Long-term Carbon Sequestration Research Articles

Effects of fresh-salt water interaction on spatial variations of soil organic carbon in reed wetland of Yellow River Estuary.

Estuarine wetlands exhibit significant interaction between fresh and salt water, with long-term carbon sequestration capability. We set up 60 sampling sites in the reed wetlands of the fresh-salt water interaction zone of the Yellow River Estuary, covering four different zones of the weak-intensity fresh-salt water interaction zone (WIZ), medium-intensity fresh-salt water interaction zone (MIZ), high-intensity interaction fresh-salt water zone (HIZ) and strong-intensity fresh-salt water interaction zone (SIZ). We investigated how fresh-salt water interaction affected the spatial variation of soil organic carbon (SOC) storage. The results showed that the area of reed wetland accounted for 17.8% of the total area of the fresh-salt water interaction zone the Yellow River Estuary, which mainly distributed in the WIZ and MIZ. The SOC content of reed wetland in the fresh-salt water interaction zone ranged from 1.09 to 3.65 g·kg-1, the SOC density was between 1.85-5.84 kg·m-2, and the SOC storage was (17.32±3.64)×104 t. The SOC content and SOC density decreased with increasing fresh-salt water interaction. There were significant differences in surface SOC content between different subzones of the fresh-salt water interaction zone. The surface SOC content decreased significantly with the increases of fresh-salt water interaction intensity. SOC density was positively correlated with SOC, TN, NH4+-N, and biomass, but negatively correlated with salt ions, soil bulk density, pH, and EC. SOC storage in the 0-30 cm soil layer accounted for 50.9%-64.2% of that in the 0-60 cm soil layer, while SOC storage in the 0-60 cm soil layer occupied 19.1%-37.7% of that in the 0-400 cm soil layer. The results could provide a scientific basis for accurately evaluating SOC storage of estuarine wetlands, improving carbon sink function and wetland management.

Nanoscale profiling of the relationship between in-situ organic matter roughness, adhesion, and wettability under ScCO2 based on contact mechanics

Understanding the interface and wetting phenomenon between CO2 and shale in the reservoir environment plays a key role in realizing efficient shale gas development and long-term stable carbon sequestration in the formation. However, previous studies on the interaction between CO2 and reservoir rocks focused on macro-scale and batch experiments of inorganic minerals, and the mechanism at the nanoscale, especially the micro-wetting behavior of the organic interface, remains unclear and needs to be investigated urgently. In this paper, based on the atomic force microscopy (AFM) tapping mode and the AM-FM viscoelastic mapping mode, the in-situ organic matter (OM) morphology and the change of the relationship between the adhesion force and the interfacial wettability under carbon dioxide immersion are investigated, respectively, and the carbon dioxide wettability behavior at the organic interfaces is deeply revealed in the nanoscale. Among them, the contact angle is obtained by the adhesion work combined with the Johnson-Kendall-Roberts (JKR) adhesive contact theory. The results show that the surface roughness of the OM keeps increasing with the ScCO2 immersion time, while the surface adhesion keeps decreasing at the same time. Although the contact angle decreases continuously with immersion time, the OM is always hydrophobic, i.e., CO2 wetting. It can be seen that the surface roughness has a negative correlation with the contact angle, which keeps decreasing with decreasing adhesion. This indicates that ScCO2 immersion expands the gas adsorption sites and at the same time reduces the interfacial energy of the OM slightly, which is extremely beneficial for CO2 to enhance shale gas recovery and to implement long-term stable carbon geologic sequestration. Therefore, this study reveals the mechanism of the carbon sequestration process at the organic interface in depth within the nanoscale for the first time, which provides a new perspective to deeply understand the long-term adsorption and capture variation process of OM in deep reservoirs.

Biochar Production and Characteristics, Its Impacts on Soil Health, Crop Production, and Yield Enhancement: A Review.

