首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
Geochemical processes occurring in cold environments on Earth, Mars, and Europa have elicited considerable interest in the application of geochemical models to subzero temperatures. Few existing geochemical models explicitly include acid chemistry and those that do are largely restricted to temperatures ≥0°C or rely on the mole-fraction scale rather than the more common molal scale. This paper describes (1) use of the Clegg mole-fraction acid models to develop a molal-based model for hydrochloric, nitric, and sulfuric acids at low temperatures; (2) incorporation of acid chemistry and nitrate minerals into the FREZCHEM model; (3) validation and limitations of the derived acid model; and (4) simulation of hypothetical acidic brines for Europa.The Clegg mole-fraction acid models were used to estimate activities of water and mean ionic activity coefficients that serve as the database for estimating molal Pitzer-equation parameters for HCl (188 to 298 K), HNO3 (228 to 298 K), and H2SO4 (208 to 298 K). Model eutectics for HNO3 and H2SO4 agree with experimental measurements to within ± 0.2°C. In agreement with previous work, the experimental freezing point depression (fpd) data for pure HCl at subzero temperatures were judged to be flawed and unreliable. Three alternatives are discussed for handling HCl chemistry at subzero temperatures. In addition to defining the solubility of solid-phase acids, this work also adds three new nitrate minerals and six new acid salts to the FREZCHEM model and refines equilibria among water ice, liquid water, and water vapor over the temperature range from 180 to 298 K. The final system is parameterized for Na-K-Mg-Ca-H-Cl-SO4-NO3-OH-HCO3-CO3-CO2-H2O.Simulations of hypothetical MgSO4-H2SO4-H2O and Na2SO4-MgSO4-H2SO4-H2O brines for Europa demonstrate how freezing can convert a predominantly salt solution into a predominantly acid solution at subzero temperatures. This result has consequences for the effects of salinity, acidity, and temperature as limiting factors for potential life on Europa. Strong acidity would limit life-forms to highly acidophilic organisms.  相似文献   

2.
Laboratory experiments on the thermal decarboxylation of solutions of acetic acid at 200°C and 300°C were carried out in hydrothermal equipment allowing for on-line sampling of both the gas and liquid phases for chemical and stable-carbon-isotope analyses. The solutions had ambient pH values between 2.5 and 7.1; pH values and the concentrations of the various acetate species at the conditions of the experiments were computed using a chemical model.Results show that the concentrations of acetic acid, and not total acetate in solution, control the reaction rates which follow a first order equation based on decreasing concentrations of acetic acid with time. The decarboxylation rates at 200°C (1.81 × 10?8 per second) and 300°C (8.17 × 10?8 per second) and the extrapolated rates at lower temperatures are relatively high. The activation energy of decarboxylation is only 8.1 kcal/mole. These high decarboxylation rates, together with the distribution of short-chained aliphatic acid anions in formation waters, support the hypothesis that acid anions are precursors for an important portion of natural gas.Results of the δ13C values of CO2, CH4, and total acetate show a reasonably constant fractionation factor of about 20 permil between CO2 and CH4 at 300°C. The δ13C values of CO2 and CH4 are initially low and become higher as decarboxylation increases.  相似文献   

3.
Polymerizations of organic monomers including amino acids, nucleotides and monosaccharides are essential processes for chemical evolution of life. Since these reactions proceed with “dehydration” reactions, they are possibly promoted if combined with thermodynamically favorable “hydration” reactions of minerals and salts. To test the possibility, we conducted heating experiments of the simplest amino acid “glycine (Gly)” mixed with four simple anhydrous salts (MgSO4, SrCl2, BaCl2 and Li2SO4) at 140 °C up to 20 days. Gly polymerization was strongly promoted by mixing with the salts in the order of MgSO4 > SrCl2 > BaCl2 > Li2SO4. Up to 6-mer of Gly polymers were synthesized in the Gly-MgSO4 mixture, and a total yield of Gly polymers attained about 7% of the initial amount of Gly by the 20 days heating. The total yield was about 200 times larger than that from the heating of Gly alone. XRD measurements of the Gly-MgSO4 mixture revealed the generation of MgSO4 monohydrate during Gly polymerization. These observations indicate that Gly polymerization was promoted by the salt hydrations through the hydration-dehydration interactions. Based on the observations, we tried to find a relationship between thermodynamic characteristics of the interactions and the promotion effects of each salt on Gly polymerization. It was found that the salts having lower hydration ΔrG0 (easier to hydrate) promote Gly polymerization more strongly. The relationship was used to estimate promotion effects of simple oxide minerals on Gly polymerization. The estimations were consistent with previous observations about the effects of these minerals on Gly polymerization. The fact suggests that the hydration-dehydration interactions between amino acids and minerals are an important mechanism for amino acids’ polymerizations on minerals.  相似文献   

