N-alkane Distribution Patterns Research Articles

Consistency of plant-specific n-alkane patterns in plaggen ecosystems: A review

Plaggen soils, formed by various vegetational inputs during century-long plaggen (i.e. sod) application, comprise remarkably stable organic matter. Source identification could contribute to a better understanding of carbon stabilization mechanisms in soils and reconstruction of Holocene vegetation and land-use history. Cuticular-derived n-alkane distribution patterns as present in current vegetation are recognized as valuable tools to discriminate input sources, but an assessment of their consistency and variability is lacking to date. Therefore, this review synthesizes information on published n-alkane patterns of vegetation species and their various parts that contributed to plaggen soil formation (i.e. Calluna vulgaris, Betula pendula, Quercus robur, Pinus sylvestris, Lolium perenne, Deschampsia flexuosa, Molinia caerulea and Poa annua). This provided in addition valuable information on potential sources of systematic variation (e.g. geography/climate, environmental conditions, ontogeny and seasonality). Method of extraction/analysis showed no evident effects on n-alkanes. n-Alkanes showed predominantly distinct patterns for different plaggen vegetation species and parts in the range C17–36. Prominent n-alkanes C27, C29, C31 and C33 allowed clear distinction between input by shrubs, trees and grasses to plaggen soils. Nevertheless, systematic variability was indicated among n-alkane patterns. Unfortunately, the current limited data set of n-alkane patterns did not allow for exact quantification of the controls of variation. The need for more systematic studies and the setup of a reference data base for vegetation species is highlighted to (1) advance application of n-alkane patterns in source identification, (2) gain more insight into controls on, magnitude and timing of variations and (3) improve our knowledge concerning input sources, carbon dynamics and stabilization mechanisms in (plaggen) soils.

Red palaeosols development in response to the enhanced east asia summer monsoon since the mid-pleistocene in South China: Evidence derived from magnetic properties and molecular fossil records

Although Pleistocene red paleosols are widely distributed in South China, paleoenvironmental interpretation has proved difficult because of intense weathering. Here we combine data from molecular fossil and magnetic properties to reconstruct a record of changes in pedogenic intensity for red paleosols in Southeast China. Depth distribution pattern of magnetic properties indicates that lower (higher) χ but higher (lower) values of HIRM (hard isothermal remanent magnetization) and SIRM (saturation isothermal remanent magnetization)/χ has tight relationship with the intensity of pedogenesis, especially the occurrence of well-developed net-like veins, which is absolutely responsible for the presence of anti-ferromagnetic minerals at the cost of fine-grained SP (superparamagnetic)/SD (single domain) ferrimagnetic minerals. The carbon distribution pattern of n-alkanes, n-alkanols, and n-alkanoic acids reflects the predominant contributions of microorganisms to the organic matter during pedogenesis, which provide direct evidence for strong microbial activities in response to the extremely hot-humid condition while white coarse net-like veins occurrence. Our results demonstrate that the presence of the enhanced East Asia summer monsoon has played a key role in the oxide-dominated weathering regime, and pedogenesis, and microbial activities. Changes in molecular ratios and magnetic properties are used to show that red paleosols have undergone three stages of soil formation in striking response to the evolution of the East Asia summer monsoon: (1) the most effective since the Middle Pleistocene; (2) moderately effective since 270 ka or so; (3) least effective since the last glacial. Our research provides important evidence to understand how red paleosols espond to global change since the Middle Pleistocene.

