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1.
《Applied Geochemistry》2006,21(9):1455-1468
Cyclic base extraction is a commonly used method for the isolation of humic acids from soils and sediments. However, every extract may differ in chemical composition due to the complex nature of humic acids. To better understand the chemical composition of each extract, the heterogeneous property of humic acids and their speciation in environmental samples, eight fractions of humic acids were obtained in the present work by progressive base-extraction of Pahokee peat, and their chemical composition was characterized using two complementary pyrolytic techniques, namely conventional pyrolysis and methylation pyrolysis (TMAH) GC/MS. These quick and effective procedures provide an insight into the structure of macromolecules. The work shows that the lignin-derived aromatic compounds are major components of pyrolysates in both pyrolytic techniques, while aliphatic compounds originating from microorganisms and plants are minor components. Other compounds derived from proteins and carbohydrates at lower concentrations were also detected. Fatty acids were found in the pyrolysis without methylation, indicating their association with humic acid in a free state. These compounds are different from those formed during pyrolysis with in situ methylation, where fatty acids are generally believed to be the cleavage products of carboxylic groups bound to humic acids. A relative decreasing abundance of aromatic components and increasing abundance of aliphatic components in the pyrolysates as the peat was progressively extracted was also observed in this work, suggesting that the extraction of more hydrophobic aliphatics may be delayed in comparison to the aromatic components. Speciation and origin differences may also be important particularly considering that the contribution from lignin organic matter decreased with extraction number, as the contribution of microbial organic matter increased. The observed change in chemical composition with the extracted fractions indicates again that the humic acid distribution and their speciation are complex, and complete extractions are necessary to obtain a representative humic acid sample.  相似文献   

2.
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3.
The concentration and composition of lignin-derived phenols, which are often used as biomarkers for terrigenous organic matter (OM) inputs, were examined in North Atlantic Ocean sediments from IODP core U1302A (50°9.985′N, 45°38.271′W, 3568 m water depth), Orphan Knoll, 650 km NE of St. John’s, Newfoundland, Canada for the period of ca. 1100–810 ka BP. Lignin-derived phenols were extracted from sediments using CuO oxidation which yielded eight characteristic phenols. The majority of sediments have low syringyl phenol to vanillyl phenol (S/V) ratios and high cinnamyl phenol to vanillyl phenol (C/V) ratios, suggesting predominant concentrations of gymnosperm-derived organic matter inputs from adjacent continents (most likely eastern Canada and possibly southern Greenland). The S/V values were lower for the period of ca. 958–840 ka BP relative to ca. 1090–1078, 1042–958 and 840–818 ka BP, indicating fluctuations in the proportion of angiosperm- and gymnosperm-derived lignin delivery to the ocean. The greater fraction of gymnosperms for the period of 958–840 ka BP likely reflects the response of vegetation in source regions to climate cooling in the early part of the mid-Pleistocene. Lignin-derived phenol concentrations also displayed high variability during the investigated period, which did not show positive correlations with magnetic susceptibility or Gamma Ray Attenuation density. Considering that a fundamental climate change (41–100 ka cyclicity) occurred within the mid-Pleistocene, large variations in abundance and composition of lignin-derived phenols in core U1302A is likely indicative of dynamic environmental conditions, reflected by the variability in both concentrations and types of vegetation on adjacent continents and/or different mechanisms to transport terrigenous organic matter to the deep ocean.  相似文献   

4.
In this first study of lignin geochemistry in the world’s longest river on an island, surface sediments were collected along the Kapuas River, three lakes in the upper river, a tributary in the lower river and a separate river during June-July 2007 and December 2007-January 2008. The samples were analyzed for lignin-derived phenols and bulk elemental and stable carbon isotope compositions. Λ values (the sum of eight lignin phenols, expressed as mg/100 mg organic carbon (OC)) ranged from 0.13 to 3.70. Ratios of syringyl/vanillyl (S/V) and cinnamyl/vanillyl (C/V) ranged from 0.34 to 1.18 and 0.28 to 1.40, respectively, indicating the presence of non-woody angiosperm tissues. The high vanillic acid to vanillin (Ad/Al)v (0.71-2.01) and syringic acid to syringaldehyde (Ad/Al)s (0.72-2.12) ratios indicate highly degraded lignin materials. In the upper Kapuas River, highly degraded soil materials discharged from lands that were barren as a result of deforestation activities were detected in the locations directly in those vicinities. The middle Kapuas River showed rapid organic matter degradation, probably due to the presence of fresh terrestrial and phytoplankton organic matter fueling the biogeochemical cycling. The Kapuas Kecil River, one of the two branches in the lower reach of the Kapuas River, showed higher levels and diagenesis of sedimentary organic matter due to input from anthropogenic sources and increased marine organic matter near the mouth. This study shows that different stretches along the river exhibit different levels and composition of sedimentary organic matter, as well as different carbon dynamics, which is directly attributable to the varying landscapes and quality of organic matter.  相似文献   