4.
Organic acids and acid anions occur in substantial concentrations in many aqueous geologic fluids and are thought to take part in a variety of geochemical processes ranging from the transport of metals in ore-forming fluids to the formation of natural gas to serving as a metabolic energy source for microbes in subsurface habitats. The widespread occurrence of organic acids and their potential role in diverse geologic processes has led to numerous experimental studies of their thermal stability, yet there remain substantial gaps in our knowledge of the factors that control the rates and reaction pathways for the decomposition of these compounds under geologic conditions. In order to address some of these uncertainties, a series of laboratory experiments were conducted to examine the behavior of organic acids and acid anions under hydrothermal conditions in the presence of minerals. Reported here are results of experiments where aqueous solutions of acetic acid, sodium acetate, or valeric acid (n-pentanoic acid) were heated at 325°C, 350 bars in the presence of the mineral assemblages hematite + magnetite + pyrite, pyrite + pyrrhotite + magnetite, and hematite + magnetite. The results indicate that aqueous acetic acid and acetate decompose by a combination of two reaction pathways: decarboxylation and oxidation. Both reactions are promoted by minerals, with hematite catalyzing the oxidation reaction while magnetite catalyzes decarboxylation. The oxidation reaction is much faster, so that oxidation dominates the decomposition of acetic acid and acetate when hematite is present. In contrast to previous reports that acetate decomposed more slowly than acetic acid, we found that acetate decomposed at slightly faster rates than the acid in the presence of minerals. Although longer-chain monocarboxylic acids are generally thought to decompose by decarboxylation, valeric acid appeared to decompose primarily by “deformylation” to 1-butene plus formic acid. Subsequent decomposition of 1-butene and formic acid generated a variety of short-chain (≤C4) hydrocarbons and moncarboxylic acids as well as CO2. Valeric acid decomposition proceeded more rapidly (by a factor of 2) in the presence of hematite-magnetite-pyrite than with the other mineral assemblages, with the greater reaction rate apparently attributable to the effects of fluid chemistry. Valeric acid was observed to decompose at a substantially faster rate than acetic acid under similar conditions. The results suggest that decomposition of aqueous monocarboxylic acids may make a significant contribution to the conversion of petroleum to light hydrocarbons in natural gas and thermal fluids.  相似文献   

5.
We report hydrogen isotopic fractionations between water and fatty acids of the sulfate-reducing bacterium Desulfobacterium autotrophicum. Pure cultures were grown in waters with deuterium (D) contents that were systematically varied near the level of natural abundance (−37‰ ? δD ? 993‰). H2 of constant hydrogen isotope (D/H) ratio was supplied to the cultures. The D/H ratios of water, H2, and specific fatty acids were measured by isotope-ratio mass spectrometry. The results demonstrate that D. autotrophicum catalyzes hydrogen isotopic exchange between water and H2, and this reaction is conclusively shown to approach isotopic equilibrium. In addition, variation in the D/H ratio of growth water accounts for all variation in the hydrogen isotopic composition of fatty acids. The D/H ratios of fatty acids from cultures grown on H2/CO2 are compared with those from a separate set of cultures grown on D-enriched formate, an alternative electron donor. This comparison rules out H2 as a significant source of fatty acid hydrogen. Grown on either H2/CO2 or formate, D. autotrophicum produces fatty acids in which all hydrogen originates from water. For specific fatty acids, biosynthetic fractionation factors are mostly in the range 0.60 ? αFA-water ? 0.70; the 18:0 fatty acid exhibits a lower fractionation factor of 0.52. The data show that αFA-water generally increases with length of the carbon chain from C14 to C17 among both saturated and unsaturated fatty acids. These results indicate a net fractionation associated with fatty acid biosynthesis in D. autotrophicum that is slightly smaller than in another H2-consuming bacterium (Sporomusa sp.), but much greater than in most photoautotrophs.  相似文献   

