Lignin Phenol Compositions Research Articles

Size-fractionated distribution of glycerol dialkyl glycerol tetraether core lipids in surface sediments of a large-river delta-front estuary

Glycerol dialkyl glycerol tetraether core lipids (GDGTs) are microbial biomarkers ubiquitously distributed in terrestrial and marine environments. Dispersal and fate of GDGTs in an estuary largely depends on sediment grain size, however, their size distribution patterns remain poorly understood. Here, surface sediments collected from the Changjiang Estuary were separated into <20, 20–32, 32–63, 63–125 and >125 μm fractions, and analyzed for GDGTs as well as total organic carbon (TOC), stable isotopic composition (δ13C) of TOC and lignin phenols, to investigate the size and spatial distributions of GDGTs and the particle size effects on GDGTs proxies in this large river delta-front estuary. The concentrations of isoprenoidal GDGTs (isoGDGTs) were higher in the finest fractions and in off-estuary sites. On the contrary, branched GDGTs (brGDGTs) were high not only in the finest fractions but in coarser fractions (>32 μm fractions), and thus at both near- and off-estuary sites. The branched and isoprenoid tetraether (BIT) index increased with increasing grain size, and decreased sharply from the estuary (~0.52) to the shelf (~0.16). BrGDGTs were positively correlated with crenarcheaol in both high and low BIT regions. The brGDGTIIIa/IIa ratios in all size fractions were <0.59, further indicating that the brGDGTs were mainly derived from terrestrial input with minimum in-situ production. Fractional TOC source assignments derived from the BIT index was significantly positively correlated with the fractions of terrestrial OC from a mixing model based on δ13C-TOC and lignin contents, indicating that BIT may track a broader pool of terrestrial OC than just soil OC. This work provides novel, yet preliminary insights into the size fractionated distribution characteristics of GDGTs and the applicability of BIT as a proxy for OC sources in estuarine sediments. More work is needed to further clarify the particle size effects on other GDGTs proxies in estuarine systems.

Lignin phenol quantification from machine learning‐assisted decomposition of liquid chromatography‐absorbance spectroscopy data

AbstractAnalysis of lignin in seawater is essential to understanding the fate of terrestrial dissolved organic matter (DOM) in the ocean and its role in the carbon cycle. Lignin is typically quantified by gas or liquid chromatography, coupled with mass spectrometry (GC‐MS or LC‐MS). MS instrumentation can be relatively expensive to purchase and maintain. Here we present an improved approach for quantification of lignin phenols using LC and absorbance detection. The approach applies a modified version of parallel factor analysis (PARAFAC2) to 2nd derivative absorbance chromatograms. It is capable of isolating individual elution profiles of analytes despite co‐elution and overall improves sensitivity and specificity, compared to manual integration methods. For most lignin phenols, detection limits below 5 nmol L−1 were achieved, which is comparable to MS detection. The reproducibility across all laboratory stages for our reference material showed a relative standard deviation between 1.47% and 16.84% for all 11 lignin phenols. Changing the amount of DOM in the reaction vessel for the oxidation (dissolved organic carbon between 22 and 367 mmol L−1), did not significantly affect the final lignin phenol composition. The new method was applied to seawater samples from the Kattegat and Davis Strait. The total concentration of dissolved lignin phenols measured in the two areas was between 4.3–10.1 and 2.1–3.2 nmol L−1, respectively, which is within the range found by other studies. Comparison with a different oxidation approach and detection method (GC‐MS) gave similar results and underline the potential of LC and absorbance detection for analysis of dissolved lignin with our proposed method.

Lignin phenols as a basis for biopreparations

The content and composition of lignin phenols in plants and soils of latitudinal zones and vertical natural zones of the North Caucasus and Northwest Tien Shan have been studied. The special role of lignin phenols of underground plant organs in the process of humification was revealed. It was shown that the oxidation degree of the biopolymer increases during the transformation of organic matter from living plant tissues to humic acids in soils. The fraction of lignin fragments that remain unchanged during the biotransformation of the polymer in the row plant tissues – fall – litter – soils – humic acids – buried humic acids is calculated. It has also been demonstrated that the biochemical composition of plants has a decisive effect on the structure of humic acids in soils. With the help of quantitative analysis of lignin phenols and 13C NMR spectroscopy, it is proved that lignin of higher plants is involved in the formation of humic acids, both aliphatic and aromatic parts of molecules. The areas of application of lignin phenols in the practice of agriculture and medicine are proposed.

