Lignin Oxidation Products Research Articles

Linkages between fluorescent dissolved organic matter and lignin phenols in the Canada Basin, Arctic Ocean

Lignin is one of the more refractory components of dissolved organic matter (DOM) and its concentration and composition are used to trace terrigenous DOM in the ocean. In this study, lignin oxidation products (LOP), and chromophoric and fluorescent DOM were measured in Polar Mixed Layer (PML), Atlantic water (AW), and Canada Basin Deep Water (CBDW) layers in the Canada Basin to elucidate the composition and source of terrestrial DOM. Significant differences in total lignin phenol concentration (Σ11) and cinnamyl to vanillyl ratio (C/V) measured with CuO oxidation in PML, AW, and CBDW samples were found. The fluorescence intensities of humic-like C1 were correlated with Σ11 in PML, congruent with the humic-like terrestrial origin. However, no significant correlation was found when all layers are considered (p > 0.05), suggesting a change in the molecular composition of C1. The protein-like C3 and C5 intensities were strongly correlated with Σ11 (rs = 0.55–0.64) corroborating that lignins can contribute to the protein-like fluorescence in the water column. The principal component analysis (PCA) confirmed the origin and composition of DOM vary between the different water masses, especially in terms of C/V, DOC, and fluorescent components. Significant relationships between humic-like fluorescence intensities and C/V reveal the significant contribution of woody sources to humic material in the Canada Basin. Elevated S/V and humic-like C6 levels were associated with a cold eddy DOM sample but further studies are required to validate the use of these DOM characteristics to trace deep eddy.

Linked fire activity and climate whiplash in California during the early Holocene

Recent wildfire activity in semi-arid regions like western North America exceeds the range of historical records. High-resolution paleoclimate archives such as stalagmites could illuminate the link between hydroclimate, vegetation change, and fire activity in pre-anthropogenic climate states beyond the timescale of existing tree-ring records. Here we present an analysis of levoglucosan, a combustion-sensitive anhydrosugar, and lignin oxidation products (LOPs) in a stalagmite, reconstructing fire activity and vegetation composition in the California Coast Range across the 8.2 kyr event. Elevated levoglucosan concentrations suggest increased fire activity while altered LOP compositions indicate a shift toward more woody vegetation during the event. These changes are concurrent with increased hydroclimate volatility as shown by carbon and calcium isotope proxies. Together, these records suggest that climate whiplash (oscillations between extreme wetness and aridity) and fire activity in California, both projected to increase with anthropogenic climate change, were tightly coupled during the early Holocene.

Development of a Method for Anodic Degradation of Lignin for the Analysis of Paleo‐Vegetation Proxies in Speleothems

AbstractHere we present an electrochemical method for the anodic oxidation and subsequent degradation of lignin in speleothems to utilize the resulting lignin oxidation products (LOPs) as paleo‐vegetation markers. LOPs were analyzed using an ultra‐high performance liquid chromatography (UHPLC) system coupled to a high‐resolution mass spectrometer (HRMS). The method presented here achieved comparable or even higher LOP concentrations than established CuO and CuSO4 oxidation methods. The method represents a new tool for the analysis and reconstruction of paleo‐vegetation and has the potential to be applied to other climate archives.

Lignin oxidation products in soil, dripwater and speleothems from four different sites in New Zealand