Tectonic and climate control of oil shale deposition in the Upper Cretaceous Qingshankou Formation (Songliao Basin, NE China)

Oil shales were deposited in the Songliao Basin (NE China) during the Upper Cretaceous period, representing excellent hydrocarbon source rocks. High organic matter (OM) contents, a predominance of type-I kerogen, and a low maturity of OM in the oil shales are indicated by bulk geochemical parameters and biomarker data. A major contribution of aquatic organisms and minor inputs from terrigenous land plants to OM input are indicated by n-alkane distribution patterns, composition of steroids, and organic macerals. Strongly reducing bottom water conditions during the deposition of the oil shale sequences are indicated by low pristane/phytane ratios, high C14-aryl-isoprenoid contents, homohopane distribution patterns, and high V/Ni ratios. Enhanced salinity stratification with mesosaline and alkaline bottom waters during deposition of the oil shales are indicated by high gammacerane index values, low MTTC ratios, high β-carotene contents, low TOC/S ratios, and high Sr/Ba ratios. The stratified water column with anoxic conditions in the bottom water enhanced preservation of OM. Moderate input of detrital minerals during the deposition of the oil shale sequences is reflected by titanium concentrations. In this study, environmental conditions in the paleo-lake leading to OM accumulation in the sediments are related to sequence stratigraphy governed by climate and tectonics. The first Member of the Qingshankou Formation (K2qn1) in the Songliao Basin, containing the oil shale sequence, encompasses a third-order sequence that can be divided into three system tracts (transgressive system tract—TST, highstand system tract—HST, and regressive system tract—RST). Enrichment of OM changed from low values during TST-I to high-moderate values during TST-II/III and HST-I/II. Low OM enrichment occurs during RST-I and RST-II. Therefore, the highest enrichment of OM in the sediments is related to stages of mid-late TST and early HST.

Organofacies and paleoenvironment of the Oligocene Maikop series of Angeharan (eastern Azerbaijan)

The Maikop Formation, deposited in eastern Azerbaijan during Oligocene and Early Miocene times, contains prolific source rocks with primarily Type II organic matter. Paleontological analyses of dinoflagellate cysts revealed a Lower to Upper Oligocene age for the investigated succession near Angeharan. A major contribution of aquatic organisms (diatoms, green algae, dinoflagellates, chrysophyte algae) and minor inputs from macrophytes and land plants to organic matter accumulation is indicated by n-alkane distribution patterns, composition of steroids and δ13C of hydrocarbon biomarkers. Microbial communities included heterotrophic bacteria, cyanobacteria, chemoautotrophic bacteria, as well as green sulfur bacteria. Higher inputs of terrigenous organic matter occurred during deposition of the Upper Oligocene units of the Maikop Formation from Angeharan mountains. The terpenoid hydrocarbon composition argues for angiosperm dominated vegetation in the Shamakhy–Gobustan area.High primary bioproductivity resulted in a stratified water column and the accumulation of organic matter rich sediments in the Lower Oligocene units of the Maikop Formation. Organic carbon accumulation during this period occurred in a permanently (salinity-) stratified, mesohaline environment with free H2S in the water column. This is indicated by low pristane/phytane ratios of all sediments (varying from 0.37–0.69), lower methylated-(trimethyltridecyl)chromans ratio in the lower units and their higher contents of aryl isoprenoids and highly branched isoprenoid thiophenes. Subsequently, the depositional environment changed to normal marine conditions with oxygen deficient bottom water. The retreat of the chemocline towards the sediment–water interface and enhanced oxic respiration of OM during deposition of the Upper Oligocene Maikop sediments is proposed.Parallel depth trends in δ13C of total OM, n-alkanes, isoprenoids and steranes argue for changes in the regional carbon cycle, associated with the changing environmental conditions. Increased remineralisation of OM in a more oxygenated water column is suggested to result in low TOC and hydrocarbon contents, as well as 15N enriched total nitrogen of the Upper Oligocene units.

Facies evolution and stratigraphic correlation in the early Oligocene Tard Clay of Hungary as revealed by maceral, biomarker and stable isotope composition