Rapid urban expansion and a booming population are placing immense pressure on our agricultural systems, leading to detrimental impacts on soil fertility and overall health. Due to the extensive use of agrochemicals in agriculture, the necessity to meet the expanding demand for food has also resulted in unsustainable farming practices. Around the world, biochar, a multipurpose carbonaceous material, is being used to concurrently solve issues with enhancing soil fertility, plant growth, and development under both normal and stressful circumstances. It improves water retention, fosters nutrient absorption, and promotes microbial activity, creating a fertile environment that supports sustainable and resilient agriculture. Additionally, biochar acts as a carbon sink, contributing to long-term carbon sequestration and mitigating climate change impacts. The major benefit of biochar is that it helps the adsorption process with its highly porous structures and different functional groups. Understanding the elements involved in biochar formation that determine its characteristics and adsorptive capacity is necessary to assure the viability of biochar in terms of plant productivity and soil health, particularly biological activity in soil. This paper focuses on the development, composition, and effects of biochar on soil fertility and health, and crop productivity.

Preliminary Environmental and Economic Assessment of Mineral Carbonation of Steel Slags as a Carbon Capture, Utilization and Storage Technology

To shift towards a sustainable steel production practice, circular economy principles can be applied in the value chain by valorizing the 2 in flue gases and the generated steel slags to produce stable silicates and carbonates via mineral carbonation, leading to long-term stable carbon sequestration. Carbonated slags can then be considered as a carbon capture, utilization and storage technology. However, it is important to quantify the environmental benefits and economic viability to evaluate a system's sustainability. This study aims (1) to evaluate the environmental and economic impacts of steel slag mineral carbonation and (2) to identify hotspots and process parameters of the systems. In this study, lab-scale experimental mineral carbonation data is upscaled to a TRL 6 scenario via an upscaling simulation with a power law learning curve. Subsequently, life cycle assessment and life cycle costing are performed to quantify the environmental and economic performances in agriculture. Contribution analyses are performed to ascertain the hotspots and process parameters of the systems. The results obtained in this study can encourage industrial symbiosis among different stakeholders in and around the steel industry to promote a more sustainable steel manufacturing value chain, incorporating circular economy principles.

Experimental investigation of moisture influence on biochar and biochar-soil blends thermophysical properties

Biochar is a carbonaceous and porous material obtained through pyrolysis or gasification. It can be extremely valuable as soil amendment since it increases the organic matter content and fertility, the microbial activity, the water retention, and the crop yields. Moreover, biochar soil application has the potential for long-term carbon sequestration which makes its application to soil interesting even outside agricultural crops. In recent years, the study of the variation of the thermophysical properties of the soil induced by mixing with biochar has attracted interest.In this work, the effect of the water content on thermal conductivity of biochar was investigated by means of the guarded hot plate apparatus λ-Meter EP500e. The same procedure was applied to various mixtures of biochar and soil. Furthermore, the specific heat was measured in order to obtain the thermal diffusivity in the various conditions through a calorimeter. Solar reflectance was also measured following the ASTM C1549 using a solar spectrum reflectometer SSR-ER. The obtained thermophysical properties can be used for the evaluation of the temperature trend of soil at different depths during the seasonal variations.

Desalination brines as a potential vector for CO2 sequestration in the deep sea

Freshwater scarcity, driven by population growth and climate change, is increasingly mitigated by seawater desalination, globally. As an energy-intensive process, desalination is a substantial source of atmospheric CO2. Nevertheless, desalination may hold a potential for ocean-based atmospheric carbon removal. Here we describe, for the first time, the carbonate chemistry of desalination brines near the submerged marine outfalls of a large desalination plant, their unique CO2 buffering capacity, and potential for deep sea carbon sequestration. We show that reverse osmosis acts as a carbon concentration factory and that the high-density brine plumes could create a vector for long-term CO2 removal to the deep sea below the seasonal thermocline. At present desalination capacity, we estimate that Desalination Assisted Carbon Concentration (DACC) and Carbon Dioxide Removal (CDR) could potentially remove 3.8 Mton CO2/year globally, with a negligible contribution to ocean acidification. This mechanism partially mitigates the high carbon print associated with desalination. SynopsisDesalination reject brines pose environmental challenges upon disposal to sea, but due to their unique properties, may become an opportunity for long-term carbon sequestration.