Abstract. Lignin oxidation products (LOPs) are widely used as vegetation proxies in climate archives, such as sediment and peat cores. The total LOP concentration, Σ8, provides information on the abundance of vegetation, while the ratios C/V and S/V of the different LOP groups also provide information on the type of vegetation. Recently, LOP analysis has been successfully applied to speleothem archives. However, there are many open questions concerning the transport and microbial degradation of LOPs on their way from the soil into the cave system. These processes could potentially alter the original source-dependent LOP signals, in particular the C/V and S/V ratios, and thus complicate their interpretation in terms of past vegetation changes. We analyzed LOPs in leaf litter and different soil horizons as well as dripwater and flowstone samples from four different cave sites from different vegetation zones in New Zealand using ultrahigh-performance liquid chromatography coupled to high-resolution mass spectrometry. We test whether the original source-dependent LOP signal of the overlying vegetation is preserved and can be recovered from flowstone samples and investigate how the signal is altered by the transport from the soil to the cave. The LOP concentrations range from mg g−1 in the soil to ng g−1 in the flowstones. Our results demonstrate that, from the soil to the flowstone, the C/V and S/V ratios both increase, while the total lignin content, Σ8, strongly decreases. This shows that the LOP signal is strongly influenced by both transport and degradation processes. Nevertheless, the relative LOP signal from the overlying soil at the different cave sites is preserved in the flowstone. We emphasize that for the interpretation of C/V and S/V ratios in terms of past vegetation changes, it is important to compare only samples of the same type (e.g., speleothem, dripwater or soil) and to evaluate only relative variations.

Photocatalytic Pretreatment of Commercial Lignin Using TiO2-ZnO Nanocomposite-Derived Advanced Oxidation Processes for Methane Production Synergy in Lab Scale Continuous Reactors

The photocatalytic pretreatment of lignocellulosic biomass to oxidize lignin and increase biomass stability has gained attention during the last few years. Conventional pretreatment methods are limited by the fact that they are expensive, non-renewable and contaminate the anaerobic digestate later on. The present study was focused to develop a metal-derived photocatalyst that can work with visible electromagnetic spectra light and oxidize commercial lignin liquor. During this project the advanced photocatalytic oxidation of lignin was achieved by using a quartz cube tungsten T3 Halogen 100 W lamp with a laboratory manufactured TiO2-ZnO nanoparticle (nanocomposite) in a self-designed apparatus. The products of lignin oxidation were confirmed to be vanillic acid (9.71 ± 0.23 mg/L), ferrulic acid (7.34 ± 0.16 mg/L), benzoic acid (6.12 ± 0.17 mg/L) and p-coumaric acid (3.80 ± 0.13 mg/L). These all products corresponded to 85% of the lignin oxidation products that were detectable, which is significantly more than any previously reported lignin pretreatment with even more intensity. Furthermore, all the pretreatment samples were supplemented in the form of feedstock diluent in uniformly operating continuously stirred tank reactors (CSTRs). The results of pretreatment revealed 85% lignin oxidation and later on these products did not hinder the CSTR performance at any stage. Moreover, the synergistic effects of pretreated lignin diluent were seen that resulted in 39% significant increase in the methane yield of the CSTR with constant operation. Finally, the visible light and nanoparticles alone could not pretreat lignin and when used as diluent, halted and reduced the methane yield by 37% during 4th HRT.

A Techno-economic Analysis for Integrating an Electrochemical Reactor into a Lignocellulosic Biorefinery for Production of Industrial Chemicals and Hydrogen.

In this study, we present a techno-economic analysis for integrating an electrochemical reactor into a lignocellulosic biorefinery for the purpose of converting biorefinery lignin to higher-value industrial chemicals with co-generation of hydrogen. We consider how the electrochemical reactor impacts the manufacturing costs for producing biofuel and determine a break-even value for the lignin oxidation product stream, which is the minimum lignin conversion product stream value that renders the cost to produce biofuel the same as in the typical biorefinery concept. We conclude that at low extents of lignin conversion, the break-even product stream value is likely too high for the process to be feasible. However, at higher extents of lignin conversion, the break-even product stream value may be between $1.00 and $2.00/kg, depending on capital cost and other manufacturing costs like depreciation. Potential markets for the biomass conversion products include resin manufacturing, where the products would compete with petroleum-derived resin precursors.