6.
  相似文献   

7.
《Applied Geochemistry》2001,16(7-8):947-961
During dry season baseflow conditions approximately 20% of the flow in Boulder Creek is comprised of acidic metals-bearing groundwater. Significant amounts of efflorescent salts accumulate around intermittent seeps and surface streams as a result of evaporation of acid rock drainage. Those salts include the Fe-sulfates — rhomboclase ((H3O)Fe3+(SO4)2·3H2O), ferricopiapite (Fe3+5(SO4)6O(OH)·20H2O), and bilinite (Fe2+Fe23+(SO4)4·22H2O); Al-sulfates — alunogen (Al2(SO4)3·17H2O) and kalinite (KAl(SO4)2·11H2O); and Ca- and Mg-sulfates — gypsum (CaSO4·2H2O), and hexahydrite (MgSO4·6H2O). The dissolution of evaporative sulfate salt accumulations during the first major storm of the wet season at Iron Mountain produces a characteristic hydrogeochemical response (so-called “rinse-out”) in surface waters that is subdued in later storms. Geochemical modeling shows that the solutes from relatively minor amounts of dissolved sulfate salts will maintain the pH of surface streams near 3.0 during a rainstorm. On a weight basis, Fe-sulfate salts are capable of producing more acidity than Al- or Mg-sulfate salts. The primary mechanism for the production of acidity from salts involves the hydrolysis of the dissolved dissolved metals, especially Fe3+. In addition to the lowering of pH values and providing dissolved Fe and Al to surface streams, the soluble salts appear to be a significant source of dissolved Cu, Zn, and other metals during the first significant storm of the season.  相似文献   

8.
《Organic Geochemistry》1999,30(8):901-909
Deuterium nuclear magnetic resonance spectroscopy (2H-NMR) spin–lattice relaxation (T1) experiments were used to measure noncovalent interactions between deuterated monoaromatic compounds (phenol-d5, pyridine-d5, benzene-d6) and fulvic acids isolated from the Suwannee River and Big Soda Lake. Noncovalent interactions, in aqueous solution, were examined as a function of monoaromatic hydrocarbon functional groups, fulvic acid concentration and identity, and solution pH. Phenol did not exhibit noncovalent interactions with either fulvic acid at any pH. Pyridine, in a pH range from 3 to 8, interacted with Suwannee River fulvic acid, forming a bond involving the lone pair of electrons on nitrogen. Conversely, no interactions were observed between pyridine and Big Soda Lake fulvic acid; the difference in noncovalent interactions is attributed to the structural and chemical differences of the two fulvic acids. The translational and rotational molecular motion of benzene increased in the presence of both fulvic acids, indicating that in aqueous solution, fulvic acids solubilize benzene rather than forming discrete bonds as with pyridine. The results of this study demonstrate that monoaromatic functional groups, solution pH, and identity and concentration of fulvic acid can influence the type and degree of noncovalent interactions with dissolved organic matter.  相似文献   

9.
We report on the crystallization behavior and the salt weathering potential of Na2SO4, MgSO4 and an equimolar mixture of these salts in natural rock and porous stone. Geochemical modeling of the phase diagram of the ternary Na2SO4–MgSO4–H2O system was used to determine the equilibrium pathways during wetting (or deliquescence) of incongruently soluble minerals and evaporation of mixed electrolyte solutions. Model calculations include stable and metastable solubilities of the various hydrated states of the single salts and the double salts Na2Mg(SO4)2·4H2O (bloedite), Na2Mg(SO4)2·5H2O (konyaite), Na12Mg7(SO4)13·15H2O (loeweite) and Na6Mg(SO4)4 (vanthoffite). In situ Raman spectroscopy was used to study the phase transformations during wetting of pure MgSO4·H2O (kieserite) and of the incongruently soluble salts bloedite and konyaite. Dissolution of kieserite leads to high supersaturation resulting in crystallization of higher hydrated phases, i.e. MgSO4·7H2O (epsomite) and MgSO4·6H2O (hexahydrite). This confirms the high damage potential of magnesium sulfate in salt damage of building materials. The dissolution of the incongruently soluble double salts leads to supersaturation with respect to Na2SO4·10H2O (mirabilite). However, the supersaturation was insufficient for mirabilite nucleation. The damage potential of the two single salts and an equimolar salt mixture was tested in wetting–drying experiments with porous sandstone. While the high damage potential of the single salts is confirmed, it appears that the supersaturation achieved during wetting of the double salts at room temperature is not sufficient to generate high crystallization pressures. In contrast, very high damage potentials of the double salts were found in experiments at low temperature under high salt load.1  相似文献   

