were made or the depths from which they were obtained. Finally, Sayok et al. [2007] present K values for Malaysian swamp forest, obtained by using slug tests in auger holes, with a mean value of 3.9 × 10 4 m s 1 (n = 15). Notwithstanding uncertainty over the reliability of some of these estimates, they show that our values are mostly within the range of, but also exceed, the values for Southeast Asian peatlands.
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Physical controls of oxygen fluxes at pelagic and benthic oxyclines in a lake

Physical controls of oxygen fluxes at pelagic and benthic oxyclines in a lake

F ~{K z :LC=Lz~w’:C’ ð1Þ where the overbar denotes temporal averaging. Turbulent transport is energized by wind, internal waves, or buoyancy-driven currents (Imberger 1998; Wu¨est and Lorke 2003) and thus is highly variable in space and time. This high temporal variability of the resulting DO fluxes has been studied intensively in the benthic zone (Lorke et al. 2003; Brand et al. 2008; Bryant et al. 2010). However, in the pelagic zone, only an indirect assessment exists where Bouffard et al. (2013) recently demonstrated the potential effect of highly variable physical forcing on vertical DO fluxes by inferring temporal variations of turbulent transport from time series of current shear and density stratification. Here, we apply the eddy correlation (EC) technique to quantify the high-frequency temporal vari- ability of DO fluxes within the water column and above the sediment–water interface in a lake. The flux observations are complemented by detailed measurements of current velocity, density stratification, and concentrations of DO and other redox-relevant dissolved substances.
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Shipborne eddy covariance observations of methane fluxes constrain Arctic sea emissions

Shipborne eddy covariance observations of methane fluxes constrain Arctic sea emissions

was about three orders of magnitude lower than the extent de- scribed for seep areas in that earlier work (2). Resolving this spatial extent discrepancy is an important future task. High bubble fluxes a few kilometers from the shore in the ESAS should not be extrapolated to the vast deeper regions farther offshore without a better under- standing of the distribution of these high-flux regions. Accounting for small fluxes within the noise of our EC system, we estimate total ESAS CH 4 emissions at 3.02 Tg year −1 . If emissions from shallower

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A multi-year estimate of methane fluxes in Alaska from CARVE atmospheric observations

A multi-year estimate of methane fluxes in Alaska from CARVE atmospheric observations

and stochastic components of that estimate. We also compare the spatial distribution of our fluxes against the spatial distributions from a number of process-based model estimates. Figure 4 displays the spatial distribution of our posterior flux estimate (May – Oct. of 2012– 2014). Our estimate yields the largest fluxes in southwestern Alaska, the Seward Peninsula, and the North Slope (Fig. 4a). The Yukon Delta National Wildlife Refuge and Yukon– Kuskokwim Delta of southwestern Alaska are a subarctic, lowland tundra with extensive wetlands, lakes, and rivers. The Seward Peninsula is covered by tundra and contains both lowland regions covered in wetlands and lakes as well as several small mountain chains less than 1,500m in height. The North Slope is an arctic, lowland tundra underlain with thick permafrost and many thermokarst features. All three regions have few or no trees and generally saturated soils. In contrast to these areas, CH 4 fluxes are smaller in Alaska’s
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Methane and carbon dioxide fluxes from open and blocked ditches in a blanket bog

Methane and carbon dioxide fluxes from open and blocked ditches in a blanket bog

linear models the candidate explanatory variables were air temperature, soil temperature at 10 cm depth (modelled at each collar from the 5 cm depth AWS readings), a temperature sum index that ‘tracks’ the summer growth curve of peatland vegetation (Alm et al. 1997; Green and Baird 2017), water-table depth, and a measure of the abundance of the three PFTs within the area enclosed by the collars/chambers. Further de- tails on our methods may be found in Green and Baird (2017). Except for PFTs, all of these variables were measured or estimated at hourly or two-hourly intervals. The models were run at hourly time intervals and the hourly fluxes summed to give annualised fluxes. To obtain hourly water tables from the two-hourly modelled values (see BFlux chamber measurements^ section), linear interpolation was used. The plant abun- dance data were obviously not available at hourly inter- vals, but were entered for each hour and updated twice per year (see BEnvironmental/ecological conditions^ section).
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Understanding spatial variability of methane fluxes in Arctic wetlands through footprint modelling

Understanding spatial variability of methane fluxes in Arctic wetlands through footprint modelling

