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1.
Molecular stratigraphic analyses using gas chromatograph-mass spectrometry have been performed in the upper section (S0, L1, S1) of the Yuanbo loess-paleosol sequences in northwest China, with a record extending from the last interglaciation through the present interglaciation. The CPI (Carbon Preference Index) values of both n-alkanols and n-alkan-2-ones display variations between loess deposits and paleosols, showing a correlation with the magnetic susceptibility record, an indicator of the East Asian summer monsoon. The observed variations in the indexes in relation to changes in lithology/paleoclimate are proposed to result from microbial degradation of higher plant lipids in the paleosols. The CPI values of n-alkanes, n-alkanols, and n-alkan-2-ones are negatively correlated with δ13C of bulk organic matter. The correlations suggest that the observed glacial-interglacial variations of δ13C data in the loess stratigraphy reflect the relative importance of the contribution of paleovegetation compared with microorganisms (including both the degradation and the addition of organic matter) and allochthonous loess/soil parent materials. It is thus necessary to evaluate the contributions of the latter two before the paleovegetation can be reconstructed based on the δ13C analysis of bulk organic matter in some loess-paleosol sequences of the Chinese Loess Plateau.  相似文献   

2.
Peats in a sediment core from Ruoergai bog, which has a cold and moist plateau climate with major source input from herbaceous plants, have been studied by GC–MS in order to understand the composition and diagenetic processes of lipids in this depositional environment. Long chain components (C21–C35) predominate in the n-alkanes, n-alk-1-enes, n-fatty acids, n-alkan-2-ones and n-alkanols with a maximum of C31, C27, C22 or C24, C23 or C25 and C22, respectively. A herbaceous origin for these long chain compounds is suggested, and this is supported by their stable carbon isotopic compositions. Diterpenoid hydrocarbons with abietane, pimarane and kaurane skeletons, some of which have not been reported often in modern sediments, are prominent and are derived from higher plants. Several triterpenoid ketones and alcohols with oleanane or lupane skeletons, and a series of des-A-triterpenoid hydrocarbons which have not been reported often in modern sediments are also present, and are assigned to a higher plant source. Hopanoids, including their alkanes, alkenes, ketones, alcohols and esters, are abundant and of bacterial origin. Steroid ketones and alkanols are dominated by C29 homologues. C28 and C29 steroids are derived mainly from higher plants, whereas the C27 component is assigned to a microbial source. The presence of short-chain n-alkanes with no odd-even carbon predominance, bacterially derived fatty acids (C14, C15, iso- and unsaturated acids), n-alkan-2-ones, des-A-triterpenoid hydrocarbons, hopanoids and some steroid ketones indicate that intense microbial reworking of the organic matter has taken place in this depositional environment. The chemical and biochemical conversions of some cyclic alkenes to alkanes, such as tricyclic diterpenoids, tetracyclic terpenoids and steroid ketones, are also evident with depth. The dominance of C20 components in the diterpenoid hydrocarbons may reflect an oxidizing or reducing depositional condition.  相似文献   

3.
Previous studies on lipid biomarkers preserved in Chinese stalagmites have indicated that ratios of low‐molecular‐weight (LMW) to high‐molecular‐weight (HMW) n‐alkanes, n‐alkan‐2‐ones, n‐alkanols and n‐alkanoic acids can be used as an index of vegetation versus microbial organic matter input to the system and, by extension, a marker of climatic changes, with increases in the proportion of LMW compounds coinciding with colder periods. Here we test whether this hypothesis is equally applicable to a different geographical region (north‐west Scotland), by examining a stalagmite record of the past 200 years, and a wider range of lipid markers. We also test the applicability of other lipid proxies in this context, including the use of n‐alkane ratios, to interpret vegetation changes, and unsaturated alkanoic acid ratios as climatic indicators. The results show that lipid proxies preserved in stalagmites, and especially those related to vegetation, are potentially extremely useful in palaeoenvironmental research. Of particular value is the use of C27/C31 n‐alkane ratios as a proxy for vegetation change, clearly indicating variations between herbaceous and arboreal cover. This proxy has now been successfully applied to samples from diverse environments, and can be considered sufficiently robust to be of use in analysing future stalagmite records. It will be of particular value in areas where reliable pollen records are not available, as is often the case with deeper cave deposits. However, the division between LMW and HMW aliphatic compounds is not a clear‐cut case of microbial versus plant activity, with the changes in LMW compounds relating more closely to those in their HMW analogues than in specific bacterial biomarkers. The use of unsaturated alkanoic acid ratios here gives conflicting results, with the observed variation through time depending on the isomer measured. The discrepancies between the findings of this study and previous work are likely to be due to the varying controls on the lipids (original organic matter input, and compound degradation), which in turn will be affected by whether the main climatic limiting factor on the soil is temperature or precipitation. This suggests that lipid proxies preserved in stalagmites must be interpreted with care, particularly in the case of bacterial compounds which may be derived from within the cave or from the soil. However, many of these issues can be resolved by the use of multi‐proxy studies. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