Biochar-integrated reactive filtration of wastewater for P removal and recovery, micropollutant catalytic oxidation, and negative CO2 e: Life cycle assessment and techno-economic analysis.

Life cycle assessment (LCA) and techno-economic analysis (TEA) models are developed for a tertiary wastewater treatment system that employs a biochar-integrated reactive filtration (RF) approach. This innovative system incorporates the utilization of biochar (BC) either in conjunction with or independently of iron-ozone catalytic oxidation (CatOx)-resulting in two configurations: Fe-CatOx-BC-RF and BC-RF. The technology demonstrates 90%-99% total phosphorus removals, adsorption of phosphorus to biochar for recovery, and >90% destructive removal of observed micropollutants. In this work, we conduct an ISO-compliant LCA of a 49.2 m3 /day (9 gpm) field pilot-scale Fe-CatOx-BC-RF system and a 1130 m3 /day (0.3 MGD) water resource recovery facility (WRRF)-installed RF system, modeled with BC addition at the same rate of 0.45 g/L to quantify their environmental impacts. LCA results indicated that the Fe-CatOx-BC-RF pilot system is a BC dose-dependent carbon-negative technology at -1.21 kg CO2 e/m3 , where biochar addition constitutes a -1.53 kg/m3 CO2 e beneficial impact to the process. For the WRRF-installed RF system, modeled with the same rate of BC addition, the overall process changed from 0.02 kg CO2 e/m3 to a carbon negative -1.41 kg CO2 e/m3 , demonstrating potential as a biochar dose-dependent negative emissions technology. Using the C100 100-year carbon accounting approach rather than Cnet reduces these CO2 e metrics for the process by about 25%. A stochastic TEA for the cost of water treatment using this combinatorial P removal/recovery, micropollutant destructive removal, and disinfection advanced technology shows that at scale, the mean cost for treating 1130 m3 /day (0.3 MGD) WRRF secondary influent water with Fe-CatOx-BC-RF using the C100 metric is US$0.18 ± US$0.01/m3 to achieve overall process carbon neutrality. Using the same BC dose in an estimation of a 3780 m3 /day (1 MGD) Fe-CatOx-BC-RF facility, the carbon neutral cost of treatment is reduced further to US$0.08 ± $0.01 with added BC accounting for US$0.03/m3 . Overall, the results demonstrate the potential of carbon negativity to become a water treatment performance standard as important and attainable as pollutant and pathogen removal. PRACTITIONER POINTS: Life cycle assessment (LCA) of a pilot scale tertiary biochar water treatment process with or without catalytic ozonation at a WRRF shows a carbon negative global warming potential of -1.21-kg CO2e/m3 while removing 90%-99% TP and >90% of detected micropollutants. Biochar-integrated reactive filtration use can aid in long-term carbon sequestration by reducing the carbon footprint of advanced water treatment in a dose-dependent manner, allowing an overall carbon-neutral or carbon-negative process. A companion paper to this work (Yu et al., 2023) presents the details related to the process operation and mechanism and evaluates the pollutant removal performance of this Fe-CatOx-BC-RF process in engineering laboratory pilot research and field WRRF pilot-scale water resource recovery trials. Techno-economic analysis (TEA) of this biochar catalytic oxidation reactive filtration process using Monte Carlo stochastic modeling shows a forecasted carbon-neutral process cost with low P and micropollutant removal as US$0.11/m3 ± 0.01 for a 3780-m3/day (1 MGD) scale installation with BC cost at US$0.03/m3 of that total. The results demonstrate the potential of carbon negativity to become a water treatmentperformance standard as important and attainable as pollutant and pathogen removal.

