Mechanisms Of Carbon Sequestration Research Articles

Microorganisms Directly Affected Sediment Carbon–Nitrogen Coupling in Two Constructed Wetlands

Clarifying the carbon–nitrogen coupling pattern in wetlands is crucial for understanding the driving mechanism of wetland carbon sequestration. However, the impacts of plants and environmental factors on the coupling of carbon–nitrogen in wetland sediments are still unclear. Sediment samples from plant (Typha angustifolia and Phragmites australis)-covered habitats and bare land were collected in two constructed wetlands in northern China. The contents of different forms of carbon and nitrogen in sediments and plants, and the sediment microbial community were detected. It was found that the sediment carbon to nitrogen (C/N) ratios did not differ significantly in the bare sites of different wetlands, but did in the plant-covered sites, which highlighted the different role of plants in shifting the carbon–nitrogen coupling in different constructed wetlands. The effects of plants on the sediment carbon–nitrogen coupling differed in two constructed wetlands, so the structural equation model was used and found that sediment microorganisms directly affected sediment C/N ratios, while water and sediment physicochemical properties indirectly affected sediment C/N ratios by altering sediment microbial functions. Multiple linear regression models showed that water pH, sediment moisture content, water dissolved oxygen, and water depth had a greater influence on the carbon metabolism potential of the sediment microbial community, while sediment moisture content had the greatest impact on the sediment microbial nitrogen metabolism potential. The study indicates that variations in environmental conditions could alter the influence of plants on the carbon and nitrogen cycles of wetland sediments. Water environmental factors mainly affect microbial carbon metabolism functions, while soil physicochemical factors, especially water content, affect microbial carbon and nitrogen metabolism functions.

Estimation of Mariculture Carbon Sinks in China and Its Influencing Factors

The scientific assessment of mariculture carbon sinks is crucial to recognize its potential as a significant component of marine blue carbon in global climate change mitigation. Therefore, the objective of the research was to estimate the seaweed and shellfish mariculture carbon sink of different varieties in various sea areas. The paper emphasized the distinction between short-term carbon sequestration in seaweed and shellfish that can be removed and long-term carbon sequestration that is deposited. Methodologically, the evaluation was based on the carbon sequestration mechanism and systematic pathways in shellfish and seaweeds. Additionally, the carbon sequestration of shellfish and seaweed aquaculture over the last decade was evaluated by the carbon sink assessment model, and the reasons for the differences in the carbon sink capacity of mariculture in China’s coastal provinces were discussed by using the LMDI decomposition model. The results indicated the carbon sequestration of offshore seaweeds and shellfish mariculture in China was huge. From 2010 to 2020, offshore seaweed aquaculture in China amounted to 7.959 Mt C/a, while shellfish aquaculture contributed 33.542 Mt C/a to the carbon sinks. Sedimentary carbon sequestration by shellfish accounted for 51% of the total carbon sequestration in mariculture involving shellfish and seaweeds. Especially noteworthy is the sedimentary carbon sequestration by shellfish, which is an indispensable and crucial component of mariculture carbon sequestration estimation. It is concluded that improvements in farming efficiency exerted the greatest influence on the variations of the mariculture carbon sink, while adjustments in farming structure had a relatively minor impact in the case of little change in aquaculture yield. Enhancing farming efficiency emerges as a practical approach to bolstering the carbon sink potential of marine aquaculture fisheries in the future.

