Organic Carbon Source Research Articles

Nickel-rich ternary cathode material as a novel capping layer to improve lithium iron phosphate electrochemical performance

We use a facile high-temperature solid-phase method to coat a layer of Ni-rich ternary material (LiNi0.8Co0.1Mn0.1O2) on the surface of lithium iron phosphate. This active coating greatly improves the intrinsic conductivity of LiFePO4. Compared to the conventional carbon material cladding, since this cladding layer is electrochemically active, the problem of decreasing the proportion of active material due to the addition of a cladding layer can be avoided to a certain extent. Compared with the samples capped with conventional organic carbon source (151.2 mAh g−1) and inorganic carbon source (155.9 mAh g−1) at 0.2 C, the discharge specific capacity was as high as 165.7 mAh g−1. Capacity retention after 200 cycles is up to 98 %, which is much higher than that of glucose and graphene oxide (GO)-coated samples (95.9 %, 96.6 %). Even when charging and discharging cycles are performed at different multipliers (2C and 10C), the retention rate remains higher than the latter.

The impacts of pullulan soaking on radish seed germination and seedling growth under salt stress.

Pullulan can not only provide a source of organic carbon but also has excellent properties. However, current research is mostly limited to the physical properties of the high-molecular-weight components of pullulan, and little is known about the application of its low-molecular-weight components. This study was designed to explore the impact of presoaking of radish seeds in a pullulan solution on seed germination and subsequent seedling growth under salt stress conditions. Pullulan soaking was found to enhance the germination rates of radish seeds subjected to salt stress, while also enhancing the aboveground growth of radish seedlings. Pullulan soaking resulted in increases in chlorophyll, soluble protein, and soluble sugar concentrations in the leaves of these seedlings, together with greater peroxidase activity and root activity as well as decreases in Na+ and malondialdehyde concentrations. This provides an important reference for the application of pullulan in plant protection.

Organic Farming vs. Integrated Nutrient Management: A Comparative Review of Agricultural Productivity and Sustainability

In an era where sustainable agriculture is crucial for global food security and environmental preservation, organic farming and Integrated Nutrient Management (INM) have emerged as leading practices. This review paper offers a comprehensive comparison of these two approaches, focusing on their impact on agricultural productivity and sustainability. Organic farming, with its emphasis on reducing the use of chemical fertilizers, pesticides, growth hormones, and feed additives, aligns closely with the principles of sustainability. It enhances food quality, promotes soil health, and mitigates adverse environmental effects by encouraging natural recovery cycles. However, organic farming's limitations, such as lower yields and a more labour-intensive approach have prompted interest in innovative solutions that blend organic practices with modern technologies. Integrated Nutrient Management (INM) presents a compelling alternative. By combining organic, inorganic, and biological nutrient sources, INM seeks to optimize nutrient use efficiency and maintain soil health. This approach offers a flexible nutrient management strategy, balancing organic and inorganic inputs to maintain crop productivity while reducing environmental impact. Studies have shown that INM can improve soil properties, such as bulk density, porosity, and water-holding capacity, leading to enhanced crop yields and lower greenhouse gas emissions. The paper explores how INM's integrated approach not only stabilizes crop production but also supports the growth of soil microbes, providing a source of energy and organic carbon. By using a combination of specific microorganisms, organic matter, and minimal doses of inorganic fertilizers, INM can achieve a harmonious balance that reduces environmental pollution and ensures long-term soil fertility. Ultimately, this review underscores the potential of combining organic and INM practices to create a sustainable and productive agricultural system. Through a comparative analysis, the paper aims to guide researchers, policymakers, and farmers towards adopting strategies that foster agricultural sustainability without compromising productivity.