5.
The role of organic matter (OM) concentration, structure and composition and how these relate to mineral protection is important for the understanding of long term soil OM dynamics. Various OM–clay complexes were constructed by sequential sorption of lignin and dodecanoic acid to montmorillonite. Humic acid–montmorillonite complexes were prepared at pH 4 and 7 to vary OM conformation prior to sorption. Results obtained with constructed OM–clay complexes were tested with isolated mineral fractions from two soils. Oxidation with an acidic NaClO2 solution was used to chemically oxidize lignin in the OM–clay complexes, sand-, silt- and clay-size soil fractions to test whether or not it can be protected from chemical attack. Gas chromatography–mass spectrometry was used to analyze lignin-derived phenols, cutin OH–acid (after CuO oxidation), fatty acid and n-alkanol concentrations and composition. We found that carbon content was not solely responsible for lignin stability against chemical oxidation. Lignin was protected from chemical oxidation through coating with dodecanoic acid and sorption of humic acid to clay minerals in a stretched conformation at pH 7. Therefore, interactions between OM constituents as well as OM conformation are important factors that protect lignin from chemical oxidation. Lignin-derived phenol dimers in the Grassland-Forest Transition soil fractions were protected from chemical oxidation to a greater extent compared to those in Grassland soil fractions. Therefore, although lignin was protected from degradation through mineral association, the extent of this protection was also related to OM content and the specific stability of lignin components.  相似文献   

6.
Sources of sedimentary humic substances: vascular plant debris   总被引：1，自引：0，他引：1  
A modern Washington continental shelf sediment was fractionated densimetrically using either an organic solvent, CBrCl3, or aqueous ZnCl2. The resulting low density materials (<2.06 g/ml) account for only 1% of the sediment mass but contain 25% of the sedimentary organic carbon and 53% of the lignin. The C/N ratios (30–40) and lignin phenol yields (Λ = 8) and compositions indicate that the low density materials are essentially pure vascular plant debris which is slightly enriched in woody (versus nonwoody) tissues compared to the bulk sediment. The low density materials yield approximately one-third of their organic carbon as humic substances and contribute 23% and 14% of the total sedimentary humic and fulvic acids, respectively. Assuming that the lignin remaining in the sedimentary fraction is also contained in plant fragments that yield similar levels of humic substances, then 50% and 30% of the total humic and fulvic acids, respectively, arise directly from plant debris.Base-extraction of fresh and naturally degraded vascular plant materials reveals that significant levels of humic and fulvic acids are obtained using classical extraction techniques. Approximately 1–2% of the carbon from fresh woods and 10–25% from leaves and bark were isolated as humic acids and 2–4 times those levels as fulvic acids. A highly degraded hardwood yielded up to 44% of its carbon as humic and fulvic acids. The humic acids from fresh plants are generally enriched in lignin components relative to carbohydrates and recognizable biochemicals account for up to 50% of the total carbon. Humic and fulvic acids extracted directly from sedimentary plant debris could be responsible for a major fraction of the biochemical component of humic substances.  相似文献   

7.
Models of peat accumulation assume that peat decomposition occurs mostly above the water table, with little or no decomposition once it enters the deeper, saturated, anoxic zone. Few studies have used molecular biomarkers for tracing post depositional, decomposition-related trends in peat deposits. We studied the major diagenetic changes in the phenolic constituents within a Sphagnum-dominated ombrotrophic bog deposit. The yield of lignin-derived phenols and degree of decomposition, measured using alkaline cupric oxide oxidation of bulk peat samples and their corresponding humic acids, revealed that most of the degradation takes place in the surface layers corresponding to the acrotelm. In fact, total phenolic constituents of peat samples decrease from 36.1 to 21.6 mg g−1 OC (organic carbon) over the first 36 cm, whereas in the deeper anoxic layers, phenolic constituents tend to accumulate, reaching a highest concentration of 71.0 mg g−1 OC. The diagenetic alteration of these phenolic constituents during peat accumulation involves significant demethoxylation and an increasing yield of vanillyl oxidation products despite the low redox potential. Syringyl phenols tend to be particularly resistant to diagenetic alteration and are significantly enriched within the humic acid fraction (twofold) with respect to the bulk peat. This, together with the higher degree of oxidation, suggests that this organic matter fraction is enriched in more resistant, but nonetheless diagenetically altered, phenolic constituents. This suggests that humic acids constitute a refractory pool of organic C with a relatively low turnover rate. Our results confirm that the major processes involved in the variation in phenolic constituents with depth are strongly related to the post depositional environment and that evaluation of diagenetic trends in phenolic constituents may provide molecular-level information on the changes that fresh biomass undergoes during early diagenesis in peatlands.  相似文献   

