scholarly journals Radiocarbon Measurements of Ecosystem Respiration and Soil Pore-Space CO<sub>2</sub> in Utqiaġvik (Barrow), Alaska

2018 ◽  
Author(s):  
Lydia J. S. Vaughn ◽  
Margaret S. Torn
Keyword(s):  
Soil Carbon ◽  
Ecosystem Respiration ◽  
Pore Space ◽  
Co2 Flux ◽  
Co2 Production ◽  
Data Repository ◽  
Carbon Pools ◽  
Environmental Controls ◽  
Soil Pore Space ◽  
Pool Model

Abstract. Radiocarbon measurements of ecosystem respiration and soil pore space CO2 are useful for determining the sources of ecosystem respiration, identifying environmental controls on soil carbon cycling rates, and parameterizing and evaluating models. We measured flux rates and radiocarbon contents of ecosystem respiration, as well as radiocarbon in soil profile CO2 in Utqiaġvik (Barrow), Alaska, during the summers of 2012, 2013, and 2014. We found that radiocarbon in ecosystem respiration ranged from &amp;plus;60.5 to −160 ‰ with a median value of &amp;plus;23.3 ‰. Ecosystem respiration became more depleted in radiocarbon from summer to autumn, indicating increased decomposition of old soil organic carbon and/or decreased CO2 production from fast-cycling carbon pools. Across permafrost features, ecosystem respiration from high-centered polygons was depleted in radiocarbon relative to other polygon types. Radiocarbon content in soil pore-space CO2 varied between −7.1 and −280 ‰, becoming more negative with depth in individual soil profiles. These pore-space radiocarbon values correspond to CO2 mean ages of 410 to 3350 years, based on a steady-state, one-pool model. Together, these data indicate that soil respiration is derived primarily from old, slow-cycling carbon pools, but that total CO2 fluxes depend largely on autotrophic respiration and heterotrophic decomposition of fast-cycling carbon within the shallowest soil layers. The relative contributions of these different CO2 sources are highly variable across microtopographic features and time in the sampling season. The highly negative Δ14C values in soil pore-space CO2 and autumn ecosystem respiration indicate that when it is not frozen, very old soil carbon is vulnerable to decomposition. Radiocarbon data and associated CO2 flux and temperature data are stored in the data repository of the Next Generation Ecosystem Experiments (NGEE-Arctic) at http://dx.doi.org/10.5440/1364062.

scholarly journals Radiocarbon measurements of ecosystem respiration and soil pore-space CO<sub>2</sub> in Utqiaġvik (Barrow), Alaska

2018 ◽  
Vol 10 (4) ◽  
pp. 1943-1957 ◽  
Author(s):  
Lydia J. S. Vaughn ◽  
Margaret S. Torn
Keyword(s):  
Soil Carbon ◽  
Ecosystem Respiration ◽  
Pore Space ◽  
Co2 Flux ◽  
Co2 Production ◽  
Data Repository ◽  
Deep Soil ◽  
Environmental Controls ◽  
Soil Pore Space ◽  
Pool Model

Abstract. Radiocarbon measurements of ecosystem respiration and soil pore space CO2 are useful for determining the sources of ecosystem respiration, identifying environmental controls on soil carbon cycling rates, and parameterizing and evaluating models of the carbon cycle. We measured flux rates and radiocarbon content of ecosystem respiration, as well as radiocarbon in soil profile CO2 in Utqiaġvik (Barrow), Alaska, during the summers of 2012, 2013, and 2014. We found that radiocarbon in ecosystem respiration (Δ14CReco) ranged from +60.5 to −160 ‰ with a median value of +23.3 ‰. Ecosystem respiration became more depleted in radiocarbon from summer to autumn, indicating increased decomposition of old soil organic carbon and/or decreased CO2 production from fast-cycling carbon pools. Across permafrost features, ecosystem respiration from high-centered polygons was depleted in radiocarbon relative to other polygon types. Radiocarbon content in soil pore-space CO2 varied between −7.1 and −280 ‰, becoming more negative with depth in individual soil profiles. These pore-space radiocarbon values correspond to CO2 mean ages of 410 to 3350 years, based on a steady-state, one-pool model. Together, these data indicate that deep soil respiration was derived primarily from old, slow-cycling carbon, but that total CO2 fluxes depended largely on autotrophic respiration and heterotrophic decomposition of fast-cycling carbon within the shallowest soil layers. The relative contributions of these different CO2 sources were highly variable across microtopographic features and time in the sampling season. The highly negative Δ14C values in soil pore-space CO2 and autumn ecosystem respiration indicate that when it is not frozen, very old soil carbon is vulnerable to decomposition. Radiocarbon data and associated CO2 flux and temperature data are stored in the data repository of the Next Generation Ecosystem Experiments (NGEE-Arctic) at http://dx.doi.org/10.5440/1364062 and https://doi.org/10.5440/1418853.

scholarly journals Oscillatory behavior of two nonlinear microbial models of soil carbon decomposition

