Organic sulfur and organic matter redox processes contribute to electron flow in anoxic incubations of peat

2016 ◽  
Vol 13 (5) ◽  
pp. 816 ◽  
Author(s):  
Zhi-Guo Yu ◽  
Jörg Göttlicher ◽  
Ralph Steininger ◽  
Klaus-Holger Knorr
Keyword(s):  
Carbon Dioxide ◽  
Organic Matter ◽  
Electron Acceptor ◽  
Electron Acceptors ◽  
Organic Sulfur ◽  
Co2 Production ◽  
Bacterial Sulfate Reduction ◽  
Sulfur Species ◽  
Ch4 Production

Environmental contextThe extent to which organic matter decomposition generates carbon dioxide or methane in anaerobic ecosystems is determined by the presence or absence of particular electron acceptors. Evaluating carbon dioxide and methane production in anaerobic incubation of peat, we found that organic matter predominated as an electron acceptor over considered inorganic electron acceptors. We also observed changes in organic sulfur speciation suggesting a contribution of organic sulfur species to the electron-accepting capacity of organic matter. AbstractAn often observed excess of CO2 production over CH4 production in freshwater ecosystems presumably results from a direct or indirect role of organic matter (OM) as electron acceptor, possibly supported by a cycling of oxidised and reduced sulfur species. To confirm the role of OM electron-accepting capacities (EACOM) in anaerobic microbial respiration and to elucidate internal sulfur cycling, peat soil virtually devoid of inorganic electron acceptors was incubated under anaerobic conditions. Thereby, production of CO2 and CH4 at a cumulative ratio of 3.2:1 was observed. From excess CO2 production and assuming a nominal oxidation state of carbon in OM of zero, we calculated a net consumption rate of EACOM of 2.36µmol electron (e–)cm–3day–1. Addition of sulfate (SO42–) increased CO2 and suppressed CH4 production. Moreover, subtracting the EAC provided though SO42–, net consumption rates of EACOM had increased to 3.88–4.85µmol e–cm–3day–1, presumably owing to a re-oxidation of sulfide by OM at sites otherwise not accessible for microbial reduction. As evaluated by sulfur K-edge X-ray absorption near-edge structure spectroscopy, bacterial sulfate reduction presumably involved not only a recycling of inorganic sulfur species, but also a sulfurisation of OM, yielding reduced organic sulfur, and changes in oxidised organic sulfur species. Organic matter thus contributes to anaerobic respiration: (i) directly by EAC of redox-active functional groups; (ii) directly by oxidised organic sulfur; and (iii) indirectly by re-oxidation of sulfide to maintain bacterial sulfate reduction.

scholarly journals Carbon dioxide and methane fluxes at the air–sea interface of Red Sea mangroves

2018 ◽  
Vol 15 (17) ◽  
pp. 5365-5375 ◽  
Author(s):  
Mallory A. Sea ◽  
Neus Garcias-Bonet ◽  
Vincent Saderne ◽  
Carlos M. Duarte
Keyword(s):  
Carbon Dioxide ◽  
Organic Matter ◽  
Red Sea ◽  
Ghg Emissions ◽  
Eastern Coast ◽  
Relative Role ◽  
Emission Rates ◽  
Mangrove Forests ◽  
Ch4 Production

Abstract. Mangrove forests are highly productive tropical and subtropical coastal systems that provide a variety of ecosystem services, including the sequestration of carbon. While mangroves are reported to be the most intense carbon sinks among all forests, they can also support large emissions of greenhouse gases (GHGs), such as carbon dioxide (CO2) and methane (CH4), to the atmosphere. However, data derived from arid mangrove systems like the Red Sea are lacking. Here, we report net emission rates of CO2 and CH4 from mangroves along the eastern coast of the Red Sea and assess the relative role of these two gases in supporting total GHG emissions to the atmosphere. Diel CO2 and CH4 emission rates ranged from −3452 to 7500 µmol CO2 m−2 d−1 and from 0.9 to 13.3 µmol CH4 m−2 d−1 respectively. The rates reported here fall within previously reported ranges for both CO2 and CH4, but maximum CO2 and CH4 flux rates in the Red Sea are 10- to 100-fold below those previously reported for mangroves elsewhere. Based on the isotopic composition of the CO2 and CH4 produced, we identified potential origins of the organic matter that support GHG emissions. In all but one mangrove stand, GHG emissions appear to be supported by organic matter from mixed sources, potentially reducing CO2 fluxes and instead enhancing CH4 production, a finding that highlights the importance of determining the origin of organic matter in GHG emissions. Methane was the main source of CO2 equivalents despite the comparatively low emission rates in most of the sampled mangroves and therefore deserves careful monitoring in this region. By further resolving GHG fluxes in arid mangroves, we will better ascertain the role of these forests in global carbon budgets.