Limitation of lignin derivatives as biomarkers of land derived organic matter in the coastal marine sediments

• The provenience of sedimentary organic matter was investigated. • δ 13 C and lignin phenols characteristics of riverine (R), marine planktonic (P) and marine vascular plants (V) were measured. • Three end members model used proved ratio of organic matter sources equal to 30(R): 40(P): 30(V). Lignin oxidation products (vanillyl, syringil and cummaryl phenols), and δ 13 C were measured in a variety of land and marine samples collected in Inner Puck Bay – dominated by marine vascular plants, small river run-off, and shallow bottom, and in Gdańsk Bay – characterized by large river run-off, small marine vascular plants population, and the average depth exceeding euphotic zone. Both study areas are parts of the Gdańsk Basin, Southern Baltic. Typical δ 13 C values (δ 13 C = -28‰) and both composition and concentrations of lignin phenols were measured in samples originating from land. Small, yet easily measurable amounts of lignin phenols were found in marine vascular plants biomass (Σ8 = 90 µg/100 mg organic matter). The biomass was characterized by exceptionally high δ 13 C values (-12‰). No lignin phenols and typical δ 13 C values (-22‰) were measured in marine phytoplankton biomass. δ 13 C and both composition and content of lignin phenols in organic matter of surface sediments collected in the study area fall in the range marked by the end members. The proportion of land derived organic matter calculated using lignin phenols, or δ 13 C in Gdańsk Bay were comparable, while in Puck Bay they differed substantially. It was concluded that a) in areas with substantial bottom coverage with vascular plants the two end members approach, usually employed to establish the contribution of organic matter sources, is insufficient, b) organic matter originating from three sources: riverine, phytoplankton, and vascular plants contribute to sedimentary organic matter in Puck Bay with the respective proportion 30:40:30.

Utilization of Lignin-Derived Small Molecules: Epoxy Polymers from Lignin Oxidation Products.

Much effort has been invested in developing methods for producing small molecules from lignin as a way to source feedstock chemicals from renewable sources. Significant progress is being made, and methods for deconstructing lignin are producing good yields of small, mononuclear aromatic products-sufficient amounts to enable studies of the potential use of these compounds as replacements for compounds currently produced from petroleum. To investigate the use of lignin products in epoxies, we begin with aromatic acids that can be produced from lignin, treat them with epichlorohydrin to make glycidyl ethers, and investigate the thermal and mechanical properties of cured mixtures of these compounds with a commercial epoxy resin (EPON 826) and an anhydride curing agent (NMA). While most of the lignin-modified epoxy polymers exhibit good physical and thermal properties, the polymer prepared from p-hydroxybenzoic acid (compound 6) has a higher glass-transition temperature (Tg = 159 °C) than do thermosets made with other lignin-derived materials, such as vanillic acid diglycidyl ether (compound 4) and matches the Tg of cured samples of the commercial EPON-826/NMA epoxy system. This is significant, as p-hydroxybenzoic acid is readily available by simple hydrolysis of several different lignins and functions as a drop-in replacement for 50% of the BPA-based material in this commercial system without significant degradation of material properties. The use of lignin-derived small molecules in high-value systems such as epoxies may help improve the economics of biorefineries.

Dynamics of Lignin Destruction in Pine Wood under the Action of Ozone

The destruction of lignin in pinewood during ozonization is studied via diffuse reflection IR spectroscopy (DRIFT) and Raman spectroscopy. The DRIFT spectra are deconvoluted into Lorentz components. Samples of dioxanlignin obtained from wood are analyzed by means of UV spectroscopy (second derivatives). Based on the DRIFT, Raman, and UV spectra, specific rates of ozone (Qr) consumption corresponding to the oxidation of different structures on the wood surface are determined. In the range of Qr ≤ 1.5 mmol/g, the predominant process is the breakdown of aromatic rings. In the range of 1.5–3.0 mmol/g, hydroxyaromatic compounds formed at the first stage of ozonization are oxidized. At Qr higher than 2.0 mmol/g, aliphatic structures of lignin are also oxidized by ozone, along with carbonyl and carboxylic oxidation products occurring on the surface. These lignin oxidation products block to some extent the accessibility of lignin for ozone.

