Impact of naturally leaking carbon dioxide on soil properties and ecosystems in the Qinghai-Tibet plateau

Contribution of agricultural land conversion to global GHG emissions: A meta-analysis

Greenhouse gases (GHG) have extensive environmental effects by trapping heat and causing climate change and air pollution. Land plays a key role in the global cycles of GHG (i.e., carbon dioxide (CO₂), methane (CH₄), and nitrogen oxide (N₂O)), and land use change (LUC) can lead to the release of such gases into the atmosphere or the removal of them from the atmosphere. One of the most common forms of LUC is agricultural land conversion (ALC) where agricultural lands are converted for other uses. This study aimed to review 51 original papers from 1990 to 2020 that investigate the contribution of ALC to GHG emissions from a spatiotemporal perspective using a meta-analysis method. The results of spatiotemporal effects on GHG emissions showed that the effects were significant. The emissions were affected by different continent regions representing the spatial effects. The most significant spatial effect was relevant to African and Asian countries. In addition, the quadratic relationship between ALC and GHG emissions had the highest significant coefficients, showing an upward concave curve. Therefore, increasing ALC to more than 8 % of available land led to increasing GHG emissions during the economic development process. The implications of the current study are important for policymakers from two perspectives. First, to achieve sustainable economic development, policymaking should prevent the conversion of more than 90 % of agricultural land to other uses based on the turning point of the second model. Second, policies to control global GHG emissions should take into account spatial effects (e.g., continental Africa and Asia), which show the highest contribution to GHG emissions.

A state-of-the-art review of CO2 enhanced oil recovery as a promising technology to achieve carbon neutrality in China

Although there are some review papers on carbon capture, utilization and storage (CCUS), hardly any of these reviews are focused on the role of CO₂ enhanced oil recovery (EOR) in accelerating carbon neutrality in China. In this review, strategies to achieve carbon neutrality is briefly but critically discussed, followed by a review of CO₂-EOR as a promising technology. Especially, data analysis, including the number of publications on China's carbon neutrality, per capita CO₂ emissions, China's power generation, and the crude oil production of China's large oilfields, is carried out to make the discussion more comprehensive. Given the large amount of coal consumed in China, the high percent of electricity generated with coal, and the slow penetration of renewables already observed, it seems unlikely that 2060 targets will be met without CCUS. In order to achieve carbon neutrality, both reduction in carbon emissions and increase in carbon sequestration are inevitable. Furthermore, it is concluded that CO₂ storage through EOR is likely to have a bright future. However, there are some critical issues to be solved, including the technical issues, leakage and safety issues, cost issues, policy issues, etc. In order to turn CO₂-EOR into a reliable and more favorable technology, more research and efforts are needed to solve these issues, including advancing carbon capture technologies, improving storage technologies, developing effective monitoring technologies, deploying government support and incentive policies, etc.

Leakage of CO2 from geological storage and its impacts on fresh soil-water systems: a review

Leakage of CO₂ from the geological storage is a serious issue for the sustainability of the receiving fresh soil-water systems. Subsurface water quality issues are no longer related to one type of pollution in many regions around the globe. Thus, an effort has been made to review studies performed to investigate supercritical CO₂ (scCO₂) and CO₂ enrich brine migration and it's leakage from geological storage formations. Further, the study also reviewed it's impacts on fresh soil-water systems, soil microbes, and vegetation. The first part of the study discussed scCO₂/CO₂ enrich brine migration and its leakage from storage formations along with it's impact on pore dynamics of hydrological regimes. Later, a state-of-the-art literature survey has been performed to understand the role of CO₂-brine leakage on groundwater dynamics and its quality along with soil microbes and plants. It is observed in the literature survey that most of the studies on CO₂-brine migration in storage formations reported significant CO₂-brine leakage due to over-pressurization through wells (injections and abandoned), fracture, and faults during CO₂ injection. Thus, changes in the groundwater flow and water table dynamics can be the first impact of the CO₂-brine leakage. Subsequently, three major alterations may also occur-(i) drop in pH of subsurface water, (ii) enhancement of organic compounds, and (iii) mobilization of metals and metalloids. Geochemical alteration depends on the amount of CO₂ leaked and interactions with host rocks. Therefore, such alteration may significantly affect soil microbial dynamics and vegetation in and around CO₂ leakage sites_. In-depth analysis of the available literature fortifies that a proper subsurface characterization along with the bio-geochemical analysis is extremely important and should be mandatory to predict the more accurate risk of CO₂ capture and storage activities on soil-water systems.