4.
Lipid biomarkers from a peat plateau profile from the Northeast European Russian Arctic were analyzed. The peat originated as a wet fen ca. 9 ka BP and developed into a peat bog after the onset of permafrost ca. 2.5 ka BP. The distributions and abundances of n-alkanols, n-alkanoic acids, n-alkanes, n-alkan-2-ones and sterols were determined to study the effect of degradation on their paleoclimate proxy information. Plant macrofossil analysis was also used in combination with the lipid distributions. The n-alkanol and n-alkanoic acid distributions in the upper part of the sequence generally correspond to compositions expected from plant macrofossil assemblages. Their carbon preference index (CPI) values increase with depth and age, whereas those of the n-alkanes decrease. The different CPI patterns suggest that n-alkanoic acids and n-alkanols deeper in the sequence may be produced during humification through alteration of other lipids. Excursions in the n-alkanoic acid content also suggest an important contribution of invasive roots to the lipid biomarker composition. The CPIs associated with these compounds show that under permafrost conditions organic material from Sphagnum is better preserved than material from vascular plants. Increasing stanol/stenol ratio values and decreasing n-alkane CPI values indicate progressive degradation of organic matter (OM) with depth. The n-alkan-2-one/n-alkane and n-alkan-2-one/n-alkanoic acid ratios were shown to be useful proxies that can reflect the degree of OM preservation and suggest that both microbial oxidation of n-alkanes and decarboxylation of n-alkanoic acids produce n-alkan-2-ones in this peat sequence.  相似文献   

5.
Studies on long-chain n-alkan-2-ones from lake sediments remain sparse. In this study, we present an n-alkan-2-one record from Qionghai Lake, southwest China, to assess the paleoclimate significance of variations in their compositions. A homologous series of n-alkan-2-ones ranging from C21 to C35 were identified, with maximum concentrations of the C29 or C31 chain lengths and a strong odd-over-even predominance. This type of n-alkan-2-one is considered to derive mainly from microbial oxidation of the corresponding n-alkanes, and partial inputs from plants. The n-alkan-2-one-derived average chain length (ACL) and carbon preference index (CPI) values changed significantly over the past 28k cal a bp , consistent with the sediment grain size and n-alkane proxies from the same core. Generally, the high CPI27-33-ket and low ACL27-33-ket values indicated cold and dry climates such as for the Last Glacial Maximum (23.2–19.7k cal a bp ), Heinrich 1 event (17.6–15.6k cal a bp ) and Younger Dryas (12.8–11.6k cal a bp ), but low CPI27-33-ket and high ACL27-33-ket values denoted a warm and humid Holocene Climatic Optimum (7.0–4.3k cal a bp ). Therefore, n-alkan-2-ones have great paleoclimatic potential and can be applied together with other biomarkers to reconstruct a reliable paleoclimate record in lake sediments.  相似文献   

6.
The most widely accepted origin of n-alkan-2-ones in peats is the microbial oxidation of the related n-alkanes and/or oxidative decarboxylation of fatty acids derived from plant input. The distributions of n-alkanes and n-alkan-2-ones in 48 samples from the Roñanzas 6000 cal. yr BP peat bog profile (N Spain) do not justify a single source. The n-alkan-2-ones typically dominate the n-alkanes, maximizing at C19 or C25/C27, whereas the n-alkanes maximized either at C23 or at C31/C33. The averaged δ13C values of the n-alkanes ranged from −32.3‰ to −33.1‰, but those of the n-alkan-2-ones were consistently higher (−29.2‰ to −29.9‰), suggesting a different, probably bacterial, source for the ketones.  相似文献   