10.
Humic acid was titrated by sodium methoxide in dimethylsulfoxide using platinum-calomel electrode systems. Adding benzoic acid and phenol as internal standards to humic acid yielded two inflections. The titer at the first inflection point was equivalent to the carboxyl groups whose pKa (H2O) values were less than 7. The difference between the titers at the two inflection points was equivalent to the phenolic hydroxyl groups whose pKa (H2O) values were 7–10. Calculated results for the carboxyl and phenolic hydroxyl groups in humic acid obtained by the nonaqueous titration method agreed closely with those obtained by conventional methods.  相似文献   

11.
Between pH 3.5 and 7, humic acids form a water-soluble uranyl-humic acid complex with the uranyl ion, UO22+ (log β1 = 7.8 ± 0.4 at μ = 0.1). The stability constant of the complex is practically independent of the ionic strength (μ). Experimental results can be explained by the formation of a complex in which every uranyl ion is simultaneously bonded to one phenolic oxygen and one dissociated carboxyl group. The bonding through the phenolic group is considerably stronger than that through carboxylic groups.  相似文献   

12.
Amino acid biogeo- and stereochemistry in coastal Chilean sediments   总被引：1，自引：0，他引：1  
The spatial distribution of total hydrolysable amino acids (THAA) and amino acid enantiomers (d- and l-forms) was investigated in sediments underlying two contrasting Chilean upwelling regions: at ∼23 °S off Antofagasta and at ∼36 °S off Concepción. The contribution of amino acids to total organic carbon (%TAAC: 7-14%) and total nitrogen (%TAAN: 23-38%) in surface sediments decreased with increasing water depth (from 126 to 1350 m) indicating that organic matter becomes increasingly decomposed in surface sediments at greater water depth. Changes in the ratio between the protein amino acid aspartate and its non-protein degradation product β-alanine confirmed this observation. Furthermore, estimates of THAA mineralization showed that sedimentary amino acid reactivity decreased with both increasing water depth as well as progressive degradation status of the organic matter that was incorporated into the sediment. Reactivity of organic matter in the sediment was also assessed using the Degradation Index (DI) developed by [Dauwe, B., Middelburg, J.J., 1998. Amino acids and hexosamines as indicators of organic matter degradation state in North Sea sediments. Limnol. Oceanogr.43, pp. 782-798.]. Off Concepción, DI was successfully applied to examine the degradation status of sedimentary organic matter at different water depths. However, unexpected results were obtained at the Antofagasta stations as DI increased with sediment depth, suggesting more degraded organic matter at the surface than deeper in the cores. The contribution of peptidoglycan amino acids to THAA was estimated from the concentrations of d-aspartate, d-glutamic acid, d-serine, and d-alanine. Peptidoglycan amino acids accounted for >18% of THAA in all investigated samples. In surface sediments peptidoglycan amino acids accounted for a progressively larger fraction of THAA at increasing water depths (up to >26%). Further, the contribution of peptidoglycan amino acids to THAA increased with increased sediment depth and age (up to 288-year-old) reaching up to 59%. Independent estimates based on d-amino acid concentrations in selected laboratory strains, bacterial counts and the sedimentary concentrations of d-amino acids indicate that a large fraction of the measured d-amino acids (>47 to >97%) originated from cell wall residues rather than from enumerated cells.  相似文献   

13.
Two fractions of soil fulvic acid (FA) were separated by gel filtration chromatography. An observed increase in volume of the heavier fraction (FA I) with increasing pH was attributed to aggregation, intramolecular negative charge repulsions and the rupture of hydrogen bonds, which control molecular conformation. Optical absorption properties and elemental analyses of both fractions were determined. The stability constants and stoichiometries of FA complexes with vanadyl, VO2+, at pH 5.0 and ionic strength of 0.04 M were measured by electron paramagnetic resonance (EPR) spectroscopy. EPR spectra of model VO2+ complexes with phthalic and salicylic acids, which are the probable functional groups present in FA, are identical to those of the VO2+-FA complexes. Aggregation of FA I occurs in the presence of VO2+ to form a complex that can be approximated as ‘(VO)2(FA I)6’. The average site distance between vanadyl ions in this complex is shown to be greater than 1.2 nm. EPR parameters for FA I suggest binding by carboxylate groups. These parameters are compared with those of other vanadyl complexes with fulvic and humic acids reported by others. Reduction of VO3? to VO2+ by these materials is discussed.  相似文献   