scholarly journals Organic matter and sediment properties determine in-lake variability of sediment CO<sub>2</sub> and CH<sub>4</sub> production and emissions of a small and shallow lake

2020 ◽  
Vol 17 (20) ◽  
pp. 5057-5078
Author(s):  
Leandra Stephanie Emilia Praetzel ◽  
Nora Plenter ◽  
Sabrina Schilling ◽  
Marcel Schmiedeskamp ◽  
Gabriele Broll ◽  
...  
Keyword(s):  
Organic Matter ◽  
Negative Correlation ◽  
Sediment Quality ◽  
Significant Negative Correlation ◽  
Electron Acceptors ◽  
Co2 Production ◽  
Emission Rates ◽  
Production Rates ◽  
Sediment Properties ◽  
Ch4 Production

Abstract. Inland waters, particularly small and shallow lakes, are significant sources of carbon dioxide (CO2) and methane (CH4) to the atmosphere. However, the spatial in-lake heterogeneity of CO2 and CH4 production processes and their drivers in the sediment remain poorly studied. We measured potential CO2 and CH4 production in slurry incubations from 12 sites within the small and shallow crater lake Windsborn in Germany, as well as fluxes at the water–atmosphere interface of intact sediment core incubations from four sites. Production rates were highly variable and ranged from 7.2 to 38.5 µmol CO2 gC−1 d−1 and from 5.4 to 33.5 µmol CH4 gC−1 d−1. Fluxes ranged from 4.5 to 26.9 mmol CO2 m−2 d−1 and from 0 to 9.8 mmol CH4 m−2 d−1. Both CO2 and CH4 production rates and the CH4 fluxes exhibited a significant and negative correlation (p<0.05, ρ<−0.6) with a prevalence of recalcitrant organic matter (OM) compounds in the sediment as identified by Fourier-transformed infrared spectroscopy. The carbon / nitrogen ratio exhibited a significant negative correlation (p<0.01, ρ=-0.88) with CH4 fluxes but not with production rates or CO2 fluxes. The availability of inorganic (nitrate, sulfate, ferric iron) and organic (humic acids) electron acceptors failed to explain differences in CH4 production rates, assuming a competitive suppression, but observed non-methanogenic CO2 production could be explained up to 91 % by prevalent electron acceptors. We did not find clear relationships between OM quality, the thermodynamics of methanogenic pathways (acetoclastic vs. hydrogenotrophic) and electron-accepting capacity of the OM. Differences in CH4 fluxes were interestingly to a large part explained by grain size distribution (p<0.05, ρ=±0.65). Surprisingly though, sediment gas storage, potential production rates and water–atmosphere fluxes were decoupled from each other and did not show any correlations. Our results show that within a small lake, sediment CO2 and CH4 production shows significant spatial variability which is mainly driven by spatial differences in the degradability of the sediment OM. We highlight that studies on production rates and sediment quality need to be interpreted with care, though, in terms of deducing emission rates and patterns as approaches based on production rates only neglect physical sediment properties and production and oxidation processes in the water column as major controls on actual emissions.

scholarly journals Organic sediment formed during inundation of a degraded fen grassland emits large fluxes of CH<sub>4</sub> and CO<sub>2</sub>

2011 ◽  
Vol 8 (6) ◽  
pp. 1539-1550 ◽  
Author(s):  
M. Hahn-Schöfl ◽  
D. Zak ◽  
M. Minke ◽  
J. Gelbrecht ◽  
J. Augustin ◽  
...  
Keyword(s):  
Organic Matter ◽  
Plant Litter ◽  
Electron Acceptors ◽  
Sediment Layer ◽  
Organic Substrates ◽  
Peat Layer ◽  
Ch4 Production ◽  
Fresh Plant ◽  
Fresh Organic Matter ◽  
Organic Sediment