Hydrocarbon source rocks (i.e. Tard Clay Formation), containing type-II organic matter, were deposited in the Hungarian Paleogene Basin during Lower Oligocene. A major contribution of aquatic organisms (green algae, dinoflagellates, Chrysophyte algae) and minor inputs from macrophytes and land plants to organic matter accumulation is indicated by n-alkane distribution patterns, composition of steroids, and δ13C of hydrocarbon biomarkers. Microbial communities included heterotrophic bacteria, cyanobacteria, chemoautotrophic bacteria, as well as green sulphur bacteria. The presence of methanotrophic bacteria is indicated by 13C-depleted hop-17(21)-ene. Higher inputs of terrestrial organic matter occurred during deposition of the lower and uppermost units of the Tard Clay Formation. The terpenoid hydrocarbon composition argues for angiosperm-dominated vegetation in the area of the Hungarian Paleogene Basin. Diterpenoid hydrocarbons, derived from the resins of conifers, are about 2–3‰ enriched in 13C compared to the angiosperm biomarkers.Environmental conditions changed from marine to brackish, accompanied by oxygen-depletion in the lower parts of the water column. Organic carbon accumulation during this period was a consequence of stagnant bottom water conditions in the Hungarian Paleogene Basin due to salinity stratification. This is indicated by low pristane/phytane ratios (varying from 0.27 to 1.44), enhanced ratios of dimethylated versus trimethylated MTTCs (0.14–0.59), and the presence of aryl isoprenoids (from 0.4 to 14.1 μg/g TOC). A major marine incursion is evidenced by stable isotope ratios of organic matter and carbonates. In the uppermost member of the Tard Clay, a transition from brackish towards normal marine conditions is proposed.Up to 3 anoxic cycles are recognized in the drill core sections, separated by minima in pristane/phytane ratios and maxima in the depth trends of di-/tri-methylated MTTCs and aryl isoprenoid concentrations. In combination with the position of maxima of δ13C of carbonate and organic matter and an abrupt decrease in perylene concentrations, the cycles can be used for intra-formational correlation of the Tard Clay.

Impact of Oil Field-Produced Water Discharges on Sediments: A Case Study of Sabkhat Boujemal, Sfax, Tunisia

Oil companies are considered to be a source of chronic pollution with continual discharge of wastewaters into the environment. Thus, the impact of petroleum contamination from French–Tunisian Oil Company on the endorheic basin Sabkhat Boujemal is assessed. This area is a continental depression that has no relation with the sea; instead this basin is just an evaporative system. The results show that aliphatic n-alkanes and polycyclic aromatic hydrocarbons (PAH) concentrations, measured on surficial (0–4 cm) sandy sediments, range from 705 to 4560 mg/kg −1 dry sediment and from 11 to 1124 mg Kg −1 dry sediment, respectively. The spatial distribution of these concentrations shows high levels in the vicinity of the oiled water discharge. The distribution pattern of n-alkanes with no odd or even dominance, high levels of unresolved complex mixture (UCM) (198.1–1500 μg/g−1 dry sediment), associated to the combination of different evaluation indices enhance this assessment. Indeed, levels close to 1 for both carbon preference index (CPI) and low molecular weight to high molecular weight ratios (≤C24:>C24) as well as values of n-alkanes/C16 <50 and pristane/phytane close to 1 suggests the presence of petroleum hydrocarbon inputs from the effluents rejected by the French Tunisian oil company in the Sabkhat. To elucidate sources of PAHs, three molecular indices (phenanthrene (Phen)/anthracene (Ant), fluranthene (Flu)/pyrene (Pyr), and Σmethyl phenanthrenes/phenanthrene) are used. As Ant, Flu, and alkylated PAH are respectively less thermodynamically stable than Phen, Pyr and unsubstituted PAH homologues, ratios of Phen/Ant <1, Flt/Pyr >10, and ΣMethyl Phen/Phen >2 indicate petrogenic origin of PAH. Conversely, ratios of Phen/Ant >1, Flt/Pyr <10, and ΣMethyl Phen/Phen <2 are characteristics of pyrogenic PAH. The results show intermediate values of PAH indices, which indicate a mixture of pyrogenic and petrogenic origins.