2014 ◽  
Vol 11 (7) ◽  
pp. 1817-1831 ◽  
Author(s):  
Y. P. Wang ◽  
B. C. Chen ◽  
W. R. Wieder ◽  
M. Leite ◽  
B. E. Medlyn ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Microbial Biomass ◽  
Soil Carbon ◽  
Nonlinear Model ◽  
Linear Models ◽  
Nonlinear Models ◽  
Oscillatory Behavior ◽  
Carbon Pools ◽  
Carbon Decomposition ◽  
Pool Model

Abstract. A number of nonlinear models have recently been proposed for simulating soil carbon decomposition. Their predictions of soil carbon responses to fresh litter input and warming differ significantly from conventional linear models. Using both stability analysis and numerical simulations, we showed that two of those nonlinear models (a two-pool model and a three-pool model) exhibit damped oscillatory responses to small perturbations. Stability analysis showed the frequency of oscillation is proportional to √(&amp;varepsilon;−1−1) Ks/Vs in the two-pool model, and to √(&amp;varepsilon;−1−1) Kl/Vl in the three-pool model, where &amp;varepsilon; is microbial growth efficiency, Ks and Kl are the half saturation constants of soil and litter carbon, respectively, and /Vs and /Vl are the maximal rates of carbon decomposition per unit of microbial biomass for soil and litter carbon, respectively. For both models, the oscillation has a period of between 5 and 15 years depending on other parameter values, and has smaller amplitude at soil temperatures between 0 and 15 °C. In addition, the equilibrium pool sizes of litter or soil carbon are insensitive to carbon inputs in the nonlinear model, but are proportional to carbon input in the conventional linear model. Under warming, the microbial biomass and litter carbon pools simulated by the nonlinear models can increase or decrease, depending whether &amp;varepsilon; varies with temperature. In contrast, the conventional linear models always simulate a decrease in both microbial and litter carbon pools with warming. Based on the evidence available, we concluded that the oscillatory behavior and insensitivity of soil carbon to carbon input are notable features in these nonlinear models that are somewhat unrealistic. We recommend that a better model for capturing the soil carbon dynamics over decadal to centennial timescales would combine the sensitivity of the conventional models to carbon influx with the flexible response to warming of the nonlinear model.

scholarly journals Oscillatory behavior of two nonlinear microbial models of soil carbon decomposition

2013 ◽  
Vol 10 (12) ◽  
pp. 19661-19700 ◽  
Author(s):  
Y. P. Wang ◽  
B. C. Chen ◽  
W. R. Wieder ◽  
Y. Q. Luo ◽  
M. Leite ◽  
...  
Keyword(s):  
Stability Analysis ◽  
Microbial Biomass ◽  
Soil Carbon ◽  
Nonlinear Model ◽  
Linear Models ◽  
Nonlinear Models ◽  
Oscillatory Behavior ◽  
Carbon Pools ◽  
Carbon Decomposition ◽  
Pool Model

Abstract. A number of nonlinear models have recently been proposed for simulating soil carbon decomposition. Their predictions of soil carbon responses to fresh litter input and warming differ significantly from conventional linear models. Using both stability analysis and numerical simulations, we showed that two of those nonlinear models (a two-pool model and a three-pool model) exhibit damped oscillatory responses to small perturbations. Stability analysis showed the frequency of oscillation is proportional to √ (&amp;varepsilon; −1−1)Ks/Vs in the two-pool model, and to √ (&amp;varepsilon; −1−1)Kl/Vl in the three-pool model, where &amp;varepsilon; is microbial growth efficiency, Ks and Kl are the half saturation constants of soil and litter carbon, respectively, and Vs and Vl are the maximal rates of carbon decomposition per unit of microbial biomass for soil and litter carbon, respectively. For both models, the oscillation has a period between 5 and 15 yr depending on other parameter values, and has smaller amplitude at soil temperatures between 0 °C to 15 °C. In addition, the equilibrium pool sizes of litter or soil carbon are insensitive to carbon inputs in the nonlinear model, but are proportional to carbon input in the conventional linear model. Under warming, the microbial biomass and litter carbon pools simulated by the nonlinear models can increase or decrease, depending whether &amp;varepsilon; varies with temperature. In contrast, the conventional linear models always simulate a decrease in both microbial and litter carbon pools with warming. Based on the evidence available, we concluded that the oscillatory behavior and insensitivity of soil carbon to carbon input in the nonlinear models are unrealistic. We recommend that a better model for capturing the soil carbon dynamics over decadal to centennial timescales would combine the sensitivity of the conventional models to carbon influx with the flexible response to warming of the nonlinear model.