The growth and nutrient removal properties of heterotrophic microalgae Chlorella sorokiniana in simulated wastewater containing volatile fatty acids

To reduce the high cost of organic carbon sources in waste resource utilization in the cultivation of microalgae, volatile fatty acids (VFAs) derived from activated sludge were used as the sole carbon source to culture Chlorella sorokiniana under the heterotrophic cultivation. The addition of VFAs in the heterotrophic condition enhanced the total nitrogen (TN) and phosphorus (TP) removal of C. sorokiniana, which proved the advantageous microalgae in using VFAs in the heterotrophic culture after screening in the previous study. To discover the possible mechanism of nitrogen and phosphorus adsorption in heterotrophic conditions by microalgae, the effect of different ratios of VFAs (acetic acid (AA): propionic acid (PA): butyric acid (BA)) on the nutrient removal and growth properties of C. sorokiniana was studied. In the 8:1:1 group, the highest efficiency (77.19%) of VFAs assimilation, the highest biomass (0.80 g L−1) and lipid content (31.35%) were achieved, with the highest TN and TP removal efficiencies of 97.44 % and 91.02 %, respectively. Moreover, an aerobic denitrifying bacterium, Pseudomonas, was determined to be the dominant genus under this heterotrophic condition. This suggested that besides nitrate uptake and utilization by C. sorokiniana under the heterotrophy, the conduct of the denitrification process was also the main reason for obtaining high nitrogen removal efficiency.

Advancing autotrophic nitrogen removal in low C/N ratio wastewater: Innovative application of supercapacitor to enhance microbial electrolysis cells

This study presents a novel approach, the Supercapacitor Microbial Electrolysis Cell (SC-MEC), which utilizes a supercapacitor as an external power source to enhance the efficiency of autotrophic nitrogen removal in low C/N ratio wastewater. The results demonstrated that the SC-MEC system, operating under anaerobic conditions and devoid of any organic carbon source, exhibited exceptional performance in ammonia oxidation and total nitrogen (TN) removal when solely relying on ammonia nitrogen as the electron donor. Operating at a voltage of 1.8 V with a capacitance capacity of 30 F, ammonium oxidation rated up to 56.51 mg/L/day and TN removal rated up to 54.64 mg/L/day, in which 97% of ammonium nitrogen was converted to gaseous nitrogen. Furthermore, the charging and discharging process of supercapacitors autonomously regulated the bipolar potentials. Cyclic voltammetry (CV) analysis showed the significantly enhanced electrochemical activity of the SC-MEC system during the reaction process. Based on in-situ CV test results, it was inferred that this enhancement was associated with extracellular electron transfer mediators. The microbial community analysis revealed a process of synchronous nitrification and denitrification (SND) coupled with anammox, involving multiple genera, such as Candidatus Kuenenia, Nitrosomonas, Truepera, and Bosea. In conclusion, this study highlights the tremendous potential of SC-MEC in achieving efficient autotrophic nitrogen removal, offering more feasible and economical solutions for addressing low C/N water pollution issues.

Exogenous Carbon is Unlikely to be the Source of Methane Microseepage Emissions on Mars

A complete understanding of methane in the atmosphere of Mars requires information on putative sources. Organic carbon derived from meteoritic sources, such as interplanetary dust particles (IDPs), over geologic time is the best-defined source of organic carbon on the surface of Mars. Here we examine two different mechanisms for degrading this material to produce methane (1) Ultraviolet photolysis and (2) thermal decomposition. Neither of these mechanisms can produce sufficient methane under realistic assumptions to explain observed methane at Gale Crater, suggesting that IDPs are not the primary source material producing methane on Mars.

The Treatment of Antibiotic Excess Sludge via Catalytic Wet Oxidation with Cu-Ce/γ-Al2O3 and the Production of a Carbon Source

In the present study, the effectiveness of catalytic wet oxidation triggered by using Cu-Ce/γ-Al2O3 to degrade antibiotic excess sludge was investigated, during which some small molecule carboxylic acids were produced, which are valuable in biological wastewater treatment as an organic carbon source. The influence of reaction parameters on the degradation efficiency was explored through single-factor and orthogonal experiments, including catalyst amount, reaction temperature and time, and oxygen supply amount. The results illustrated that the treatment system can achieve 81.2% COD and 93.8% VSS removal rates under optimized reaction conditions. Carboxylic acids produced after the sludge degradation mainly included acetic acid, propanoic acid, etc. The results of wastewater biological treatment experiments exhibited that the degraded solution after catalytic wet oxidation has potential to be used as a carbon source to meet the demand of biological treatment, which helps the removal of COD and TN. This work confirms the effectiveness of catalyst for enhancing antibiotic excess sludge treatment, which provided a new idea for the rational disposal of antibiotic excess sludge.