Bacterial magnetofossil evidence for enhanced Pacific Ocean respired carbon storage during buildup of Antarctic glaciation

Global cooling with the onset of Antarctic glaciation ca. 34 Ma across the Eocene–Oligocene transition (EOT) terminated the early Cenozoic greenhouse climate state and marked the beginning of icehouse conditions. Although a pCO2 decline is considered to have been a major cause of this climate shift, the associated carbon-sequestration mechanism remains unclear. Here, we assessed ocean production and circulation changes across the EOT using numerical simulations combined with a novel proxy, namely, bacterial magnetofossils, the abundance and morphology of which are sensitive to sedimentary organic matter accumulation and oxygenation. We detected production and oxygenation declines in the equatorial Pacific Ocean coeval with increased biological production in the Southern Ocean after the EOT. Corroborated by simulation results and evidence from the Subantarctic region, we interpret this counterintuitive combination as a result of enhanced bottom-water formation and biological pump efficiency in the Southern Ocean due to Antarctic glacial buildup across the EOT. These results provide key evidence for deep Pacific Ocean deoxygenation and increased respired carbon concentrations, which amplified CO2 decline across the EOT.

Effects of grazing on the relationship between plant functional diversity and soil carbon sequestration are regulated by livestock species

Abstract Grazing exerts a profound influence on both the plant diversity and productivity of grasslands, while simultaneously exerting a significant impact on regulating grassland soil carbon sequestration. Moreover, besides altering the taxonomic diversity of plant communities, grazing can also affect their diversity of functional traits. However, we still poorly understand how grazing modifies the relationship between plant functional diversity and soil carbon sequestration in grassland ecosystems. Here we conducted a grazing manipulation experiment to investigate the effects of different grazing regimes (no grazing; sheep grazing; cattle grazing) on the relationships between plant functional diversity and soil carbon sequestration in meadow and desert steppe. Our findings showed that different livestock species changed the relationships between plant functional diversity and soil organic carbon (SOC) in the meadow steppe. Sheep grazing decoupled the originally positive relationship between functional diversity and SOC, whereas cattle grazing changed the relationship from positive to negative. In desert steppe both sheep and cattle grazing strengthened the positive relationship between functional diversity and SOC. Our study illuminates the considerable impact of livestock species on the intricate mechanisms of soil carbon sequestration, primarily mediated through the modulation of various measures of functional trait diversity. In ungrazed meadows and grazed deserts, maintaining high plant functional diversity is conducive to soil carbon sequestration, whereas in grazed meadows and ungrazed deserts, this relationship may disappear or even reverse. By measuring the traits and controlling the grazing activities, we can accurately predict the carbon sequestration potential in grassland ecosystems.

Experimental investigation into the self-carbonation mechanism of magnesium oxide carbon sequestration foamed concrete

A novel technique involves the preparation of foamed concrete utilizing MgO as a substitute for Portland cement (PC) and CO2 foam in place of air foam. This technique is referred to as “magnesium oxide (MgO) carbon sequestration foamed concrete (MCFC)" that enables self-carbonation of Reactive MgO cement-based concrete under ambient conditions without any accelerated carbonation curing conditions. The developed technology enhances the carbonation efficiency of MgO-based materials by combining a foaming agent with CO2 curing. The even mixing of CO2 foam with MgO, referred to the uniform distribution and incorporation of CO2 throughout the sample, facilitated by the foaming agent, leads to the production of ions within the cement, promoting the carbonation of dissolved Mg2+ ions and the formation of hydrated magnesium hydroxyl carbonates (HMHCs). Eight sample groups were prepared to explore the potential of MCFC in CO2 sequestration. XRD, TG-DTA, and SEM techniques were employed to investigate the mineral phase and carbonation products in MCFC. The pore structure, pore-size distribution, and porosity of MCFC under different curing conditions were investigated using X-ray and NMR. The self-carbonation enabled by CO2 foams improved the microstructure and mechanical performance of MgO-based samples. Notably, the morphology, microstructure, and carbonate content improvements resulted in a significant 100% increase in the 28-day compressive strengths (2 MPa) compared to the control sample cured under ambient conditions.