Abstract. Peatland restoration by inundation of drained areas can alter local greenhouse gas emissions as CO2 and CH4. Factors that can influence these emissions include the quality and amount of substrates available for anaerobic degradation processes and the sources and availability of electron acceptors. In order to learn about possible sources of high CO2 and CH4. emissions from a rewetted degraded fen grassland, we performed incubation experiments that tested the effects of fresh plant litter in the flooded peats on pore water chemistry and CO2 and CH4. production and emission. The position in the soil profile of the pre-existing drained peat substrate affected initial rates of anaerobic CO2 production subsequent to flooding, with the uppermost peat layer producing the greatest specific rates of CO2 evolution. CH4 production rates depended on the availability of electron acceptors and was significant only when sulfate concentrations were reduced in the pore waters. Very high specific rates of both CO2 (maximum of 412 mg C d−1 kg−1 C) and CH4 production (788 mg C d−1 kg−1 C) were observed in a new sediment layer that accumulated over the 2.5 years since the site was flooded. This new sediment layer was characterized by overall low C content, but represented a mixture of sand and relatively easily decomposable plant litter from reed canary grass killed by flooding. Samples that excluded this new sediment layer but included intact roots remaining from flooded grasses had specific rates of CO2 (max. 28 mg C d−1 kg−1 C) and CH4 (max. 34 mg C d−1 kg−1 C) production that were 10–20 times lower than for the new sediment layer and were comparable to those of a newly flooded upper peat layer. Lowest rates of anaerobic CO2 and CH4 production (range of 4–8 mg C d−1 kg−1 C and <1 mg C d−1 kg−1 C) were observed when all fresh organic matter sources (plant litter and roots) were excluded. In conclusion, the presence of fresh organic substrates such as plant and root litter originating from plants killed by inundation has a high potential for CH4 production, whereas peat without any fresh plant-derived material is relatively inert. Significant anaerobic CO2 and CH4 production in peat only occurs when some labile organic matter is available, e.g. from remaining roots or root exudates.

scholarly journals Belowground in situ redox dynamics and methanogenesis recovery in a degraded fen during dry-wet cycles and flooding

2012 ◽  
Vol 9 (8) ◽  
pp. 11655-11704 ◽  
Author(s):  
C. Estop-Aragonés ◽  
K.-H. Knorr ◽  
C. Blodau
Keyword(s):  
Organic Matter ◽  
Water Table ◽  
Methane Production ◽  
Solid Phase ◽  
Electron Flow ◽  
Organic Matter Content ◽  
Matter Content ◽  
Electron Acceptors ◽  
Oxygen Penetration ◽  
Ch4 Production

Abstract. Climate change induced drying and flooding may alter the redox conditions of organic matter decomposition in peat soils. The seasonal and intermittent changes in pore water solutes (NO3−, Fe2+, SO42−, H2S, acetate) and dissolved soil gases (CO2, O2, CH4, H2) under natural water table fluctuations were compared to the response under a reinforced drying and flooding in fen peats. Oxygen penetration during dryings led to CO2 and CH4 degassing and to a regeneration of dissolved electron acceptors (NO3−, Fe3+ and SO42−). Drying intensity controlled the extent of the electron acceptor regeneration. Iron was rapidly reduced and sulfate pools ~ 1 mmol L−1 depleted upon rewetting and CH4 did not substantially accumulate until sulfate levels declined to ~ 100 μmoll−1. The post-rewetting recovery of soil methane concentrations to levels ~ 80 μmoll−1 needed 40–50 days after natural drought. This recovery was prolonged after experimentally reinforced drought. A greater regeneration of electron acceptors during drying was not related to prolonged methanogenesis suppression after rewetting. Peat compaction, solid phase content of reactive iron and total reduced inorganic sulfur and organic matter content controlled oxygen penetration, the regeneration of electron acceptors and the recovery of CH4 production, respectively. Methane production was maintained despite moderate water table decline of 20 cm in denser peats. Flooding led to accumulation of acetate and H2, promoted CH4 production and strengthened the co-occurrence of iron and sulfate reduction and methanogenesis. Mass balances during drying and flooding indicated that an important fraction of the electron flow must have been used for the generation and consumption of electron acceptors in the solid phase or other mechanisms. In contrast to flooding, dry-wet cycles negatively affect methane production on a seasonal scale but this impact might strongly depend on drying intensity and on the peat matrix, whose structure and physical properties influence moisture content.

scholarly journals Carbon Dioxide and Methane Emissions from Red Sea Mangrove Sediments

2018 ◽  
Author(s):  
Mallory A. Sea ◽  
Neus Garcias-Bonet ◽  
Vincent Saderne ◽  
Carlos M. Duarte
Keyword(s):  
Carbon Dioxide ◽  
Organic Matter ◽  
Red Sea ◽  
Ghg Emissions ◽  
Relative Role ◽  
Emission Rates ◽  
Mangrove Forests ◽  
Carbon Sinks ◽  
Mangrove Sediments