Is the maximum carbon number of long-chain n-alkanes an indicator of grassland or forest? Evidence from surface soils and modern plants

The molecular distribution of long-chain n-alkanes in 62 soil samples collected from diverse locations across eastern China was analyzed. The long-chain n-alkanes were mostly dominated by n-C29 or n-C31, regardless of the overlying vegetation type at each site. The results were compared with those summarized from the literature, covering more than 100 soil samples within China and more than 300 genera of modern plants distributed worldwide. There were similar n-alkane distribution patterns for most genera, with no clear differences among grasses, shrubs, and trees. The evidence from analyses of surface soils and modern plants indicates that the relationship between the molecular distribution of long-chain n-alkanes of surface soils and source vegetation is highly complex, and is influenced by many factors. Further, it is suggested that source vegetation types should not be simply inferred from distribution patterns of long-chain n-alkanes in sediments.

Climatic and environmental implications from n-alkanes in glacially eroded lake sediments in Tibetan Plateau: An example from Ximen Co

Gas chromatography-mass spectrometry was used to identify a series of n-alkanes in the sediments of a typical glacially eroded lake in the eastern Tibetan Plateau. By comparing the distribution patterns of n-alkanes in lake sediments, surface soils and cow manure, it was shown that n-C27-n-C33 alkanes in the soil ecosystem of Ximen Co are derived from vascular plant species and that the distribution pattern of n-C27-n-C33 alkanes remains unchanged during the feeding and digestion processes of herbivores. The relative percentage of C27, C29 and C31 n-alkanes decreased from the bottom to the top of the sediment core showing a trend of degradation of higher plants in the Ximen Co lake region during the formation of the 44 cm core. 210Pb dating, combined with pre-existing AMS 14C dating results showed that the depositional core reflects climatic and environmental variations since about 900 years before present. The n-alkane indexes (ACL27–33, P aq, P wax) are comparable with regional temperature variation, especially recording the Little Ice Age event (LIA). This study highlights that n-alkanes are valid proxies for paleo-climate and paleo-environment reconstruction, despite the same distribution patterns in n-alkane molecular fossils derived from a typical glacially eroded lake.

Optimisation of focused ultrasound extraction (FUSE) and microwave-assisted extraction (MAE) of hydrocarbons in geological chert samples

The analysis of hydrocarbons in chert rocks provides a worthwhile source of information regarding the geochemical features of a depositional setting. Since the typical analytical procedure requires long Soxhlet extractions and the use of large quantities of sample (30–50 g), in this work we have optimised the focused ultrasound extraction (FUSE) and the microwave-assisted extraction (MAE) to make available a less severe procedure. In both cases a full experimental design including solvent mixture composition (Dichloromethane/Hexane/Acetone) and process variables (sonication time and cycles, and extraction temperature and time) by means of D-optimal designs. In the extracted fractions hydrocarbons (C 16–C 40) were analysed by gas-chromatography-mass spectrometry. In the case of FUSE the process variables were the most sensitive variables and the optimum conditions were defined at 60:40 DCM/Hex mixture and a sonication time of 30 min and 9 cycles. In the case of MAE all the variables shown a significant effect on the extraction yield and the most adequate conditions (60:30:10 DCM/Hex/Ace mixture and an irradiation time of 15 min at 110 °C) were established from the analysis of the response surface. Both methods were systematically applied with different chert samples collected in Cucho (Trebiño County, Burgos, Spain) and we were able to assure quantitative extractions (>85%) in the first extraction. Additionally, from the distribution patterns of n-alkanes obtained in the different chert samples (nodular chert, laminar chert and massive-brechoid chert) collected in Cucho, we were able to distinguish different origins and diagenetic history.

Interfacial and Thermal Characterization of Asphaltenes Separated from Crude Oils Having Different Geological Origins

Three crude oils having different geological origins, namely, DK from Eocene (Sylhet limestone and Langpar), SL from Barail (Oligocene), and JN from Tipam (lower Miocene), were selected. Asphaltenes were separated and characterized. Fourier transform infrared (FTIR) spectroscopy showed the presence of polar groups. Interfacial tension studies of the asphaltenes between benzene–water, toluene–water, and xylene–water showed the lowest interfacial tension with SL asphaltenes in a toluene–water system. Thermogravimetric analysis of asphaltenes indicates greater thermal degradation for DK asphaltenes. Asphaltenes were pyrolyzed and the pyrolyzed products were analyzed by gas chromatography/mass spectrometry (GC/MS). Based on the distribution pattern of n-alkanes in pyrolyzed product of asphaltenes, crude oils, and kerogens, it was concluded that crude oil and asphaltenes originate from the same source and asphaltenes are the unconverted parts of kerogens.

