Peatlands contain one-third of the world's soil carbon (C). If destabilized, decomposition of this vast C bank could accelerate climate warming; however, the likelihood of this outcome remains ...unknown. Here, we examine peatland C stability through five years of whole-ecosystem warming and two years of elevated atmospheric carbon dioxide concentrations (eCO
). Warming exponentially increased methane (CH
) emissions and enhanced CH
production rates throughout the entire soil profile; although surface CH
production rates remain much greater than those at depth. Additionally, older deeper C sources played a larger role in decomposition following prolonged warming. Most troubling, decreases in CO
:CH
ratios in gas production, porewater concentrations, and emissions, indicate that the peatland is becoming more methanogenic with warming. We observed limited evidence of eCO
effects. Our results suggest that ecosystem responses are largely driven by surface peat, but that the vast C bank at depth in peatlands is responsive to prolonged warming.
Peatlands contain one-third of soil carbon (C), mostly buried in deep, saturated anoxic zones (catotelm). The response of catotelm C to climate forcing is uncertain, because prior experiments have ...focused on surface warming. We show that deep peat heating of a 2 m-thick peat column results in an exponential increase in CH
emissions. However, this response is due solely to surface processes and not degradation of catotelm peat. Incubations show that only the top 20-30 cm of peat from experimental plots have higher CH
production rates at elevated temperatures. Radiocarbon analyses demonstrate that CH
and CO
are produced primarily from decomposition of surface-derived modern photosynthate, not catotelm C. There are no differences in microbial abundances, dissolved organic matter concentrations or degradative enzyme activities among treatments. These results suggest that although surface peat will respond to increasing temperature, the large reservoir of catotelm C is stable under current anoxic conditions.
Large uncertainties in the budget of atmospheric methane, an important greenhouse gas, limit the accuracy of climate change projections. Thaw lakes in North Siberia are known to emit methane, but the ...magnitude of these emissions remains uncertain because most methane is released through ebullition (bubbling), which is spatially and temporally variable. Here we report a new method of measuring ebullition and use it to quantify methane emissions from two thaw lakes in North Siberia. We show that ebullition accounts for 95 per cent of methane emissions from these lakes, and that methane flux from thaw lakes in our study region may be five times higher than previously estimated. Extrapolation of these fluxes indicates that thaw lakes in North Siberia emit 3.8 teragrams of methane per year, which increases present estimates of methane emissions from northern wetlands (< 6-40 teragrams per year; refs 1, 2, 4-6) by between 10 and 63 per cent. We find that thawing permafrost along lake margins accounts for most of the methane released from the lakes, and estimate that an expansion of thaw lakes between 1974 and 2000, which was concurrent with regional warming, increased methane emissions in our study region by 58 per cent. Furthermore, the Pleistocene age (35,260-42,900 years) of methane emitted from hotspots along thawing lake margins indicates that this positive feedback to climate warming has led to the release of old carbon stocks previously stored in permafrost.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Many developed countries have targeted landfill methane recovery among greenhouse gas mitigation strategies, since methane is the second most important greenhouse gas after carbon dioxide. Major ...questions remain with respect to actual methane production rates in field settings and the relative mass of methane that is recovered, emitted, oxidized by methanotrophic bacteria, laterally migrated, or temporarily stored within the landfill volume. This paper presents the results of extensive field campaigns at three landfill sites to elucidate the total methane balance and provide field measurements to quantify these pathways. We assessed the overall methane mass balance in field cells with a variety of designs, cover materials, and gas management strategies. Sites included different cell configurations, including temporary clay cover, final clay cover, geosynthetic clay liners, and geomembrane composite covers, and cells with and without gas collection systems. Methane emission rates ranged from −2.2 to >10,000
mg
CH
4
m
−2
d
−1. Total methane oxidation rates ranged from 4% to 50% of the methane flux through the cover at sites with positive emissions. Oxidation of atmospheric methane was occurring in vegetated soils above a geomembrane. The results of these studies were used as the basis for guidelines by the French environment agency (ADEME) for default values for percent recovery: 35% for an operating cell with an active landfill gas (LFG) recovery system, 65% for a temporary covered cell with an active LFG recovery system, 85% for a cell with clay final cover and active LFG recovery, and 90% for a cell with a geomembrane final cover and active LFG recovery.