Soil Aggregate Stability and Organic Carbon Content among Different Forest Types in Temperate Ecosystems in Northeastern China

Soil aggregates play a crucial role in substance and energy cycles in soil systems. The fixation of soil organic carbon (SOC) is closely tied to the safeguarding mechanisms of soil aggregates. Carbon fixation involves the conversion of atmospheric carbon dioxide into organic molecules by autotrophic organisms. Soil aggregates play a significant role in carbon stabilization, allowing for the physical occlusion of SOC. This study focuses on five forest types, Betula platyphylla, Betula dahurica, Quercus mongolica, Larix gmelinii, and mixed forests comprised of Larix gmelinii and Quercus mongolica, in the Heilongjiang Central Station Black-billed Capercaillie National Nature Reserve, northeast of China. This study investigated the soil aggregate stability (SAS) (water sieving) and aggregate-associated organic carbon (AAOC) at different soil depths in five forest types. Our findings demonstrated that fine macro-aggregates (0.25–2 mm) were the main types of soil aggregates among all the forest types. The SAS gradually decreased with increasing soil depth. Notably, broad-leaved forests exhibited relatively high soil stability. The fine macro-aggregates (0.25–2 mm) had the highest AAOC content, and the AAOC level was highest in the topsoil layer. The SAS and AOCC levels of the Betula platyphylla forest and Betula dahurica forest were higher than those of other forest types and were significantly affected by the forest type, soil depth, and soil physicochemical properties. Collectively, our findings reveal the key factors influencing aggregate stability and the variations in soil organic carbon content in different forest types. These observations provide a basis for studying the mechanisms of soil aggregate carbon sequestration, as well as for the sustainable development of forest soil carbon sequestration and emission reduction.

Single Sample Molecular Chronology.

ConspectusThis Account presents a new discipline, single sample molecular chronology (SSMC), which studies the relative age of an individual compound occurring in several temporal pools of a single sample in complex media. Geochemists have analytically observed for a long time that several pools of the same compound, e.g., a hydrocarbon or a pesticide, can be isolated from the same sample, e.g., a sediment or a soil, to yield a free compound pool obtained by solvent extraction and then a bound compound pool after treatment of the solid residue and further extraction. Yet the study on the significance of these pools has been limited due to the inherent lack of criteria to clearly distinguish the same compound present in various pools, and, as a consequence, the existence of these pools has been criticized as resulting from a default of extraction during analytical fractionation. Our breakthrough was to distinguish isotopically several temporal pools of a plant-derived C31 n-alkane in a soil sample containing naturally 13C-labeled carbon and then to set up a method, 13C-relative dating, to calculate the relative age of these temporal pools. We observed wide differences in the relative age of the C31 n-alkane in temporal pools of a single soil sample, ranging from -6.7 years for a soil humin-bound homologue to +25.1 years for the free homologue in the coarser soil particle-size fraction. Individual compounds can thus be used as molecular clocks to determine the relative age of temporal pools from the same sample. Moreover, our findings represented the first unambiguous proof that bound compounds are cycling slower and are somehow protected in a complex organo-mineral matrix, key information for the mechanism of carbon sequestration. SSMC could be developed in all disciplines of physical, biological, and environmental sciences manipulating complex media, to study the history of individual compounds. This chronochemistry should provide new information about the origin and transformation of individual compounds in biogeochemical systems. For example, historical information on drugs or pollutants encapsulated in temporal pools of a living organism would bring about critical new knowledge about the mechanisms of disease development. Investigations require isotope tracing using any isotope in natural or artificial abundance. Methods to separate temporal pools are suggested.

Study on improving the carbon sequestration properties of sintered red mud by regulating pressure

