Terrigenous dissolved organic matter along an estuarine gradient and its flux to the coastal ocean

The contribution of terrigenous organic matter (TOM) to high molecular weight dissolved and particulate organic matter (POM) was examined along the salinity gradient of the Delaware Estuary. Dissolved organic matter (DOM) was fractionated by ultrafiltration into 1–30 kDa (HDOM) and 30 kDa–0.2 μm (VHDOM) nominal molecular weight fractions. Thermochemolysis with tetramethylammonium hydroxide (TMAH) was used to release and quantify lipids and lignin phenols. Stable carbon isotopes, fatty acids and lignin content indicated shifts in sources with terrigenous material in the river and turbid region and a predominantly algal/planktonic signal in the lower estuary and coastal ocean. Thermochemolysis with TMAH released significant amounts of short chain fatty acids (C₉–C₁₃), not seen by traditional alkaline hydrolysis, which appear to be associated with the macromolecular matrix. Lignin phenol distributions in HDOM, VHDOM and particles followed predicted sources with higher concentrations in the river and turbid region of the estuary and lower concentrations in the coastal ocean. TOM comprised 12% of HDOM within the coastal ocean and up to 73% of HDOM within the turbid region of the estuary. In the coastal ocean, TOM from high molecular weight DOM comprised 4% of total DOC. The annual flux of TOM from the Delaware Estuary to the coastal ocean was estimated at 2.0×10¹⁰ g OC year⁻¹ and suggests that temperate estuaries such as Delaware Bay can be significant sources of TOM on a regional scale.     

Lignin geochemistry of sediments from the Narragansett Bay Estuary

Cupric oxide oxidation has been employed to characterize the lignin geochemistry of Narragansett Bay sediments. Lignin concentrations throughout the estuary are low when expressed on a carbon-normalized basis, but can be characterized as enriched when expressed on a mass-normalized basis. This implies substantial dilution of the sedimentary lignin by inputs of lignin-poor carbon. Lignin concentrations do not correlate with the ¹³C isotopic composition of the sedimentary organic matter. These results are consistent with a sediment lignin component consisting of varying amounts of vascular plant debris and lignin-depleted organic matter, the latter originating from both marine (planktonic) and terrestrial (uncharacterized) sources. Compositional plots of lignin-derived phenols show that sediments in the upper estuary are influenced to a greater extent by gymnosperm lignin sources than those in the mid-and lower estuary. Given the extent to which the upper estuary is affected by pollution sources, inputs from anthropogenic discharges are the most likely cause of these compositional differences. However, an evaluation of processed paper products as an “anthropogenic” lignin source indicates that the lignin content of these materials is insufficient to account for the levels found in the sediments. Subsurface lignin compositions at an upper estuary site reveal that lignin originating from the inferred anthropogenic sources disappears at a depth shallower than that which would be expected based on the distribution of other trace organic pollutants (hydrocarbons and several synthetic organic compounds). We speculate that differences in either the depositional history or the degree of preservation of these two compound classes are responsible for the observed trends.     

A Biogeochemical View of Estuarine Eutrophication: Seasonal and Spatial Trends and Correlations in the Delaware Estuary

The Delaware River and Bay Estuary is one of the major urbanized estuaries of the world. The 100-km long tidal river portion of the estuary suffered from major summer hypoxia in the past due to municipal and industrial inputs in the urban region; the estuary has seen remarkable water quality improvements from recent municipal sewage treatment upgrades. However, the estuary still has extremely high nutrient loading, which appears to not have much adverse impact. Since the biogeochemistry of the estuary has been relatively similar for the past two decades, our multiple year research database is used in this review paper to address broad spatial and seasonal patterns of conditions in the tidal river and 120 km long saline bay. Dissolved oxygen concentrations show impact from allochthonous urban inputs and meteorological forcing as well as biological influences. Nutrient concentrations, although high, do not stimulate excessive algal biomass due to light and multiple nutrient element limitations. Since the bay does not have strong persistent summer stratification, there is little potential for bottom water hypoxia. Elevated chlorophyll concentrations do not exert much influence on light attenuation since resuspended bottom inorganic sediments dominate the turbidity. Dissolved inorganic carbon and dissolved and particulate organic carbon distributions show significant variability from watershed inputs and lesser impact from urban inputs and biological processes. Ratios of dissolved and particulate carbon, nitrogen, and phosphorus help to understand watershed and urban inputs as well as autochthonous biological influences. Owing to the relatively simple geometry of the system and localized anthropogenic inputs as well as a broad spatial and seasonal database, it is possible to develop these biogeochemical trends and correlations for the Delaware Estuary. We suggest that this biogeochemical perspective allows a revised evaluation of estuarine eutrophication that should have generic value for understanding other estuarine and coastal waters.     