Abstract
Thermokarst lakes accelerate deep permafrost thaw and the mobilization of previously frozen soil organic carbon. This leads to microbial decomposition and large releases of carbon dioxide ...(CO
2
) and methane (CH
4
) that enhance climate warming. However, the time scale of permafrost-carbon emissions following thaw is not well known but is important for understanding how abrupt permafrost thaw impacts climate feedback. We combined field measurements and radiocarbon dating of CH
4
ebullition with (a) an assessment of lake area changes delineated from high-resolution (1–2.5 m) optical imagery and (b) geophysical measurements of thaw bulbs (taliks) to determine the spatiotemporal dynamics of hotspot-seep CH
4
ebullition in interior Alaska thermokarst lakes. Hotspot seeps are characterized as point-sources of high ebullition that release
14
C-depleted CH
4
from deep (up to tens of meters) within lake thaw bulbs year-round. Thermokarst lakes, initiated by a variety of factors, doubled in number and increased 37.5% in area from 1949 to 2009 as climate warmed. Approximately 80% of contemporary CH
4
hotspot seeps were associated with this recent thermokarst activity, occurring where 60 years of abrupt thaw took place as a result of new and expanded lake areas. Hotspot occurrence diminished with distance from thermokarst lake margins. We attribute older
14
C ages of CH
4
released from hotspot seeps in older, expanding thermokarst lakes (
14
C
CH4
20 079 ± 1227 years BP, mean ± standard error (s.e.m.) years) to deeper taliks (thaw bulbs) compared to younger
14
C
CH4
in new lakes (
14
C
CH4
8526 ± 741 years BP) with shallower taliks. We find that smaller, non-hotspot ebullition seeps have younger
14
C ages (expanding lakes 7473 ± 1762 years; new lakes 4742 ± 803 years) and that their emissions span a larger historic range. These observations provide a first-order constraint on the magnitude and decadal-scale duration of CH
4
-hotspot seep emissions following formation of thermokarst lakes as climate warms.
Mechanisms controlling CO2 and CH4 production in wetlands are central to understanding carbon cycling and greenhouse gas exchange. However, the volatility of these respiration products complicates ...quantifying their rates of production in the field. Attempts to circumvent the challenges through closed system incubations, from which gases cannot escape, have been used to investigate bulk in situ geochemistry. Efforts towards mapping mechanistic linkages between geochemistry and microbiology have raised concern regarding sampling and incubation-induced perturbations. Microorganisms are impacted by oxygen exposure, increased temperatures and accumulation of metabolic products during handling, storage, and incubation. We probed the extent of these perturbations, and their influence on incubation results, using high-resolution geochemical and microbial gene-based community profiling of anaerobically incubated material from three wetland habitats across a permafrost peatland. We compared the original field samples to the material anaerobically incubated over 50 days. Bulk geochemistry and phylum-level microbiota in incubations largely reflected field observations, but divergence between field and incubations occurred in both geochemistry and lineage-level microbial composition when examined at closer resolution. Despite the changes in representative lineages over time, inferred metabolic function with regards to carbon cycling largely reproduced field results suggesting functional consistency. Habitat differences among the source materials remained the largest driver of variation in geochemical and microbial differences among the samples in both incubations and field results. While incubations may have limited usefulness for identifying specific mechanisms, they remain a viable tool for probing bulk-scale questions related to anaerobic C cycling, including CO2 and CH4 dynamics.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Landfills are the third largest source of anthropogenic CH4 in the United States, and there is potential for reduction in this source of greenhouse gases and other contaminants. The objective of this ...work was to contrast emissions of CH4 and non-methane organic compounds (NMOCs) from landfill cells covered with soil or a biologically active cover consisting of yard waste compost. On the basis of four field campaigns over 14 months, CH4 emissions from the biocover (BC) varied from −1.73 to 1.33 g m-2 d-1, with atmospheric uptake measured in 52% of tests. BC emissions did not increase when the gas collection system was turned off. Uptake of atmospheric CH4 was measured in 54% of tests on the soil cover (SC) when the gas collection was system active and 12% when the gas collection system was off. Many (26%) relatively high fluxes (>15 g m-2 d-1) were measured from the SC as were some dramatic effects due to deactivation of the gas collection system. In tests with positive emissions, stable isotope measurements showed that the BC and SC were responsible for oxidation of 55% and 21% of the CH4 reaching the bottom of the respective cover. Seven of the highest 10 NMOC emissions were measured in the SC, and 17 of 21 fluxes for speciated organic compounds were higher in the SC. The relationship between CH4, NMOC, and individual organic compound emissions suggested a correlation between CH4 and trace organic oxidation. BCs can reduce landfill gas emissions in the absence of a gas collection system and can serve as a polishing step in the presence of an active system.
This paper reviews the
13C isotopic fractionations of the three main modes of CH
4 transport from wetlands: diffusion, ebullition and via emergent aquatic plants. Aquatic plants employ either ...diffusion or a combination of convective bulk flow in daylight and diffusion at night. Ebullition and diffusion across the air–water interface result in no to little isotopic fractionation. However, diffusion through air when conducted by plant lacunae or aerenchyma results in significantly greater rates of transport for
12CH
4 relative to
13CH
4. This difference causes the backup of
13C-enriched CH
4 in plant lacunae, which partly but not totally compensates for the isotopic fractionation out of the plant. It is also suggested that the preferential plant transport of
12CH
4 causes
13C enrichment of methane in the rhizosphere but it is difficult to separate the effects of rhizospheric methane oxidation from this process. Convective bulk flow transport via plants results in little isotopic fractionation. However, the pattern of fractionation differs significantly in convective plants from day to night as diffusion is more important in darkness.
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