Red mud was a by-product discharged from the alumina refining process, which caused serious environmental problems. Since there are relatively few studies on sintered red mud (SRM) at this stage, SRM was selected in this paper to explore its carbon sequestration capacity under different pressures. X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) were used to analyze the composition of SRM, and microstructure and elemental compositions were observed by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Meanwhile, pore structures were characterized using Brunauer Emmett Teller (BET), and the production was quantitatively analyzed in combination with thermogravimetric analysis (TGA). The results showed that the carbon sequestration capacity of SRM was increased with pressure raised, but the growth rate gradually slowed down. During the carbonation process, the majority of Ca2SiO4 (C2S) reacted with water and CO2 to produce fine CaCO3, which could provide early strength. These CaCO3 were partly distributed on the surface of SRM, partly in the pores, and partly in the aqueous solution. The best carbon sequestration effect of SRM was achieved at a pressure of 2.2 MPa, and each kilogram of SRM could absorb 71.4 g CO2. The results also showed that the number of holes larger than 50 nm in carbonated sintered red mud (CSRM) decreased and the number of voids smaller than 50 nm increased. This was favorable to improve the mechanical properties of CSRM. The effects of wet carbonation had not been further revealed on the evolution, microstructure, and CO2 uptake capacity of the reaction products. This article was innovatively combined with the microscopic analysis to reveal the carbon sequestration mechanism of SRM in water, which was of great significance for the preparation of highly active mineral admixture. Meanwhile, it proved that SRM had a certain carbon sequestration capacity, which provided theoretical support for the utilization of SRM.

Contributions of plant‐ and microbial‐derived residuals to mangrove soil carbon stocks: Implications for blue carbon sequestration

Abstract Coastal blue carbon ecosystems, particularly mangroves, are becoming increasingly recognised for their importance in mitigating climate change. Still, the specific patterns and drivers of plant lignin components and microbial necromass accumulation in these ecosystems are unclear. In response, we carried out a study along a 40‐year mangrove restoration chronosequence, measuring lignin phenol and amino sugar concentrations in soil profiles (0–100 cm) as indicators of plant‐based and microbial‐derived residues, respectively. Our results showed that restoration significantly increased plant lignin phenol and amino sugar concentrations, with mature mangroves having much higher concentrations than tidal flats. During restoration, the fungal necromass was greater than the bacterial necromass. The factors influencing the lignin phenols were tree biomass, total nitrogen, pH and salinity, while those influencing the formation of amino sugars were total biomass, soil C: N ratio and pH. While the amino sugars decreased, the lignin phenols increased with the content of SOC, providing evidence of the important role lignin phenol components play in the formation of SOC in mangrove. Synthesis: By separating soil carbon into plant‐based and microbial‐derived components, our results demonstrate that the carbon stock in mangrove sediments is vulnerable to disturbances and that changes from anaerobic to aerobic conditions cause significant carbon mineralisation. The precise identification of soil carbon sources in blue carbon ecosystems could aid in elucidating the mechanisms of soil carbon sequestration and their responses to environmental changes. Read the free Plain Language Summary for this article on the Journal blog.

Prediction and assessment of marine fisheries carbon sink in China based on a novel nonlinear grey Bernoulli model with multiple optimizations

The vigorous development of marine fisheries carbon sinks (MFCS) has become a momentous pathway to mitigate global warming and effectively cope with the climate crisis. Deservedly, based on clarifying mechanism of carbon sequestration, this paper designs a research paradigm for predicting and evaluating the potential of MFCS. Specifically, a novel nonlinear grey Bernoulli model, namely MFCSNGBM(1,1), is proposed by innovatively mining the original data law through adaptive cumulative series and introducing the compound Simpson formula to optimize background values. More precisely, we utilize a heuristic Grey Wolf Optimization algorithm to find the best power index, which enhances the adaptability. To prove usefulness and robustness of MFCSNGBM(1,1) model, yields of seven common shellfishes (oyster, clam, mussel, scallop, razor clam, bloody clam, and snail) and three main algae (kelp, pinnatifid undaria, and laver) are predicted and compared with six competing models. Based on prediction results, new model has the most accurate predictions, with all prediction errors being <10 %, and thus can achieve effective prediction of shellfish and algae production from 2022 to 2025. Further, the capacity and potential of MFCS in China are scientifically evaluated using a removable carbon sink model, considering various yield levels and biological parameters of shellfish and algae. The assessment results show that during the sample period, China's marine fisheries carbon sinks steadily increased with an annual growth rate of 57,000 tons. From 2022 to 2025, with support of policy of MFCS and improvement of disaster prevention and mitigation capacity, the potential of MFCS will be further released. The growth rate of MFCS will be increased to 94,000 tons per year, and its overall scale is expected to reach 2,198,245 tons by 2025, equivalent to fixing 8.06 million tons of CO2. The carbon sink's economic value is significantly estimated to be over 400 billion yuan.