Impacts of long-term land use on terrestrial organic matter input to lakes based on lignin phenols in sediment records from a Swedish forest lake

Organic carbon burial in lake sediments plays an important role in the global carbon cycle, and is heavily affected by the terrestrial organic matter input. However, few studies have focused on long-term changes in terrestrial organic matter input to lakes in response to land-use changes. The aim of this study was to assess variations in sedimentary terrestrial organic matter over the last 1000 years based on lignin biomarker records from two sediment cores from Lake Skottenesjön, southwestern Sweden. In combination with pollen-based quantitative land cover reconstruction, we investigated the impacts of centennial-scale land-use changes on terrestrial organic matter input to lake sediments. The results show that human activities in the catchment had significant impacts on terrestrial organic export by modifying the vegetation cover. Intensified use of the forest in the 18th and 19th centuries led to enhanced soil erosion, and increased terrestrial organic matter input to the lake. Although farmland expanded between the 12th and the middle of 14th century, no significant change in terrestrial organic matter input was observed at that time. Much higher export of terrestrial organic and minerogenic matter to the lake was observed during the period of modern forestry in the 20th century as compared to previous periods of minor forest disturbance, such as 11th century. The changes in the vegetation cover in the catchment considerably modified the composition of terrestrial organic matter deposited in the lake sediments, which is reflected by the composition of lignin phenols. This study demonstrates that the combination of lignin phenols analysis and pollen-based quantitative land cover reconstruction is a useful approach for investigating long-term changes in terrestrial organic matter delivery to lake ecosystems.

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.

Variation in soil lignin protection mechanisms in five successional gradients of mixed broadleaf–pine forests

AbstractOver 200 yr of ecosystem succession in northeastern China, conifers have replaced broadleaf trees. Vegetation changes during forest succession may affect soil organic C (SOC) stability, which is associated with altered protection mechanisms. Lignin phenol composition, a predictor of soil organic matter variation, was assessed for macroaggregates, microaggregates, and silt–clay (SC) fractions from successional gradients in five forests aged 19 to 239 yr in the Changbai Mountains nature reserve. The large macroaggregates (4.00–8.00 and 2.00–4.00 mm) comprised 45.17 to 59.87% of bulk dry weight and 40.22 to 60.89% of SOC in the 19‐, 32‐, and 48‐yr‐old pioneer forests. However, we detected increased mass proportions and SOC contents in small macroaggregates (1.00–2.00 and 0.25–1.00 mm) in the mixed broadleaf–Korean pine (Pinus koraiensis Siebold &amp; Zucc.) forest after 122 yr. Lignin in bulk soil and aggregates in the 122‐yr‐old stand had lower acid/aldehyde ratios for the vanillyl and syringyl types than other stands, indicating less lignin decomposition. The highest C (198.20 g kg−1 soil) and lignin concentrations (6.14 mg 100 mg−1 C) were detected in the bulk soil from the 239‐yr‐old stand, where SC fraction occupied 56.18% of the C and 84.17% of the lignin content in bulk soil. Forest succession from broadleaf to a broadleaf–pine mixture shifted SOC sequestration and lignin protection from aggregates to SC fractions, along with the development of plant litter composition, fine‐root biomass and turnover, and microorganism biomass, which prompted effective long‐term SOC accumulation in successional forest communities.

Recent Analysis of Carbon, Nitrogen, and Lignin Phenol Compositions in the Suspended Particulate Matters at Spermonde Archipelago, South Sulawesi, Indonesia

This study analyzed the composition of monomer lignin phenols and its derivatives at the Spermonde Archipelago, South Sulawesi-Indonesia. Water samples were collected in the dry season (June 2017) and the rainy season (January 2018) from the river estuaries of Tallo-Makassar, and Pangkep. Analysis of carbon and nitrogen contents was conducted by EA-IRMS (elemental analyzer-isotope ratio mass spectrometry), while lignin phenol was analyzed by Chromatography Gas-Mass Spectroscopy (GC-MS). Spatially, the six lignin phenols () content in the Tallo river estuary into several outermost islands is higher than of the Pangkep river mouth.  values in the rainy season were higher (0.92-2.30) than in the dry season (0.62-2.07). In the dry season, the range of values for ratios of syringyl/vanillyl and cinnamyl/vanillyl was 0.35 to 1.12 and 0.39 to 0.57 indicating a low contribution of angiosperm plant tissue. In the rainy season, the values of ratios for syringyl/vanillyl and cinnamyl/vanillyl ranged from 0.37 to 1.18 and 0.32 to 0.62. The syringyl/vanillyl ratio indicates the contribution of plant tissue to angiosperms. The cinnamyl/vanillyl value is greater than 0.1, indicating a significant contribution of non-woody plant tissue. Spatially, the range of syringyl/vanillyl and cinnamyl/vanillyl ratios at the estuary of the Tallo river (0.37 to 1.12 and 0.32 to 0.57) were higher than at the Pangkep river estuary (0.35 to 1.18 and 0.39 to 0.62).