14.
《Applied Geochemistry》1993,8(2):127-139
Ligand adsorption on δ-Al2O3 at pH 8 was examined for a series of organic ligands (aromatic acids, monochlorophenols and aliphatic acids) including both monodentate and bidentate ligands. Adsorption isotherms for the aromatic acids exhibited saturation at high dissolved ligand concentrations; saturation was not observed (over the concentration range examined) for the chlorophenols. Small, though measurable, amounts of heat were evolved on reaction of the aromatic acids, the monochlorophenols and propionate (but not of the longer chain fatty acids) with the oxide surface; overall ligand adsorption reactions wereexothermic (ΔHobs < O). For adsorption of (partially or fully) protonated ligands, the favorable ΔHobs was due largely to the exothermic proton transfer reaction between phenolic hydroxyl groups of the ligands and hydroxide ions displaced from the oxide surface. The enthalpy corresponding to the ligand-exchange reaction of surface hydroxyl groups for the various ligands (as fully deprotonated species), ΔHcorr, appeared to be related to the ligand structure. The surface ligand-exchange reaction was more exothermic for the dicarboxylic acid phthalate than for the monocarboxylic acids benzoate or propionate or for salicylate and was endothermic for the chlorophenols.  相似文献   

15.
Acid mine drainage is a major source of water pollution in the Sarcheshmeh porphyry copper mine area. The concentrations of heavy metals and rare earth elements (REEs) in the host rocks, natural waters and acid mine drainage (AMD) associated with mining and tailing impoundments are determined. Contrary to the solid samples, AMDs and impacted stream waters are enriched in middle rare earth elements (MREEs) and heavy rare earth elements (HREEs) relative to light rare earth elements (LREEs). This behavior suggests that REE probably fractionate during sulfide oxidation and acid generation and subsequent transport, so that MREE and HREE are preferentially enriched. Speciation modeling predict that the dominant dissolved REE inorganic species are Ln3+, Ln(SO4)2−, LnSO4+, LnHCO32+, Ln(CO3)2− and LnCO3+. Compared to natural waters, Sarcheshmeh AMD is enriched in REEs and SO42−. High concentrations of SO42− lead to the formation of stable LnSO4+, thereby resulting in higher concentrations of REEs in AMD samples. The model indicates that LnSO4+ is the dissolved form of REE in acid waters, while carbonate and dicarbonate complexes are the most abundant dissolved REE species in alkaline waters. The speciation calculations indicate that other factors besides complexation of the REE's, such as release of MREE from dissolution and/or desorption processes in soluble salts and poorly crystalline iron oxyhydroxy sulfates as well as dissolution of host rock MREE-bearing minerals control the dissolved REE concentrations and, hence, the MREE-enriched patterns of acid mine waters.  相似文献   

16.
The influence of hydroxybenzoic acids (HAHn), namely p-hydroxybenzoic acid (4-hydroxybenzoic acid, HPhbH) and protocatechuic acid (3,4-dihydroxybenzoic acid, HProtoH2), on the adsorption of europium(III) onto α,γ-Al2O3 particles is studied as a function of acid concentration. After measuring the adsorption edge of the Eu(III)/α,γ-Al2O3 binary system, and using the previously studied binary component system Eu(III)/HAHn—Moreau et al. (2015) Inorg. Chim. Acta 432, 81—, and HAHn/α,γ-Al2O3—Moreau et al. (2013) Colloids Surf. A 435, 97—, it is evidenced that HPhbH does not enhance Eu(III) adsorption onto α,γ-Al2O3 in the Eu(III)/HPhbH/α,γ-Al2O3 ternary system. Conversely, HProtoH2 enhances Eu(III) adsorption onto α,γ-Al2O3 in the Eu(III)/HProtoH2/α,γ-Al2O3 ternary system. Adsorption of the acids are also found higher in the Eu(III)/acid/α,γ-Al2O3 ternary systems as compared with the corresponding binary systems assessing synergetic effects. For high HPhbH concentrations, a ternary surface species involving ≡AlOH surface sites, Eu(III), and PhbH– is evidenced by time-resolved luminescence spectroscopy (TRLS). However, in the Eu(III)/HProtoH2/α,γ-Al2O3 ternary system, chemical environment of Eu(III) is found to be very close to that in the Eu(III)/HProtoH2 binary system. Ternary surface species could not be evidenced in the Eu(III)/HProtoH2/α,γ-Al2O3 ternary system with TRLS because of the very short decay time of Eu(III) in the presence of protocatechuic acid.  相似文献   