8.
Evidence of environmental and vegetation changes in the catchment area of a small pond created artificially during the Middle Ages from a swampy area was provided by coupling palynology data and a detailed study of macromolecular organic matter (OM). Tetramethylammonium hydroxide (TMAH) thermochemolysis after solvent extraction was used to characterize macromolecular OM and particularly lignin and fatty acids (FAs). Molecular ratios such as TAR(FA), C16:1/C16:0 and C18:1/C18:0 were calculated to characterize the FAs incorporated into the macromolecular OM. Moreover, syringyl vs. vanillyl phenols (S/V) and cinnamyl vs. vanillyl phenols (C/V) molecular ratios were investigated to fingerprint the lignin sources. These different markers suggested that the swampy area was dominated by a non-woody angiosperm input and gave rise to pond status over a period of several centuries. Indeed, TAR(FA) correlated with the aquatic contribution, which became predominant after creation of the pond. The use of ratios of total acid phenols to the total aldehyde phenols of syringyl or vanillyl units (Ad/Al(s), Ad/Al(v)), which are related to the degree of oxidation of lignin, revealed the irregular operation of oxidative conditions.  相似文献   

9.
A 10 m sediment core from Academician Ridge in Lake Baikal was analyzed for its molecular composition using on-line TMAH (tetramethylammomium hydroxide) thermochemolysis. Major products are lignin phenols, n-C14 to C30 fatty acids (alkanoic acids), cutin acids, hydroxy acids and aliphatic dicarboxylic acids. Lignin phenols are abundant in warmer periods (the interglacial: marine isotope stage (MIS) 5e and MIS 1), but extremely low in the other (colder) periods. This result coincides well with pollen records reported for a core near the present site, where an expansion of coniferous forests in sub-stage 5e and MIS 1 was implied. Normal C24–C30 alkanoic acids, important components of plant wax esters, are abundant in 5e and MIS 1 and are present in significant amounts in the other (colder) periods, unlike the lignin phenols. A high abundance of n-C24 to C30 alkanoic acids relative to lignin phenols in the Bølling–Allerød warm period suggests an enhanced development of herbs.It is implied from comparison of the sedimentary lignin phenol record with fossil pollen records and lignin phenol analysis of modern pollen that the ratio of cinnamyl phenols to vanillyl phenols may serve as an indicator of pollen contribution to sedimentary organic matter.  相似文献   

10.
13C- and 1H-NMR spectra were obtained for humic substances isolated from a coastal marine environment and also for the intracellular and extracellular extracts of a marine diatom. Phaeodactylum tricornutum Bohlin. Highly branched alkyl chains constitute a large proportion of the structure of the marine humic material, whereas aromatic components are less important. Carbohydrate-type materials, possibly uronic acids, are also present in appreciable amounts. Furans (derived from carbohydrates). pyrroles and nitriles (derived from proteins, nucleic acids and/or tetrapyrroles) and phenols and methylphenols (non-lignin derived) are pyrolysis products derived from pyrolysis-gas chromatography-mass spectrometry of the extracts. The results indicate the similarities in chemical structure of P. tricornutum exudate and dissolved marine humic material.  相似文献   

11.
Terrestrially-derived organic matter in sediments of the Delaware Estuary originates from riverine transport of soils and fresh litter, sewage and industrial wastes, and marsh export of organic matter. The quantity, composition, and spatial distribution of terrigenous organic matter in sediments was determined by elemental (C and N), lignin, and stable carbon isotope analyses. Sediments in the upper Delaware Estuary had low organic carbon content and high lignin content. In contrast, sediments in the lower Delaware Estuary had high organic carbon content and low lignin content. There was a slight decrease in the proportion of syringyl and cinnamyl phenols relative to vanillyl phenols between the upper estuary and lower estuary. Differences in lignin and stable carbon isotope compositions between sediments of the Delaware Estuary and sediments of the Broadkill River estuary (an adjoining salt-marsh estuary) supported previous observations that marshes do not export substantial quantities of organic matter to estuaries. Additional results suggested that lignin-rich sediments were concentrated in the upper estuary, most likely in the zone of high turbidity. Furthermore, algal material diluted lignin-rich sediments, particularly in the lower estuary. The weaker algal signal in bottom sediments compared to that in suspended particulate matter suggested algal material was decomposed either in the water column or at the sediment-water interface. Physical sorting of sediments prior to deposition was also indicated by observations of compositional differences between the upper and lower estuary bottom sediments. Finally, seasonal variations in primary productivity strongly influenced the relative abundance of terrestrial organic matter. In fall, however, the proportion of lignin was greatest because of a combination of greater inputs of terrestrially-derived organic matter, lower river discharge, and a decrease in algal biomass.  相似文献   