Unveiling the ecological resilience and industrial potential of Skeletonema marinoi through mixotrophic cultivation in Nordic winter condition.

Mixotrophy, the concurrent use of inorganic and organic carbon in the presence of light for microalgal growth, holds ecological and industrial significance. However, it is poorly explored in diatoms, especially in ecologically relevant species like Skeletonema marinoi. This study strategically employed mixotrophic metabolism to optimize the growth of a strain of Skeletonema marinoi (Sm142), which was found potentially important for biomass production on the west coast of Sweden in winter conditions. The aim of this study was to discern the most effective organic carbon sources by closely monitoring microalgal growth through the assessment of optical density, chlorophyll a fluorescence, and biomass concentration. The impact of various carbon sources on the physiology of Sm142 was investigated using photosynthetic and respiratory parameters. The findings revealed that glycerol exhibited the highest potential for enhancing the biomass concentration of Sm142 in a multi-cultivator under the specified experimental conditions, thanks to the increase in respiration activity. Furthermore, the stimulatory effect of glycerol was confirmed at a larger scale using environmental photobioreactors simulating the winter conditions on the west coast of Sweden; it was found comparable to the stimulation by CO2-enriched air versus normal air. These results were the first evidence of the ability of Skeletonema marinoi to perform mixotrophic metabolism during the winter and could explain the ecological success of this diatom on the Swedish west coast. These findings also highlight the importance of both organic and inorganic carbon sources for enhancing biomass productivity in harsh winter conditions.

Dearomatization drives complexity generation in freshwater organic matter

Dissolved organic matter (DOM) is one of the most complex, dynamic and abundant sources of organic carbon, but its chemical reactivity remains uncertain1–3. Greater insights into DOM structural features could facilitate understanding its synthesis, turnover and processing in the global carbon cycle4,5. Here we use complementary multiplicity-edited 13C nuclear magnetic resonance (NMR) spectra to quantify key substructures assembling the carbon skeletons of DOM from four main Amazon rivers and two mid-size Swedish boreal lakes. We find that one type of reaction mechanism, oxidative dearomatization (ODA), widely used in organic synthetic chemistry to create natural product scaffolds6–10, is probably a key driver for generating structural diversity during processing of DOM that are rich in suitable polyphenolic precursor molecules. Our data suggest a high abundance of tetrahedral quaternary carbons bound to one oxygen and three carbon atoms (OCqC3 units). These units are rare in common biomolecules but could be readily produced by ODA of lignin-derived and tannin-derived polyphenols. Tautomerization of (poly)phenols by ODA creates non-planar cyclohexadienones, which are subject to immediate and parallel cycloadditions. This combination leads to a proliferation of structural diversity of DOM compounds from early stages of DOM processing, with an increase in oxygenated aliphatic structures. Overall, we propose that ODA is a key reaction mechanism for complexity acceleration in the processing of DOM molecules, creation of new oxygenated aliphatic molecules and that it could be prevalent in nature.

Multiscale effects of radial mixing on mixotrophic microalgal growth and macromolecular synthesis in tubular bubble-column photobioreactors

Extremophillic microalga Chlorella sorokiniana is grown mixotrophically in a 5 L externally-illuminated tubular bubble-column photobioreactor with an external light intensity of 10,500 lx (≈195 μmol-photons.m−2.s−1) at atmospheric (0.04 %), 1 %, 2 %, 3 %, 4 %, and 5 % CO2 concentrations, with acetic acid and urea as the organic carbon and nitrogen sources, respectively, for 6–8 days. Two different setups are employed: one permits axial air flow, and another promotes radial mixing of algal particles, dissolved CO2 and nutrients along with axial sparging. We show that radial mixing increases biomass yields by reducing both photo-limitation and photo-inhibition up to CO2 concentrations <3 %, above which substrate (CO2) inhibition necessitates lower reactor mixing. Radial mixing increases the lipid yield from 1.06 and 1.61 g/L to 1.27 and 1.78 g/L at 2 % and 3 % CO2, respectively, in nitrogen-limited cases, resulting in a 10–20 % increase. We show that complete reactor mixing, facilitated by the dual effects of branched (radial) and axial sparger, is preferred only in the absence of substrate (CO2) inhibition. Subsequently, we stratify the tubular photobioreactor design strategy into two regimes based on CO2 inlet concentrations. In one regime (for inlet CO2 < 3 %), we recommend the deployment of branched sparger to facilitate both radial and axial mixing simultaneously, thereby creating a well-mixed reactor at lower CO2 concentrations. In the other regime (for inlet CO2 > 3 %), axial sparging alone is recommended since complete mixing of CO2 increases substrate inhibition by reducing the reactor pH below 7.5.