A comprehensive survey of lignin geochemistry in the sedimentary organic matter along the Kapuas River (West Kalimantan, Indonesia)

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.     

Sources,sinks and distribution of organic carbon in the St. Lawrence Estuary,Canada

Carbon isotope ratio analysis of particulate, planktonic, and sedimentary organic carbon and dissolved inorganic carbon has been used to study the sources and sinks of the organic carbon in the St. Lawrence Estuary and Gulf of St. Lawrence, Canada. Particulate organic carbon (POC) isotope ratios in the upper St. Lawrence Estuary are uniform and indistinguishable from those of POC in the St. Lawrence River and of planktonic organic carbon in both areas. The abundance of freshwater diatoms in the upper Estuary suggests that upper Estuary POC is predominantly “fresh” organic matter of riverborne origin. Upper Estuary POC is isotopically different from POC in the lower St. Lawrence Estuary and Gaspé regions, but is not different from POC from the surface waters of the open Gulf of St. Lawrence. The isotopic composition of planktonic organic carbon mirrors that of the POC, indicating that the POC in the lower Estuary and Gulf is also “fresh” organic matter. Since the lower Estuary POC forms an isotopic barrier between the upper Estuary POC and the Gulf of St. Lawrence POC, there appears to be little mixing of POC between these three reservoirs. Therefore POC in the lower Estuary and Gulf is most likely both produced and deposited (or degraded) in situ.An examination of carbon isotope ratio differences between the planktonic and dissolved inorganic carbon reservoirs shows that this difference varies significantly and somewhat unpredictably between sectors of the study area. Interpretation of environmental carbon isotope data on the basis of an assumed, constant fractionation factor may be subject to large errors. Direct measurement of both reservoirs is obviously preferable.     

Sources and transformations of organic matter in surface soils and sediments from a tidal estuary (North Inlet, South Carolina, USA)

Surface soil and sediment samples collected along a forest-brackish marsh-salt marsh transect in a southeastern U.S. estuary were separated into three different fractions (sand, macro-organic matter, and humus) based on size and density. Elemental, stable carbon isotope, and lignin analyses of these samples reveal important contrasts in the quantity, composition, and sources of organic matter, between forest and marsh sites. Elevated nitrogen contents in humus samples suggest nitrogen incorporation during humification is most extensive in forest soils relative to the marsh sites. The lignin compositions of the macro-organic and humus samples reflect the predominant type of vegetation at each site. Lignin phenol ratios indicate that woody and nonwoody litter from, gymnosperm and angiosperms trees (pines and oaks) is the major source of vascular plant-derived organic matter in the forest site and that angiosperm, grasses (Juncus andSpartina) are the major sources of lignin at the marsh sites. The phenol distributions also reveal that oxidative degradation of lignin is most extensive in the forest and brackish marsh zones whereas little lignin decay occurs in the salt marsh samples. In forest soils, most organic matter originates from highly altered forest vegetation while at the brackish marsh site organic matter is a mixture of degradedJuncus materials and microbial/algal remains. Organic matter in the salt marsh appears to be composed of a more complex mixture of sources, including degradedSpartina detritus as well as algal and microbial inputs. Microbial methane oxidation appears to be an important process and a source of¹³C depleted organic carbon in subsurface sediments at this site.     

The Molecular Composition of Lignin as an Indicator of Subaqueous Permafrost Thawing

The concentration and molecular composition of phenols, lignin derivatives, were analyzed. The material for the study was sampled from bottom sediments and subaqueous perennial frozen rocks from a well drilled in the Buor-Khaya Gulf of the Laptev Sea. The analysis was undertaken on the basis of calculation of the molecular factor. The principal difference in the molecular composition of organic matter is shown. This difference is manifested in the decrease in the total concentration of the vanillic lignin derivatives in the thawed formations in comparison with the perennial frozen rocks. This phenomenon is explained by activation of the bacterial transformation of organic matter caused by thawing of the subaqueous permafrost. It was established that the weight percentage of lignin in the organic matter of the analyzed sediments is 17% C_org.

