CO2 Accumulation Research Articles

Constraining the Fluid History of a CO2‐H2S Reservoir: Insights From Stable Isotopes, REE, and Fluid Inclusion Microthermometry

AbstractReservoirs that host CO2‐H2S‐bearing gases provide a key insight into crustal redox reactions such as thermochemical sulfate reduction (TSR). Despite this, there remains a poor understanding of the extent, duration, and the factors limiting this process on a reservoir scale. Here we show how a combination of petrography, fluid inclusion, rare earth element (REE), and carbon (δ13C), oxygen (δ18O), and sulfur (δ34S) stable isotope data can disentangle the fluid history of the world's largest CO2 accumulation, the LaBarge Field in Wyoming, USA. The carbonate‐hosted LaBarge Field was charged with oil around 80 Ma ago, which together with nodular anhydrite represent the reactants for TSR. The nodules exhibit two distinct trends of evolution in δ13C with both δ34S and δ18O that may be coupled to two different processes. The first trend was interpreted to reflect the coupled dissolution of anhydrite and reduction to elemental sulfur and the oxidation of organic compounds and associated precipitation of calcite during TSR. In contrast, the second trend was interpreted to be the result of the hydrothermal CO2 influx after the cessation of TSR. In addition, mass balance calculations were performed to estimate an approximate TSR reaction duration of 80 ka and to identify the availability of organic compounds as the limiting factor of the TSR process. Such an approach provides a tool for the prediction of TSR occurrence elsewhere and advancing our understanding of crustal fluid interactions.

Development and Application of Multi-Function Valve to Solve Major Problems of Expansion and Off-Odor Leakage in the Packaging of Kimchi

The one-way gas valve developed in this study was designed to prevent the breakage of packages from increased internal pressure, which is a problem in packaged Kimchi, and simultaneously reduce the outflow of the offodor release. The effect of the one-way gas valve on the headspace atmospheric compositions was investigated in the packaging system. The changes of atmospheric compositions and quality factors of Kimchi, such as CO2 accumulation, pH, titratable acidity, and salinity, were measured during a 4-week storage period at 4oC. The Kimchi package with the one-way gas valve dramatically reduced pressure build-up in the pouch by allowing the controlled flow of gas to the atmosphere. In addition, the package design allows the possibility of controlling the gas generated from Kimchi by adjusting the viscosity of the open pressure control oil. The one-way gas valve did not affect the sensory characteristics of Kimchi products during the storage period. Furthermore, the deodorizing capability of the activated carbon contained in the one-way gas valve effectively reduced the off-odor of Kimchi products released along with carbon dioxide. The novel one-way gas valve is considered to be an active packaging system that can solve major problems of expansion and offodor leakage in the packaging of Kimchi.

On the Theory of Electrolytic Dissociation, the Greenhouse Effect, and Activation Energy in (Electro)Catalysis: A Tribute to Svante Augustus Arrhenius.

Svante Augustus Arrhenius (1859, Vik - 1927, Stockholm) received the Nobel Prize for Chemistry in 1903 "in recognition of the extraordinary services he rendered to the advancement of chemistry by his electrolytic theory of dissociation". Arrhenius was a physicist, and he received his PhD from the University of Uppsala, where he later became a professor for phyiscal chemistry, the first in the country for this subject. He was offered several positions as professor abroad, but decided to remain in Sweden and to build a Nobel Institute for physical chemistry using the Nobel funds. He remained director of the Institute until his death. There are powerful lessons to take from Svante August Arrhenius' journey leading to a Nobel laureate as there are from his tremendous contributions to chemistry and science in general, including climate science, immunochemistry and cosmology. The theory of electrolytic dissociation for which Arrhenius received the 1903 Nobel Prize in Chemistry has had a profound impact on our understanding of the chemistry of solutions, chemical reactivity, mechanisms underlying chemical transformations as well as physiological processes. As a tribute to Arrhenius, we present a brief historical perspective and present status of the theory of electrolytic dissociation, its relevance and role to the development of electrochemistry, as well as some perspectives on the possible role of the theory to future advancements in electroanalysis, electrocatalysis and electrochemical energy storage. The review briefly highlights Arrhenius' contribution to climate science owing to his studies on the potential effects of increased anthropogenic CO2 emissions on the global climate. These studies were far ahead of their time and revealed a daunting global dilemma, global warming, that we are faced with today. Efforts to abate or reverse CO2 accumulation constitute one of the most pressing scientific problems of our time, "man's urgent strive to save self from the adverse effects of his self-orchestrated change on the climate". Finally, we review the application of the Arrhenius equation that correlates reaction rate constants (k) and temperature (T); , in determining reaction barriers in catalysis with a particular focus on recent modifications of the equation to account for reactions exhibiting non-linear Arrhenius behavior with concave curvature due to prevalence of quantum mechanical tunneling, as well as infrequent convexity of Arrhenius plots due to decrease of the microcanonical rate coefficient with energy as observed for some enzyme catalyzed reactions.