Latitudinal patterns and drivers of plant lignin and microbial necromass accumulation in forest soils: Disentangling microbial and abiotic controls

Plant- and microbial-derived compounds are the two primary sources of the soil organic carbon (SOC) pool. However, whether and how biotic and abiotic factors regulate the means through which microbes and plants contribute to SOC accumulation at a regional scale remains unclear. This study investigated the distribution patterns of plant lignin components and microbial necromass in soils, as indicated by lignin phenols and amino sugars across five latitudinal forests in eastern China. The contents of plant lignin and microbial necromass in the soil increased with increasing latitude. However, their contributions to SOC followed quadratic patterns with increasing latitude. Given its positive relationship with SOC content in all examined forests, microbial necromass seemed to play a more critical role in SOC accumulation than lignin phenols. Moreover, plant lignin and microbial necromass accumulation and their contributions to SOC were mainly influenced by the joint effects of climatic variables, microbial traits, and soil properties, but their importance was divergent. Specifically, the mean annual temperature (MAT) and soil phosphorus content were central to plant lignin accumulation, whereas MAT and the microbial richness: biomass ratio mainly controlled microbial necromass accumulation. These findings demonstrate that microbial necromass plays a more critical role than plant lignin in forest SOC accumulation and further highlight the importance of microbial traits in microbial necromass accumulation.

Multi-proxy temperature and environmental reconstruction during the Late Glacial and Early Holocene in the Bohemian Forest, Central Europe

Multi-proxy temperature reconstructions can provide robust insights into past environmental conditions. By combining different proxies we can disentangle the temperature signal from the indirect climate effects on the environment. This study uses a multi-proxy approach to reconstruct temperature and palaeoenvironmental conditions during the Late Glacial and Early Holocene (13.5–8 cal. ka BP) in the Bohemian Forest, Central Europe. We assessed the similarity of the temperature signal based on chironomids, isoprenoid glycerol dialkyl glycerol tetraether lipids (isoGDGTs), and pollen within a comparison with locally modeled temperature data generated by the CHELSA_Trace21k dataset. Pollen, macroscopic charcoal remains, and geochemistry were further used to reconstruct past environmental conditions such as vegetation dynamics, fire activity, the input of lithogenic material (Titanium), nutrient content (Total Nitrogen) and the sources of organic matter (C/N and δ13Corg). All temperature reconstructions based on independent proxies were positively correlated and followed the same long-term trend. However, results also showed that chironomids-inferred July temperature had lower amplitude variations compared to the other temperature curves. IsoGDGTs showed the most pronounced decrease in temperature values at the onset of the Younger Dryas (YD), corroborating that this cooling event was more marked during winter than summer. However, a decrease of less than 1 °C during summer and two short-term warm events at 12.6 and 12.2 cal ka BP provoked a modest and asynchronous response of the vegetation to the onset of the YD. Nevertheless, isoGDGTs appeared to react to changes in both temperature and organic carbon sources, particularly between 11.2 and 10.6 cal yr BP. These environmental changes, characterized by high values of the GDGT-0/crenarchaeol ratio, recorded an increase in methanogenic activity in the lake sediments, which likely altered the recorded climatic signal. The corresponding anoxic episodes in the lake sediments might be caused by an increasing input of organic carbon from the catchment, related to the development of the vegetation and catchment soils at the beginning of the Holocene. Finally, pollen-based temperature reconstruction showed a lag in the response to major climatic events, such as the onset of YD and Holocene. Our study increases the understanding of the climate-vegetation-environmental feedback during the Late Glacial and Early Holocene in the Bohemian Forest, Central Europe.