     

Land-derived organic matter in surface sediments from the Gulf of Mexico

Lignin oxidation products and ¹³C/¹²C ratios were compared as indicators of land-derived organic matter in surface sediments from the western Gulf of Mexico. Whole sediments were reacted with cupric oxide to yield phenolic oxidation products that indicated the types and relative amounts of the lignins that were present.Measurements of lignin concentration and carbon isotope abundances both indicated a sharp offshore decrease of land-derived organic matter in most areas of the western Gulf. This decrease results primarily from mixing of terrestrial and marine organic matter. The terrestrially derived material in these sediments has a lignin content similar to that of grasses and tree leaves. Flowering plants contribute most of the sedimented lignin compounds. These lignins apparently occur in the form of well-mixed plant fragments that are transported to sea by rivers and deposited primarily on the inner continental shelf.     

珠江中下游颗粒有机质的碳氮℃稳定同位素、氨基酸和木质素组成及其地球化学意义

从东江到珠江口采集了悬浮颗粒物,通过测定总有机质的元素（TOC、TN）、同位素（δ13C、δ15N）组成以及生物标志物（氨基酸、木质素）等地球化学性质,来揭示颗粒有机质的来源和组成。结果表明,浮游生物（13%-52%）和土壤（45%-77%）是珠江颗粒有机质的主要来源,植物（0%-11%）对颗粒物的贡献较小。颗粒有机质含有高比例的氨基酸碳（TAAC）,说明浮游生物对颗粒物的重要性。氨基酸的降解指数（DI）在-0.51到0.79之间,说明这些水生来源有机质的降解程度比较小。木质素的降解参数（Ad/Al、3,5-BD/V）较大,表明珠江颗粒有机碳的陆源来源主要是土壤。在颗粒物中检测到了少量的二氨基庚二酸（Dapa）,说明细菌对颗粒有机碳也有所贡献。不同环境中颗粒物的木质素组成主要与颗粒物丰度和粒径有关：（1）相对于河流,水库颗粒物中的木质素含量显著偏低,降解程度更高;（2）相对于中游,下游颗粒物丰度较高,木质素含量较高。     

Biogeochemical facsimile of the organic matter quality and trophic status of a micro-tidal tropical estuary

Seasonal studies were carried out from 21 stations, comprising of three zones, of Cochin Estuary, to assess the organic matter quality and trophic status. The hydographical parameters showed significant seasonal variations and nutrients and chlorophylls were generally higher during the monsoon season. However, chemical contamination along with the seasonal limitations of light and nitrogen imposed restrictions on the primary production and as a result, mesotrophic conditions generally prevailed in the water column. The nutrient stoichometries and δ ¹³C values of surficial sediments indicated significant allochthonous contribution of organic matter. Irrespective of the higher content of total organic matter, the labile organic matter was very low. Dominance of carbohydrates over lipids and proteins indicated the lower nutritive aspect of the organic matter, and their aged and refractory nature. This, along with higher amount of phytodetritus and the low algal contribution to the biopolymeric carbon corroborated the dominance of allochthonous organic matter and the heterotrophic nature. The spatial and seasonal variations of labile organic components could effectively substantiate the observed shift in the productivity pattern. An alternative ratio, lipids to tannins and lignins, was proposed to ascertain the relative contribution of allochthonous organic matter in the estuary. This study confirmed the efficiency of an integrated biogeochemical approach to establish zones with distinct benthic trophic status associated with different degrees of natural and anthropogenic input. Nevertheless, our results also suggest that the biochemical composition alone could lead to erroneous conclusions in the case of regions that receive enormous amounts of anthropogenic inputs.     