Characterizing lignin: Combining lignin phenol, methoxy quantification, and dual stable carbon and hydrogen isotopic techniques

Lignin is a major structural plant biochemical and biogeochemical compound present in peat and lignite. Its monomeric (phenolic) and polymeric structures include varying amounts of ether-bonded methyl groups (i.e., methoxy or OCH3). These methoxy groups are generally underused targets for both structural characterization and isotopic analyses. We analyzed the quantity and C and H isotopic composition of methoxy groups within a range of substrates including lignin phenols, lignin, wood, peat, lignite, and sub-bituminous and bituminous coal. We used the Zeisel method to cleave the ether bonds with hydroiodic acid to yield iodomethane which can be analyzed by gas chromatography (GC). Finding inconsistent transfer and isotope effects associated with room temperature headspace injections, we instead used isooctane as a solvent for the iodomethane analyte (the liquid method). Using the liquid method, we obtained a linear response by GC-flame ionization detection (GC-FID) for iodomethane and a linear calibration and 85 ± 6% recovery of methyl from methoxy groups from solid standards of phenolic compounds of known stoichiometry. We introduced quantification via lignin phenolic compounds to calibrate both analytical and experimental yield. Methyl yields provided structural information and confirmed that lignin oxidation products (LOPs) from copper oxide oxidation underestimate the number of methoxy-bearing phenols (yield < 0.3 of expected based on stoichiometry); in combination the two approaches provide structural information and quantification. We found that concentrations of methyl from methoxy groups in geologic sediments (lignite, sub-bituminous and bituminous coal) initially increase with diagenesis as lignin to cellulose ratio increases, and then decline to low concentrations during coalification, offering new possibilities for characterizing the transformation of peat and lignite. We assessed an array of plant biochemicals and established that natural and synthetic methoxy groups span a broad range of dual stable carbon and hydrogen isotopic compositions indicating scope for biogeochemical and forensic applications.

Lignin oxidation products as a potential proxy for vegetation and environmental changes in speleothems and cave drip water – a first record from the Herbstlabyrinth, central Germany

Abstract. Here, we present the first quantitative speleothem record of lignin oxidation products (LOPs), which has been determined in a Holocene stalagmite from the Herbstlabyrinth Cave in central Germany. In addition, we present LOP results from 16 months of drip water monitoring. Lignin is only produced by vascular plants and therefore has the potential to be an unambiguous vegetation proxy and to complement other vegetation and climate proxies in speleothems. We compare our results with stable isotope and trace element data from the same sample. In the stalagmite, LOP concentrations show a similar behavior to P, Ba and U concentrations, which have previously been interpreted as vegetation proxies. The LOP S∕V and C∕V ratios, which are usually used to differentiate between angiosperm and gymnosperm and woody and non-woody vegetation, show complex patterns suggesting additional influencing factors, such as transport and microbiological effects. The drip water from a fast drip site shows a seasonal pattern of LOPs with low LOP concentrations in winter and higher LOP concentrations in summer. These results indicate the potential of LOPs as a new proxy for vegetational and environmental changes in speleothems but also demonstrate the complexity and the current limitations of our understanding of the transport of lignin from the soil into the cave and the speleothems.

Quantification of lignin oxidation products as vegetation biomarkers in speleothems and cave drip water