Controlling organic carbon increase in oxygenated marine sediment by using decarburization slag

The chemical oxygen demand (COD) in the Seto Inland Sea, Japan has increased in the recent decades due to the increase of bottom dissolved oxygen (DO) concentration which stimulated several autotrophic microorganisms, specially sulfur oxidizing bacteria (SOB). This increased SOB activity due to the oxygenation of the bottom sediment synthesized new organic matter (OM) which contributed dissolved organic carbon to the overlying seawater. This phenomenon further led to hypoxia in some subareas in the Seto Inland Sea. Higher pH or alkaline environment has been found to be an unfavorable condition for SOB. In this research, we used decarburization slag to elevate the pH of sediment to control the SOB activity and consequently reduce OM production in the sediment. Ignition loss of the surface sediment increased from 5.14% 6.38% after 21 days of incubation with aeration; whereas the sediment showed the less ignition loss of 5.71% after 21 days when the slag was incubated in the same experimental setup. Microbial community analysis showed less SOB activity in the slag added aerated sediment which accounts for the controlled increase of OM in the sediment. An additional experiment was conducted with magnesium oxide to confirm whether elevated pH can control the OM increase in sediment due to rising DO. All these results showed that decarburization slag can elevate the pH of the sediment to a certain level which can control the SOB activity followed by controlled increase of OM in the sediment. The findings may be beneficial to control accumulation of sedimentary OM which can act as a source of organic carbon in the overlying seawater.

The roles of seagrass litter decomposition in determining blue carbon sink capacity

AbstractSeagrass litter is a crucial autochthonous source of sediment organic carbon (Corg) that contributes to Corg storage in coastal ecosystems. However, our understanding of seagrass litter decomposition effects on sediment Corg sequestration and the factors influencing the capacity for autochthonous carbon sequestration remains limited. We investigated Zostera marina litter decomposition dynamics in eelgrass meadows along the Korean coast by monitoring changes in the remaining litter mass and autochthonous Corg during the decomposition process. We used a double‐component exponential decay models to characterize the decomposition dynamics and estimate the autochthonous Corg remaining. We also identified potential factors affecting litter decay and Corg accumulation in sediments by examining site‐specific physicochemical properties. Our findings revealed that double‐component models effectively characterized litter decomposition dynamics and indicated greater preservation of litter‐derived slowly degrading Corg in sediments. The reduced decomposition of litter materials owing to low oxygen availability in the muddy sediments led to greater retention of litter mass and litter‐derived Corg in sediments. The anoxic conditions of below‐ground litterbags, compared with above‐ground litterbags, could be alleviated by the oxygen transport through fresh Z. marina roots, thereby potentially stimulating the microbial decomposition of Z. marina below‐ground litter materials at these sites. Our findings highlight the importance of understanding litter decomposition dynamics to accurately assess the carbon sink capacity of seagrass meadows, and demonstrate that physicochemical properties can influence seagrass litter decomposition.

Organic carbon source controlled microbial olivine dissolution in small-scale flow-through bioreactors, for CO2 removal

The development of carbon dioxide removal methods, coupled with decreased CO2 emissions, is fundamental to achieving the targets outlined in the Paris Agreement limiting global warming to 1.5 °C. Here we are investigating the importance of the organic carbon feedstock to support silicate mineral weathering in small-scale flow through bioreactors and subsequent CO2 sequestration. Here, we combine two bacteria and two fungi, widely reported for their weathering potential, in simple flow through bioreactors (columns) consisting of forsterite and widely available, cheap organic carbon sources (wheat straw, bio-waste digestate of pig manure and biowaste, and manure compost), over six weeks. Compared to their corresponding abiotic controls, the inoculated straw and digestate columns release more total alkalinity (~2 times more) and produce greater dissolved and solid inorganic carbon (29% for straw and 13% for digestate), suggesting an increase in CO2 sequestration because of bio-enhanced silicate weathering. Microbial biomass is higher in the straw columns compared to the digestate and manure compost columns, with a phospholipid fatty acid derived total microbial biomass 10 x greater than the other biotic columns. Scanning Electron Microscopy imaging shows the most extensive colonisation and biofilm formation on the mineral surfaces in the straw columns. The biotic straw and digestate columns sequester 50 and 14 mg C more than their abiotic controls respectively, while there is no difference in the manure columns. The selection of organic carbon sources to support microbial communities in the flow through bioreactors controlls the silicate weathering rates and CO2 sequestration.