Carbonate chemistry and carbon sequestration driven by inorganic carbon outwelling from mangroves and saltmarshes

Mangroves and saltmarshes are biogeochemical hotspots storing carbon in sediments and in the ocean following lateral carbon export (outwelling). Coastal seawater pH is modified by both uptake of anthropogenic carbon dioxide and natural biogeochemical processes, e.g., wetland inputs. Here, we investigate how mangroves and saltmarshes influence coastal carbonate chemistry and quantify the contribution of alkalinity and dissolved inorganic carbon (DIC) outwelling to blue carbon budgets. Observations from 45 mangroves and 16 saltmarshes worldwide revealed that >70% of intertidal wetlands export more DIC than alkalinity, potentially decreasing the pH of coastal waters. Porewater-derived DIC outwelling (81 ± 47 mmol m−2 d−1 in mangroves and 57 ± 104 mmol m−2 d−1 in saltmarshes) was the major term in blue carbon budgets. However, substantial amounts of fixed carbon remain unaccounted for. Concurrently, alkalinity outwelling was similar or higher than sediment carbon burial and is therefore a significant but often overlooked carbon sequestration mechanism.

A little bit of Sargassum goes a long way: seafloor observations of Sargassum fluitans and Sargassum natans in the Western Atlantic Ocean

The North Atlantic Ocean features high seasonal productivity of the brown seaweed Sargassum, which floats on the ocean surface and accumulates in large numbers in the Sargasso Sea. Sargassum blooms can stretch from the west coast of Africa to the Gulf of Mexico, and have created the largest seaweed blooms ever observed. Sargassum blooms have increased in intensity in recent years, and can negatively impact coastal communities when they wash up onshore in large quantities and decay. While seaweed sinking from surface waters to the seafloor may be an important carbon sink by removing carbon from the atmosphere, the magnitude of carbon sequestration by Sargassum and other macroalgae remains poorly understood. Given the magnitude of Sargassum blooms in the North Atlantic, they may pose a significant mechanism for carbon sequestration in the deep sea, though direct observations are rare. In this study, we documented the presence and distribution of Sargassum seaweed on the seafloor using video from ten remotely operated vehicle dives conducted on NOAA Ship Okeanos Explorer. Locations included sites in the Gulf of Mexico, in the Caribbean Sea, and off the Southeastern United States. Sargassum was observed in numbers ranging from 0 to over 112 per dive, and a frequency of between 0-11.23 observations for every 100 meters of horizontal distance. These observations suggest that Sargassum does make its way to the deep sea in potentially significant amounts. Natural systems like Sargassum sinking could serve as natural laboratories for understanding and managing seaweed burial as a climate mitigation strategy. Long-term monitoring of the fate of sunken Sargassum on the seabed is needed in order to determine how much is ultimately sequestered rather than recycled back into the system. Such observations would inform the feasibility of Sargassum farming and/or facilitated sinking as potential carbon dioxide removal strategies.

Effects of roughness on density-driven convection of dissolved CO2 in discrete fracture-matrix system

Dissolution trapping is a permanent and safe mechanism for geological carbon sequestration. An increase in density caused by the dissolution of CO2 into brine can trigger a density-driven convection process. In this study, the effect of fracture roughness on the density-driven convection process in heterogeneous saline aquifers is numerically analyzed by using a three-dimensional rough fracture-matrix model. The results show that the variation of the fracture aperture, a microscale heterogeneity phenomenon, can result in the change of the macroscopic flow characteristics. The rough fracture surface intensifies the convection inside the fracture and makes the migration path of the solute more tortuous. The spatial variability of the aperture generates the merging of convective fingers and suppresses the development of weak convective fingers, thus further enhancing the longitudinal extent of convective mixing. It is indicated that neglecting roughness during the flux growth stage can lead to an underestimation of dissolved fluxes by about 20%. The consideration of fracture roughness variation can contribute to the better understanding and prediction of the dynamics of dissolved CO2 in real reservoirs.

