scholarly journals Dynamics of CO2 fluxes and concentrations during a shallow subsurface CO2 release

2009 ◽  
Vol 60 (2) ◽  
pp. 285-297 ◽  
Author(s):  
Jennifer L. Lewicki ◽  
George E. Hilley ◽  
Laura Dobeck ◽  
Lee Spangler
Keyword(s):  
Co2 Fluxes ◽  
Shallow Subsurface ◽  
Co2 Release

scholarly journals Increasing summer net CO<sub>2</sub> uptake in high northern ecosystems inferred from atmospheric inversions and comparisons to remote-sensing NDVI

2016 ◽  
Vol 16 (14) ◽  
pp. 9047-9066 ◽  
Author(s):  
Lisa R. Welp ◽  
Prabir K. Patra ◽  
Christian Rödenbeck ◽  
Rama Nemani ◽  
Jian Bi ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Fire Frequency ◽  
The Arctic ◽  
Co2 Fluxes ◽  
Arctic Zone ◽  
Boreal Zone ◽  
High Northern Latitude ◽  
Latitude Region ◽  
Atmospheric Co2 Concentrations ◽  
Co2 Release

Abstract. Warmer temperatures and elevated atmospheric CO2 concentrations over the last several decades have been credited with increasing vegetation activity and photosynthetic uptake of CO2 from the atmosphere in the high northern latitude ecosystems: the boreal forest and arctic tundra. At the same time, soils in the region have been warming, permafrost is melting, fire frequency and severity are increasing, and some regions of the boreal forest are showing signs of stress due to drought or insect disturbance. The recent trends in net carbon balance of these ecosystems, across heterogeneous disturbance patterns, and the future implications of these changes are unclear. Here, we examine CO2 fluxes from northern boreal and tundra regions from 1985 to 2012, estimated from two atmospheric inversions (RIGC and Jena). Both used measured atmospheric CO2 concentrations and wind fields from interannually variable climate reanalysis. In the arctic zone, the latitude region above 60° N excluding Europe (10° W–63° E), neither inversion finds a significant long-term trend in annual CO2 balance. The boreal zone, the latitude region from approximately 50–60° N, again excluding Europe, showed a trend of 8–11 Tg C yr−2 over the common period of validity from 1986 to 2006, resulting in an annual CO2 sink in 2006 that was 170–230 Tg C yr−1 larger than in 1986. This trend appears to continue through 2012 in the Jena inversion as well. In both latitudinal zones, the seasonal amplitude of monthly CO2 fluxes increased due to increased uptake in summer, and in the arctic zone also due to increased fall CO2 release. These findings suggest that the boreal zone has been maintaining and likely increasing CO2 sink strength over this period, despite browning trends in some regions and changes in fire frequency and land use. Meanwhile, the arctic zone shows that increased summer CO2 uptake, consistent with strong greening trends, is offset by increased fall CO2 release, resulting in a net neutral trend in annual fluxes. The inversion fluxes from the arctic and boreal zones covering the permafrost regions showed no indication of a large-scale positive climate–carbon feedback caused by warming temperatures on high northern latitude terrestrial CO2 fluxes from 1985 to 2012.

scholarly journals Increasing summer net CO<sub>2</sub> uptake in high northern ecosystems inferred from atmospheric inversions and remote sensing

2016 ◽  
Author(s):  
Lisa R. Welp ◽  
Prabir K. Patra ◽  
Christian Rodenbeck ◽  
Rama Nemani ◽  
Jian Bi ◽  
...  
Keyword(s):  
Boreal Forest ◽  
Fire Frequency ◽  
The Arctic ◽  
Co2 Fluxes ◽  
Arctic Zone ◽  
Boreal Zone ◽  
High Northern Latitude ◽  
Latitude Region ◽  
Atmospheric Co2 Concentrations ◽  
Co2 Release