A new experimental platform connecting the rhizosphere priming effect with CO2 fluxes of plant-soil systems

Forty years of research on the rhizosphere priming effect (RPE) has demonstrated the potentially large increase (up to a factor 3) of soil organic matter mineralization induced by plant roots, but failed to directly quantify its contribution to the carbon (C) balance. Combining continuous CO2 flux measurements with RPE measurements has thus far been technically challenging. Here, we present an experimental platform of 40 mesocosms (volume = 88L; surface = 0.049 m2), including a 13C-labeled CO2 air-production system with a maximum capacity of 4 m3 min−1 and customizable labeling intensity. For this study, 13C depleted fossil C was used as source of labeled CO2 and the experiment was run for 250 days. Continuous net CO2-exchange measurements allowed us to estimate net ecosystem productivity, gross primary production and ecosystem respiration of the studied plant-soil systems. The RPE was regularly (bi-monthly to monthly) quantified by measuring the accumulation and isotopic composition of CO2 in dark chambers placed over the mesocosms. Our results show a good relationship between night plant-soil respiration (from continuous CO2-exchange measurements) and dark plant-soil respiration (from CO2 accumulation in dark chambers). This result suggests that our estimates of RPE and plant-soil fluxes based on the different methods are comparable. Preliminary results obtained in spring with grasses cultivated under ambient or elevated CO2 indicate that the RPE represents 1.22 ± 0.16% of gross primary production and 4.64 ± 1.12% of ecosystem respiration. The RPE estimates may have an uncertainty linked to the possible deviation in delta 13C between C sources (soil or plant) and released CO2 from these sources. We performed a sensitivity analysis on how the variation in intensity of isotopic labeling (difference in delta 13C between plant and soil) affects the uncertainty of RPE estimates considering 1‰ delta 13C deviation. Estimation of the RPE with an uncertainty lower than 10% of the estimated value requires a labeling intensity higher than 60‰. The developed platform will help to scale up the study of the RPE control on C cycling to the ecosystem level.

Limited ventilation causes stress and changes in Arabidopsis morphological, physiological and molecular phenotype during in vitro growth

A huge number of experiments in plant biology are conducted in sterile, sealed containers, providing environmental stability and full control of factors influencing the plant system. With respect to roots the in vitro growth has another benefit – the ease of conducting visual observations when grown in transparent media. Moreover, straightforward measurements of in vitro grown root systems make them a sensitive and convenient sensor of multiple stresses which may occur during experiments. In order to optimize root nematode infection tests for Arabidopsis mutants with relatively mild phenotypes, two Petri dish sealing techniques were tested (permeable medical adhesive tape and a popular non-permeable plastic film). Using standard experimental settings applied for infection tests, the root architecture, nematode infections, ion leakage, efficiency of photosynthesis, ethylene (ET) production, and CO2 accumulation were monitored in Arabidopsis thaliana Ws-0 wild-type and lsd1 (lesion stimulating disease 1) plants, which is a conditional dependent programmed cell death mutant.All tested parameters gave statistically significant differences between the analyzed sealing tapes, indicating the importance of air exchange. This factor is quite obvious but often ignored in experiments performed in Petri dishes. The results clearly indicate that stress is greater in air-tight sealed plates. These observations were supported by the great expression variation of several marker genes associated with reactive oxygen species (ROS), ET, salicylic (SA), and jasmonic acid (JA) biosynthesis and signaling in two-week-old seedlings. These results are discussed in light of the observed changes in the ET and CO2 concentration. Our results clearly indicate the importance of culture parameters for monitoring of abiotic and biotic stress responses in laboratory conditions, including accurate mutant phenotyping.