( 2019 ) found that 3%–4% of methane emissions in their wetland study site in the Russian Arctic were in the form of sporadic bursts; a linear model might not be ideal to capture this type of emission pattern. Fur- thermore, the snow melt season it is a period of rapid transition, where NDVI and NDWI would vary greatly. Subsequent research might signi ficantly improve the explanatory power of the spatial indices by utilising drones to collect high-resolution time ser- ies of these metrics. With appropriate development, these results could further develop upscaling methods and improve the extrapolation of the site-level data to the regional scale.
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Depletion of oxygen, nitrate and nitrite in the Peruvian oxygen minimum zone cause an imbalance of benthic nitrogen fluxes

Depletion of oxygen, nitrate and nitrite in the Peruvian oxygen minimum zone cause an imbalance of benthic nitrogen fluxes

The observations show that the sediments at the shallowest station on the shelf were releasing sulphide, possibly contributing to a sulphidic event in the water column analogous to the large event reported for the Peruvian OMZ shelf waters in January 2009 (Schunck et al., 2013). The event witnessed by these authors is the only one documented for this region, yet could re- occur if stagnation events in Peruvian OMZ become more frequent. Sulphidic conditions in surface sediments on the shelf appear to be common during the high-productivity season (Cardich et al., 2015). Clearly, the socio-economic impacts on local fishery and aquaculture industries would be devastating if benthic sulphide was released en masse. Our fluxes further show that the sediments have a high potential for sulphide release and begin to release sulphide as soon as NO 3 - and NO 2 - become depleted (c.f. Supplement and Fig. 10 in Dale et
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Indonesia's contested domains: deforestation, rehabilitation and conservation with development in Central Kalimantan's tropical peatlands

Indonesia's contested domains: deforestation, rehabilitation and conservation with development in Central Kalimantan's tropical peatlands

Indonesia’s tropical peat swamp forests (TPSF) have long been strongly ‘contested domains’ (Pathak 1994) facing competition between industrial demand for timber, the subsistence and livelihood requirements of local communities and, more recently, global concern about the need to conserve tropical peat carbon stores, ecosystem services 1 and biodiversity (Luttrell et al. 2012). Concern about carbon losses from tropical peat has risen since 1997-8 when large-scale forest and peat fires released 0.81-2.57 Gt of carbon; around 13–40% of the global carbon emissions from fossil fuels during for that year (Page et al. 2002). TPSF act as carbon sinks and stores in their natural state 2 , but rapidly become carbon sources when deforested and drained for commercial logging, plantation development or conversion for agricultural use (Rieley and Page 2005). 3 Drained peat is highly susceptible to fire which has major livelihood impacts as well as creating regional and national air pollution/smog
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The impact of permafrost degradation on methane fluxes : a field study in Abisko

The impact of permafrost degradation on methane fluxes : a field study in Abisko

In 2005 Margareta Johansson (Dept. of Physical Geography and Ecosystems Science, Lund university) started a snow manipulation project on a mire called Storflaket in the Abisko region (Figure 3) to study the effect of degrading permafrost by artificially increased snow cover thickness. The aim was to "advance" the degradation years into the future so that we will be able to predict the future of the permafrost, and learn more about the permafrost dynamics. Subsequently this has given us the chance to study possible changes in the methane cycle which is valuable since it is not as well-known as the general carbon cycle. Increased snow depth can increase the degradation rate of permafrost even more than positive annual temperatures. We know that this in turn will cause a change of greenhouse gas emissions, but not how much.
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Does litter input determine carbon storage and peat organic chemistry in tropical peatlands?

Does litter input determine carbon storage and peat organic chemistry in tropical peatlands?

Global peatlands account for approximately 3% of the Earth’s terrestrial area, of which 10% are situated within the tropics (Chimner and Ewel, 2005). Tropical peatlands consist of partially decomposed organic matter, which has accumulated under waterlogged, anaerobic conditions, typically over millennia, when vegetation input exceeds decomposition (Andriesse, 1988; Minasny et al., 2016; Wösten et al., 2008; Sjögersten et al., 2014; Hoyos-Santillan et al., 2015). Globally, peatlands are estimated to store 105 Gt C, equivalent to ca 20% of the Earth’s peatland carbon store (Jaenicke et al., 2008; Page et al., 2011; Dargie et al., 2017). However, over the last century the sink strength of tropical peatlands has been under threat from logging, drainage and fires, particularly in areas of increasing population growth and development (Chimner and Ewel, 2005; Hooijer et al., 2010; Limpens et al., 2008; Wösten et al., 2008). Climate change also has an impact on the functioning of tropical peatlands, due to changes in precipitation, which lead to increased risk of drought (Chimner and Ewel, 2005; Page et al., 2011). These changes alter vegetation inputs and organic decomposition rates, and increase the risk of peatlands becoming carbon sources (Wösten et al., 2008).
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