Abstract. Warmer temperatures and elevated atmospheric CO2 concentrations over the last several decades have been credited with increasing vegetation activity and photosynthetic uptake of CO2 from the atmosphere in the high northern latitude ecosystems: the boreal forest and Arctic tundra. At the same time, fire frequency and severity are increased, and some regions of the boreal forest show signs of stress due to drought or insect disturbance. The recent trends in net carbon balance of these ecosystems, across heterogeneous disturbance patterns, and the future implications of these changes are unclear. Here we examine CO2 fluxes from northern boreal and tundra from 1986 to 2012 estimated from two inverse models (RIGC and Jena), both using measured atmospheric CO2 concentrations and wind-fields from interannually variable reanalysis. In the arctic zone, the latitude region above 60°N excluding Europe (10° W–63° E), neither model finds a significant long-term trend in annual CO2 balance. The boreal zone, the latitude region from approximately 50° N to 60° N, again excluding Europe, absorbed an extra 8–11 Tg C yr−1 over the period from 1986 to 2006, resulting in an annual CO2 sink in 2006 that was 170–230 Tg C larger than in 1986. This same trend appears to continue through 2012 as well. In both latitudinal zones, the seasonal amplitude of monthly CO2 fluxes increased due to increased uptake in summer, and in the arctic zone, also due to increased fall CO2 release. Both models showed a seasonal flux amplitude increase of nearly 1 % yr−1 in the arctic zone, over twice the trend in the boreal zone fluxes. These findings suggest that the boreal zone has been maintaining and likely increasing CO2 sink strength over this period, despite browning trends in some regions, changes in fire frequency and land use. Meanwhile the arctic zone shows increased summer CO2 uptake, consistent with strong greening trends, is offset by increased fall CO2 release, resulting in a net neutral trend in annual fluxes. The inversion fluxes from the arctic and boreal zones covering the permafrost regions showed no indication of a large-scale positive climate-carbon feedback caused by warming temperature on high northern latitude terrestrial CO2 fluxes as of 2012.

Modeling CO2 Release Experiment in the Shallow Subsurface and Sensitivity Analysis

2013 ◽  
Vol 19 (3) ◽  
pp. 207-220 ◽  
Author(s):  
C. Yang ◽  
K. Romanak ◽  
S. Hovorka ◽  
R. Triveno
Keyword(s):  
Sensitivity Analysis ◽  
Release Experiment ◽  
Shallow Subsurface ◽  
Co2 Release

scholarly journals Modeling Gas Transport in the Shallow Subsurface During the ZERT CO2 Release Test

2009 ◽  
Vol 82 (1) ◽  
pp. 77-92 ◽  
Author(s):  
Curtis M. Oldenburg ◽  
Jennifer L. Lewicki ◽  
Laura Dobeck ◽  
Lee Spangler
Keyword(s):  
Gas Transport ◽  
Shallow Subsurface ◽  
Release Test ◽  
Co2 Release

scholarly journals Spatio-Temporal Monitoring of Soil CO2 Fluxes and Concentrations after Artificial CO2 Release

2017 ◽  
Vol 26 (2) ◽  
pp. 93-104 ◽  
Author(s):  
Hyun-Jun Kim ◽  
Seung Hyun Han ◽  
Seongjun Kim ◽  
Hyeon Min Yun ◽  
Seong-Chun Jun ◽  
...  
Keyword(s):  
Co2 Fluxes ◽  
Soil Co2 ◽  
Spatio Temporal ◽  
Co2 Release

scholarly journals CO<sub>2</sub> flux determination by closed-chamber methods can be seriously biased by inappropriate application of linear regression

2007 ◽  
Vol 4 (6) ◽  
pp. 1005-1025 ◽  
Author(s):  
L. Kutzbach ◽  
J. Schneider ◽  
T. Sachs ◽  
M. Giebels ◽  
H. Nykänen ◽  
...  
Keyword(s):  
Linear Regression ◽  
Nonlinear Regression ◽  
Co2 Flux ◽  
Exponential Model ◽  
Co2 Uptake ◽  
Co2 Fluxes ◽  
Closed Chamber ◽  
Exponential Regression ◽  
Closure Time ◽  
Over Time