Phase Relations in the Harzburgite–Hydrous Carbonate Melt at 5.5–7.5 GPa and 1200–1350°С

Phase relations are studied experimentally in the harzburgite–hydrous carbonate melt system, the bulk composition of which represents primary kimberlite. Experiments were carried out at 5.5 and 7.5 GPa, 1200–1350°С, and $${{X}_{{{\text{C}}{{{\text{O}}}_{2}}}}}$$ = 0.39–0.57, and lasted 60 hours. It is established that olivine–orthopyroxene–garnet–magnesite–melt assemblage is stable within the entire range of the studied parameters. With increase of temperature and $${{X}_{{{\text{C}}{{{\text{O}}}_{2}}}}}$$ in the system, Ca# in the melt and the olivine fraction in the peridotite matrix significantly decrease. The composition of silicate phases in run products is close to those of high-temperature mantle peridotite. Analysis of obtained data suggest that magnesite at the base of subcontinental lithosphere could be derived by metasomatic alteration of peridotite by asthenospheric hydrous carbonate melts. The process is possible in the temperature range typical of heat flux of 40–45 mW/m2, which corresponds to the conditions of formation of the deepest peridotite xenoliths. Crystallization of magnesite during interaction with peridotite matrix can be considered as experimentally substantiated mechanism of CO2 accumulation in subcratonic lithosphere.

Origin, migration, and accumulation of carbon dioxide in the East Changde Gas Field, Songliao Basin, northeastern China

CO2 reservoirs are widely distributed within the Yingcheng Formation in the Songliao Basin, but the extreme horizontal heterogeneity of CO2 content causes difficulties in the exploration and exploitation of methane. Former studies have fully covered the lithology, structure, and distribution of the reservoirs high in CO2 content, but few are reported about migration and accumulation of CO2. Using the East Changde Gas Field as an example, we studied the accumulation mechanisms of CO2 gas. Two original types of accumulation model are proposed in this study. The fault-controlled accumulation model refers to gas accumulation in the reservoir body that is cut by a basement fault (the West Xu Fault), allowing the hydrocarbon gas generated in the lower formation to migrate into the reservoir body through the fault, which results in a relatively lower CO2 content. The volcanic conduit-controlled accumulation model refers to a reservoir body that is not cut by the basement fault, which prevents the hydrocarbon gas from being mixed in and leads to higher CO2 contents. This conclusion provides useful theories for prediction of CO2 distribution in similar basins and reservoirs.

Lago Albano, the “anti-Nyos-type” lake: The past as a key for the future

On 21 August 1986 almost 1800 people were asphyxiated by a CO2 cloud violently released by Lake Nyos, Cameroon. Post-1986 monitoring of Lake Nyos revealed that CO2 steadily accumulates in bottom waters through recharge from soda-rich aquifers. The 1986 lake roll-over event triggered scientific research on volcanic lakes, creating “Nyos biased” interpretations: the search for dissolved CO2 in other lakes might have led to over-interpretations regarding hazard assessment. In this study, a thorough review of the historical literature on Lago Albano over the past approx. 2800 years shows no clear evidence of Nyos-type bursts, contrary to previous ideas. In 1989 Lago Albano was affected by a large CO2 pulse, concomitant with a seismic swarm below Colli Albani volcano. Tracing back in historical literature, at least two similar anomalous degassing episodes occurred out of five seismic crises between 1829 and 1927. Partial temperature- and density-driven roll-over of the top-9 m of Lago Albano commonly releases accumulated CO2 each winter (Chiodini et al., 2012). This degassing dynamics avoids long-term CO2 accumulation in bottom waters, as is the case at permanently stratified lakes in the tropics, such as Lake Nyos.Here we show that Lago Albano is an “anti-Nyos-type" lake: sudden recharge and regularly periodic release of CO2 (Lago Albano) vs. steady recharge and sudden release of CO2 (Lake Nyos). Despite past evidence of hazardous events, (1) the intensive well pumping from the Albano aquifer might lower lake level, and hence decrease the CO2 saturation pressure threshold, and (2) the absence of cold winters, hence avoiding yearly lake roll-over favoring CO2 accumulation at bottom layers, are modern factors that rise the need to revise hazard assessment and future monitoring strategies. Despite the fact that CO2 concentration in bottom waters was far from saturation conditions during the last survey (May 2010; Chiodini et al., 2012), making a limnic eruption highly unlikely, it is necessary to know the saturation state of CO2 in bottom waters and physical lake stability at any time, in order to be prepared for a next anomalous co-seismic CO2 degassing event of unknown quantity near Lago Albano.