7.
In response to the lack of studies focussing on the residence time of molecular biomarkers in soils, the lipid content of three soil profiles from the French Massif Central with different land use history were examined. The free neutral lipid content of two reference soil profiles developed under grassland and forest vegetation, and of a former grassland soil converted to forest about 60 years ago, was analysed using gas chromatography–mass spectrometry (GC–MS). Wax esters as well as the ratio of major homologues of n-alkanes and n-alkan-2-ones could be used to characterise the overlying vegetation in the reference forest and grassland soil profiles, but failed to distinguish the respective grassland and forest contributions to the profile of the soil that had changed use. For n-alkanes and n-alkan-2-ones, the failure might be attributed either to mixing of the molecular patterns inherited from the former and current plant cover, whereas for compounds such as wax esters simple degradation is likely to be involved. Conversely, iso- and anteiso-C15:0 fatty acid methyl esters (FAMEs; of bacterial origin), steroids (tracing cattle faecal contamination), tricyclic diterpenoids and their oxygenated derivatives, as well as methoxyserratenes (inherited from Pinaceae) and triterpenyl acetates (specific to the Asteraceae), proved to be effective in distinguishing current land use for the reference soil profiles and for the converted soil. The persistence of these compounds in the changed use soil allowed us to estimate their residence time in soil.  相似文献   

8.
Surface sediments from the subtropical Pearl River estuary and adjacent South China Sea were investigated by molecular organic geochemical methods to determine the composition, distribution and origin of extractable lipids (n-alkanes, n-alkanols and sterols). The absolute and organic C normalized concentrations of total alkane, n-alkanol, and sterol ranged from 0.16 to 2.67 μg g−1 and 0.9 to 12.3 μg g−1 OC, 24.4 to 427.3 ng g−1 and 63.2 to 1966.7 ng g−1 OC, and 9.0 to 493.5 ng g−1 and 58.4 to 1042.4 ng g−1 OC, respectively. The spatial distributions of these biomarkers indicated that terrestrial-derived molecular biomarkers such as long-chain n-alkanes, n-alkanols and plant-derived sterols were higher at the river mouth and along the coastline, suggesting that a higher proportion of terrestrial particulate organic matter was deposited there. Relatively lower amounts of marine-derived biomarkers such as short-chain n-alkanes, algal sterols at the river mouth reflected the lower primary productivity due to high turbidity. The spatial patterns of these biomarkers were partially related to the estuarine processes and conditions, evidencing an increased terrestrial signal from the Pearl River mouth to the inner estuary, and enhanced marine conditions further offshore.  相似文献   

9.
This study provides a reconstruction of the environmental evolution since 128 ka recorded by the lipid biomarkers of the C15–C35 n-alkanes, the C13–C33 n-alkan-2-ones and the C12–C30 n-alkanols isolated from the Tawan loess section, Northwest China. Variations in paleoenvironment are reconstructed from the values of the carbon preference index (CPI), the average chain length (ACL), the L/H (ratio of lower-molecular-weight to higher-molecular-weight homologues), the n-alkane C27/C31 ratios, and the n-alkan-2-one C27/C31 ratio. These parameters indicate the dominance of grasses over the west Chinese Loess Plateau (CLP) during the late Pleistocene. Lower values of the CPI and the ACL values, respectively, indicate stronger microbial reworking of organic matter and changes in plant species, which are both indicative of a warmer-wetter environment. Furthermore, the fluctuations of environment recorded in the Tawan section exhibit ten phases that show obvious cycles between warm periods and cold intervals. This study reveals that changes in the biomarker proxies agree well with changes in the magnetic susceptibility and grain size, and it indicates a huge potential for paleoenvironmental reconstructions by using the n-alkan-2-one and n-alkanol proxies.  相似文献   