Abstract. Here we present a sensitive method to analyze lignin oxidation products (LOPs) in speleothems and cave drip water to provide a new tool for paleo-vegetation reconstruction. Speleothems are valuable climate archives. However, compared to other terrestrial climate archives, such as lake sediments, speleothems contain very little organic matter. Therefore, very few studies on organic biomarkers in speleothems are available. Our new sensitive method allows us to use LOPs as vegetation biomarkers in speleothems. Our method consists of acid digestion of the speleothem sample followed by solid-phase extraction (SPE) of the organic matter. The extracted polymeric lignin is degraded in a microwave-assisted alkaline CuO oxidation step to yield monomeric LOPs. The LOPs are extracted via SPE and finally analyzed via ultrahigh-performance liquid chromatography (UHPLC) coupled to electrospray ionization (ESI) and high-resolution Orbitrap mass spectrometry (HRMS). The method was applied to stalagmite samples with a sample size of 3–5 g and cave drip water samples with a sample size of 100–200 mL from the Herbstlabyrinth-Advent Cave in Germany. In addition, fresh plant samples, soil water, and powdered lignin samples were analyzed for comparison. The concentration of the sum of eight LOPs (Σ8) was in the range of 20–84 ng g−1 for the stalagmite samples and 230–440 ng L−1 for the cave drip water samples. The limits of quantification for the individual LOPs ranged from 0.3–8.2 ng per sample or 1.5–41.0 ng mL−1 of the final sample solution. Our method represents a new and powerful analytical tool for paleo-vegetation studies and has great potential to identify the pathways of lignin incorporation into speleothems.

Centennial record of anthropogenic impacts in Galveston Bay: Evidence from trace metals (Hg, Pb, Ni, Zn) and lignin oxidation products

During the 20th century the impacts of industrialization and urbanization in Galveston Bay resulted in significant shifts in trace metals (Hg, Pb, Ni, Zn) and vascular plant biomarkers (lignin phenols) recorded within the surface sediments and sediment cores profile. A total of 22 sediment cores were collected in Galveston Bay in order to reconstruct the historical input of Hg, Pb, Ni, Zn and terrestrial organic matter. Total Hg (T-Hg) concentration ranged between 6 and 162 ng g−1 in surface sediments, and showed decreasing concentrations southward from the Houston Ship Channel (HSC) toward the open estuary. Core profiles of T-Hg and trace metals (Ni, Zn) showed substantial inputs starting in 1905, with peak concentrations between 1960 and 1970's, and decreasing thereafter with exception to Pb, which peaked around 1930–1940s. Stable carbon isotopes and lignin phenols showed an increasing input of terrestrial organic matter driven by urban development within the watershed in the early 1940s. Both the enrichment factor and the geoaccumulation index (Igeo) for T-Hg as a measure of the effectiveness of environmental management practices showed substantial improvements since the 1970s. The natural recovery rate in Galveston Bay since the peak input of T-Hg was non-linear and displayed a slow recovery during the twenty-first century.

Sources and distribution of sedimentary organic matter along the Andong salt marsh, Hangzhou Bay

Abstract Lignin oxidation products, δ 13 C values, C/N ratios and particle size were used to investigate the sources, distribution and chemical stability of sedimentary organic matter (OM) along the Andong salt marsh located in the southwestern end of Hangzhou Bay, China. Terrestrial OM was highest at the upper marshes and decreased closer to the sea, and the distribution of sedimentary total organic carbon (TOC) was influenced mostly by particle size. Terrestrial OM with a C3 signature was the predominant source of sedimentary OM in the Spartina alterniflora -dominated salt marsh system. This means that aside from contributions from the local marsh plants, the Andong salt marsh received input mostly from the Qiantang River and the Changjiang Estuary. Transect C, which was situated nearer to the Qiantang River mouth, was most likely influenced by input from the Qiantang River. Likewise, a nearby creek could be transporting materials from Hangzhou Bay into Transect A (farther east than Transect C), as Transect A showed a signal resembling that of the Changjiang Estuary. The predominance of terrestrial OM in the Andong salt marsh despite overall reductions in sedimentary and terrestrial OM input from the rivers is most likely due to increased contributions of sedimentary and terrestrial OM from erosion. This study shows that lower salt marsh accretion due to the presence of reservoirs upstream may be counterbalanced by increased erosion from the surrounding coastal areas.

