methane flux
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2021 ◽  
Vol 18 (23) ◽  
pp. 6093-6114
Author(s):  
Johan H. Scheller ◽  
Mikhail Mastepanov ◽  
Hanne H. Christiansen ◽  
Torben R. Christensen

Abstract. The carbon balance of high-latitude terrestrial ecosystems plays an essential role in the atmospheric concentration of trace gases, including carbon dioxide (CO2) and methane (CH4). Increasing atmospheric methane levels have contributed to ∼ 20 % of the observed global warming since the pre-industrial era. Rising temperatures in the Arctic are expected to promote the release of methane from Arctic ecosystems. Still, existing methane flux measurement efforts are sparse and highly scattered, and further attempts to assess the landscape fluxes over multiple years are needed. Here we combine multi-year July–August methane flux monitoring (2006–2019) from automated flux chambers in the central fens of Zackenberg Valley, northeast Greenland, with several flux measurement campaigns on the most common vegetation types in the valley to estimate the landscape fluxes over 14 years. Methane fluxes based on manual chamber measurements are available from campaigns in 1997, 1999–2000, and in shorter periods from 2007–2013 and were summarized in several published studies. The landscape fluxes are calculated for the entire valley floor and a smaller subsection of the valley floor, containing the productive fen area, Rylekærene. When integrated for the valley floor, the estimated July–August landscape fluxes were low compared to the single previous estimate, while the landscape fluxes for Rylekærene were comparable to previous estimates. The valley floor was a net methane source during July–August, with estimated mean methane fluxes ranging from 0.18 to 0.67 mg m−2 h−1. The mean methane fluxes in the fen-rich Rylekærene were substantially higher, with fluxes ranging from 0.98 to 3.26 mg m−2 h−1. A 2017–2018 erosion event indicates that some fen and grassland areas in the center of the valley are becoming unstable following pronounced fluvial erosion and a prolonged period of permafrost warming. Although such physical disturbance in the landscape can disrupt the current ecosystem–atmosphere flux patterns, even pronounced future erosion of ice-rich areas is unlikely to impact methane fluxes on a landscape scale significantly. Instead, projected changes in future climate in the valley play a more critical role. The results show that multi-year landscape methane fluxes are highly variable on a landscape scale and stress the need for long-term spatially distributed measurements in the Arctic.


2021 ◽  
Author(s):  
Gil Bohrer ◽  
Yang Ju ◽  
Justine Missik ◽  
Jorge Villa ◽  
Ethan Kubatko ◽  
...  
Keyword(s):  

Land ◽  
2021 ◽  
Vol 10 (11) ◽  
pp. 1186
Author(s):  
Hong Li ◽  
Min Zhao ◽  
Changhui Peng ◽  
Haiqiang Guo ◽  
Qing Wang ◽  
...  

Although rice paddy fields are one of the world’s largest anthropogenic sources of methane CH4, the budget of ecosystem CH4 and its’ controls in rice paddies remain unclear. Here, we analyze seasonal dynamics of direct ecosystem-scale measurements of CH4 flux in a rice-wheat rotation agroecosystem over 3 consecutive years. Results showed that the averaged CO2 uptakes and CH4 emissions in rice seasons were 2.2 and 20.9 folds of the wheat seasons, respectively. In sum, the wheat-rice rotation agroecosystem acted as a large net C sink (averaged 460.79 g C m−2) and a GHG (averaged 174.38 g CO2eq m−2) source except for a GHG sink in one year (2016) with a very high rice seeding density. While the linear correlation between daily CH4 fluxes and gross ecosystem productivity (GEP) was not significant for the whole rice season, daily CH4 fluxes were significantly correlated to daily GEP both before (R2: 0.52–0.83) and after the mid-season drainage (R2: 0.71–0.79). Furthermore, the F partial test showed that GEP was much greater than that of any other variable including soil temperature for the rice season in each year. Meanwhile, the parameters of the best-fit functions between daily CH4 fluxes and GEP shifted between rice growth stages. This study highlights that GEP is a good predictor of daily CH4 fluxes in rice paddies.


2021 ◽  
Vol 574 ◽  
pp. 117164
Author(s):  
R. Seth Wood ◽  
Aivo Lepland ◽  
Ryan C. Ogliore ◽  
Jennifer Houghton ◽  
David A. Fike

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-26
Author(s):  
Jinxiu Yang ◽  
Mingyue Lu ◽  
Zhiguang Yao ◽  
Min Wang ◽  
Shuangfang Lu ◽  
...  

Seabed methane seepage has gained attention from all over the world in recent years as an important source of greenhouse gas emission, and gas hydrates are also regarded as a key factor affecting climate change or even global warming due to their shallow burial and poor stability. However, the relationship between seabed methane seepage and gas hydrate systems is not clear although they often coexist in continental margins. It is of significance to clarify their relationship and better understand the contribution of gas hydrate systems or the deeper hydrocarbon reservoirs for methane flux leaking to the seawater or even the atmosphere by natural seepages at the seabed. In this paper, a geophysical examination of the global seabed methane seepage events has been conducted, and nearby gas hydrate stability zone and relevant fluid migration pathways have been interpreted or modelled using seismic data, multibeam data, or underwater photos. Results show that seabed methane seepage sites are often manifested as methane flares, pockmarks, deep-water corals, authigenic carbonates, and gas hydrate pingoes at the seabed, most of which are closely related to vertical fluid migration structures like faults, gas chimneys, mud volcanoes, and unconformity surfaces or are located in the landward limit of gas hydrate stability zone (LLGHSZ) where hydrate dissociation may have released a great volume of methane. Based on a comprehensive analysis of these features, three major types of seabed methane seepage are classified according to their spatial relationship with the location of LLGHSZ, deeper than the LLGHSZ (A), around the LLGHSZ (B), and shallower than LLGHSZ (C). These three seabed methane seepage types can be further divided into five subtypes considering whether the gas source of seabed methane seepage is from the gas hydrate systems or not. We propose subtype B2 represents the most important seabed methane seepage type due to the high density of seepage sites and large volume of released methane from massive focused vigorous methane seepage sites around the LLGHSZ. Based on the classification result of this research, more measures should be taken for subtype B2 seabed methane seepage to predict or even prevent ocean warming or climate change.