Stable isotope analysis of carbon cycling in the Perdido estuary, Florida

Stable carbon isotope (δ¹³C) analysis was used in the Peridido Estuary, Florida U.S. to determine the predominant carbon source that supports the bacterial assemblage. Stable carbon isotope values were measured in the suspended particulate matter (SPM), dissolved organic and inorganic matter, and bacteria. Stable nitrogen isotope (δ¹⁵N) ratios were measured in SPM and nitrate to assist in understanding carbon cycling through the estuary. Analyses were conducted on samples from riverine, coastal, and anthropogenic sources and compared with samples from the bay. Stable isotope ratio analysis was coupled with estimates of mixing of riverine and coastal waters into the bay. Preliminary observation of the °¹³C data indicates that terrestrial organic matter is the primary carbon source that is assimilated by bacteria in the ecosystem. Stable isotope data from carbon and nitrogen pools in combination with analysis of estuarine current velocities indicates that primary production is an important factor in the carbon cycle. This study demonstrates the importance of stable isotope analysis of multiple carbon and nitrogen pols to assess sources and cycling of organic matter.     

The distribution and source of organic matter in reservoir sediments

The bottom sediments of two reservoirs, one with significant river sediment input and one without, were analyzed for organic matter content. Lake Texoma sediments average 1.0% organic carbon, of which 0.26% organic carbon is deposited by the river sediments of the Red and Washita River deltas. In Fort Gibson reservoir, where there is minimal river sediment input, the organic carbon averages 1.2% and is deposited with a strong correlation to water depth (+0.9). There is a significant difference between the C/N ratio of Lake Texoma sediments (11.5) and Fort Gibson sediments (9.6). The higher C/N ratio is suggested to be a result of the larger input of terrestrial plant debris (with a high original C/N ratio) by the rivers draining into Lake Texoma and the relatively high resistance of the lignin material in the plant debris to decomposition in the reservoir sediments.     

修水地区下寒武统富铀地层特征及其铀富集机制研究

文章以修水地区下寒武统王音铺组至观音堂组下部富铀黑色页岩地层钻孔样品（U含量为9.37×10-6~202×10-6） 为研 究对象,进行了细致的显微观察和分析,并对该区下寒武统地层中U含量与沉积环境因素（沉积盆地中的生物生产力、底 层水体的氧化还原状态、及盆地与广海间的流通性） 之间的关系进行了探讨。结果表明,这些钻孔样品显示明显的沉积成 岩特征,未发现明显热液叠加/淋积作用现象,说明本区下寒武统地层只经历了沉积成岩作用,而没有经历过明显的热液作 用或者淋积作用。研究地层大部分样品中的U含量与TOC含量呈正相关,王音铺组上部U含量最高（202×10-6） 的样品沉积 时的初级生物生产力也最高。经扫描电镜观察和电子探针分析,发现其中有机质中包裹着沥青铀矿,两者关系密切,推测 U与有机质很可能是一起沉积-成岩富集的;在缺氧硫化的强还原沉积环境下沉积的王音铺组地层的U含量,明显高于在 缺氧非硫化环境下沉积的观音堂组下部地层中的U含量,而且在强还原硫化环境下,沉积时盆地处于开放流通性程度较高 时期的样品,其U含量明显高于盆地处于开放程度较低时期的样品。综合这些观察和分析得出,早寒武世王音铺组上部地 层沉积时,高生物生产力所形成的有机质降解时大量耗氧,导致底层水沉积环境处于强还原硫化状态,同时,沉积盆地处 于适当的开放程度,与广海之间水流交换使盆地上层含U氧化水体得到补充,U最终在底层水体强还原硫化环境下沉淀于 沉积物中,可达到较高程度的富集乃至矿化的水平。     

Anthropogenic impacts recorded in the sediments of Lunawa, a small tropical estuary, Sri Lanka

The Lunawa Estuary has been selected as a model for studying the long-term diagnoss of tropical estuarine pollution and its impact on ecosystems. Surface and short-core sediments from the Lunawa Estuary were collected, and analyzed for total organic carbon (TOC), nitrogen, sulfur and hydrocarbon contents, hydrogen index and other related sediment properties. Water quality and surface sediment data indicate that the Lunawa Estuary is presently an anoxic water body. The upper part of the sediment cores, characterized by very high TOC values of more than 10%, and absence of bioturbation along with strong laminations indicate anoxic water since 1970 AD, determined by ¹⁴ C dating. However, before 1970 AD, lower TOC content and presence of bioturbation and homogenous sediments with animal traces suggest the presence of oxic bottom water and thus a much better physicochemical condition. The lower part of the cores may also suggest the influence of gradual global warming. Regular laminations in the upper portions of the cores probably resulted from monsoon pulses with material preserved under anoxic condition.     