Coupled methane and nitrous oxide biotransformation in freshwater wetland sediment microcosms

Anaerobic oxidation of methane (AOM) coupled to denitrification is becoming the focus of scientific inquiry due to its potential contribution to global carbon and nitrogen cycles. AOM has been previously reported to proceed with nitrate (NO3−) or nitrite (NO2−). However, little research has been conducted on the simultaneous use of methane (CH4) and nitrous oxide (N2O). Here, coupled CH4 and N2O biotransformation in a freshwater wetland sediment was obtained in a 7-day anaerobic sediment incubation assay. The significant CO2 accumulation and decrease of CH4 emission in sediment microcosms was attributed to two mechanisms: inhibition of methanogenesis and N2O-dependent AOM. To further confirm the coupled CH4 and N2O transformation, a 13C-labelled stable isotope tracer assay after anaerobic incubation was conducted with N2O and/or CH4 amendments. The N2O-dependent AOM rate was 3.41 ± 0.13 nmol CO2 g−1 dry sediment·day−1. According to metagenomic analysis, addition of N2O stimulated AOM by increasing the activity and abundance of methanotrophic bacteria and by increasing enzymatic activities in the electron transport chain. Based on these results, we propose coupled CH4 and N2O biotransformation in the sediment microcosms for the first time, carried out by unidentified methanotroph(s) via intra‑oxygen produced in the presence of N2O. Such a process has the potential to reduce the emission of two highly potent greenhouse gases and makes a significant contribution to the link of global carbon and nitrogen cycles in anoxic environments.

Study on carbon dioxide atmospheric distribution over the Southwest Indian Ocean islands using satellite data: Part 2 –the influence of meteorology and air transportation

This investigation is a follow-up to the 3-dimensional distribution analysis of atmospheric CO2 and its surface temporal variation over the Southwest Indian Ocean (SWIO) islands (part 1). Here, we demonstrate the influence of meteorology and the associated air transport on CO2 spatial and vertical distribution determined in part 1. The Hybrid Single-Particle Lagrangian Integrated Trajectories (HYSPLIT) atmospheric model backward trajectories were used to determine the long-range air transport impacting on SWIO islands CO2 atmospheric loading, and to trace the origin of the air masses impacting on the atmosphere of SWIO islands. This study shows that meteorology and long-range air transport results in accumulation or dilution of atmospheric CO2 at various sites on the SWIO islands and this depends on the source region and type of air flow. Long-range air transport from different source regions at the upper atmospheric levels between the 700 and 500 hPa stable layers and the layer above 500 hPa is found to strengthen the inhomogeneity in the vertical distribution of CO2, caused by the decoupling effect of the upper atmosphere stable layers. This long-range air transport is also found to involve intercontinental air transport.

Carbon Dioxide and Methane Dynamics in a Small Boreal Lake During Winter and Spring Melt Events

AbstractIn seasonally ice‐covered lakes, carbon dioxide (CO2) and methane (CH4) emission at ice‐off can account for a significant fraction of the annual budget. Yet knowledge of the mechanisms controlling below lake‐ice carbon (C) dynamics and subsequent CO2 and CH4 emissions at ice‐off is limited. To understand the control of below ice C dynamics, and C emissions in spring, we measured spatial variation in CO2, CH4, and dissolved inorganic and organic carbon from ice‐on to ice‐off, in a small boreal lake during a winter with sporadic melting events. Winter melt events were associated with decreased surface water DOC in the forest‐dominated basin and increased surface water CH4 in the mire‐dominated basin. At the whole‐lake scale, CH4 accumulated below ice throughout the winter, whereas CO2 accumulation was greatest in early winter. Mass‐balance estimates suggest that, in addition to the CO2 and CH4 accumulated during winter, external inputs of CO2 and CH4 and internal processing during ice‐melt could represent significant sources of C gas emissions during ice‐off. Moreover, internal processing of CO2 and CH4 worked in opposition, with production of CO2 and oxidation of CH4 dominating at ice‐off. These findings have important implications for how small boreal lakes will respond to warmer winters in the future; increased winter melt events will likely increase external inputs below ice and thus alter the extent and timing of CO2 and CH4 emissions to the atmosphere at ice‐off.