Lignin in the Organic Matter of the Soils of the Russian Plain as Biomarker of Palaeoenvironment

It has been shown by the methods of biochemistry, nuclear magnetic resonance, and isotope geochemistry that the proportions of lignin phenols may be used as molecular traces of paleovegetation due to their biochemical and physiological specificity and high resistance to decomposition. Lignin structures have been detected in soils and in iron–manganese concretions. The comparison of the 13C NMR spectra of native lignin preparations isolated from different woody and herbaceous species with those of soil humic acids makes it possible to identify many characteristic shifts of lignin nature in humic acids at 56, 102, 115, 119, 131, 147, 151–152, 160, and 166 ppm. The information role of biomarker has been tested at the reconstruction of paleovegetation in the uplands of the Russian Plain. The representativeness of information has been increased using the isotope analysis (δ13C) and the radiocarbon dating; a new parameter—the composition of lignin phenols—has been introduced to the existing system of biomarkers.

Origin and processing of terrestrial organic carbon in the Amazon system: lignin phenols in river, shelf, and fan sediments

Abstract. The Amazon River transports large amounts of terrestrial organic carbon (OCterr) from the Andean and Amazon neotropical forests to the Atlantic Ocean. In order to compare the biogeochemical characteristics of OCterr in the fluvial sediments from the Amazon drainage basin and in the adjacent marine sediments, we analysed riverbed sediments from the Amazon mainstream and its main tributaries as well as marine surface sediments from the Amazon shelf and fan for total organic carbon (TOC) content, organic carbon isotopic composition (δ13CTOC), and lignin phenol compositions. TOC and lignin content exhibit positive correlations with Al ∕ Si ratios (indicative of the sediment grain size) implying that the grain size of sediment discharged by the Amazon River plays an important role in the preservation of TOC and leads to preferential preservation of lignin phenols in fine particles. Depleted δ13CTOC values (−26.1 to −29.9 ‰) in the main tributaries consistently correspond with the dominance of C3 vegetation. Ratios of syringyl to vanillyl (S ∕ V) and cinnamyl to vanillyl (C ∕ V) lignin phenols suggest that non-woody angiosperm tissues are the dominant source of lignin in the Amazon basin. Although the Amazon basin hosts a rich diversity of vascular plant types, distinct regional lignin compositions are not observed. In the marine sediments, the distribution of δ13CTOC and Λ8 (sum of eight lignin phenols in organic carbon (OC), expressed as mg/100 mg OC) values implies that OCterr discharged by the Amazon River is transported north-westward by the North Brazil Current and mostly deposited on the inner shelf. The lignin compositions in offshore sediments under the influence of the Amazon plume are consistent with the riverbed samples suggesting that processing of OCterr during offshore transport does not change the encoded source information. Therefore, the lignin compositions preserved in these offshore sediments can reliably reflect the vegetation in the Amazon River catchment. In sediments from the Amazon fan, low lignin content, relatively depleted δ13CTOC values and high (Ad ∕ Al)V ratios indicating highly degraded lignin imply that a significant fraction of the deposited OCterr is derived from petrogenic (sourced from ancient rocks) sources.