12.
We studied the degradation of lignin in leaf and needle litter of ash, beech, maple, pine and spruce using 13C-labelled tetramethylammonium hydroxide (13C TMAH) thermochemolysis. Samples were allowed to decompose for 27 months in litter bags at a German spruce forest site, resulting in a range of mass loss from 26% (beech) to 58% (ash). In contrast to conventional unlabelled TMAH thermochemolysis, 13C-labelling allows thermochemolysis products from lignin, demethylated lignin and other polyphenolic litter compounds (e.g. tannins) to be distinguished. Proxies for lignin degradation (phenol yield; acid/aldehyde ratio of products) changed considerably upon correction for the contribution of non-lignin sources to the thermochemolysis products. Using the corrected values, we found increasing acid/aldehyde values as well as decreasing or constant yield of lignin derived phenols normalised to litter carbon, suggesting pronounced lignin degradation by wood-rotting fungi. No indication for build up of demethylated lignin through the action of brown rot fungi on ring methoxyls was found. The results were compared with those of other analytical techniques applied in previous studies. Like 13C-TMAH thermochemolysis, CuO oxidation showed increasing lignin oxidation (acid/aldehyde ratio) and no/little enrichment of lignin derived phenols in the litter. Molecular lignin degradation patterns did not match those from analysis of total acid unhydrolysable residues (AURs). In particular, the long assumed selective preservation of lignin during the first months of litter decomposition, based on AUR analysis, was not supported by results from the CuO and 13C TMAH methods.  相似文献   

13.
Cross polarization, magic-angle spinning 13C nuclear magnetic resonance spectroscopy was used to characterize humic fractions isolated from different soils. The acid fractions are more aromatic than the humin fractions, probably due to the higher polyssaccharide content of humins. However, fulvic acid fractions are more aromatic than the corresponding humic acid and humin fractions. These results can be interpreted in terms of the isolation procedure, because the high affinity of Polyclar AT for phenols results in higher aromaticities as compared with other isolation methods (e.g. charcoal).  相似文献   

14.
The molecular weight distribution of the humic and fulvic acid fractions of two sediments was determined using Amicon ultrafiltrat ion techniques. All fractions of humic substances had a molecular weight range of less than 500 to greater than 300,000. The largest component of humic acids was in the greater than 300,000 molecular weight range, whereas, the largest percentages of fulvic acids were in the less than 500 molecular weight range and the 100,000–300,000 molecular weight range. From this preliminary investigation there appears to be a qualitative relationship between the molecular weight composition of the humic substances in the sediment and the salinity of the overlying water within an estuarine environment.  相似文献   

15.
Humic matter fractions from modern sediments of Lake Huron and Lake Michigan have been compared. Large yields of saccharinic acids from alkaline hydrolysis suggest that these fractions contain large portions of carbohydrate materials. Evidence for contributions of aquatic lipid (C-16 fatty acids) and of liginin (phenolic acids) to these sediments is also present in the hydrolysis products. Qualitative differences among fulvic acid, humic acid and humin from the same lake are minor, suggesting common (or similar) organic sources for these fractions. The lability of sedimentary humic matter to alkaline hydrolysis is inversely related to its degree of exposure to oxidative weathering. Lability may also be related to diagenetic state as fulvic acids generally yield greater quantities of hydrolysis components than humic acids which in turn yield more than humin.  相似文献   

16.
The phosphorus content of marine humic acids (HA) is in the range of 0.1–0.2%. The C/P ratios of the HA are 300 to 400. Marine fulvic acids (FA) contain 0.4–0.8% P and have C/P ratios of 80 to 100. High molecular weight organic matter dissolved in pore waters (DOM) contains 0.5% P and has C/P of 90. The data suggest that during the formation sequence: Plankton → DOM → FA → HA → Kerogen, phosphorus is lost, mainly in the FA → HA (and possibly also in the HA → Kerogen) step. Diagenesis of sedimentary humic acids is accompanied by loss of phosphorus (as well as of nitrogen) to form HA with C/P ratios of 1000.Soil humic substances resemble marine humates in P content (0.3%) and soil FA's are about three to fivefold enriched in P relative to HA. C/P ratios are lower in soil HA (ca. 200) as compared with marine HA. Humic acids from diagenetic products such as peat and lignite are highly depleted in P. Rough calculations indicate that humate bound P may account for 20–50% of the organic phosphorus reservoir in sediments. The chemical speciation of this P is unknown, but lack of correlation with ash, Fe, Ca or Al content (in marine humates, at least) indicates that it is organically bound.  相似文献   