Potential CO2 intrusion in near-surface environments: a review of current research approaches to geochemical processes

Carbon dioxide (CO₂) capture and storage (CCS) plays a crucial role in reducing carbon emissions to the atmosphere. However, gas leakage from deep storage reservoirs, which may flow back into near-surface and eventually to the atmosphere, is a major concern associated with this technology. Despite an increase in research focusing on potential CO₂ leakage into deep surface features and aquifers, a significant knowledge gap remains in the geochemical changes associated with near-surface. This study reviews the geochemical processes related to the intrusion of CO₂ into near-surface environments with an emphasis on metal mobilization and discusses about the geochemical research approaches, recent findings, and current knowledge gaps. It is found that the intrusion of CO₂(g) into near-surface likely induces changes in pH, dissolution of minerals, and potential degradation of surrounding environments. The development of adequate geochemical research approaches for assessing CO₂ leakage in near-surface environments, using field studies, laboratory experiments, and/or geochemical modeling combined with isotopic tracers, has promoted extensive surveys of CO₂-induced reactions. However, addressing knowledge gaps in geochemical changes in near-surface environments is fundamental to advance current knowledge on how CO₂ leaks from storage sites and the consequences of this process on soil and water chemistry. For reliable detection and risk management of the potential impact of CO₂ leakage from storage sites on the environmental chemistry, currently available geochemical research approaches should be either combined or used independently (albeit in a manner complementarily to one another), and the results should be jointly interpreted.

Monitoring of Carbon Dioxide Using Hollow-Core Photonic Crystal Fiber Mach-Zehnder Interferometer

Monitoring of greenhouse gases is essential to understand the present state and predict the future behavior of greenhouse gas emissions. Carbon dioxide (CO₂) is the greenhouse gas of most immediate concern, because of its high atmospheric concentration and long lifetime. A fiber-optic Mach–Zehnder interferometer (MZI) is proposed and demonstrated for the laboratory-scale monitoring of carbon dioxide concentration. The interferometric sensor was constructed using a small stub of hollow-core photonic crystal fiber between a lead-in and lead-out standard single mode fiber, with air-gaps at both interfaces. At room temperature and atmospheric pressure, the sensor shows the sensitivity of 4.3 pm/% CO₂. The device was packaged to demonstrate the laboratory-scale leakage detection and measurement of CO₂ concentration in both subsurface and aqueous environments. The experimental study of this work reveals the great potential of the fiber-optic approach for environmental monitoring of CO₂.

Impact assessment of high soil CO2 on plant growth and soil environment: a greenhouse study

To ensure the safety of carbon capture and storage (CCS) technology, insight into the potential impacts of CO₂ leakage on the ecosystem is necessary. We conducted a greenhouse experiment to investigate the effects of high soil CO₂ on plant growth and the soil environment. Treatments comprised 99.99% CO₂ injection (CG), 99.99% N₂injection (NG), and no injection (BG). NG treatment was employed to differentiate the effects of O₂ depletion from those of CO₂ enrichment. Soil CO₂ and O₂ concentrations were maintained at an average of 53% and 11%, respectively, under CG treatment. We verified that high soil CO₂ had negative effects on root water absorption, chlorophyll, starch content and total biomass. Soil microbial acid phosphatase activity was affected by CG treatment. These negative effects were attributed to high soil CO₂ instead of low O₂ or low pH. Our results indicate that high soil CO₂ affected the root system, which in turn triggered further changes in aboveground plant tissues and rhizospheric soil water conditions. A conceptual diagram of CO₂ toxicity to plants and soil is suggested to act as a useful guideline for impact assessment of CCS technology.