Variations in lignin-derived phenols in sediments of Japanese lakes over the last century and their relation to watershed vegetation

Lignins have been used as a biomarker to explore changes in terrestrial organic matter input into lakes and to investigate past watershed vegetation. Burial of organic carbon (OC) in lake sediments, an important component of the global C cycle, is likely associated with the terrestrial OC input. However, few studies have explored changes in terrestrial C input into lakes in the last century. Furthermore, the relationship between lignin phenol compositions and watershed vegetation remains poorly examined. In this study, we examined changes in OC concentrations, OC mass accumulation rates (MAR), and lignin phenol compositions over the last century in sediments from six lakes in Japan that differ in watershed land-use and vegetation. The sediments were dated using 210Pb and 137Cs, and showed increased OC concentrations and MARs in three lowland lakes over the last century. This pattern was not found in three mountain lakes. In one of the lowland lakes, lignin phenol concentrations normalized to OC did not change during the periods with high OC concentrations and MARs. This indicates that not only eutrophication but also enhanced terrestrial OC input could lead to greater burial of OC. The lignin phenol compositions did not show clear trends over the last century in most of the lakes examined. The ratios of syringyl to vanillyl phenols and the lignin phenol vegetation index had significant relationships with proportions of angiosperms in watershed vegetation. These results demonstrate that lignin phenols are useful in inferring recent as well as past changes in lake watershed environments.

Changes in northeast African hydrology and vegetation associated with Pliocene-Pleistocene sapropel cycles.

East African climate change since the Late Miocene consisted of persistent shorter-term, orbital-scale wet-dry cycles superimposed upon a long-term trend towards more open, grassy landscapes. Either or both of these modes of palaeoclimate variability may have influenced East African mammalian evolution, yet the interrelationship between these secular and orbital palaeoclimate signals remains poorly understood. Here, we explore whether the long-term secular climate change was also accompanied by significant changes at the orbital-scale. We develop northeast African hydroclimate and vegetation proxy data for two 100 kyr-duration windows near 3.05 and 1.75 Ma at ODP Site 967 in the eastern Mediterranean basin, where sedimentation is dominated by eastern Sahara dust input and Nile River run-off. These two windows were selected because they have comparable orbital configurations and bracket an important increase in East African C4 grasslands. We conducted high-resolution (2.5 kyr sampling) multiproxy biomarker, H- and C-isotopic analyses of plant waxes and lignin phenols to document orbital-scale changes in hydrology, vegetation and woody cover for these two intervals. Both intervals are dominated by large-amplitude, precession-scale (approx. 20 kyr) changes in northeast African vegetation and rainfall/run-off. The δ(13)Cwax values and lignin phenol composition record a variable but consistently C4 grass-dominated ecosystem for both intervals (50-80% C4). Precessional δDwax cycles were approximately 20-30‰ in peak-to-peak amplitude, comparable with other δDwax records of the Early Holocene African Humid Period. There were no significant differences in the means or variances of the δDwax or δ(13)Cwax data for the 3.05 and 1.75 Ma intervals studied, suggesting that the palaeohydrology and palaeovegetation responses to precessional forcing were similar for these two periods. Data for these two windows suggest that the eastern Sahara did not experience the significant increase in C4 vegetation that has been observed in East Africa over this time period. This observation would be consistent with a proposed mechanism whereby East African precipitation is reduced, and drier conditions established, in response to the emergence of modern zonal sea surface temperature gradients in the tropical oceans between 3 and 2 Ma.This article is part of the themed issue 'Major transitions in human evolution'.

Linkages among fluorescent dissolved organic matter, dissolved amino acids and lignin-derived phenols in a river-influenced ocean margin

Excitation emission matrix (EEM) fluorescence spectroscopy coupled with parallel factor analysis (PARAFAC) is commonly used to investigate the dynamics of dissolved organic matter (DOM). However, a lack of direct comparisons with known biomolecules makes it difficult to substantiate the molecular composition of specific fluorescent components. Here, coincident surface-water measurements of EEMs, dissolved lignin, and total dissolved amino acid (TDAA) acquired in the northern Gulf of Mexico were used to investigate the relationships between specific fluorescent components and DOM biomolecules. Two terrestrial humic-like components identified by EEM-PARAFAC using samples obtained from river to offshore waters were strongly linearly correlated with dissolved lignin concentrations. In addition, changes in terrestrial humic-like abundance were correlated with those in lignin phenol composition, suggesting such components are largely derived from lignin and its alteration products. By applying EEM-PARAFAC to offshore samples, two protein-like components were obtained. The tryptophan-like component was strongly correlated with TDAA concentrations, corroborating the suggested protein/peptide origin of this component. The ratios of tryptophan-like component to tyrosine-like component or dissolved organic carbon (DOC) concentrations were also correlated with DOC-normalized yields of TDAA, suggesting these proxies are useful indicators of the bioavailability of DOM in marine waters of the studied ecosystem.