10.
The δ13C values of higher plant wax C27–33 n-alkanes were determined in three, time-equivalent Pliocene (2.943 Ma) sapropels and homogeneous calcareous ooze from three different sites forming an east-west transect in the eastern Mediterranean Basin in order to study the composition of the vegetation on the continents surrounding the Mediterranean Sea. A two-end member mixing model transformed the measured δ13C values into the contribution of C4 plants to the terrestrial vegetation. These calculations indicated a high C4 plant contribution (i.e. 40–50%) in the periods just before and just after sapropel formation. During sapropel deposition the C4 plant contribution increased by up to 20% at all sites. This is interpreted to record the increased overall plant coverage of the Mediterranean borderlands resulting from the change in formerly barren desert areas into C4 grass-dominated savannahs as a response to the wetter climate during sapropel deposition. Enhanced accumulation rates (ARs) of long-chain n-alkanes (C27–33) and n-alkan-1-ols (C26–30) towards the middle of the sapropel in concert with a decrease in the Ti/Al ratio confirm an increased delivery of terrigenous organic matter at all sites. These biomarkers were probably predominantly fluvially transported to the Mediterranean Sea, not only by the Nile but by fossil wadi river systems on the northern African continent.  相似文献   

11.
《Applied Geochemistry》2005,20(3):553-568
Seven coal and carbonaceous mudstone samples were collected from outcropping Jurassic coal beds, on the margin of the Dingxi Basin, Northwestern China. The n-alkane distributions in all of the samples are characterised by high concentrations of the C19–C29 homologues, and very much lower amounts outside of this range. C23 or C24 are usually the most abundant n-alkanes. Straight chain n-alkanes from C23 to C29 show moderate odd-to-even C number predominances (CPI range: 1.26–2.70). Long-chain acyclic n-alkan-2-ones, n-alkan-3-ones and n-alkan-4-ones ranging from C15 to C33 with moderate odd-to-even C number predominances, were detected together with one isoprenoid methyl ketone (6,10,14-trimethylpentadecan-2-one) in all of the samples. The C number distributions of the three series of alkanones show a similar distribution to that of the n-alkanes, but the correspondence is not sufficient to substantiate a product–precursor relationship. It can be concluded that the n-alkan-2-ones are a mixture of the products of microbially-mediated β-oxidation of corresponding n-alkanes in the sediments and from the microbial oxidation of higher plant-derived n-alkanes prior to incorporation in the sediments. The n-alkan-3-ones and n-alkan-4-ones were formed from microbially mediated oxidation of the corresponding n-alkanes in the γ and δ positions, respectively. Generation of the ketones from higher plant n-fatty alcohols and n-alkanoic acids could be a possible way to form some of the ketones observed, but it can only play a minor role in the samples analysed.  相似文献   

12.
The relationship between the lipid composition of organisms in the water column of an eutrophic lake and the lipid composition of underlying sediments, previously examined for n-alkanols and steroids, is now reported for hydrocarbons, ketones and carboxylic acids.The n-C7 alkane and alkenoic acids from two primary sources are rapidly metabolized in the water column and surficial sediment. Bacterial biomarkers, including hopenes and fatty acids, were detected in the photosynthetic bacterial layer occurring just above the sediment-water interface.Within the sediment the apparent conversion of free n-alkanes, alkan-2-ones and ω-hydroxy acids to the corresponding bound form is noted; microbiological oxidation of n-alkanes to alkan-2-ones is supported by the detection of the intermediate alkan-2-ols with a distribution similar to that of the ketones. The geochemistry of sediment deposited c. 1900, prior to biological study of the site, was interpreted from stable biomarkers and the diagenetic changes recognised in the study of contemporary deposition. A qualitative difference in algal input to the older sediment is inferred from the low Δ7-sterol content and presence of 2,6,10-trimethyl-7-(3-methylbutyl)-dodecane. However, there was still significant dinoflagellate input, as indicated by the presence of 4α-methylsterols. A difference in higher-plant input to the older sediment, indicated from the n-alkane, alkene and triterpenoid ketone distributions, is consistent with the recent development of tree cover.  相似文献   

