Episodic fluxes of methane from subarctic fens

1992 ◽  
Vol 72 (4) ◽  
pp. 441-452 ◽  
Author(s):  
J. Windsor ◽  
T. R. Moore ◽  
N. T. Roulet
Keyword(s):  
Seasonal Pattern ◽  
Methane Flux ◽  
Spatial And Temporal Variability ◽  
Surface Layers ◽  
Overburden Pressure ◽  
Episodic Events ◽  
Episodic Event ◽  
Before And After ◽  
Peat Profile ◽  
Northern Peatlands

Measurements of methane flux from northern peatlands to the atmosphere are complicated by high spatial and temporal variability. We quantified the variability of methane flux from two subarctic fens near Schefferville, northern Quebec, using a static chamber technique. Within the seasonal pattern of increasing fluxes associated with the warming of the peat profile, episodic fluxes of methane were observed. One set of episodic events occurred during the spring thaw of the upper layers of the peat, which released methane stored in ice over the winter. The second set, generally of short duration (< 2 d), occurred in mid-summer and appeared to be related primarily to the lowering of the water table. In four of six subjectively-identified, episodic fluxes during the 1990 summer the flux during the episodic event was equal to or greater than the upper 95% confidence level of the three fluxes before and after the event (t-statistic probabilities ranged from < 0.001 to 0.038). Mechanisms to account for these episodic fluxes of methane include increased methane diffusivity, removal of overburden pressure and reduced rates of methane consumption in the surface layers of the peat. Omission of these episodic fluxes could lower estimates of seasonal methane emissions by 7–22%. Key words: Peatlands, fens, methane

scholarly journals Methane flux from drained northern peatlands: Effect of a persistent water table lowering on flux

1993 ◽  
Vol 7 (4) ◽  
pp. 749-769 ◽  
Author(s):  
Nigel T. Roulet ◽  
R. Ash ◽  
W. Quinton ◽  
Tim Moore
Keyword(s):  
Water Table ◽  
Methane Flux ◽  
Northern Peatlands

Soil water dynamics after fire in a Portuguese shrubland

2006 ◽  
Vol 15 (1) ◽  
pp. 99 ◽  
Author(s):  
Joaquim S. Silva ◽  
Francisco C. Rego ◽  
Stefano Mazzoleni
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Plant Community ◽  
Root Distribution ◽  
Control Plot ◽  
The Other ◽  
Water Dynamics ◽  
Soil Water Dynamics ◽  
Surface Layers ◽  
Before And After

This paper presents a study where soil water content (SW) was measured before and after an experimental fire in a shrubland dominated by Erica scoparia L. in Portugal. Two plots were established: one was kept as a control plot and the other was burned by an experimental fire in June 2001. Measurements were taken before fire (2000), and after fire (2001, 2002, and 2003) at six depths down to 170 cm, from June to December. Measurements before fire allowed comparison of the two plots in terms of the SW differential, using 2000 as a reference. Results for 2001 showed that SW decreased less during the drying season (June–September) and increased more during the wetting season (October–December) in the burned plot than in the control plot. The magnitude of these effects decreased consistently in 2002 and 2003, especially at surface layers. The maximum gain of SW for the total profile in the burned plot was estimated as 105.5 mm in 2001, 70.2 mm in 2002, and 35.6 mm in 2003. The present paper discusses the mechanisms responsible for the increase in SW taking into account the characteristics of the plant community, including the root distribution, and the results of other studies.