Temporal variability of particulate organic carbon in the lower Changjiang (Yangtze River) in the post‐Three Gorges Dam period: Links to anthropogenic and climate impacts

AbstractSuspended particles from the lower Changjiang were collected monthly from 2003 to 2011, which corresponds to the three construction periods of the Three Gorges Dam. Organic carbon (%OC), organic carbon to total nitrogen molar ratio, stable carbon isotope, and terrestrial biomarkers were examined. Rating curve studies were applied for the temporal trend analysis. The composition of particulate lignin phenols exhibited clear annual and periodic variations but only minor seasonal changes. Lignin phenol ratios (vanillyl/syringyl and cinnamyl/vanillyl) indicated that the terrigenous organic matter (OM) was primarily composed of woody and nonwoody tissue derived from angiosperm plants. The low‐lignin phenol yields (Λ8) in combination with higher acid to aldehyde ratios reflected a substantial contribution from soil OM to the particle samples or modifications during river transport. The temporal shift of the lignin phenol vegetation index with the sediment load during the flood seasons revealed particulate organic matter (POM) erosion from soils and the impact of hydrodynamic processes. The dam operations affected the seasonal variability of terrigenous OM fluxes, although the covariation of lignin and sediment loads with discharged water implies that unseasonal extreme conditions and climate change most likely had larger influences, because decreases in the sediment load and lignin flux alter the structure and composition of particulate OM (POM) on interannual time scales, indicating that they may be driven by climate variability. The modification of the composition and structure of POM will have significant impacts on regional carbon cycles and marine ecosystems.

Lignin phenols in soils as biomarkers of paleovegetation

It has been shown by the methods of biochemistry, nuclear magnetic resonance, and isotope geochemistry that the proportions of lignin phenols may be used as molecular traces of paleovegetation due to their biochemical and physiological specificity and high resistance to decomposition. Lignin structures have been detected in iron–manganese concretions. The comparison of the 13 NMR spectra of native lignin preparations isolated from different woody and herbaceous species with those of soil humic acids makes it possible to identify many characteristic shifts of lignin nature in humic acids at 56, 102, 115, 119, 131, 147, 151–152, 160, and 166 ppm. The information role of biomarker has been tested at the reconstruction of paleovegetation in the uplands of the Russian Plain: an upward shift of the forest boundary has been recorded on the Northern Caucasus; the hypothesis about the steppe period of landscape development in the Tien Shan mountain valleys during the middle Holocene has been confirmed, and molecular traces of tropical flora have been revealed in the buried soils of Pleistocene age. The representativeness of information has been increased using the isotope analysis (δ13C); a new parameter—the composition of lignin phenols—has been introduced in the existed system of biomarkers.

Sources of organic matter in Changjiang (Yangtze River) bed sediments: Preliminary insights from organic geochemical proxies

Insight into the content and composition of organic carbon (OC) in river systems contributes to our understanding of the global carbon cycle. The Changjiang (Yangtze River) plays a significant role in global carbon and hydrological cycles, as it is an important supplier of sediment, nutrients and OC to the East China Sea. To provide a preliminary insight into the source of OC transported by the Changjiang, we analyzed bulk (grain size, organic carbon content, δ13C), and molecular (lignin phenols, branched and isoprenoid GDGTs) characteristics of organic matter in bed sediments at eight locations along the river. The δ13C values and lignin phenol composition indicate that the OC originates from a mixture of primarily soils and plants. Comparison between branched GDGT (br GDGT) distributions in riverbed sediments and those in the different soil types in the drainage basin indicate that the br GDGT signal in the upper reaches is largely derived from soils from the Qinghai-Tibet Plateau. Downstream changes in br GDGT distributions can be linked to subsequent input of local soil material. The observed variation in br GDGT composition along the river implies that a portion of the OC may be oxidized or replaced by the local input during transit. Although the relationship between δ13C and lignin phenol composition indicates that the contribution of phytoplankton is limited, comparison of GDGT ratios (GDGT-0:crenarchaeol, iso GDGTs:br GDGTs, BIT index) for the sediments and surrounding soils indicates that at least part of the iso GDGTs has an aquatic origin. Overall, the downstream evolution of br GDGTs in the Changjiang implies that their use as paleoclimate proxy in downcore applications will likely yield a local, rather than a basin-integrated continental climate record.