Abstract. Mangrove forests are highly productive tropical and subtropical coastal systems that provide a variety of ecosystem services, including the sequestration of carbon. While mangroves are reported to be the most intense carbon sinks among all forests, their sediments can also support large emissions of greenhouse gases (GHG), such as carbon dioxide (CO2) and methane (CH4), to the atmosphere. However, data derived from arid mangrove systems like the Red Sea are lacking. Here, we report emission rates of CO2 and CH4 from mangrove sediments along the Saudi Arabian coast of the Red Sea, and assess the relative role of these two gases in supporting total GHG emissions. Diel CO2 and CH4 emission rates in Red Sea mangrove sediments ranged from −3452 to 7500 µmol CO2 m−2 d−1 and from 0.9 to 13.3 µmol CH4 m−2 d−1, respectively. The rates reported here fall within previously reported ranges for both CO2 and CH4, but maximum CO2 and CH4 flux rates in the Red Sea are 10 to 100-fold below those previously reported for mangroves elsewhere. Based on the isotopic composition of the CO2 and CH4 produced by mangrove sediments, we identified the origin of the organic matter that supports GHG emissions. In most of the mangrove stands, GHG emissions were supported by organic matter from mixed sources while only in one mangrove stand the GHG emissions were supported by organic matter derived from mangrove tissues. Moreover, the organic matter derived from mangrove tissues reduced CO2 fluxes and enhanced CH4 production, pointing out the importance of the origin of the organic matter in GHG emissions. Methane was the main source of CO2-equivalents, despite the comparatively low emission rates, in most of the sampled mangroves, and therefore deserves careful monitoring in this region. Despite the mean net emission of CO2 and CH4 by Red Sea mangroves reported here, these forests become net organic carbon sinks when taking into account the existing carbon burial rates for the Red Sea mangroves. By further resolving GHG fluxes in arid mangroves, we will better ascertain the role of these forests in global carbon budgets.

The Phanerozoic Carbon Cycle

2004 ◽  
Author(s):  
Robert A. Berner
Keyword(s):  
Carbon Dioxide ◽  
Organic Matter ◽  
Carbon Cycle ◽  
Carbonate Rocks ◽  
Large Scale ◽  
Fossil Fuels ◽  
Land Plants ◽  
Current Debate ◽  
The Past

The term "carbon cycle" is normally thought to mean those processes that govern the present-day transfer of carbon between life, the atmosphere, and the oceans. This book describes another carbon cycle, one which operates over millions of years and involves the transfer of carbon between rocks and the combination of life, the atmosphere, and the oceans. The weathering of silicate and carbonate rocks and ancient sedimentary organic matter (including recent, large-scale human-induced burning of fossil fuels), the burial of organic matter and carbonate minerals in sediments, and volcanic degassing of carbon dioxide contribute to this cycle. In The Phanerozoic Carbon Cycle, Robert Berner shows how carbon cycle models can be used to calculate levels of atmospheric CO2 and O2 over Phanerozoic time, the past 550 million years, and how results compare with independent methods. His analysis has implications for such disparate subjects as the evolution of land plants, the presence of giant ancient insects, the role of tectonics in paleoclimate, and the current debate over global warming and greenhouse gases

The Role of N ADPH in the Reversible Phototransformation of Chlorophyllide P682 into Chlorophyllide P678 in Etioplasts of Oat

1985 ◽  
Vol 40 (11-12) ◽  
pp. 832-838 ◽  
Author(s):  
Fabrice Franck ◽  
Georg H. Schmid
Keyword(s):  
Absorption Band ◽  
Electron Acceptor ◽  
Absorption Maximum ◽  
Room Temperature ◽  
Physiological Role ◽  
Electron Acceptors ◽  
Illumination Time ◽  
Light Excitation ◽  
The Hill

Abstract Absorption spectra and room temperature fluorescence variations upon light excitation were studied in etioplasts in which the protochlorophyllide had been reduced to chlorophyllide prior to the experiment. In the presence of 1 mᴍ NADPH, the absorption band was located around 682 nm and the fluorescence variations reflected the occurrence of the chlorophyllide microcycle (reversible phototransformation of chlorophyllide P682 into chlorophyllide P678), whereas, in the absence of NADPH, the absorption band was located around 676 nm and the fluorescence exhibited only a slow decrease with illumination time. After washing, NADPH-treated etioplasts still exhibited an absorption maximum of 682 nm, which shifted irreversibly to 678 nm upon illumination. Re-addition of only 10 μᴍ NADPH restored the reversibility of the reaction. Plastids were also prepared after a brief illumination of the intact leaves. These plastids contained the P682 chlorophyllide. In this preparation, essentially the same phenomena were observed as in NADPH-treated etioplasts after washing. Moreover, enzymic oxidation of NADPH resulted in the transformation of P682 into P678 in darkness. Addition of the Hill electron acceptors 2,6- dimethylbenzoquinone on FeCN caused an acceleration of the phototransformation of P682 into P678. We interpret these results as being due to the oxidation of NADPH during the phototransformation of P682 into P678. The nature of the electron acceptor and the physiological role of this reaction is discussed.

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