Application of phase correction to improve the characterization of photooxidation products of lignin using 7 Tesla Fourier-transform ion cyclotron resonance mass spectrometry

Lignin is the second most abundant natural biopolymer and potentially a valuable alternative energy source for conventional fossil fuels. In this study, Fourier-transform ion cyclotron resonance-mass spectrometry (FTICR-MS) in conjunction with phase correction was applied to study photooxidation products of lignin using a 7 Tesla (T) mass spectrometer. The application of 7 T FTICR-MS has often been inadequate for the analysis of complex natural organic matter because of insufficient resolving power as compared with high-field FTICR, which led to incorrect assignments of elemental formulae and discontinuous plots in graphical and statistical analyses. Here, the application of phase correction to the FTICR mass spectra of lignin oxidation products greatly improved the spectral quality, and thus, readily permitted characterization of photooxidation processes of lignin compounds under simulated solar radiation conditions.

Oxidative degradation of biorefinery lignin obtained after pretreatment of forest residues of Douglas Fir

Harvested forest residues are usually considered a fire hazards and used as “hog-fuel” which results in air pollution. In this study, the biorefinery lignin stream obtained after wet explosion pretreatment and enzymatic hydrolysis of forestry residues of Douglas Fir (FS-10) was characterized and further wet oxidized under alkaline conditions. The studies indicated that at 10% solids, 11.7wt% alkali and 15min residence time, maximum yields were obtained for glucose (12.9wt%), vanillin (0.4wt%) at 230°C; formic acid (11.6wt%) at 250°C; acetic acid (10.7wt%), hydroxybenzaldehyde (0.2wt%), syringaldehyde (0.13wt%) at 280°C; and lactic acid (12.4wt%) at 300°C. FTIR analysis of the solid residue after wet oxidation showed that the aromatic skeletal vibrations relating to lignin compounds increased with temperature indicating that higher severity could result in increased lignin oxidation products. The results obtained, as part of the study, is significant for understanding and optimizing processes for producing high-value bioproducts from forestry residues.

Signatures of Biomass Burning Aerosols in the Plume of a Saltmarsh Wildfire in South Texas.

The most conventional and abundant tracers of biomass combustion in aerosol particles include potassium and biomarkers derived from thermally altered cellulose/hemicellulose (anhydrosugars) and lignin (methoxyphenols). However, little is known of the role biomass combustion plays as a particulate source of major plant polymers to the atmosphere. Here, concentrations of solvent-extractable anhydrosugars and methoxyphenols are compared to the yields of polymeric lignin oxidation products (LOPs) during a smoke plume event in Houston, Texas. Downwind aerosol samples (PM2.5) were collected surrounding a two-day wildfire in the McFaddin National Wildlife Refuge, 125 km southeast of Houston, which was 12-16 h directly downwind during the peak of the burn. Concentrations of all organic markers, potassium, and calcium increased by a factor of 2-13 within 1-2 days of the start of the fire and dropped to prefire levels 3 days after the peak event. Source signatures of anhydrosugars and methoxyphenols during the peak of the plume were identical to those of grass charcoals collected from the site, confirming the use of charcoals as end-members for source input reconstruction during atmospheric transport. An enrichment factor of 20 in the anhydrosugar to methoxyphenol ratio of aerosols versus charcoals can be explained partially by differences in degradation rate constants between the biomarker groups. LOPs comprised 73-91% of all lignin material in the aerosols, pointing to fires as major sources of primary biogenic aerosol particles in which lignin phenols occur predominantly in polymeric form.

Organic geochemical approaches to identifying formation processes for middens and charcoal-rich features