Characterization of particulate organic matter in the Lena River delta and adjacent nearshore zone, NE Siberia – Part 2: Lignin-derived phenol compositions

Abstract. The Lena River in central Siberia is one of the major pathways translocating terrestrial organic matter (OM) from its vast catchment area to the coastal zone of the Laptev Sea and the Arctic Ocean. The permafrost soils of its far south-stretching catchment, which store huge amounts of OM, will most likely respond differently to climate warming and remobilize previously frozen OM with distinct properties specific for the source vegetation and soil. To characterize the material discharged by the Lena River, we analyzed the lignin phenol composition in total suspended matter (TSM) from surface water collected in spring and summer, surface sediments from Buor Khaya Bay along with soils from the Lena Delta's first (Holocene) and third terraces (Pleistocene ice complex), and plant samples. Our results show that lignin-derived cinnamyl : vanillyl (C / V) and syringyl : vanillyl (S / V) ratios are &gt; 0.14 and 0.25, respectively, in TSM and surface sediments, whereas in delta soils they are &gt; 0.16 and &gt; 0.51, respectively. These lignin compositions are consistent with significant inputs of organic matter from non-woody angiosperm sources mixed with organic matter derived from woody gymnosperm sources. We applied a simple linear mixing model based on the C / V and S / V ratios, and the results indicate the organic matter in delta TSM samples and Buor Khaya Bay surface sediments contain comparable contributions from gymnosperm material, which is primarily derived from the taiga forests south of the delta, and angiosperm material typical for tundra vegetation. Considering the small catchment area covered by tundra (~ 12%), the input is substantial and tundra-derived OM input is likely to increase in a warming Arctic. The similar and high acid to aldehyde ratios of vanillyl and syringyl (Ad / AlV, S) in Lena Delta summer TSM (&gt; 0.7 and &gt; 0.5, respectively) and Buor Khaya Bay surface sediments (&gt; 1.0 and &gt; 0.9, respectively) suggest that the OM is highly degraded and Lena River summer TSM could be a possible source of the surface sediments. The Ad / AlV, S ratios of the first and third delta terraces were generally lower (mean ratios &gt; 0.4 and &gt; 0.4, respectively) than summer TSM and surface sediments. This implies that TSM contains additional contributions from a more degraded OM source (southern catchment and/or finer more degraded particle size). Alternatively, OM degradation on land after permafrost thawing and subaqueously during transport and sedimentation could be considerable. Despite the high natural heterogeneity of OM stored in delta soils and exported by the Lena River, the catchment-characteristic vegetation is reflected by the lignin biomarker composition. Climate-warming-related changes in the Lena River catchment may be detectable in changing lignin biomarker composition and diagenetic alteration.

Biochemical evidence for minimal vegetation change in peatlands of the West Siberian Lowland during the Medieval Climate Anomaly and Little Ice Age

AbstractPeatland vegetation is controlled primarily by the depth of the water table, making peat paleovegetation a useful climate archive. We applied a biochemical approach to quantitatively estimate the plant sources of peat carbon based on (1) neutral sugar compositions of Sphagnum, vascular plants, and lichens and (2) lignin phenol compositions of vascular plants. We used these biochemical indices to characterize vegetation change over the last 2000 years in four peat cores from the West Siberian Lowland (Russia) to investigate climate change during the Medieval Climate Anomaly and Little Ice Age. The vegetation was dominated by Sphagnum in all four cores, but was punctuated by several rapid but transient transitions to vascular plant dominance in the two cores from the southern West Siberian Lowland (&lt;60°N latitude). Lichen contributions were evident at the end of the Medieval Climate Anomaly and during the Little Ice Age in the two cores from northern West Siberian Lowland (&gt;60°N), possibly indicating permafrost development. However, there was no evidence for sustained vegetation change in response to either climatic event in cores from southern West Siberian Lowland. This suggests that these climatic events were relatively mild in the southern West Siberian Lowland, although the sensitivity of bog plant communities to climate change remains poorly understood.