13.
Two sediment cores of up to 550 cm length from an intertidal flat of the German Wadden Sea near the island of Spiekeroog were investigated for the quantity and composition of fossil organic matter (OM). The lowermost parts of the cores are dominated by grey mud of a salt marsh facies containing mainly terrestrial OM estimated to account for 60–75% of the total OM, based on δ13C values and the ratio of short to long chain n-alkanols. The terrigenous origin of the dominant fraction is indicated, among others, by high proportions of C29 sterols and long chain n-alkanes typical of plant waxes. Coarse shell beds overlying the grey mud at 2–2.5 m depth represent a flooding and erosion event possibly related to heavy storm floods in the Middle Ages. Within the intertidal sand-dominated sediments in the upper parts of the cores total organic carbon (TOC) contents are generally low, ranging from 0.1% to 0.5%, and correlate well with the amount of mud fraction (r2 0.90). At the surface, marine OM has not undergone intense diagenetic alteration and so is the dominant fraction. Eroded peat particles are common throughout most of the sequence and values of the Phragmites peat indicator (PPI) > 5 indicate an origin from reed peat due to a high relative abundance of the n-C24 alkane. Changes in the composition of microbial communities over the depth interval investigated are documented by varying compositions of unsaturated fatty acids with 16 and 18 carbons. Eicosapentaenoic acid (EPA) was detected along the entire cores and indicates the presence of EPA-producing bacterial strains.  相似文献   

14.
Most research on long chain methyl ketones has focused on their origins and distributions. Their application in paleoclimate studies is less common than that of other n-alkyl lipids. The goal of this research was to explore this potential by studying n-alkan-2-ones from the Hani peat sequence in northeastern China. They were identified using gas chromatography-mass spectrometry (GC-MS) and showed a distribution ranging from C19 to C31 with a strong odd/even predominance. This type of distribution is considered to derive from Sphagum and microbial oxidation of n-alkanes. Comparison with climate sensitive indicators and macrofossil analysis shows that microbial oxidation of n-alkanes derived from higher plants was enhanced during the warm early Holocene period. This led us to develop three n-alkan-2-one proxies - C27/ΣC23-31 (C27/HMW-KET), carbon preference index (CPIH-KET) and average chain length (ACL(27-31)-KET) - as possible indicators of paleoclimate in the peat-forming environment. These proxies, in combination with C27n-alkane δD values and peat cellulose δ18O records, might allow examination of paleo-ecosystem behavior during climatic evolution in northeastern China over the past 16,000 yr.  相似文献   

15.
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.  相似文献   

16.
A hundred-year stalagmite lipid biomarker record from Mechara, southeastern Ethiopia, is presented. The record has been recovered at a 10-yr temporal resolution, marking the first time this has been achieved in stalagmite biomarker work and providing the first opportunity to investigate the relationship between stalagmite lipid records and hydrological transport lags, a vital issue in interpreting palaeoenvironmental signals. Preserved plant-derived n-alkanes and n-alkanols show clear changes in composition over time, relating to known land-use changes in the area, particularly the expansion of agriculture in the early twentieth century. The level of environmental detail provided by this technique, combined with the long-term chronological framework offered by stalagmites, holds significant promise for the investigation of early human environments and their associated climatic and anthropogenic controls.  相似文献   

17.
M. Doi  G. Warren  M.E. Hodson   《Applied Geochemistry》2005,20(12):2207-2216
Ochre is an unwanted waste product that accumulates in wetlands and streams draining abandoned coal and metal mines. A potential commercial use for ochre is to remediate As contaminated soil. Arsenic contaminated soil (605 mg kg−1) was mixed with different ochres (A, B and C) in a mass ratio of 1:1 and shaken in 20 mL of deionised water. After 72 h As concentration in solution was ca. 500 μg kg−1 in the control and 1–2.5 μg kg−1 in the ochre treated experiments. In a second experiment soil:ochre mixtures of 0.05–1:1 were shaken in 20 mL of deionised water for 24 h. For Ochres A and C, as solution concentration was reduced to ca. 1 μg kg−1 by 0.2–1:1 ochre:soil mixtures. For Ochre B, as concentration only reached ca. 1 μg kg−1 in the 1:1 ochre:soil mix. Sorption of As was best modelled by a Freundlich isotherm using As sorption per mass of goethite in the ochre (log K = 1.64, n = 0.79, R2 = 0.76, p 0.001). Efficiency of ochre in removing As from solution increased with increasing total Fe, goethite, citrate dithionite extractable Fe and surface area.  相似文献   