Charcoal is an important component of archaeological sites that can yield fundamental information useful in understanding past human activities. We applied a suite of organic geochemical tools to identify and quantify anthropogenic molecular charcoal fragments in an archaeological site in Panola County, N Texas to determine the provenance of a buried melanic horizon. The site is a small Middle-Late Caddo occupation inhabited principally between ca. 1450 and 1600 AD. We tested three molecular techniques to determine their ability to constrain site formation processes: solid state 13C nuclear magnetic resonance spectroscopy (NMR), lignin free phenols and lignin oxidation products (LOPs) and anhydrosugar analysis. We demonstrated that, in conjunction, the three afforded the identification and quantification of anthropogenic molecular charcoal fragments at this archaeological site.The approach allowed reconstruction of the fire history and vegetation type around the site during the occupation period. The NMR and anhydrosugar analysis pointed to temperature conditions associated with thermal refuse in different contexts. In particular, geochemical signatures in a smudge pit indicated a higher combustion temperature than for the charcoals in the other paleosol samples, suggesting multiple fire uses. The data also showed differential persistence of fire signals in environmental samples, likely as a result of differential decomposition rate and solubility, which may lead to heterogeneous fates of different forms of pyrogenic C in the environment. The techniques expand the tool kit available to archaeologists and soil scientists in detecting the human footprint in soil formation, especially in warm, humid climates where decomposition is rapid.

Electrochemical Oxidation of Lignin to Value-Added Chemicals

Lignin represents a significant waste in pulping mill streams, and is generally burned during the chemical recovery process to generate heat. However, its high heating value results in a bottleneck on the pulping process, and as the only renewable raw material for aromatic compounds, it is woefully underutilized as a heat source. Our work focuses on electrochemical oxidation of lignin-rich streams to generate value-added chemicals of industrial relevance. We have begun to investigate the mechanism of lignin oxidation, in which several proceeding chemical or electrochemical reactions are possible that influence the product distribution and depend on oxidation conditions. Because lignin is soluble in alkaline solutions, we are able to oxidize lignin on inexpensive, nonprecious metal electrodes. We will present voltammetric data that show the potentials at which lignin oxidizes, and will show GC/MS results that identify lignin oxidation products as a function of oxidation conditions (i.e., potential and time). We will present our work in elucidating the mechanism that lignin undergoes during electrochemical oxidation, with an eye toward controlling the oxidation products.

The effect of particle density on the sources, distribution, and degradation of sedimentary organic carbon in the Changjiang Estuary and adjacent shelf

Hydrodynamic sorting processes have a significant influence on the dispersal of sedimentary organic carbon (OC) in large-river delta-front estuaries (LDEs). Density fractionation was conducted on 6 sediments from the Changjiang LDE to investigate the sources, distribution, and degradation of OC among density fractions. Mass, elemental composition (C and N) and stable carbon isotope ratios, lignin, and specific surface area (SSA) of density fractions and bulk sediments were determined. Mass was concentrated in high density fractions (2.0–2.5gcm−3 and >2.5gcm−3) (up to 67.8%) while OC was dominated in 2.0–2.5gcm−3 fraction (up to 77.3%) due to extremely low OC in the highest density fraction (%OC<0.10%). The less dense fractions (<1.6gcm−3 and 1.6–2.0gcm−3) contained the highest OC (up to 21.4%) and lignin concentrations (up to 3.17mgg−1 or 2.85mg/100mg OC), and thus were most depleted δ13C (down to −25.2‰). A three end-member mixing model using δ13C and lignin content (Λ8) as source markers and Monte-Carlo simulation, to distinguish the relative importance of terrestrial vascular plant, soil, and marine plankton OC sources, showed that less dense fractions were dominated by terrestrial OC (the sum of soil- and vascular plant-derived OC), whereas marine OC was the predominant OC source in high density fractions. Distributions of OC from different sources in density fractions and bulk sediments both indicated a differential transport and deposition of OC along the coast, showing a gradual decreasing of terrestrial OC and addition of marine OC. Ratios of vanillic acid to vanillin (Ad/Al)v, 3,5-Bd to total V phenols (3,5-Bd/V) and total p-hydroxy phenols to sum of vanillyl and syringyl (P/(S+V)) among lignin oxidation products increased with increasing particle density suggesting selective degradation of lignin among the different density fractions. Distinctively low OC/SSA loadings (<0.40mgm−2) were observed in the highest density fraction and the bulk sediments, indicating low preservation of OC in these sediments, consistent with the results of lignin decay parameters.