Comparison of bulk and compound-specific δ 13C analyses and determination of carbon sources to salt marsh sediments using n-alkane distributions (Maine, USA)

Sources of sedimentary organic matter to a Morse River, Maine (USA) salt marsh over the last 3390 ± 60 RCYBP (Radiocarbon Years Before Present) are determined using distribution patterns of n-alkanes, bulk carbon isotopic analysis, and compound-specific carbon isotopic analysis. Marsh foraminiferal counts suggest a ubiquitous presence of high marsh and higher-high marsh deposits (dominated by Trochammina macrescens forma macrescens, Trochammina comprimata, and Trochammina inflata), implying deposition from ∼0.2 m to 0.5 m above mean high water. Distributions of n-alkanes show a primary contribution from higher plants, confirmed by an average chain length value of 27.5 for the core sediments, and carbon preference index values all >3. Many sample depths are dominated by the C 25 alkane. Salicornia depressa and Ruppia maritima have similar n-alkane distributions to many of the salt marsh sediments, and we suggest that one or both of these plants is either an important source to the biomass of the marsh through time, or that another unidentified higher plant source is contributing heavily to the sediment pool. Bacterial degradation or algal inputs to the marsh sediments appear to be minor. Compound-specific carbon isotopic analyses of the C 27 alkane are on average 7.2‰ depleted relative to bulk values, but the two records are strongly correlated ( R 2 = 0.89), suggesting that marsh plants dominate the bulk carbon isotopic signal. Our study underscores the importance of using caution when applying mixing models of plant species to salt marsh sediments, especially when relatively few plants are included in the model.

Sources, transport, and partitioning of organic matter at a highly dynamic continental margin

Continental shelves play a major role as transition zone during transport of multiply-sourced organic matter into the deep sea. In order to obtain a comprehensive understanding of the origin and fractionation processes of organic matter at the NW Iberian margin, 40 surface sediment samples were analyzed for a structurally diverse range of lipid biomarkers, lignin phenols, grain size distribution, organic carbon content (TOC), its stable carbon isotopic composition ( δ 13C TOC), and the organic carbon to nitrogen ratio (TOC/TN). The biomarker inventory reflected a heterogeneous mixture of organic matter from various marine and terrestrial sources. Soil- and vascular plant-derived continental organic matter, indicated by lignin phenols and plant-derived triterpenoids, was primarily associated with the silt fraction and transported by river run-off. The spatial distribution patterns of higher plant-derived waxes, long-chain n-alkanes, n-alcohols, and n-fatty acids suggested distinct different transport mechanisms and/or sources. The branched tetraether index, a molecular proxy expressing the relative abundance of branched dialkyl tetraethers vs. crenarchaeol and considered to signal soil-derived organic matter, was not as sensitive as the other molecular indicators in detecting continental organic matter. Hydrodynamic sorting processes on the shelf resulted in a separation of different types of terrestrial organic matter; grass and leaf fragments and soil organic matter were preferentially transported offshore and deposited in areas of lower hydrodynamic energy. Algal lipid biomarker distributions indicated a complex community of marine plankton contributing to organic matter. Spatial and seasonal patterns of phytoplankton growth primarily controlled the distribution of algal organic matter components. The interplay of all of these processes controls production, distribution, and deposition of organic matter and results in three distinct provinces at the Galicia–Minho shelf: (I) fresh marine organic matter dominated the inner shelf region; (II) high inputs of terrestrial organic matter and high TOC content characterized the mid-shelf deposited mudbelt; (III) lower concentrations of relatively degraded organic matter with increased proportions of refractory terrestrial components dominated the outer shelf and continental slope.