Evolution of the Mechanical Properties of the Surface Layers of Aluminum Alloys under the Conditions of Sliding Friction

2021 ◽  
Vol 901 ◽  
pp. 219-225
Author(s):  
Elena V. Torskaya ◽  
Alexey M. Mezrin
Keyword(s):  
Mechanical Properties ◽  
Aluminum Alloys ◽  
Sliding Friction ◽  
Surface Layers ◽  
Before And After ◽  
Wear And Tear ◽  
Friction Path ◽  
Compliant Layer

Mechanical properties of surface layers of aluminum alloys before and after friction tests are studied by nanoindentation. The influence of the composition of the alloys on these properties is analyzed. It is obtained that as a result of wear and tear, relatively compliant layer is formed on the surface of one of the alloys. Another sample demonstrates relatively rigid film at the surface of the friction path. Conclusions about different mechanisms of the wear and tear of alloys are made based on the analysis.

scholarly journals Validation of MODIS snow cover images over Austria

2006 ◽  
Vol 3 (4) ◽  
pp. 1569-1601 ◽  
Author(s):  
J. Parajka ◽  
G. Blöschl
Keyword(s):  
Snow Cover ◽  
Classification Accuracy ◽  
Snow Depth ◽  
Seasonal Pattern ◽  
Acquisition Time ◽  
Spatial And Temporal Variability ◽  
Temporal Shift ◽  
Early Afternoon ◽  
Moderate Resolution Imaging Spectroradiometer

Abstract. This study evaluates the Moderate Resolution Imaging Spectroradiometer (MODIS) snow cover product over the territory of Austria. The aims are (a) to analyse the spatial and temporal variability of the MODIS snow product classes, (b) to examine the accuracy of the MODIS snow product against in situ snow depth data, and (c) to identify the main factors that may influence the MODIS classification accuracy. We use daily MODIS grid maps (version 4) and daily snow depth measurements at 754 climate stations in the period from February 2000 to December 2005. The results indicate that, on average, clouds obscured 63% of Austria, which may significantly restrict the applicability of the MODIS snow cover images to hydrological modelling. On cloud-free days, however, the classification accuracy is very good with an average of 95%. There is no consistent relationship between the classification errors and dominant land cover type and local topographical variability but there are clear seasonal patterns to the errors. In December and January the errors are around 15% while in summer they are less than 1%. This seasonal pattern is related to the overall percentage of snow cover in Austria, although in spring, when there is a well developed snow pack, errors tend to be smaller than they are in early winter for the same overall percent snow cover. Overestimation and underestimation errors balance during most of the year which indicates little bias. In November and December, however, there appears to exist a tendency for overestimation. Part of the errors may be related to the temporal shift between the in situ snow depth measurements (07:00 a.m.) and the MODIS acquisition time (early afternoon).

scholarly journals Explosive and thermochemical treatment of multi-layer metallic composites

2019 ◽  
pp. 51-56
Author(s):  
Jerzy Nowaczewski ◽  
Milena Kita ◽  
Justyna Świeczak ◽  
Jacek Rudnicki
Keyword(s):  
Cross Sections ◽  
Intermediate Phase ◽  
Intermetallic Layer ◽  
Thermochemical Treatment ◽  
Ion Nitriding ◽  
Surface Layers ◽  
Before And After ◽  
The Individual ◽  
Current Systems ◽  
Composite Samples

The paper describes methods for the explosive hardening of metals which were performed with a view to increasing the hardness of previously obtained composites, as well as treatment of their surface layers to increase the efficiency of further thermochemical treatment. Typical systems for explosive hardening of metals and the construction of current systems, are discussed. The resulting effects of explosive hardening are illustrated with before and after diagrams of microhardness distributions in cross-sections of the processed composites hardening. In a further processing stage, the tested composite samples were subjected to ion nitriding. As a result of this process, in addition to the typical increase in hardness of the individual layers, an intermediate phase with a distinctly higher hardness was observed in the junction zone. Preliminary analysis of the photographs and the results from a scanning electron microscope (SEM) with an energy dispersive spectroscopy (EDS) attachment suggests that the particularly beneficial properties of the composites are attributed to the presence of the intermetallic layer.