Fjords Are Potential Hotspots of Refractory Dissolved Organic Matter Production: Insights From 1 Year of Weekly Time‐Series Observations of Fluorescent Dissolved Organic Matter in the Bedford Basin, a Northwestern Atlantic Fjord

AbstractFjords are representative marine ecosystems that play an important role in regulating coastal carbon cycling. As fingerprints of the dissolved organic matter (DOM) pool, fluorescent DOM (FDOM) is widely used to study the ocean carbon cycle. Here, we report on 1‐year of weekly observations of FDOM (from May 2018 to May 2019) in the Bedford Basin, a well‐studied northwestern Atlantic fjord. Results showed that differences in FDOM indices (biological index, fluorescence index, and humification indices) between the euphotic and aphotic layers changed during the investigation period, suggesting that classical definitions of these indices may not apply consistently. Spearman rank correlations showed that the surface FDOM was affected by physical and biological factors, while water mass renewal was the major control for the deeper layer. Humic‐like FDOM (FDOMH) changed following the Atlantic deep‐water intrusion, indicating that FDOMH may be used to trace water mass movements in this region. FDOMH shows a significantly positive linear correlation with apparent oxygen utilization (AOU). Their slopes were higher than those from the open ocean, suggesting that the Bedford Basin is a hotspot of RDOM production. Hence, we proposed a possible carbon sequestration mechanism that fjords play as “RDOM producing hot spots” and that the produced RDOM is then transported to the open ocean via water mass movement and finally stored in the ocean for extended periods of time. The proposed biogeochemical processes may also occur, more generally, in the global coastal ocean.

Research progress on biomass ash carbon capture and storage

Carbon capture and storage (CCS) technology is an important way to slow down the continuous increase in atmospheric CO2 concentration and to achieve the dual carbon target. Carbon capture and storage through biomass ash is a secure, permanent, and environment friendly way. To better understand the characteristics of biomass ash carbon capture and storage, we summarized progresses on biomass ash carbon capture and storage, clarified the mechanisms of biomass ash carbon sequestration, analyzed the influencing factors, and explored its applications in various domains. The capacity of CCS by biomass ash mainly derived from alkaline earth metal oxides of CaO and MgO. The actual carbon sequestration efficiency is affected by factors such as biomass source, chemical composition, temperature, humidity, pressure, and CO2 concentration. However, the underlying mechanism is unclear. The CCS capacity of biomass ash significantly impacts its potential applications in building materials reuse, soil quality improvement, and adsorbents carbon capture and storage absorbent preparation. Long-term research is critically needed. For future studies, we should strengthen the research on the carbonization efficiency of biomass ash from multiple sources, establish a database related to the impact of biomass ash carbonization, build a methodological system to promote scientific management of biomass ash, develop biomass ash carbon capture and storage technologies, and quantitatively assess its role in carbon sequestration.

The Influence of Exogenous Nitrogen Input on the Characteristics of Phytolith-Occluded Carbon in the Kandelia obovata Soil System