Distribution patterns and stable carbon isotopic composition of alkanes and alkan-1-ols from plant waxes of African rain forest and savanna C3 species

Leaf wax components of terrestrial plants are an important source of biomass in the geological records of soils, lakes and marine sediments. Relevant to the emerging use of plant wax derived biomarkers as proxies for past vegetation composition this study provides key data for C3 plants of tropical and subtropical Africa. We present analytical results for 45 savanna species and 24 rain forest plants sampled in their natural habitats. Contents and distribution patterns of long chain n-alkanes (n-C25 to n-C35) and n-alkan-1-ols (n-C24 to n-C34) as well as bulk and molecular carbon isotopic data are presented. The variations of the analysed parameters among different growth forms (herb, shrub, liana and tree) are small within the vegetation zones, whereas characteristic differences occur between the signatures of rain forest and savanna plants. Therefore, we provide averaged histogram representations for rain forest and savanna C3 plants.The findings were compared to previously published data of typical C4 grass waxes of tropical and subtropical Africa. Generally, trends to longer n-alkane chains and less negative carbon isotopic values are evident from rain forest over C3 savanna to C4 vegetation. For n-alkanols of rain forest plants the maximum of the averaged distribution pattern is between those of C3 savanna plants and C4 grasses. The averaged presentations for tropical and subtropical vegetation and their characteristics may constitute useful biomarker proxies for studies analysing the expansion and contraction of African vegetation zones.

Data handling of complex GC–MS chromatograms: characterization of n-alkane distribution as chemical marker in organic input source identification

The paper describes a signal method for processing GC-MS signals to extract usable information hidden in the chromatogram thus reducing the labour and time required to handle the data and increasing the quality and objectivity of the results. The method is focused on two relevant parameters for identification and characterization of the n-alkane series present in complex samples (in particular the C(14)-C(33) terms): the number of n-alkanes, n(max), and the Carbon Preference Index (CPI) describing the odd/even carbon-number predominance. This is a key diagnostic parameter to determine the biogenic and anthropogenic nature of n-alkane sources, useful as chemical markers in source identification and differentiation. The method is a further extension of the approach based on the AutoCovariance Function (ACVF(tot)): new mathematical equations have been derived and a new computation algorithm implemented to extract information on the n-alkane series--n(max) and CPI--directly from the EACVF(tot) computed on the acquired chromatographic signal. The procedure was validated on simulated chromatograms where the distribution of the terms of the series describing experimental GC signals was known: the obtained results prove that the parameters n(max) and CPI of the homologous series can be estimated with good accuracy and precision. The method applicability was tested on experimental chromatograms of real samples: gasoils and plant extracts were studied to identify n-alkane distribution patterns characteristic of petrogenic and natural samples.

Thermal degradation of rye and maize straw: Lipid pattern changes as a function of temperature

Future climatic conditions may coincide with an increased potential for wildfires in grassland and forest ecosystems, whereby charred biomass would be incorporated into soils. Molecular changes in biomass upon charring have been frequently analysed with a focus on black carbon. Aliphatic and aromatic hydrocarbons, known to be liberated during incomplete combustion of biomass have been preferentially analysed in soot particles, whereas determinations of these compounds in charred biomass residues are scarce. We discuss the influence of increasing charring temperature on the aliphatic and aromatic hydrocarbon composition of crop grass combustion residues. Straw from rye, representing C3 grasses and maize, representing C4 grasses, was charred in the presence of limited oxygen at 300, 400 and 500°C. Typical n-alkane distribution patterns with a strong predominance of long chain odd-numbered n-alkanes maximising at C31 were observed in raw straw. Upon combustion at 300°C aliphatic hydrocarbons in char were dominated by sterenes, whereas at 400°C sterenes disappeared and medium chain length n-alkanes, maximising around n-C20, with a balanced odd/even distribution were present. At a charring temperature of 500°C n-alkane chain length shifted to short chain homologues, maximising at C18 with a pronounced predominance of even homologues. Even numbered, short chain n-alkanes in soils may thus serve as a marker for residues of charred biomass. Aromatic hydrocarbons indicate an onset of aromatization of biomass already at 300°C, followed by severe aromatization upon incomplete combustion at 400–500°C. The diagnostic composition of aliphatic and aromatic hydrocarbons from charred biomass affords potential for identifying residues from burned vegetation in recent and fossil soils and sediments.