18.
Stable carbon (δ13C) and hydrogen (δD) isotopic compositions of n-alkanes, anteiso-alkanes, n-alkanoic acids, n-alkanols, phytol and sterols in raw leaves of Acer argutum and Acer carpinifolium, their fallen leaves, mold and soils from a natural Acer forest were measured in order to: (1) understand isotopic variation of the plant biomarkers in a plant-soil system and (2) evaluate which biomarker is the most effective recorder of soil vegetation. Long-chain (> C24) n-alkanes, n-alkanoic acids and n-alkanols are gradually enriched in 13C up to 12.9‰ (average of 4.3‰) and depleted in D up to 94‰ (average of 55‰) from raw leaves to soils. However, anteiso-alkanes, phytol and sterols show little variation in both δ13C (< ± 1‰) and δD (< ± 2‰) from raw leaves to soils. These isotope signatures in a plant-soil system indicate that isoprenoid plant biomarkers such as sterols in soils faithfully preserve the isotopic compositions of dominant higher plants growing on the soils without a diagenetic effect upon the isotopic compositions. In contrast, long-chain n-alkyl molecules in soils undergo specific isotopic modification during biodegradation associated with early diagenesis and/or a significant contribution from heterotrophic reworking.  相似文献   

19.
The molecular distributions of homologous aliphatic lipid compounds (n-alkanes, n-alkanoic acids, n-alkanols, n-alkanals and n-alkan-2-ones) were investigated in sediments of Lake Bera, Malaysia as well as in plant waxes from the vicinity using gas chromatography-mass spectrometry. In addition, triterpenoids of the oleanane, ursane, lupane and friedelane series, and their diagenetic products were also identified. Using the aquatic proxy Paq, it was found that the n-alkanes present in surface sediments S1, S5 and S6 correspond to an input from emergent macrophytes, whereas in sediments collected from open water (S2, S3 and S4) they correspond to input from submerged/floating macrophytes. The presence of n-alkan-2-ols, a commonly found homologous series in the sediments as well as in the plant wax, is novel here. In addition, the presence of 24-methylcycloart-22-enol and 24-ethylcycloart-22-enol in sediments as well as the plant wax of Pandanus helicopus, a dominant reed around the lake, also supports the input of plant biomarkers to the sediments. The occurrence of 5-membered ring triterpenoid derivatives as major diagenetic products of the triterpenoids identified (e.g. friedelan-2,3-dione) shows that the degradation of the organic matter in the sediments occurs mainly under oxic conditions. Also, the presence of ring-A degraded triterpenoids (dihydroputranjivic acid, 3-nor-2,4-seco-friedelane, 4α- and 4β-3-norfriedelanes, A-norfriedel-10-one, and A-norfriedel-8-en-10-one) and the aromatized triterpenoid hydrocarbons (mono- and triaromatic derivatives) as minor diagenetic products indicates photochemical and microorganism-mediated alteration reactions of natural products in the sediments. Additional novel polyfunctional friedelane derivatives, namely friedelane-2,3-dione, friedelane-1,3-diol-2-one and friedel-1(10)-ene-1,3-diol-2-one were identified for the first time in this study. These novel polyfunctional triterpenoids were inferred to derive from the oxidation of the triterpenoids from higher plants in this oxic tropical environment. For future reference purposes, the mass spectra of the identified polar triterpenoids are also presented here. This study provides important data on the biogeochemistry of organic matter in a tropical lake of SE Asia.  相似文献   

20.
Shallow surface sediment samples from the Mesopotamian marshlands of Iraq were collected and analyzed to determine the distribution, concentrations and sources of aliphatic lipid compounds (n-alkanes, n-alkanols, n-alkanoic acids, and methyl n-alkanoates) and molecular markers of petroleum in these wetlands. The sediments were collected using a stainless steel sediment corer, dried, extracted with a dichloromethane/methanol mixture and then analyzed by gas chromatography-mass spectrometry (GC–MS). The aliphatic lipid compounds included n-alkanes, n-alkanoic acids, n-alkanols and methyl n-alkanoates with concentrations ranged from 6.8 to 31.1 μg/g, 4.1 to 5.0 μg/g, 5.9 to 7.7 μg/g and from 0.3 to 5.9 μg/g, respectively. The major sources of aliphatic lipids were natural from waxes of higher plants (24–30%) and microbial residues (42–30%), with a significant contribution from anthropogenic sources (27–30%, petroleum), based on the organic geochemical parameters and indices. Further studies are needed to characterize the rate, accumulation and transformation of various organic matter sources before and after re-flooding of these wetlands.  相似文献   

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