Rotation of the principal stress directions due to earthquake faulting and its seismological implications

1995 ◽  
Vol 85 (5) ◽  
pp. 1513-1517
Author(s):  
Z.-M. Yin ◽  
G. C. Rogers
Keyword(s):  
Shear Stress ◽  
Normal Stress ◽  
Principal Stress ◽  
Stress Drop ◽  
Rotation Angle ◽  
Overburden Pressure ◽  
Rupture Area ◽  
Earthquake Faulting ◽  
Stress Directions ◽  
Before And After

Abstract Earthquake faulting results in stress drop over the rupture area. Because the stress drop is only in the shear stress and there is no or little stress drop in the normal stress on the fault, the principal stress directions must rotate to adapt such a change of the state of stress. Using two constraints, i.e., the normal stress on the fault and the vertical stress (the overburden pressure), which do not change before and after the earthquake, we derive simple expressions for the rotation angle in the σ1 axis. For a dip-slip earthquake, the rotation angle is only a function of the stress-drop ratio (defined as the ratio of the stress drop to the initial shear stress) and the angle between the σ1 axis and the fault plane, but for a strike-slip earthquake the rotation angle is also a function of the stress ratio. Depending on the faulting regimes, the σ1 axis can either rotate toward the direction of fault normal or rotate away from the direction of fault normal. The rotation of the stress field has several important seismological implications. It may play a significant role in the generation of heterogeneous stresses and in the occurrence and distribution of aftershocks. The rotation angle can be used to estimate the stress-drop ratio, which has been a long-lasting topic of debate in seismology.

Full year of continuous N2O flux measurements in a drained agricultural peatland in northern Finland

2021 ◽  
Author(s):  
Stephanie Gerin ◽  
Tuomas Laurila ◽  
Liisa Kulmala ◽  
Juha-Pekka Tuovinen ◽  
Henriikka Vekuri ◽  
...  
Keyword(s):  
Seasonal Pattern ◽  
N2o Emission ◽  
Soil Freezing ◽  
Spatial And Temporal Variability ◽  
N2o Emissions ◽  
Short Term ◽  
Meadow Fescue ◽  
Boreal Peatlands ◽  
Annual Budget ◽  
Data Points

&lt;p&gt;Pristine boreal peatlands are often considered neutral or even small sinks for nitrous oxide (N2O). However, drained peatlands are a significant source of N2O. In these managed sites, oxygen becomes more available, increasing denitrification and therefore N2O release into the atmosphere. N2O emissions do not typically follow a strong seasonal pattern like carbon dioxide but instead, have high spatial and temporal variability. Short-term N2O peak emissions can be observed after various meteorological or soil management events throughout the year, for example after soil freezing or thawing, or fertilization. However, it is not well known how exactly those events trigger the N2O emission peaks. Therefore, N2O annual budget based on punctual chamber measurement can introduce large uncertainties. That is why it is important to measure N2O emissions with a continuous method to better understand the controlling factors and to estimate the annual budgets more accurately.&lt;/p&gt;&lt;p&gt;For the first time in the boreal region of Europe, N2O emissions were continuously observed during a full year in a drained agricultural peatland with the eddy covariance (EC) technique. The study site is a managed peatland in northern Finland, in Ruukki (Latitude: 64.684010; Longitude: 25.106473), with a peat depth between 10 and 90 cm. It is currently managed as a grass field, composed of a mixture of timothy and meadow fescue. We will show a first overview of the N2O fluxes measured since November 2019 with the EC technique. We will present how various meteorological and management events can explain some short-term variations. Then, we will compare the N2O annual budget estimated from the EC measurements to the IPCC emission factor and to different estimates achieved using several sets of non-continuous data points, representing manual chamber measurements with varying frequency.&lt;/p&gt;

Microstructure and Corrosion Behavior in Al-Mg Based Alloys Subjected to Continuous Cyclic Bending and Annealing