Sources, distributions, and early diagenesis of sedimentary organic matter in the Pearl River region of the South China Sea

Suspended particles from the Pearl River, and surface sediments from the northern South China Sea (NSCS) were analyzed for elemental composition (C, N), stable carbon isotopic composition (δ13C), lignin phenols, and total hydrolyzable amino acids (THAA). Organic matter (OM) in riverine particles was depleted in 13C (avg. −28.3‰) and was derived primarily from plankton and soils, with minor contributions from C3 plant material. The δ13C of sedimentary OM became increasingly enriched in 13C (avg. −21.3‰) from the inner shelf to the slope of the NSCS, and C/N ratios decreased from the inner shelf to the slope, indicating increasing contributions of marine organic carbon (OC). Lignin phenol yields in sedimentary OM decreased from the inner shelf to the slope, indicating declining contributions of terrestrial OC. Lignin phenol compositions in riverine particles and marine sediments reflected a predominately angiosperm source. Degradation indices (DI) of sedimentary amino acids indicated increasing diagenetic alteration of marine OM with water depth and distance offshore. Increasing acid:aldehyde ratios (Ad/Al) in lignin phenols and 3,5-dihydroxybenzoic acid:vanillyl phenols (3,5-BD/V) ratios also indicated a seaward increase in the diagenetic state of terrestrial OM, presumably due to hydrodynamic sorting and biogeochemical processing. A three end-member mixing model based on lignin phenol yields and stable C isotopic compositions was used to distinguish sources of OM. Marine OM accounted for an increasing fraction (62–82%) of sedimentary OC from the inner shelf to the slope, whereas soil-derived OM accounted for a decreasing fraction (39–18%) of sedimentary OC from inner shelf to the slope. The contribution of C3 plant OM was negligible. The significant contributions of terrestrial OM in NSCS sediments are ascribed to the relatively refractory nature of soil OM and the bioavailable nature of marine OM.

Comparison of soil organic matter composition after incubation with maize leaves, roots, and stems

As plants are major contributors to soil organic matter (OM), the chemical composition of plant tissues entering the soil should be related to the soil OM composition. We examined the OM composition of maize leaves, stems, and roots, to determine if differences in plant tissue composition altered the soil OM composition during a 36-week degradation experiment. Lignin phenols were measured by gas chromatography/mass spectrometry (GC/MS), and soil OM and humic substances were characterized using solid-state 13C and solution-state 1H nuclear magnetic resonance (NMR) spectroscopy respectively. Lignin phenol composition, oxidation, and depletion relative to cutin-derived OH-acids changed less in leaf- compared to stem- and root-amended soils over time, and may be due to greater vanillyl concentrations in leaves. Soil amended with stems had higher concentrations of carbohydrates in soil OM. Humic substances from leaf-amended soils had higher concentrations of aliphatic components, likely due to higher concentrations of aliphatic compounds in leaf tissues, which suggests that compounds derived from leaves are potential contributors to the stable pool of soil OM. After 36-weeks of incubation, the contribution of microbial-derived OM was greatest in humic extracts from root-amended soils, and increased contribution from these compounds was detected earlier in these soils than stem- and leaf-amended soils. This indicates that root amendment may enhance contributions from microbial-derived OM. Our study suggests that changes in soil OM composition over time was related to the chemical composition of the plant tissue, and demonstrates the important link between plant chemistry and soil OM turnover.

Dissolved organic matter sources in large Arctic rivers

The biomarker composition of dissolved organic carbon (DOC) of the six largest Arctic rivers was studied between 2003 and 2007 as part of the PARTNERS Project. Samples were collected over seasonal cycles relatively close to the river mouths. Here we report the lignin phenol and p-hydroxybenzene composition of Arctic river DOC in order to identify major sources of carbon. Arctic river DOC represents an important carbon conduit linking the large pools of organic carbon in the Arctic/Subarctic watersheds to the Arctic Ocean. Most of the annual lignin discharge (>75%) occurs during the two month of spring freshet with extremely high lignin concentrations and a lignin phenol composition indicative of fresh vegetation from boreal forests. The three large Siberian rivers, Lena, Yenisei, and Ob, which also have the highest proportion of forests within their watersheds, contribute about 90% of the total lignin discharge to the Arctic Ocean. The composition of river DOC is also characterized by elevated levels of p-hydroxybenzenes, particularly during the low flow season, which indicates a larger contribution from mosses and peat bogs. The lignin composition was strongly related to the average 14C-age of DOC supporting the abundance of young, boreal-vegetation-derived leachates during spring flood, and older, soil-, peat-, and wetland-derived DOC during groundwater dominated low flow conditions, particularly in the Ob and Yukon Rivers. We observed significant differences in DOC concentration and composition between the rivers over the seasonal cycles with the Mackenzie River being the most unique, the Lena River being similar to the Yenisei, and the Yukon being most similar to the Ob. The observed relationship between the lignin phenol composition and watershed characteristics suggests that DOC discharge from these rivers could increase in a warmer climate under otherwise undisturbed conditions.