Middle Eocene greenhouse warming facilitated by diminished weathering feedback

The Middle Eocene Climatic Optimum (MECO) represents a ~500-kyr period of global warming ~40 million years ago and is associated with a rise in atmospheric CO2 concentrations, but the cause of this CO2 rise remains enigmatic. Here we show, based on osmium isotope ratios (187Os/188Os) of marine sediments and published records of the carbonate compensation depth (CCD), that the continental silicate weathering response to the inferred CO2 rise and warming was strongly diminished during the MECO—in contrast to expectations from the silicate weathering thermostat hypothesis. We surmise that global early and middle Eocene warmth gradually diminished the weatherability of continental rocks and hence the strength of the silicate weathering feedback, allowing for the prolonged accumulation of volcanic CO2 in the oceans and atmosphere during the MECO. These results are supported by carbon cycle modeling simulations, which highlight the fundamental importance of a variable weathering feedback strength in climate and carbon cycle interactions in Earth’s history.

Mesoporous tin oxide for electrocatalytic CO2 reduction

The increasing accumulation of CO2 in the atmosphere has been leading to serious environmental problems. Electrochemical reduction of CO2 is a potential means of carbon recycling for energy storage and environmental sustainability. However, it is limited by the lack of highly active and selective electrocatalysts. Here we demonstrate the development of mesoporous tin oxide (SnO2) for electrocatalytic CO2 reduction, which facilitates the adsorption and electrochemical reduction of CO2 inside mesopores. The highly-ordered and uniform pore sizes of the mesoporous SnO2 electrocatalyst favor the enhancement of formation of carbon monoxide (CO) and formate during the electrochemical reduction. The combined faradaic efficiencies of CO and formate reach a peak value of ∼80% at a current density of 5 mA cm−2 at −0.8 V vs. reversible hydrogen electrode. This work suggests attractive development of mesoporous electrocatalysts with a variety of pore size and structures for efficient energy conversion and electrochemical CO2 reduction.

Soil organic matter and CO2 fluxes in small tropical watersheds under forest and cacao agroforestry.

Annual estimates of CO2 and dissolved carbon concentrations in the soil profile provide valuable insight into the dynamics of organic matter in soil and the effect of changes to vegetation cover. The aim of this study was to observe the spatial influence of litter decomposition in the first few centimeters of the soil for CO2 fluxes and to describe the processing of soil organic matter throughout the soil profile by comparing three small tropical watersheds. Data were collected biweekly for six months, from December 2015 to May 2016. CO2 was measured using an infrared gas analyzer in fixed chambers and the dissolved carbon of soil solution was analyzed in a TOC analyzer. No differences were found in the total soil CO2 fluxes (control flux treatments) between the three study areas. In both cacao agroforestry systems (managed and unmanaged), total CO2 fluxes were influenced by the decomposition of litter. CO2 emissions in the soil profile of the cacao agroforestry systems were highly variable, compared to the preserved forest, and highly dependent on the soil characteristics attributed to the type of vegetation cover. Although a definite pattern between the temperature and soil moisture was not identified, these parameters showed a strong relationship in controlling the release of CO2 between treatments. The organic and inorganic dissolved carbon patterns in the soil solution of the three areas revealed different responses of soil organic matter processing related to soil characteristics and vegetation. The results confirm the hypothesis that the top of soils (total CO2 fluxes) of both cacao agroforestry systems (managed and unmanaged) emits fluxes of CO2, which do not differ statistically from the preserved forest. However, depending on the soil characteristics, the cacao agroforestry system can result in an accumulation of CO2 and dissolved inorganic carbon in the soil profile that is prone to being transported by hydrological routes to groundwater and stream water.

Geographical CO2 sensitivity of phytoplankton correlates with ocean buffer capacity.