Leveraging google earth engine cloud computing for large-scale arctic wetland mapping

Climate-driven permafrost degradation and an intensification of the hydrological cycle are rapidly altering the intricate ecohydrological processes of Arctic wetlands, threatening their long-term carbon sequestration capabilities. Addressing this concern through effective management holds immense potential for climate regulation, mitigation, and adaptation efforts. As such, there is growing need for timely spatial inventory data identifying Arctic wetlands with sufficient accuracy, resolution, and detail. Wetland mapping at large scales necessitates the processing of large volumes of Earth observation (EO) data, a challenge known as “Big Data”. Consequently, in this study, we present a cloud-based methodology exploiting the remarkable collection of EO data and computational power of Google Earth Engine (GEE) to map Arctic wetlands at 10 m spatial resolution. Our workflow evaluated temporally aggregated optical and radar satellite imagery and novel hydro-physiographic layers as inputs into a robust Random Forest (RF) machine learning (ML) algorithm. Both pixel and object-based classification approaches were assessed, whereby ML models were calibrated with a training dataset of sufficient and comprehensive samples. The study was conducted over Canada’s Southern Arctic ecozone (830,000 km2). GEE enabled the efficient preprocessing and classification of large volumes of EO data and resulted in excellent yet similar statistical performance for both pixel and object-based approaches, achieving overall accuracies of > 89 % and mean F1-scores of > 0.79. Moreover, McNemar tests indicated that these classifications were not statistically different, which has significant implications regarding computing time and processing efficiencies. These results demonstrate the efficacy and scalability of our cloud-based GEE methodology, and as such can support future endeavors around Pan-Arctic wetland mapping and monitoring.

Drought limits vegetation carbon sequestration by affecting photosynthetic capacity of semi-arid ecosystems on the Loess Plateau

Drought is the driver for ecosystem production in semi-arid areas. However, the response mechanism of ecosystem productivity to drought remains largely unknown. In particular, it is still unclear whether drought limits the production via photosynthetic capacity or phenological process. Herein, we assess the effects of maximum seasonal photosynthesis, growing season length, and climate on the annual gross primary productivity (GPP) in vegetation areas of the Loess Plateau using multi-source remote sensing and climate data from 2001 to 2021. We found that maximum seasonal photosynthesis rather than growing season length dominates annual GPP, with above 90 % of the study area showing significant and positive correlation. GPP and maximum seasonal photosynthesis were positively correlated with self-calibrating Palmer Drought Severity Index (scPDSI), standardized precipitation and evapotranspiration index (SPEI) in >95 % of the study area. Structural equation model demonstrated that both drought indices contributed to the annual GPP by promoting the maximum seasonal photosynthesis. Total annual precipitation had a positive and significant effect on two drought indices, whereas the effects of temperature and radiation were not significant. Evidence from wood formation data also confirmed that low precipitation inhibited long-term carbon sequestration by decreasing the maximum growth rate in forests. Our findings suggest that drought limits ecosystem carbon sequestration by inhibiting vegetation photosynthetic capacity rather than phenology, providing a support for assessing the future dynamics of the terrestrial carbon cycle and guiding landscape management in semi-arid ecosystems.

Particulate Organic Carbon Released during Macroalgal Growth Has Significant Carbon Sequestration Potential in the Ocean.

Substantial amounts of particulate organic carbon (POC) are released during macroalgal growth; however, the fate of these POCs and their carbon sequestration effects remain unclear. Here, field investigations found that Ulva prolifera caused a significant increase of POC in seawater below the surface during a macroalgal bloom. However, laboratory simulations revealed that 77.6% of these POC was easily degraded by microorganisms in a short period of time, concurrently resulting in the production of dissolved organic carbon (DOC) from POC transformation. Over a period of 3 months, the bioavailable components of macroalgae-released POC and POC-transformed DOC were degraded, leaving 39.6% of the antibiodegradable substances composed of biorecalcitrant POC and biorecalcitrant DOC. However, although the biorecalcitrant POC was rich in humic-like components resisting biodegradation, the biorecalcitrant POC exhibited greater sensitivity to photodegradation than biorecalcitrant DOC. The photodegradation removal rate of biorecalcitrant POC (14.1%) was more than 10 times that of biorecalcitrant DOC (1.2%). Ultimately, a substantial portion (36.3%) of the POC released by growing macroalgae could potentially perform long-term carbon sequestration after conversion to recalcitrant POC and recalcitrant DOC, and these inert carbons derived from macroalgal POC have been previously ignored and should also be included in macroalgal carbon sequestration accounting.