Petroleum Hydrocarbon Contamination in Surface Sediments of Beiluohe Basins, China

Twenty-two surface sediment samples were collected from Beiluohe River, China, in 2005. Saturated hydrocarbons analysis was carried out on different river sediments in order to detect possible contaminations by petroleum development. Total concentrations of hydrocarbons in the sediments ranged from 6.4-147.3 microg g(-1) (dry wt) with an average of 76.8 microg g(-1), revealing relatively low to medium contamination in studied areas in spite of oil development for many years. The THC levels in the mainstream of Beiluohe River were relatively low. Sediment samples with higher total hydrocarbon concentrations were from the sites related to the petroleum activities or urban discharges. Gas chromatographic distribution patterns of n-alkanes are characteristic of petroleum in most samples. They show a strong unresolved complex mixture (UCM) with a small predominance of odd on even numbered n-alkanes. On the other hand, pentacyclic triterpanes and steranes occurred in all analyzed sediments and displayed similar signatures that are characteristic of mature organic matter contribution from oil contaminations. Hydrocarbons of terrestrial origin were also detected in the samples. However, contribution from plantwax hydrocarbons is overshadowed in samples by hydrocarbons of petroleum origin. This is obvious by the presence of the high relative abundance of UCM, and the identification of mature hopane and sterane in samples.

Characterization and source identification of polycyclic aromatic hydrocarbons (PAHs) in river bank soils

Elevated PAH concentrations were detected in bank soils along the Mosel and Saar Rivers in Germany. Information on the identification of PAH sources in this area however remains unclear. This study was able to characterize the PAH sources by application of several approaches, including consideration of the distribution patterns of 45 PAHs (including 16 EPA PAHs and some alkyl PAHs), specific PAH ratios, distribution patterns of n-alkanes and principal component analysis (PCA). In addition, the efficiency of the tested approaches was assessed. The results from the application of the various source identification methods showed that pyrogenic PAHs dominate soil samples collected upstream of the confluence of the Mosel and Saar Rivers, and petrogenic and pyrogenic PAHs dominate samples downstream of the confluence. Based on the analysis of reference materials and organic petrography, the petrogenic input was found to be dominated by coal particles. More detailed information on the petrogenic sources was provided by the n-alkane analyses. The current study concludes that to accurately determine the origin of PAHs, several identification methods must be applied.

Molecular indicators of palaeosalinity and depositional environment of small scale basins within carbonate platforms: The Late Triassic Hauptdolomite Wiestalstausee section near Hallein (Northern Calcareous Alps, Austria)

Microfacies and biomarker analyses are used to determine the environmental conditions during deposition of marly dolomicrites from the Hauptdolomite Wiestalstausee section near Hallein (Salzburg, Austria), part of the Late Triassic Hauptdolomite/Dachstein carbonate platform of the Northern Calcareous Alps. Phytoplankton and photosynthetic bacteria are considered to be the major primary producers of the organic matter in these immature (∼0.5% equivalent vitrinite reflectance), carbonate-rich rocks. Contributions from vascular plants are suggested from the n-alkane distribution pattern and high content of C 29 steranes. Enhanced microbial activity in the depositional environment is proposed on the basis of the hopanoid content. The occurrence of aryl isoprenoids, probably derived from carotenoids of the photosynthetic green sulfur bacteria ( Chlorobiaceae) indicates the presence of free H 2S in the bottom water. Mesohaline conditions in the upper part of the water column are deduced from the presence of dimethylated and trimethylated 2-methyl-2-(tridecylchromans) (MTTCs). Co-variation in the distribution of MTTCs and pristane/phytane ratio and the concentration of a C 16 aryl isoprenoid argue for photic zone anoxia due to salinity stratification. The biomarker composition points to a high productivity marine environment with limited water exchange and a stratified water column confirmed by microfacies analysis. A small scale basin formed within the restricted inner lagoonal area of the Hauptdolomite/Dachstein carbonate platform through erosion by currents, followed by a sea level rise is considered the most appropriate depositional environment of the dolomicrites of the Wiestalstausee section.