2010 ◽  
Vol 654-656 ◽  
pp. 1002-1005
Author(s):  
Yoshimasa Takayama ◽  
Yuki Kido ◽  
Hajime Kato ◽  
Hideo Watanabe
Keyword(s):  
High Strain ◽  
Grain Structure ◽  
Coarse Grained ◽  
Central Layer ◽  
Surface Layers ◽  
Cyclic Bending ◽  
Lower Strain ◽  
Before And After ◽  
Corrosion Behaviors ◽  
Ebsd Technique

Coarsening of grain structure in surface layers in 5454 and 5083 Al-Mg based alloy sheets has been made by continuous cyclic bending (CCB), which is a useful straining technique to produce the high strain on the surface layers and the lower strain in the central layer of the sheet, and subsequent annealing. The microstructure on cross-section of the samples was analyzed by SEM/EBSD technique. For the samples before and after CCB/Annealing corrosion behaviors in NaCl or HCl solution were investigated. As a result, the samples subjected to CCB/Annealing showed higher corrosion resistance on coarse-grained surface layers. Less change in the corrosive solutions was observed on the grains parallel to {001} or {111} plane.

X-ray photoelectron spectroscopic analysis of halloysites with different composition and particle morphology

Clay Minerals ◽  
1992 ◽  
Vol 27 (4) ◽  
pp. 413-421 ◽  
Author(s):  
M. Soma ◽  
G. J. Churchman ◽  
B. K. G. Theng
Keyword(s):  
Photoelectron Spectroscopy ◽  
Cation Exchange Capacity ◽  
Spectroscopic Analysis ◽  
Surface Composition ◽  
Particle Morphology ◽  
Exchange Capacity ◽  
Surface Layers ◽  
X Ray ◽  
Fe Content ◽  
Before And After

AbstractThe surface composition of some halloysites with different particle morphology has been investigated by X-ray photoelectron spectroscopy (XPS) before and after removal of external Fe. The Fe(III) 2p3/2 binding energy of external Fe is appreciably smaller than that of structural Fe. Particle morphology is influenced by structural Fe content. The long-tubular halloysite has very little surface Fe, and its concentration tends to increase with the proportion of non-tubular particles in the samples. The spheroidal sample contains the most structural Fe which, however, does not appear to influence particle shape directly. Study by XPS indicates that Fe substitutes for Al in octahedral positions in approximately 1 : 2 proportion. As a result, an increase in octahedral vacancies and cation exchange capacity would be predicted. Further, halloysite layers within a crystal are generally inhomogeneous in composition. Built up like “onion skins”, the surface layers would either be enriched or depleted in Fe depending on the chemical environment in which crystal growth occurs.

A Description of the Kinetics and Mechanisms which Control the Release of Hlw Elements from Synroc

1990 ◽  
Vol 212 ◽  
Author(s):  
K. L. Smith ◽  
K. P. Hart ◽  
G. R. Lumpkin ◽  
P. McGlinn ◽  
P. Lam ◽  
...  
Keyword(s):  
Emission Spectroscopy ◽  
Optical Emission Spectroscopy ◽  
Optical Emission ◽  
Effect Of Temperature ◽  
Secondary Phases ◽  
Surface Layers ◽  
Before And After ◽  
Bicarbonate Solutions ◽  
Icp Mass Spectrometry ◽  
Kinetics Of

ABSTRACTLeaching tests were carried out on well-characterised Synroc C specimens containing 10 wt% simulated HLW. The effect of temperature and leachant composition on the mechanisms and kinetics of leaching were investigated by leaching Synroc specimens in deionised water at 70°C and 150°C, and in silicate and bicarbonate solutions at 70°C. SEM and TEM were used before and after leaching to characterise the primary and secondary phases in and on the Synroc samples, and to describe the morphological and chemical changes which occurred. Leachants were analysed using ICP/optical emission spectroscopy and ICP/mass spectrometry.Titaniferous surface layers were observed on the surface after exposure to leachants. Analysis of the leaching data has established that these surface layers can reduce the release of HLW elements from Synroc and that variations in temperature and leachant composition can hinder or promote the formation of secondary phases.

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