Phytolith-occluded Ccarbon (PhytOC) is an important carbon sink in wetland ecosystems and a mechanism for long-term carbon sequestration. In recent years, nitrogen pollution has become increasingly severe and poses a threat to the healthy development of coastal ecological environments and socio-economic development; therefore, studying the impact of nitrogen deposition on the sequestration potential of PhytOC in the soil of coastal wetlands is highly significant. In the present study, two indoor tidal simulation experiments were set up with and without the planting of vegetation. The sequestration capacity and factors that influence soil PhytOC in the Kandelia obovata soil system were compared and analyzed under five nitrogen concentrations. The analysis shows that with the introduction of Kandelia obovata, the occluded carbon content of the soil phytoliths was significantly increased by 31.45% compared with the non-plant group, and the PhytOC content of the soil increased by 7.94%. The exogenous nitrogen input reduced the PhytOC content of the soil, with a rate of decline exceeding 26%. The PhytOC of the soil phytoliths and the PhytOC content of the soil in the planting group increased with increasing nitrogen concentration, while that of the non-plant group decreased as the concentration of nitrogen increased. The non-plant group was more affected by the exogenous nitrogen concentration than the planting group, and the soil microbial biomass carbon and microbial biomass nitrogen were the main factors that influenced changes in the PhytOC. In conclusion, nitrogen input has a significant inhibitory effect on soil PhytOC sequestration potential in coastal wetlands. Planting Kandelia obovata helps to improve the stability of carbon in wetland soil.

Stabilization of organic carbon in top- and subsoil by biochar application into calcareous farmland

Biochar is recognized for its role in carbon sequestration and emission mitigation in farmland topsoil. However, the mechanisms by which biochar affects soil organic carbon (SOC), its composition, and stability, in the topsoil (0–20 cm) and subsoil (140–160 cm) remain unclear. Applying biochar to the calcareous farmland topsoil significantly increased the topsoil SOC contents by 33 % after a decade, with a 5 % increase in dissolved organic carbon (DOC) contents (topsoil) and a substantial increase of 162 % in subsoil DOC contents. Additionally, humic substances showed an increase of 24 % (topsoil), while low-molecular-weight water-extracted DOC exhibited a remarkable increase of 142 % in the subsoil. The application of biochar significantly increases the contents of SOC, DOC, and microbial biomass carbon (MBC) in the topsoil, as well as SOC and DOC contents in the subsoil. However, a slight decrease is observed for MBC content in the subsoil. Biochar-amended soil significantly suppressed enzyme activity in the topsoil and decreased α diversity in topsoil and subsoil while increasing the content of mineral-associated soil organic matter (MAOM). These observed changes are conducive to stabilizing SOC, emphasizing MAOM formation as a primary mechanism for carbon sequestration in both topsoil and subsoils. This study provides evidence that biochar contributes to the long-term organic carbon sequestration in calcareous farmland, highlighting the importance of considering both topsoil and subsoil when evaluating the dynamic impacts of biochar on SOC.

Goethite-enriched biochar mitigates soil emissions of CO2 during arsenic passivation: Effect and mechanisms

Iron-enriched biochar has excellent adsorption capacity for contaminants, which is a sustainable multifunctional potential material to mitigate environmental pollution. Both biochar and Fe (hydr)oxides are important materials for accumulating and preserving soil organic carbon. However, it is unclear that the potential of iron-enriched biochar for mitigating CO2 emission from contaminated soil. In this study, soil incubation and extraction experiments were conducted to determine the effects and mechanisms of goethite-enriched wheat straw biochars (GWBs) prepared at two pyrolysis temperatures (GWB450 and GWB600) on mitigation of CO2 emissions in arsenic (As) contaminated soil. The results showed that compared to the control, GWBs significantly reduced the soil available arsenic (As), decreased soil Eh, and promoted the water stability of soil aggregates (<1mm). GWBs also regulated bacterial community structures, and efficiently improved microbial carbon use efficiency (CUE) in contaminated soil, thereby significantly reducing CO2 emission by 37.2 %−40.9 % in 37 days. Spectroscopic and microscopic analysis indicated that microbial colonization widely occurred on the surfaces of the goethite-enriched biochar, and promoted the formation of organo-mineral layers, which resulted in the significant decrease in the CO2 emission. These findings enhance the understanding of the mechanisms of soil carbon sequestration induced by metal-enriched biochar and indicate a new strategy of biochar-based multifunctional soil amendment that can mitigate heavy metal pollution and reduce CO2 emission simultaneously in contaminated soils.