A Preliminary Study of N-alkanes in a Sedimentary Core from Chaohu Lake

对巢湖湖心沉积物柱样样品的正构烷烃和有机碳进行了分析.利用正构烷烃碳数分布类型、L/H、OEP指标和有机碳数据, 对该区近110年来正构烷烃的来源进行初步探讨.研究结果表明:21-25cm和16-20cm处正构烷烃以高等植物和低等生物输入并重;11-15cm即1952-1967年处具有外源性石油污染;从10cm开始, 正构烷烃以细菌、藻类为代表的低等生物输人为主;尤其是1-5cm样品正构烷烃和TOC含量明显高值, 表明该时期湖泊富营养化加剧.;The core sample was collected in Chaohu Lake in December 2001. The sediment layers were dated by ²¹⁰Pb. The results show that the sediment core represents 110 years of depositional time. Organic compounds were extracted from sediments using Soxhlet extraction by dichloromethane and methane. The n-alkanes were analyzed by chromatography/mass spectrometry. Distribution patterns of n-alkanes were presented. The sources of n-alkanes were discussed. The results show that from the depth 21 to 25cm and 16 to 20cm n-alkanes was attributed to the mixture of terrestrial plants and aquatic algae; from the depth 11 to 15cm, with sedimentary time of 1952-1967, the sample was contaminated by petroleum hydrocarbon; from the depth 10cm to surface, the source of algae and bacterium dominated n-alkanes, especially the top 5cm sample with high concentration of n-alkanes and TOC, which meant that the nutrient level especially eutrophication was increased in Caohu lake during this stage.

Organic geochemistry of the Lower Miocene Oberdorf lignite (Styrian Basin, Austria): its relation to petrography, palynology and the palaeoenvironment

In the Oberdorf trough at the northwestern margin of the Styrian Basin (Austria), an up to 36-m thick Lower Miocene (Ottnangian) lignite seam occurs within the fluvial Köflach–Voitsberg Formation. Previous results indicate that the lignite originated in a topogenous mire within a wet-forest swamp palaeoenvironment. Differences in soluble organic matter (SOM) yield of borehole samples from the lignite seam are related to free lipids present in plant waxes or resins and the presence of thermally labile polymers indicated by the contents of liptinite macerals (i.e., resinite, suberinite, and liptodetrinite). The n-alkane distribution patterns are dominated by high-molecular weight lipids with marked odd over even predominance, originating from plant waxes. A contribution of algae to the even numbered short-chain lipids, observed in considerable amounts in the footwall sediments is proposed. Terpenoid biomarkers characteristic for conifers and angiosperms were detected, consistent with palynomorphic spectra which are dominated by forest swamp pollen (Taxodiaceae–Cupressaceae) and pollen from plants living in a mixed mesophytic forest. Excellent relationships between higher plant biomarker composition and palynologic data indicate that the organic geochemical results reflect the varying inputs of coniferales vs. angiosperms. The data further imply that cuparene may be used for taxonomical differentiation of coniferales families. Organic geochemical data provide evidence that the content of land plant-derived biomarkers is controlled by the input of resin-rich conifers. Concentrations of hopanoids, dominated by hop-17(21)-ene, generally increase towards the top of the lignite, a section characterised by high extents of aromatisation of triterpenoid biomarkers. The results suggest that the aromatisation of angiosperm-derived biomarkers may be governed by the activity of anaerobic rather than by aerobic bacteria. However, changes in the depositional environment and palynologic facies during peat formation probably influenced the origin and fate of angiosperm-derived triterpenoids. The results indicate how biomarker composition may contribute to the evaluation of environmental changes. Cross-correlations of organic geochemical parameters with palynological data and petrography-based facies indicators will provide further insights in the peat-forming vegetation and biogeochemical activities in the mire.