17.
Humic acids isolated from marine sediments were found to be effective in absorption of various metal ions through chelation, cation exchange and surface adsorption. The quantities of metal ions complexed varied from 40 to 205 mg/g of organic matter. In the presence of equal concentrations of Co, Cu, Mn, Ni and Zn in the reaction media, humic acid and peatmoss, a rich source of humic compounds, showed preferential absorption for Cu. Copper constituted more than 50% of the metal ions complexed by organic matter. As compared with the other metal ions, its bonding strength was very firm because it could not be displaced by ferric ion or cation exchange reagents.Peatmoss, a rich source of humic acid, was found to absorb significant quantities of various metal ions. Under laboratory conditions each kg of peat absorbed about 1500 mg of various metal ions from solutions containing equal concentrations of Co, Cu, Mn, Ni and Zn. However, in the field trials with sea water, absorption of metals was limited to Zn (28.7 mg/kg), Cu (3.66 mg/kg) and Fe (2.0 mg/kg). Under-saturation of sea water for transition metals and super-saturation for alkali and alkaline earth metals appears to be a bottleneck in the effective utilization of peat as a means of recovery of metals from sea water.  相似文献   

18.
Spruce, alder, and oak woods deposited in coastal sediments were characterized versus their modern counterparts by quantification of individual neutral sugars and lignin-derived phenols as well as by scanning electron microscopy, 13C NMR, and elemental analysis. The buried spruce wood from a 2500 yr old deposit was unaltered whereas an alder wood from the same horizon and an oak wood from an open ocean sediment were profoundly degraded. Individual sugar and lignin phenol analyses indicate that at least 90 and 98 wt% of the initial total polysaccharides in the buried alder and oak woods, respectively, have been degraded along with 15–25 wt% of the lignin. At least 75% of the degraded biopolymer has been physically lost from these samples. This evidence is supported by the SEM, 13C NMR and elemental analyses, all of which indicate selective loss of the carbohydrate moiety. The following order of stability was observed for the major biochemical constituents of both buried hardwoods: vanillyl and p-hydroxyl lignin structural units > syringyl lignin structural units > pectin > α-cellulose > hemicellulose. This sequence can be explained by selective preservation of the compound middle lamella regions of the wood cell walls. The magnitude and selectivity of the indicated diagenetic reactions are sufficient to cause major changes in the chemical compositions of wood-rich sedimentary organic mixtures and to provide a potentially large in situ nutrient source.  相似文献   

19.
Humic acids from Recent lacustrine and marine sediments were divided into five components by extractions with organic solvents and characterized by elementary composition, ultraviolet, visible and infrared absorption spectra and n.m.r. spectra. The results suggest that sedimentary humic acids have a cyclic structure (40–50% of the total carbon), which is considered to be alicyclic rather than aromatic. No marked differences except for an absorption near 410 mμ were observed between humic acids from lake and marine sediments.  相似文献   

20.
Analysis of river, estuary and marine sediments from the Atlantic coast of Spain using thermogravimetry–differential scanning calorimetry–quadrupole mass spectrometry–isotope ratio mass spectrometry (TG–DSC–QMS–IRMS) was used to (a) distinguish bulk chemical hosts for C within a sediment and humic acid fraction, (b) track C pools with differing natural C isotope ratios and (c) observe variation with distance from the coast. This is the first application of such a novel method to the characterisation of organic matter from marine sediments and their corresponding humic acid fractions. Using thermal analysis, a labile, a recalcitrant and a refractory carbon pool can be distinguished. Extracted humic fractions are mainly of recalcitrant nature. The proportion of refractory carbon is greatest in marine sediments and humic acid fractions. Quadrupole mass spectrometry confirmed that the greatest proportion of m/z 44 (CO2) and m/z 18 (H2O) were detected at temperatures associated with recalcitrant carbon (510–540 °C). Isotope analysis detected progressive enrichment in δ13C for the sediment samples with an increase in marine influence. Isotopic heterogeneity in the refractory organic matter in marine sediments could be due to products of anthropogenic origin or natural combustion products. Isotope homogeneity of humic acids confirms the presence of terrigenous C in marine sediments, allowing the terrestrial input to be characterised.  相似文献   

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