The spatial patterns and driving mechanisms of blue carbon ‘loss’ and ‘gain’ in a typical mangrove ecosystem: A case study of Beihai, Guangxi Province of China

The role of mangroves in carbon sequestration is critical in mitigating climate change. For better identifying the carbon conservation hotspots of mangroves influenced by environmental factors, the spatial distribution and driving mechanisms of mangrove vegetation and soil carbon sequestration, as well as the future carbon dynamics of mangroves, required clarification. Firstly, we assessed the spatial pattern of vegetation biomass and soil depth-varied soil total organic carbon (TOC) in Xiaoguansha, Guangxi Province of China, and its relationships with duration of inundation (DTI) were explored. Additionally, the carbon storage capacity of adjacent mangrove tidal flats as potential carbon reservoirs was quantified. Thirdly, freshwater, and nutrient inputs, biotic factors of mangrove, and soil composition were selected as impact factors, and their mechanisms in carbon sequestration were elucidated by using Partial least squares path modeling (PLS-PM). Finally, medium values of environmental factors on mangrove carbon sequestration were revealed, based on which future loss and gain patterns of carbon sequestration under the combined effects were fully discussed. The results showed that: (1) The Above-ground biomass (AGB) and TOC densities were 32.89 Mg C/ha and 185.10 Mg C/ha in the study area, and both were enriched in the Interior areas. The carbon sequestration in the tidal flats was equivalented to >1/5 of total carbon sequestration of mangroves. (2) DTI was the most critical factor affecting the carbon sequestration pattern and was found to be positive correlated with AGB and TOC via changing soil contents (SC), whereas it exhibits a negative correlation with AGB and TOC through influencing canopy density (CD). CD and TP were identified as significant predictors. (3) Median analysis indicated that future carbon ‘gain’ area will move nearshore, whereas the carbon-rich intertidal area may undergo carbon loss. This study provided new insights and scientific understanding for management of mangrove blue carbon function.

Occurrence and Genesis of Cold‐Seep Authigenic Carbonates from the South‐Eastern Mediterranean Sea

AbstractMethane‐derived authigenic seep carbonates occur globally along continental margins. These carbonates are important archives to identify seep dynamics, the source of the ascending methane‐enriched fluids together with their timing, and are an important carbon sequestration mechanism. Recently, seep carbonates were discovered in the Levant Basin in the south‐eastern Mediterranean Sea. To elucidate past seepage activity and dynamics across the basin, different seep carbonate morphologies (chimneys, crusts and pavements) retrieved from the Levant Basin were mapped based on remotely operating vehicle data and analysed using standard sediment petrographic techniques, X‐ray diffraction and stable carbon and oxygen isotope analyses. Carbonate chimneys consist of micrite (δ13CVPDB of −10‰ to +5‰) with dispersed baryte and dolomite crystals, fan‐shaped aragonite (δ13CVPDB of −52‰ to −30‰) and high‐magnesium calcite cements, with the latter often growing from low‐magnesium calcite spherules. Botryoidal low‐magnesium calcite cements are forming in small cavities. Carbonate crusts consist of micrite with low‐magnesium calcite breccias, high‐magnesium calcite nodules (δ13CVPDB of −35‰ to −20‰) and cements, and partially replaced fan‐shaped aragonite cements. Carbonate pavements consist of low‐magnesium calcite microsparite, micritic dolomite and high‐magnesium calcite. Fan‐shaped aragonite is locally present as pore‐lining cement. Iron oxides are often seen coating the low‐magnesium calcite, high‐magnesium calcite and dolomite cements. Chimneys and crusts, characterised by high amounts of high‐magnesium calcite and aragonite, are interpreted to have formed through advective methane fluxes. Pavements, with high quantities of dolomite, are explained as the product of diffusive methane flux. Sediment petrographic and geochemical analysis of the different carbonate morphologies and cement phases therein witness distinct modes of ascending fluid fluxes and their mixing with marine pore water and/or sea water during precipitation of the individual phases.