Organic Matter Sources Supporting Lower Food Web Production in the Tidal Freshwater Portion of the York River Estuary, Virginia

The Mattaponi River is part of the York River estuary in Chesapeake Bay. Our objective was to identify the organic matter (OM) sources fueling the lower food web in the tidal freshwater and oligohaline portions of the Mattaponi using the stable isotopes of carbon (C) and nitrogen (N). Over 3 years (2002–2004), we measured zooplankton densities and C and N stable isotope ratios during the spring zooplankton bloom. The river was characterized by a May–June zooplankton bloom numerically dominated by the calanoid copepod Eurytemora affinis and cladocera Bosmina freyi. Cluster analysis of the stable isotope data identified four distinct signatures within the lower food web: freshwater riverine, brackish water, benthic, and terrestrial. The stable isotope signatures of pelagic zooplankton, including E. affinis and B. freyi, were consistent with reliance on a mix of autochthonous and allochthonous OM, including OM derived from vascular plants and humic-rich sediments, whereas macroinvertebrates consistently utilized allochthonous OM. Based on a dual-isotope mixing model, reliance on autochthonous OM by pelagic zooplankton ranged from 20% to 95% of production, declining exponentially with increasing river discharge. The results imply that discharge plays an important role in regulating the energy sources utilized by pelagic zooplankton in the upper estuary. We hypothesize that this is so because during high discharge, particulate organic C loading to the upper estuary increased and phytoplankton biomass decreased, thereby decreasing phytoplankton availability to the food web.     

长江口沉积物碳氮元素地球化学特征及有机质来源分析

根据对长江口水下三角洲上部(CJ16)和口门浅滩(CJ19)柱状样的粒度、总有机碳(TOC)、总氮(TN)和有机碳同位素(δ13C)以及长江口表层样TOC的测定,得出其粒度及碳氮元素特征,利用C/N和δ13C分析有机质来源及不同来源的贡献率。研究结果表明:(1)沉积物中有机碳含量在0.19%～1.17%之间,CJ16柱中有机碳含量比CJ19柱略高;总氮含量均比较少,且变化幅度小;C/N比值在5～17间变化;CJ16柱的δ13C值在24.70‰～22.86‰间变化,CJ19柱为24.88‰～22.37‰,且CJ19柱δ13C值在36 cm以上段较下段明显增大,推测可能与南汇边滩互花米草(C4植物)的引种有关;(2)长江口表层沉积物TOC的含量范围为0.17%～1.16%,平均值为0.52%;(3)粒度特征显示长江口主要以粉砂和粘土为主,砂含量较少,粒度与长江口TN、TOC含量有较好的相关性;(4)C/N和δ13C值的特征均显示该区有机质为陆源和海洋混合,利用C/N比值估算出来自陆源的有机碳比例在CJ16柱约为40%,而在CJ19柱中约为60%;根据δ13C值估算出CJ16柱陆源和海源两种有机质来源几乎是各占一半的比例,CJ19柱来自陆源的有机碳占总有机碳的60%,与用C/N比值法测得的结果较一致。上述结果显示长江口的不同空间位置碳氮元素分布特征不同,沉积记录受到粒度、河口区物源的影响,还受到陆源和海源不同有机质来源输入的影响。     

Fluxes of dissolved combined neutral sugars (polysaccharides) in the Delaware estuary