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.

Near-term investments in forest management support long-term carbon sequestration capacity in forests of the United States.

The forest carbon sink of the United States offsets emissions in other sectors. Recently passed US laws include important climate legislation for wildfire reduction, forest restoration, and forest planting. In this study, we examine how wildfire reduction strategies and planting might alter the forest carbon sink. Our results suggest that wildfire reduction strategies reduce carbon sequestration potential in the near term but provide a longer term benefit. Planting initiatives increase carbon sequestration but at levels that do not offset lost sequestration from wildfire reduction strategies. We conclude that recent legislation may increase near-term carbon emissions due to fuel treatments and reduced wildfire frequency and intensity, and expand long-term US carbon sink strength.

Long-term carbon sequestration in the Eocene of the Levant Basin through transport of organic carbon from nearshore to deep marine environments

This study addresses a specific component associated with mass transport complexes in marine systems: the role of hyperpycnal flows, dense shelf water cascading, submarine canyons, distributary channels, and other transport mechanisms in transferring organic matter from continental and shallow marine settings into deep-marine environments. We speculate that during the Eocene, allowing for only 0.1‰ of shelf carbon to be preserved through transport mechanisms would account for up to 13.7% of all organic carbon burial. As such, the potential to mobilize through this mechanism large quantities of organic carbon is significant.Our case study focuses on a 150 m Eocene sequence composed of organic-rich chalks interleaved with displaced neritic limestones. TOC values range between 1.5 and 14%, averaging 4.5%. Displaced limestones are composed of a variety of poorly cemented mud- and wackestones, with low-diversity assemblages of large benthic foraminifera associated with planktonic foraminifera, suggesting deposition under low-energy conditions within the oligophotic zone on the outer ramp. Transport overprints include soft-sediment deformation, partially lithified rip-ups, folds, small diapirs, bed-scale imbrication, brecciation and syn-sedimentary shear. These features indicate detachment, movement and emplacement following initial sedimentation, in some cases more than once. Emplacement occurs into a chalk facies that can vary in appearance from darker (higher TOC) and lighter (lower TOC) lithofacies.Combination between the sedimentological, petrophysical, and elemental analyses indicates shifts between autochthonous and allochthonous sedimentation, whereas the organic geochemical analysis reveals a correlation between modes of sedimentation and preservation/composition of organic matter. Organic richness seems to increase within intervals of allochthonous sedimentation, with lower TOC values within intervals of autochthonous sedimentation. Organic matter preservation is enhanced due to poor oxygenation of the sea floor, further depleted by rapid burial beneath mass-transport deposits, increasing sedimentation rates and thus organic matter preservation. Horizons rich in organic matter may be derived from three different sources: organic matter with a fingerprint of terrestrial sources (e.g., enhanced contribution of plant leaf waxes) transported from nearshore environments; an allochthonous marine fingerprint with sulfurized hopanoids, which seem to be reworked from pre-existing Cretaceous organic-rich carbonates entrained within fined-grained micro-turbidites in the para-autochthonous facies; and productivity-derived organic matter deposited on the seafloor of the deep marine environment.This study demonstrates how transport mechanisms allow for the long-term burial of organic carbon in marine systems. When taking into consideration similar processes reported to occur in the world oceans today, it is clear that sediment transport and long-term burial of organic carbon is a fundamental part of the global carbon cycle.