Accumulation of anthropogenic CO2 is significantly altering ocean chemistry. A range of biological impacts resulting from this oceanic CO2 accumulation are emerging, however, the mechanisms responsible for observed differential susceptibility between organisms and across environmental settings remain obscure. A primary consequence of increased oceanic CO2 uptake is a decrease in the carbonate system buffer capacity, which characterizes the system's chemical resilience to changes in CO2 , generating the potential for enhanced variability in pCO2 and the concentration of carbonate [ ], bicarbonate [ ], and protons [H+ ] in the future ocean. We conducted a meta-analysis of 17 shipboard manipulation experiments performed across three distinct geographical regions that encompassed a wide range of environmental conditions from European temperate seas to Arctic and Southern oceans. These data demonstrated a correlation between the magnitude of natural phytoplankton community biological responses to short-term CO2 changes and variability in the local buffer capacity across ocean basin scales. Specifically, short-term suppression of small phytoplankton (<10μm) net growth rates were consistently observed under enhanced pCO2 within experiments performed in regions with higher ambient buffer capacity. The results further highlight the relevance of phytoplankton cell size for the impacts of enhanced pCO2 in both the modern and future ocean. Specifically, cell size-related acclimation and adaptation to regional environmental variability, as characterized by buffer capacity, likely influences interactions between primary producers and carbonate chemistry over a range of spatio-temporal scales.

Differential diagnosis of nonepileptic twilight state with convulsive manifestations after febrile seizures

BackgroundNonepileptic twilight state with convulsive manifestations (NETC) is a nonepileptic state following a febrile seizure (FS), which may be misdiagnosed as a prolonged seizure and result in overtreatment. We aimed to describe clinical manifestations of NETC and to determine characteristics that are helpful to distinguish NETC from other pathological conditions. MethodsWe conducted a retrospective chart review from January 2010 to December 2016 and selected the patients who presented with symptoms resembling status epilepticus with fever and a confirmed diagnosis using an electroencephalogram (EEG). We compared the NETC clinical features and venous blood gas analysis results with those of other conditions that mimic NETC. We also compared the characteristics of NETC with past reports. ResultsOur NETC patients presented with short durations of the preceding generalized convulsions followed by tonic posturing, closed eyes, no cyanosis, responsiveness to painful stimulation, and no accumulation of CO2 in the venous blood gas. Most of these characteristics were consistent with past reports. Prolonged FS or acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) showed several of these features, but all the characteristics were not consistent with our study. ConclusionsProlonged FS and AESD need to be differentiated from NETC, and close clinical observation makes it possible to partially distinguish NETC from the other conditions. EEG is recommended for patients with symptoms that are inconsistent with these features.

High-efficiency utilization of CO2 in the methanol production by a novel parallel-series system combining steam and dry methane reforming

Global warming caused by the accumulation of atmospheric CO2 has received widespread attention in recent years. The direct CO2 integration process in NG-based methanol (MeOH) synthesis plant is one of the predominant CO2 utilization technologies. However, a large amount of water produced in the MeOH reactor increasing the difficulty in the subsequent purification system and the high direct CO2 emissions are caused by the low CO2 conversion rate. In view of such issues, we propose an innovative MeOH production approach based on a parallel-series system combining steam methane reforming (SMR) and dry methane reforming (DMR) to achieve a high-efficiency utilization of CO2. In this approach, the CO2 from SMR and that from additional feeding are converted into CO with a proper amount in the DMR reformer, and thus the content of CO2 in the make-up gas becomes more appropriate than that of existing processes, and the conversion rate of CO2 to MeOH could be obviously increased, what is more, the corresponding direct emissions of CO2 could be significantly reduced. On the other hand, the carbon efficiency is introduced to evaluate the conversion efficiency of all raw material (i.e., CH4 and CO2) containing the carbon atoms. The comparative evaluations are carried out using Aspen Plus V8.4® and the proposed improved process is demonstrated to be more efficient than existing ones from views of technological, economic, and environmental metrics.