Sequestering Atmospheric CO2 Inorganically: A Solution for Malaysia’s CO2 Emission

Malaysia is anticipating an increase of 68.86% in CO2 emission in 2020, compared with the 2000 baseline, reaching 285.73 million tonnes. A major contributor to Malaysia’s CO2 emissions is coal-fired electricity power plants, responsible for 43.4% of the overall emissions. Malaysia’s forest soil offers organic sequestration of 15 tonnes of CO2 ha−1·year−1. Unlike organic CO2 sequestration in soil, inorganic sequestration of CO2 through mineral carbonation, once formed, is considered as a permanent sink. Inorganic CO2 sequestration in Malaysia has not been extensively studied, and the country’s potential for using the technique for atmospheric CO2 removal is undefined. In addition, Malaysia produces a significant amount of solid waste annually and, of that, demolition concrete waste, basalt quarry fine, and fly and bottom ashes are calcium-rich materials suitable for inorganic CO2 sequestration. This project introduces a potential solution for sequestering atmospheric CO2 inorganically for Malaysia. If lands associated to future developments in Malaysia are designed for inorganic CO2 sequestration using demolition concrete waste, basalt quarry fine, and fly and bottom ashes, 597,465 tonnes of CO2 can be captured annually adding a potential annual economic benefit of €4,700,000.

Effect of CO2 Phase States and Flow Rate on Salt Precipitation in Shale Caprocks-A Microfluidic Study

Fracture networks inside the caprock for CO₂ storage reservoirs may serve as leakage pathways. Fluid flow through fractured caprocks and bypass conduits, however, can be restrained or diminished by mineral precipitations. This study investigates precipitation of salt crystals in an artificial fracture network as a function of pressure-temperature conditions and CO₂ phase states. The impact of CO₂ flow rate on salt precipitation was also studied. The primary research objective was to examine whether salt precipitation can block potential CO₂ leakage pathways. In this study, we developed a novel microfluidic high-pressure high-temperature vessel to house geomaterial micromodels. A fracture network was laser-scribed on the organic-rich shales of the Draupne Formation, the primary caprock for the Smeaheia CO₂ storage in Norway. Experimental observations demonstrated that CO₂ phase states influence the magnitude, distribution, and precipitation patterns of salt accumulations. The CO₂ phase states also affect the relationship between injection rate and extent of precipitated salts due to differences in solubility of water in CO₂ and density of different CO₂ phases. Injection of gaseous CO₂ resulted in higher salt precipitation compared to liquid and supercritical CO₂. It is shown that micrometer-sized halite crystals have the potential to partially or entirely clog fracture apertures.

Global Sequestration Potential of Increased Organic Carbon in Cropland Soils

The role of soil organic carbon in global carbon cycles is receiving increasing attention both as a potentially large and uncertain source of CO₂ emissions in response to predicted global temperature rises, and as a natural sink for carbon able to reduce atmospheric CO₂. There is general agreement that the technical potential for sequestration of carbon in soil is significant, and some consensus on the magnitude of that potential. Croplands worldwide could sequester between 0.90 and 1.85 Pg C/yr, i.e. 26–53% of the target of the “4p1000 Initiative: Soils for Food Security and Climate”. The importance of intensively cultivated regions such as North America, Europe, India and intensively cultivated areas in Africa, such as Ethiopia, is highlighted. Soil carbon sequestration and the conservation of existing soil carbon stocks, given its multiple benefits including improved food production, is an important mitigation pathway to achieve the less than 2 °C global target of the Paris Climate Agreement.