Enzyme Activity and Dissolved Organic Carbon Content in Soils Amended with Different Types of Biochar and Exogenous Organic Matter

Biochars are proposed as a strategy for long-term carbon sequestration. High resistance for decomposition, low decay rate and long estimated lifetime allow for stable forms of carbon to be retained in the environment. Nevertheless, the application of pyrolyzed feedstock, particularly along with exogenous organic matter, may affect carbon dynamics in soil through the introduction of labile compounds and the stimulation of extracellular enzymes. The aim of this research was to evaluate the influence of biochars and unprocessed organic amendments in two agricultural soils on the dissolved organic carbon (DOC) content and activity of three enzymes involved in carbon turnover. In the incubation experiment, the activity of dehydrogenase, β-glucosidase, and cellulase and the DOC content were measured on days 30, 60, 90, 180, and 360. The addition of biochars stimulated dehydrogenase and β-glucosidase, while cellulase was suppressed. Fresh biomass enhanced the activity of the enzymes through a priming effect. DOC content was the highest in treatments with high enzyme activity, suggesting that it acted as a source of energy for microbes. The findings suggest that the biochar properties and the presence of exogenous organic matter affect microbial response in soil, which might be crucial for carbon sequestration. However, long-term studies are recommended to fully understand the mechanisms that determine the response of soil biota to biochar.

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.

Black Carbon in Deep-Sea Seamount Sediment Cores: Vertical Variation and Non-negligible Char Black Carbon.

Deep-sea sediments (>1000 m) are often considered to be the ultimate sink for black carbon (BC), and the long-term buried BC in these sediments is believed to potentially provide a negative feedback effect on climate warming. The burial flux of BC in marine sediments is predominantly estimated based on soot BC (SBC) in most studies, frequently ignoring the contribution of char BC (CBC). While this methodology may result in an underestimation of the BC burial flux, the precise extent of this underestimation is yet to be determined. This study used the benzene poly(carboxylic acid) (BPCA) method and chemothermal oxidation (CTO) method to analyze CBC and SBC in four deep-sea sediment cores from the Zhongnan seamount in the South China Sea, respectively. The CBC content increased from 0.026 ± 0.010% at the seamount upper part (1432 m) to 0.039 ± 0.012% at the seamount foot (4278 m), constituting approximately 25 to 42% of the SBC content. The content disparity between CBC and SBC diminishes as depth increases. In deep-sea sediments, biogeochemical factors influence the variation of CBC molecules with depth. In the seamount middle-upper part (1432 and 2465 m), highly condensed CBC gradually accumulated along the core downward profile. In the sediment core profile of the seamount middle-lower part (3497 m), benzenetricarboxylic acid and benzenetetracarboxylic acid content decreased while the BC condensation degree rose, i.e., less condensed CBC was preferentially consumed. Afterward, CBC molecules reached a relatively stable state at the seamount foot. This study reveals that CBC possesses the capacity for long-term carbon sequestration in deep-sea sediments, and its content is not negligible.

Dissolved organic matter cycling revealed from the molecular level in three coastal bays of China

As the widespread distributed and critical zones connecting the land and ocean systems, coastal bays are special units with semi-enclosed landforms to accommodate and process dissolved organic matter (DOM) in the context of increasing anthropogenic effects globally. However, compared to other common systems that have been paid much attention to (e.g., large river estuaries, wetlands), the roles of the coastal bays in coastal carbon cycling are less explored. To fill this knowledge gap, here we combined optical techniques and ultra-high-resolution mass spectrometry to systematically investigate the DOM chemistry of the three typical coastal bays in different nutrient levels, Xiangshan Bay, Jiaozhou Bay, and Sishili Bay, in China. Results show that terrestrial signals and anthropogenic imprints were observed in these three bays to various extents. Besides, Xiangshan Bay with a higher nutrient level had the DOM characterized by lower humification and aromaticity degree than Jiaozhou Bay and Sishili Bay, which not likely mainly resulted from the differences in the primary production or photochemical processing. Further examination reveals that microbial processing likely contributes to the differences in DOM chemistry among the three bays, as indicated by different proportions of potentially transformed nitrogen-containing molecules and relative abundances of the island of stability molecules. Considering the nutrient levels in different bays, we speculate that the lower nutrient concentrations would promote the efficiency of the microbial carbon pump (MCP), which hypothesized that heterotrophic microorganisms might contribute to the formation of marine recalcitrant organic carbon. Additionally, the enrichment of oxygen-rich compounds in the unique carboxyl-rich alicyclic molecule pool of Jiaozhou Bay and Sishili Bay suggests that the efficient MCP might preferentially form them in these two bays. This study emphasizes the importance of coordinating the land and ocean systems and controlling the nutrient discharge to coastal bays, thus, to potentially promote long-term marine carbon sequestration.