Study on the performance of accessory microbial fuel cell (MFC) integrated to the constructed wetlands (CWs) for deep wastewater treatment

Deep nitrogen removal is difficult due to inefficient organic carbon sources in tail water from sewage treatment facilities. Microbial fuel cell integrated with constructed wetlands (MFC-CWs) filled with high density polyethylene (HDPE) as the biocarriers were constructed for deep denitrification of tail water, and was compared with MFC and CW. The influences of electrode gap and hydraulic retention time (HRT) on denitrification as well as electricity generation performance were investigated. It was found that appropriate electrode gap extension might enhance chemical oxygen demand (COD) and nitrogen removal, and MFC-CW got the highest electricity generation and nitrogen removal with the electrode gap at 25 cm. Extending HRT promoted deep denitrification, resulting in an initial increase followed by a subsequent decrease in power generation performance. The maximum power density of MFC-CW attained 1.95 mW/m2 with an HRT of 2 d. It was found that microbial abundances in the upper cathode of the systems were higher, and the growth and metabolisms of microorganisms were enhanced in MFC-CWs. Saccharimonadales and SBR1031 in MFC-CW were the dominant genera, which promoted nitrogen removal. The results provide a reference for the study of synchronous denitrification and electricity generation performance in MFC-CW with HDPE as bio-fillers.

Unraveling Environmental Forces Shaping Surface Sediment Geochemical “Isodrapes” in the East Asian Marginal Seas

AbstractAs major sites of carbon burial and remineralization, continental margins are key components of the global carbon cycle. However, heterogeneous sources of organic matter (OM) and depositional environments lead to complex spatial patterns in sedimentary organic carbon (OC) content and composition. To better constrain the processes that control OM cycling, we focus on the East Asian marginal seas as a model system, where we compiled extensive data on the OC content, bulk isotopic composition (δ13C and Δ14C), total nitrogen, and mineral surface area of surficial sediments from previous studies and new measurements. We developed a spatial machine learning modeling framework to predict the spatial distribution of these parameters and identify regions where sediments with similar geochemical signatures drape the seafloor (i.e., “isodrapes”). We demonstrate that both provenance (44%–77%) and hydrodynamic processes (22%–53%) govern the fate of OM in this margin. Hydrodynamic processes can either promote the degradation of OM in mobile mud‐belts or preserve it in stable mud‐deposits. The distinct isotopic composition of OC sources from marine productivity and individual rivers regulates the age and reactivity of OM deposited on the sea‐floor. The East Asian marginal seas can be separated into three main isodrapes: hydrodynamically energetic shelves with coarser‐grained sediment depleted in OC, OM‐enriched mud deposits, and a deep basin with fine‐grained sediments and aged OC affected by long oxygen exposure times and petrogenic input from rivers. This study confirms that both hydrodynamic processes and provenance should be accounted for to understand the fate of OC in continental margins.

Effect of organic carbon sources on growth, lipid production and fatty acid profile in mixotrophic culture of Scenedesmus dimorphus (Turpin) Kützing