This project examined concentrations, composition and turnover neutral sugars in the Delaware estuary to gain insights into dissolved inorganic nitrogen (DIN) use by heterotrophic bacteria and into the lability and diagenetic state of dissolved organic material (DOM) during passage through the estuary. Dissolved free monosaccharides were not measurable (<5 nM) in the estuary whereas concentrations of dissolved combined neutral sugars (DCNS) were high, much higher than observed in oceanic waters. DCNS made up a similar fraction of dissolved organic carbon (DOC) as in the oceanic waters examined to date, and the monosaccharide composition of the DCNS pool was similar to that of oceanic waters. The composition did not vary substantially within the estuary or seasonally, but it did vary among three size fractions of the organic matter pool. Glucose was enriched in the low molecular weight fraction of DOC and in particulate material, whereas the high molecular weight DOC fraction was slightly depleted in glucose. Depletion experiments indicated that DCNS is not used extensively on the day time scale in the Delaware estuary, although freshly-produced polysaccharides may still be important carbon sources for heterotrophic bacteria. The very low concentrations of free monosaccharides in the Delaware estuary help to explain why DIN use by heterotrophic bacteria is relatively low in this estuary. Although DOC-DIN interactions in the Delaware apparently differ from oceanic waters, the portion of DOM traced by DCNS, which is thought to be the labile fraction, appears to be similar to that of oceanic DOM, suggesting that organic material in the estuary is degraded extensively before being exported to the coastal ocean.     

Understanding distribution and abundance of metals with space and time in estuarine mudflat sedimentary environment

Spatial and depth-wise distribution of sediment components, organic carbon and selected metals (Fe, Mn, Al, Ni, Cr, Co, Zn and Pb) is studied across upper and middle tidal flats from lower and middle estuarine regions of Kundalika Estuary, central west coast of India. Silt and clay form the major components in lower and middle estuary, respectively. Sand, silt, clay and organic carbon showed band-type distribution along the estuary. The sediment deposition over the years took place in varying hydrodynamic conditions in lower and middle estuarine regions. Upper flats of the lower estuary represent mud while middle flats of the lower estuary facilitated the deposition of sandy mud. Correlation results indicated the importance of clay and organic carbon in removal and trapping of metals at lower and middle estuary, respectively. Factor analysis indicated that the distribution of metals is largely controlled by Fe–Mn oxyhydroxides and organic carbon. The middle flats of the lower estuary showed an anthropogenic source for Ni, Cr and Co while middle flats of the middle estuary showed a mainly lithogenic source.     

Phosphorus distribution in sediments of the Delaware River estuary

In order to determine the primary factors related to the accumulation of phosphorus in estuarine sediments, a study of phosphorus fractions in sediments of the Delaware River Estuary was undertaken. A correlation matrix between the phosphorus fractions, determined by serial extraction, and 14 sediment variables was computed. Total phosphorus and total inorganic phosphorus in the sediment-phosphorus reservoir decreases with increasing salinity. This variation is correlated with decreasing iron oxyhydroxide content in the sediment. Neither clay content nor calcium carbonate content appear to be significantly correlated with variation in total inorganic phosphorus content in the fine-grained sediments of this estuary. Although calcium phosphate is concluded to be a major constituent of the sediment-phosphorus reservoir, there was no evidence found that it is authigenic in this environment.     

The lignin component of humic substances: Distribution among soil and sedimentary humic,fulvic, and base-insoluble fractions

Vanillyl, syringyl and cinnamyl phenols occur as CuO oxidation products of humic, fulvic and base-insoluble residual fractions from soils, peat and nearshore marine sediments. However, none of these lignin-derived phenols were released by CuO oxidation of deepsea sediment or its base-extractable organic fractions. Lignin analysis indicated that peat and coastal marine sediments contained significantly higher levels of recognizable vascular plant carbon (20–50%) than soils and offshore marine sediments (0–10%).Although accounting for less than 20% of the total sedimentary (bulk) lignin, lignin components of humic acid fractions compositionally and quantitatively resembled the corresponding bulk samples and baseinsoluble residues. Recognizable lignin, presumably present as intact phenylpropanoid units, accounted for up to 5% of the carbon in peat and coastal humic acids but less than 1% in soil humic acids. Fulvic acid fractions uniformly yielded less lignin-derived phenols in mixtures that were depleted in syringyl and cinnamyl phenols relative to the corresponding humic acid fractions.Within the vanillyl and syringyl families the relative distribution of acidic and aldehydic phenols is a sensitive measure of the degree of oxidative alteration of the lignin component The high acid/aldehyde ratios and the low phenol yields of soils and their humic fractions compared to peat and coastal sediments indicate extensive degradation of the lignin source material. Likewise, the progressively higher acid/aldehyde ratios and lower phenol yields along the sequence: plant tissues (plant debris)-humic acids-fulvic acids suggest that this pattern represents the diagenetic sequence for the aerobic degradation of lignin biopolymers.