Author(s):  
M. J. Gondwe ◽  
C. Helfter ◽  
M. Murray-Hudson ◽  
P. E. Levy ◽  
E. Mosimanyana ◽  
...  

Data-poor tropical wetlands constitute an important source of atmospheric CH 4 in the world. We studied CH 4 fluxes using closed chambers along a soil moisture gradient in a tropical seasonal swamp in the Okavango Delta, Botswana, the sixth largest tropical wetland in the world. The objective of the study was to assess net CH 4 fluxes and controlling environmental factors in the Delta's seasonal floodplains. Net CH 4 emissions from seasonal floodplains in the wetland were estimated at 0.072 ± 0.016 Tg a −1 . Microbial CH 4 oxidation of approximately 2.817 × 10 −3  ± 0.307 × 10 −3  Tg a −1 in adjacent dry soils of the occasional floodplains accounted for the sink of 4% of the total soil CH 4 emissions from seasonal floodplains. The observed microbial CH 4 sink in the Delta's dry soils is, therefore, comparable to the global average sink of 4–6%. Soil water content (SWC) and soil organic matter were the main environmental factors controlling CH 4 fluxes in both the seasonal and occasional floodplains. The optimum SWC for soil CH 4 emissions and oxidation in the Delta were estimated at 50% and 15%, respectively. Electrical conductivity and pH were poorly correlated ( r 2  ≤ 0.11, p  < 0.05) with CH 4 fluxes in the seasonal floodplain at Nxaraga. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part1)'.


2021 ◽  
Vol 8 ◽  
Author(s):  
Ingeborg Bussmann ◽  
Holger Brix ◽  
Götz Flöser ◽  
Uta Ködel ◽  
Philipp Fischer

Although methane is a widely studied greenhouse gas, uncertainties remain with respect to the factors controlling its distribution and diffusive flux into the atmosphere, especially in highly dynamic coastal waters. In the southern North Sea, the Elbe and Weser rivers are two major tributaries contributing to the overall methane budget of the southern German Bight. In June 2019, we continuously measured methane and basic hydrographic parameters at a high temporal and spatial resolution (one measurement per minute every 200–300 m) on a transect between Cuxhaven and Helgoland. These measurements revealed that the overall driver of the coastal methane distribution is the dilution of riverine methane-rich water with methane-poor marine water. For both the Elbe and Weser, we determined an input concentration of 40–50 nmol/L compared to only 5 nmol/L in the marine area. Accordingly, we observed a comparatively steady dilution pattern of methane concentration toward the marine realm. Moreover, small-scale anomalous patterns with unexpectedly higher dissolved methane concentrations were discovered at certain sites and times. These patterns were associated with the highly significant correlations of methane with oxygen or turbidity. However, these local anomalies were not consistent over time (days, months). The calculated diffusive methane flux from the water into the atmosphere revealed local values approximately 3.5 times higher than background values (median of 36 and 128 μmol m–2 d–1). We evaluate that this occurred because of a combination of increasing wind speed and increasing methane concentration at those times and locations. Hence, our results demonstrate that improved temporal and spatial resolution of methane measurements can provide a more accurate estimation and, consequently, a more functional understanding of the temporal and spatial dynamics of the coastal methane flux.


Atmosphere ◽  
2021 ◽  
Vol 12 (9) ◽  
pp. 1126
Author(s):  
Ji Hu ◽  
Wei Guan ◽  
Huai Chen

The surfaces of rivers are considered important sources of atmospheric methane (CH4), however research on this topic is still constrained, especially in freshwater rivers and with the consideration of spatial heterogeneity. Three regions (upper reaches, midstream and downstream) were selected to examine the CH4 fluxes from a freshwater river surface in a mangrove forest wetland from 2012 to 2013, using floating chambers. Results showed that the CH4 fluxes varied significantly among the three regions, with the lowest fluxes at downstream (0.50 ± 0.20 mg m−2 h−1), and highest at upper reaches (1.19 ± 0.36 mg m−2 h−1). The average emission rate at midstream was 0.95 ± 0.37 mg m−2 h−1. The methane flux also varied with seasons, with higher flux in rain-abundant seasons. On average, the CH4 flux in our research river was 0.88 ± 0.31 mg m−2 h−1, which was less than other tropical rivers. In addition, we found that the CH4 flux was significantly correlated with the water characteristics of temperature and atmospheric pressure. Thereby, this study quantified the methane emission from a freshwater river surface in a tropical mangrove forest, enriching the existing knowledge of river surface CH4 flux.


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