17.
Fatty acids have been isolated and quantitatively determined from a 1.5 m sediment core of Lake Suwa, a eutrophic lake in the central districts of Japan.The fatty acids identified by combined gas chromatography-mass spectrometry were straight-chain saturated (C12 to C34), monounsaturated with even carbon number (C16 to C24) and branched-chain (iso, anteiso, 10-methyloctadecanoic) acids. The concentrations of the higher molecular weight (? C20) saturated fatty acids remained nearly constant throughout the core, suggesting a high degree of preservation of those acids, whereas the monounsaturated and the lower molecular weight saturated fatty acids indicated a great decrease in concentration with depth to an approximately 20cm level. It is suggested that the microbial activity in sediments causes a significant reconstruction of the fatty acid distribution during early diagenesis.  相似文献   

18.
Phosphonoformic acid, oxalic acid, glyoxylic acid, and 10 additional organic compounds that are structurally related to them have been reacted with synthetic MnO2 (birnessite), consisting of 22% MnIII and 78% MnIV, and synthetic MnOOH (manganite), consisting solely of MnIII. Significant concentrations of dissolved MnIII were detected in reactions of phosphonoformic acid with MnOOH, indicating that ligand-assisted dissolution took place. Reaction of phosphonoformic acid with MnO2, and reaction of all other organic reactants with either MnOOH or MnO2, yielded only MnII, indicating that reductive dissolution was predominant. As far as reductive dissolution reactions are concerned, MnO2 yields a range of reactivity that is nearly 20-times greater than that of MnOOH. Oxidation converts phosphonoformic acid into orthophosphate ion, glyoxylic acid into formic acid, pyruvic acid into acetic acid, and 2,3-butanedione into acetic acid. When differences in surface area loading are accounted for, oxalic acid, pyruvic acid, and 2,3-butanedione yield virtually the same dissolution rates for the two (hydr)oxides. At pH 5.0, glyoxylic acid reacts 14-times faster with MnO2 than with MnOOH. MnO2 reacts more slowly than MnOOH by a factor of 1/16th with oxamic acid, 1/20th with lactic acid, and 1/33rd with dimethyl oxalate. Adsorptive, complexant, and reductant properties of the 13 organic reactants are believed responsible for the observed reactivity differences.  相似文献   

19.
Fatty acids (FAs), β- and ω-hydroxy acids, α,ω-dicarboxylic acids and n-alkanes were studied in a 200 m sediment core taken from Lake Biwa, Japan. FAs showed bimodal distribution with peaks at C16 and C22-C28. Their distribution patterns clearly changed with depth from lower molecular weight (C12-C19) predominance to higher molecular weight (C20-C32) predominance in the upper 20 m interval. Analyses of related compounds (β- and ω-hydroxy acids and α, ω-dicarboxylic acids) suggest that β- and ω-oxidative degradation of C12-C19 FAs has occurred in the sediments.The ratio of bound C12-C19 to unbound FAs increases with depth in the upper 0–1 m sediments, suggesting that unbound FAs are more labile. However, the ratio varies significantly in deeper sections and may be associated with water temperature.In the sediments deeper than 20 m in depth, C12-C19 FAs gradually decrease. On the other hand, higher molecular weight FAs (HFAs: C20-C32), which were probably derived from terrestrial plants, increase in concentration from 20 m to 100 m, suddenly decrease at 100 m and show progressively lower concentration in deeper sediments. These fluctuations are interpreted in relation to paleolimnological changes of the lake and the drainage basin. ω-Hydroxy C20-C30 acids and C20-C30α, ω-dicarboxylic acids show a distribution pattern similar to HFAs. Branched chain FAs, ω-hydroxy acids and C9-C19α,ω-dicarboxylic acids show a major peak around 3–15 m in depth. This peak is probably caused by increased bacterial activity in the water column and surface sediments in the past, which may be associated with an increase in primary production of the lake.  相似文献   

20.
  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号