Interplay Between Permeability Retardation and Capillary Trapping of Rising Carbon Dioxide in Storage Reservoirs

SummaryThe main objective of this work is to understand, by analytical and numerical study, how permeability retardation interacts with capillary-barrier trapping to cause accumulation as carbon dioxide (CO2) migrates upward in saline aquifers during geological sequestration.The study is of one-dimensional (1D) two-phase (CO2 and water) countercurrent flow. The analytical model describes CO2 buoyant migration and accumulation at a “flow-barrier zone” (low permeability) above a “flow-path zone” (high permeability). The relative importance of permeability retardation and capillary trapping is examined under different magnitudes of buoyant-source fluxes and porous-media properties. In the limiting case of zero capillary pressure, the model equation is solved using the method of characteristics (MOC). Permeability-retarded accumulation, induced by the permeability difference between the flow path and the barrier zone, is illustrated through CO2-saturation profiles and time/distance diagrams. Capillary trapping is subsequently accounted for by graphically incorporating a capillary pressure curve and capillary-threshold effect.Results demonstrate that the accumulation contributions from both the permeability hindrance and capillary trapping are convolved at sufficiently large fluxes. At a given time, the total CO2 accumulated by permeability hindrance is greater than that accumulated by capillary trapping, but the former approaches the latter at large time. The low-permeability zone need not be completely impermeable for accumulation to occur. We demonstrate that considering only capillary trapping understates the amount of CO2 accumulated beneath low-permeability structures during significant periods of a sequestration operation.

Impact of Pseudomonas graminis strain CPA-7 on respiration and ethylene production in fresh-cut ‘Golden delicious’ apple according to the maturity stage and the preservation strategy

The effect of the biocontrol agent (BCA) Pseudomonas graminis CPA-7 on the accumulation of CO2 and ethylene (C2H4) in fresh-cut apples at two maturity stages was evaluated in refrigerated conditions. Factors involved in the preservation strategy applied upon commercial conditions such as the antioxidant (AOX) treatment and the storage system were included in the analysis. Regardless of the maturity stage, the BCA reduced C2H4 levels within the MAP atmosphere in AOX-untreated apples wedges, by 29 and 43% in immature and mature apples, respectively. Nevertheless, the addition of ascorbate as antioxidant counteracted this effect. In vitro tests suggested that the reduction of C2H4 levels was not associated to the uptake of this molecule by CPA-7. Interestingly, in non-inoculated samples AOX treatment showed contradictory effects on C2H4 production in MAP conditions by significantly reducing C2H4 levels in immature apples (by 23%) while increasing it in mature ones (by 40%). Similarly, CPA-7 had opposite effects on the CO2 accumulation pattern depending on the storage system or the fruit maturity stage. In this sense, CPA-7 was associated to a higher fruit respiratory activity at an advanced maturity stage yet without inducing the fruit fermentative metabolism or altering the fruit quality during a week of refrigerated storage. Overall, these results show that CPA-7 may contribute to the maintenance of the microbiological and physicochemical quality of fresh-cut apple by modulating the fruit ethylene production and/or respiration.

Water bicarbonate modulates the response of the shore crab Carcinus maenas to ocean acidification.

Ocean acidification causes an accumulation of CO2 in marine organisms and leads to shifts in acid-base parameters. Acid-base regulation in gill breathers involves a net increase of internal bicarbonate levels through transmembrane ion exchange with the surrounding water. Successful maintenance of body fluid pH depends on the functional capacity of ion-exchange mechanisms and associated energy budget. For a detailed understanding of the dependence of acid-base regulation on water parameters, we investigated the physiological responses of the shore crab Carcinus maenas to 4weeks of ocean acidification [OA, P(CO2)w = 1800µatm], at variable water bicarbonate levels, paralleled by changes in water pH. Cardiovascular performance was determined together with extra-(pHe) and intracellular pH (pHi), oxygen consumption, haemolymph CO2 parameters, and ion composition. High water P(CO2) caused haemolymph P(CO2) to rise, but pHe and pHi remained constant due to increased haemolymph and cellular [HCO3-]. This process was effective even under reduced seawater pH and bicarbonate concentrations. While extracellular cation concentrations increased throughout, anion levels remained constant or decreased. Despite similar levels of haemolymph pH and ion concentrations under OA, metabolic rates, and haemolymph flow were significantly depressed by 40 and 30%, respectively, when OA was combined with reduced seawater [HCO3-] and pH. Our findings suggest an influence of water bicarbonate levels on metabolic rates as well as on correlations between blood flow and pHe. This previously unknown phenomenon should direct attention to pathways of acid-base regulation and their potential feedback on whole-animal energy demand, in relation with changing seawater carbonate parameters.