A review of climate change mitigation and agriculture sustainability through soil carbon sequestration

As a result of human activities such as burning fossil fuels, organic materials, and engaging in unsustainable land practices, atmospheric carbon dioxide (CO2) levels have been steadily rising, heightening worldwide concerns about climate change. It is expected concentrations to grow and changes in CO2 sequestration in agricultural soils as a result of the industrial revolution's acceleration of CO2 emissions. These emissions have been intensified by changes in land use, such as cutting down trees, burning biomass, altering farming operations, draining natural wetlands, and using the wrong methods for managing soil. The present study utilized the systematic literature review method to investigate soil carbon sequestration options as a possible means of reducing the impact of climate change and improving agriculture sustainability. As a result of soil degradation and poor management, soil organic carbon (SOC) levels have decreased, which in turn has increased atmospheric CO2 levels. But cutting-edge land application and modern agricultural management methods have the ability to reduce CO2 emissions. Several methods exist for replenishing depleted SOC, such as repurposing marginal lands for restoration purposes, advocating for reduced or zero-tillage methods in conjunction with cover as well as residue crops, and introducing nutrient cycling through composting, manure usage, and other environmentally friendly approaches to managing soil and water. One holistic approach to fighting climate change is long-term soil carbon sequestration. Soil carbon sequestration offers a comprehensive and efficient strategy for reducing the impact of climate change by recharging depleted soils, increasing biomass production, cleaning surface and underground water sources, and compensating for CO2 emissions through fossil fuels. Soil carbon sequestration presents an exciting opportunity for management of the problems caused by contemporary changes in the environment, and the adoption of these novel approaches is essential for meeting these issues.

Sphagnum increases soil’s sequestration capacity of mineral-associated organic carbon via activating metal oxides

Sphagnum wetlands are global hotspots for carbon storage, conventionally attributed to the accumulation of decay-resistant litter. However, the buildup of mineral-associated organic carbon (MAOC) with relatively slow turnover has rarely been examined therein. Here, employing both large-scale comparisons across major terrestrial ecosystems and soil survey along Sphagnum gradients in distinct wetlands, we show that Sphagnum fosters a notable accumulation of metal-bound organic carbon (OC) via activating iron and aluminum (hydr)oxides in the soil. The unique phenolic and acidic metabolites of Sphagnum further strengthen metal-organic associations, leading to the dominance of metal-bound OC in soil MAOC. Importantly, in contrast with limited MAOC sequestration potentials elsewhere, MAOC increases linearly with soil OC accrual without signs of saturation in Sphagnum wetlands. These findings collectively demonstrate that Sphagnum acts as an efficient ‘rust engineer’ that largely boosts the rusty carbon sink in wetlands, potentially increasing long-term soil carbon sequestration.

Evidence for the formation of fused aromatic ring structures in an organic soil profile in the early diagenesis

The presence of fused aromatic ring (FAR) structures in soil define the stability of the recalcitrant soil organic matter (RSOM). FAR are important skeletal features in RSOM that contribute to its extended residence time. During the early diagenesis, FAR structures are formed through condensation and polymerization of biomolecules produced during plant residue and microbial product decay. Molecular level characterization of the RSOM extracted from an organic soil profile gives important insights into the formation of FAR. Advanced solid-state 13C nuclear magnetic resonance (NMR) spectroscopy, including recoupled long-range C–H dipolar dephasing experiments on extracted humic acids (HA) showed that they contain diagenetically formed FAR different from charcoal and lignin. Peaks characteristic of FAR are observed at all depths in the soil profile, with a greater prevalence observed in the HA extracts from the clay soil layer at the bottom. In the clay soil layer, 78% of the aromatic carbon was non-protonated, and this was 2.2-fold higher than the topsoil. These data further strengthen our understanding of the humification process that could occur in early diagenesis and help explain the importance of incorporating diagenesis as an important phenomenon for long-term carbon sequestration in soil.