Sustainable Management of Soil for Carbon Sequestration

2017 ◽  
Vol 5 (2) ◽  
pp. 132-140 ◽  
Author(s):  
Kewat Sanjay Kumar ◽  
Keyword(s):  
Carbon Sequestration ◽  
Soil Carbon ◽  
Sustainable Management ◽  
Management Practices ◽  
Atmospheric Co2 ◽  
Carbon Pools ◽  
Carbon Stabilization ◽  
Organic C ◽  
Soil Ecosystems ◽  
C Stocks

Mechanisms governing carbon stabilization in soils have received a great deal of attention in recent years due to their relevance in the global carbon cycle. Two thirds of the global terrestrial organic C stocks in ecosystems are stored in below ground components as terrestrial carbon pools in soils. Furthermore, mean residence time of soil organic carbon pools have slowest turnover rates in terrestrial ecosystems and thus there is vast potential to sequester atmospheric CO2 in soil ecosystems. Depending upon soil management practices it can be served as source or sink for atmospheric CO2. Sustainable management systems and practices such as conservation agriculture, agroforestry and application of biochar are emerging and promising tools for soil carbon sequestration. Increasing soil carbon storage in a system simultaneously improves the soil health by increase in infiltration rate, soil biota and fertility, nutrient cycling and decrease in soil erosion process, soil compaction and C emissions. Henceforth, it is vital to scientifically explore the mechanisms governing C flux in soils which is poorly understood in different ecosystems under anthropogenic interventions making soil as a potential sink for atmospheric CO2 to mitigate climate change. Henceforth, present paper aims to review basic mechanism governing carbon stabilization in soils and new practices and technological developments in agricultural and forest sciences for C sequestration in terrestrial soil ecosystems.

scholarly journals Gamma-Ray Attenuation to Evaluate Soil Porosity: An Analysis of Methods

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Luiz F. Pires ◽  
André B. Pereira
Keyword(s):  
Gamma Ray ◽  
Particle Density ◽  
Pore Space ◽  
Physical Property ◽  
Soil Bulk Density ◽  
Soil Porosity ◽  
Porous System ◽  
Soil Pore Space ◽  
Gamma Ray Attenuation ◽  
Dry Soil

Soil porosity (ϕ) is of a great deal for environmental studies due to the fact that water infiltrates and suffers redistribution in the soil pore space. Many physical and biochemical processes related to environmental quality occur in the soil porous system. Representative determinations ofϕare necessary due to the importance of this physical property in several fields of natural sciences. In the current work, two methods to evaluateϕwere analyzed by means of gamma-ray attenuation technique. The first method uses the soil attenuation approach through dry soil and saturated samples, whereas the second one utilizes the same approach but taking into account dry soil samples to assess soil bulk density and soil particle density to determineϕ. The results obtained point out a good correlation between both methods. However, whenϕis obtained through soil water content at saturation and a 4 mm collimator is used to collimate the gamma-ray beam the first method also shows good correlations with the traditional one.

scholarly journals Can land degradation drive differences in the C exchange of two similar semiarid ecosystems?

2018 ◽  
Vol 15 (1) ◽  
pp. 263-278 ◽  
Author(s):  
Ana López-Ballesteros ◽  
Cecilio Oyonarte ◽  
Andrew S. Kowalski ◽  
Penélope Serrano-Ortiz ◽  
Enrique P. Sánchez-Cañete ◽  
...  
Keyword(s):  
Vadose Zone ◽  
Land Degradation ◽  
Ecosystem Respiration ◽  
Gross Primary Production ◽  
Co2 Flux ◽  
C Sequestration ◽  
Co2 Exchange ◽  
Striking Difference ◽  
Soil Variables ◽  
Natural Site

Abstract. Currently, drylands occupy more than one-third of the global terrestrial surface and are recognized as areas vulnerable to land degradation. The concept of land degradation stems from the loss of an ecosystem's biological productivity due to long-term loss of natural vegetation or depletion of soil nutrients. Drylands' key role in the global carbon (C) balance has been recently demonstrated, but the effects of land degradation on C sequestration by these ecosystems still need to be investigated. In the present study, we compared net C and water vapor fluxes, together with satellite, meteorological and vadose zone (CO2, water content and temperature) measurements, between two nearby (∼ 23 km) experimental sites representing “natural” (i.e., site of reference) and “degraded” grazed semiarid grasslands. We utilized data acquired over 6 years from two eddy covariance stations located in southeastern Spain with highly variable precipitation magnitude and distribution. Results show a striking difference in the annual C balances with an average net CO2 exchange of 196 ± 40 (C release) and −23 ± 2 g C m−2 yr−1 (C fixation) for the degraded and natural sites, respectively. At the seasonal scale, differing patterns in net CO2 fluxes were detected over both growing and dry seasons. As expected, during the growing seasons, greater net C uptake over longer periods was observed at the natural site. However, a much greater net C release, probably derived from subterranean ventilation, was measured at the degraded site during drought periods. After subtracting the nonbiological CO2 flux from net CO2 exchange, flux partitioning results point out that, during the 6 years of study, gross primary production, ecosystem respiration and water use efficiency were, on average, 9, 2 and 10 times higher, respectively, at the natural site versus the degraded site. We also tested differences in all monitored meteorological and soil variables and CO2 at 1.50 m belowground was the variable showing the greatest intersite difference, with ∼ 1000 ppm higher at the degraded site. Thus, we believe that subterranean ventilation of this vadose zone CO2, previously observed at both sites, partly drives the differences in C dynamics between them, especially during the dry season. It may be due to enhanced subsoil–atmosphere interconnectivity at the degraded site.

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