Due to non-renewability of fossil fuels and various environmental problems associated with their use, there is a growing interest in producing biodiesel from microalgae. Finding novel microalgal strains with desired characteristics such as rapid growth rates, high lipid productivity, and suitable fatty acid compositions is important for the production of biodiesel. Comparatively, photoautotrophic cultivation of microalgae results in low biomass yields and lipid productivities. Mixotrophic and heterotrophic cultures, in contrast, lead to higher biomass and lipid productivities but their productivities are species specific and depend a lot on the organic carbon source and culture conditions. In the present study, the potential of Scenedesmus dimorphus for biodiesel oil production under mixotrophic culture was investigated. The effects of organic carbon sources (glucose, ethanol and glycerol) on growth, biomass yields, lipid contents, lipid productivities and fatty acids compositions of Scenedesmus dimorphus in mixotrophic cultures were investigated. In comparison to photoautotrophic cultures, mixotrophic cultures produced significantly higher biomass concentration, lipid content, and lipid productivities (P≤0.05) under all the cultivation conditions investigated. The maximum biomass and lipid productivities achieved by mixotrophic culture were 83.88±0.05 and 17.11±0.04 mg L−1 day−1 respectively which are more than 2.6 and 3.1 folds higher than those obtained under photoautotrophic condition. Using glucose as the organic carbon source was better than ethanol and glycerol in terms of biomass and lipid productivities (glucose > ethanol > glycerol). The majority of the produced fatty acids were composed of C16 and C18 fatty acids. The two most abundant fatty acids in all the cultures were linolenic and palmitic acids. The values of biodiesel properties of oil obtained from S. dimorphus are within the American (ASTM D6751) and European (EN 14214) biodiesel specifications. The results show that S. dimorphus has good potentials for biodiesel oil production and that the productivity can be enhanced by mixotrophic cultivation.

Effects of erosion on macroaggregation, aggregate associated organic carbon sources and compositions in a Mollisol agricultural landscape

Macroaggregation is widely recognized as an important soil carbon (C) stabilization mechanism. However, in eroding landscapes, the relationships among soil aggregation, organic carbon (OC) sources, and chemical composition are poorly understood. In this study, we aimed to explore the effects of erosion and deposition on macroaggregation, OC sources, and chemical compositions in topsoil (0–20 cm) versus subsoil (80–100 cm) in a Mollisol agricultural landscape. The bulk soil was fractionated into macroaggregates (0.25–2 mm), microaggregates (0.053–0.25 mm), and clay and silt (<0.053 mm) using a wet sieving procedure. The plant sources of soil OC were quantified based on the stable isotope 13C (δ13C), and the chemical composition of macroaggregate associated OC (MaOC) was determined by solid-state nuclear magnetic resonance techniques. The results indicated that macroaggregates and MaOC comprised 45–72% of soil mass and 50–66% of soil OC, respectively. There was a reduction in macroaggregate-associated C3-derived C (C3-C) in the eroding position compared to that in the non-eroding position. However, similar amounts of C4-derived C (C4-C) were detected among three topographical areas, indicating the re-macroaggregation of eroded materials in the depositional position and preferential protection of C3-C. In the up-slope positions, topsoil MaOC was composed primarily of O-alkyl C (52%). Compared with the up-slope position, there was a considerable increase in the amount of aromatic C in the erosional macroaggregate fraction. However, at the eroding position, there was a marked increase in the proportion of substituted alkyl-C in the topsoil material, and deposition resulted in an increase in aromatic C in the subsoil. Overall, erosion and deposition change soil aggregation, and sources and composition of OC in different functional pools have important implications for the stabilization of organic matter along an eroding Mollisol hillslope.

Burial of Organic Carbon in Swedish Fjord Sediments: Highlighting the Importance of Sediment Accumulation Rate in Relation to Fjord Redox Conditions

AbstractFjords are net carbon sinks with high organic carbon (OC) burial rates; however, the key drivers of OC burial in these systems are not well constrained. To study the role of water column redox condition and OC composition on OC preservation in fjord sediments, we determined OC accumulation rates (OCAR), OC source, and OC degradation in three Swedish fjords with variable redox conditions (long‐term oxic, seasonally hypoxic, and long‐term anoxic). Average OCARs were variable between and within the fjords studied (2–122 g OC m−2 yr−1), but highest rates were at the mouth for each fjord. Based on a δ13C mixing model, Swedish fjords bury predominantly marine‐derived OC (∼83% of the total OC burial) likely because of relatively gentle slopes, low riverine discharge, and high marine inflow. Using a multi‐biomarker approach (lignin, photosynthetic pigments, and total hydrolyzable amino acids) we found, terrestrially‐ and marine‐derived OC were moderately degraded under the various redox conditions sampled, suggesting water column redox and OC source are not primary drivers of OC burial in these fjords. Rather, high sediment accumulation rates, common to fjords globally, lead to low oxygen exposure times, thus promoting efficient burial of OC regardless of its chemical composition.