Abstract. Closed (non-steady state) chambers are widely used for quantifying carbon dioxide (CO2) fluxes between soils or low-stature canopies and the atmosphere. It is well recognised that covering a soil or vegetation by a closed chamber inherently disturbs the natural CO2 fluxes by altering the concentration gradients between the soil, the vegetation and the overlying air. Thus, the driving factors of CO2 fluxes are not constant during the closed chamber experiment, and no linear increase or decrease of CO2 concentration over time within the chamber headspace can be expected. Nevertheless, linear regression has been applied for calculating CO2 fluxes in many recent, partly influential, studies. This approach has been justified by keeping the closure time short and assuming the concentration change over time to be in the linear range. Here, we test if the application of linear regression is really appropriate for estimating CO2 fluxes using closed chambers over short closure times and if the application of nonlinear regression is necessary. We developed a nonlinear exponential regression model from diffusion and photosynthesis theory. This exponential model was tested with four different datasets of CO2 flux measurements (total number: 1764) conducted at three peatlands sites in Finland and a tundra site in Siberia. Thorough analyses of residuals demonstrated that linear regression was frequently not appropriate for the determination of CO2 fluxes by closed-chamber methods, even if closure times were kept short. The developed exponential model was well suited for nonlinear regression of the concentration over time c(t) evolution in the chamber headspace and estimation of the initial CO2 fluxes at closure time for the majority of experiments. However, a rather large percentage of the exponential regression functions showed curvatures not consistent with the theoretical model which is considered to be caused by violations of the underlying model assumptions. Especially the effects of turbulence and pressure disturbances by the chamber deployment are suspected to have caused unexplainable curvatures. CO2 flux estimates by linear regression can be as low as 40% of the flux estimates of exponential regression for closure times of only two minutes. The degree of underestimation increased with increasing CO2 flux strength and was dependent on soil and vegetation conditions which can disturb not only the quantitative but also the qualitative evaluation of CO2 flux dynamics. The underestimation effect by linear regression was observed to be different for CO2 uptake and release situations which can lead to stronger bias in the daily, seasonal and annual CO2 balances than in the individual fluxes. To avoid serious bias of CO2 flux estimates based on closed chamber experiments, we suggest further tests using published datasets and recommend the use of nonlinear regression models for future closed chamber studies.

CO2 fluxes of two lakes in volcanic caves in the Azores, Portugal

2019 ◽  
Vol 102 ◽  
pp. 218-228 ◽  
Author(s):  
César Andrade ◽  
Fátima Viveiros ◽  
J Virgílio Cruz ◽  
Rui Coutinho ◽  
Rafael Branco
Keyword(s):  
Co2 Fluxes

scholarly journals Integrated magnetotelluric and seismic investigation of Cenozoic graben structure near Obrzycko, Poland

2021 ◽  
Author(s):  
Adam Cygal ◽  
Michał Stefaniuk ◽  
Anna Kret
Keyword(s):  
Seismic Data ◽  
Geophysical Methods ◽  
Geological Structure ◽  
Data Sets ◽  
Low Velocity ◽  
Shallow Subsurface ◽  
Geophysical Model ◽  
Novel Approach ◽  
Loose Deposits ◽  
Static Corrections

AbstractThis article presents the results of an integrated interpretation of measurements made using Audio-Magnetotellurics and Seismic Reflection geophysical methods. The obtained results were used to build an integrated geophysical model of shallow subsurface cover consisting of Cenozoic deposits, which then formed the basis for a detailed lithological and tectonic interpretation of deeper Mesozoic sediments. Such shallow covers, consisting mainly of glacial Pleistocene deposits, are typical for central and northern Poland. This investigation concentrated on delineating the accurate geometry of Obrzycko Cenozoic graben structure filled with loose deposits, as it was of great importance to the acquisition, processing and interpretation of seismic data that was to reveal the tectonic structure of the Cretaceous and Jurassic sediments which underly the study area. Previously, some problems with estimation of seismic static corrections over similar grabens filled with more recent, low-velocity deposits were encountered. Therefore, a novel approach to estimating the exact thickness of such shallow cover consisting of low-velocity deposits was applied in the presented investigation. The study shows that some alternative geophysical data sets (such as magnetotellurics) can be used to significantly improve the imaging of geological structure in areas where seismic data are very distorted or too noisy to be used alone

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