Organic Geochemistry最新文献

{"title":"Spatial distribution of n-alkanes and GDGTs in the central Arctic Ocean during Marine Isotope Stages 1, 2 and 3","authors":"Akanksha Singh ,&nbsp;Sze Ling Ho ,&nbsp;Min-Te Chen ,&nbsp;Pei-Ling Wang ,&nbsp;Martin Jakobsson ,&nbsp;Richard Gyllencreutz ,&nbsp;Ludvig Löwemark","doi":"10.1016/j.orggeochem.2024.104920","DOIUrl":"10.1016/j.orggeochem.2024.104920","url":null,"abstract":"<div><div>Arctic sea ice affects Earth’s albedo, marine productivity and organic matter (OM) transport. Lipid biomarkers have been used to trace OM transport in the Arctic Ocean, but uncertainties remain regarding their spatio-temporal variations and sources over the last glacial cycle. Our study addresses these gaps by analyzing glycerol dialkyl glycerol tetraethers (GDGTs), <em>n</em>-alkanes, and total organic carbon (TOC) in nine central Arctic sediment cores spanning the Marine Isotope Stages (MISs) 3–1. Elevated IIIa/IIa values of branched GDGTs (brGDGTs) in the central Arctic throughout the studied interval suggest a marine origin, contrasting to the #rings_tetra ratios which indicate a terrigenous brGDGT source. We propose that the IIIa/IIa ratio may be a more sensitive indicator of in situ brGDGT production in the central Arctic marine sediments. TOC and biomarker concentrations in the Central Lomonosov Ridge (CLR) cores were higher compared to those from the Lomonosov Ridge off Greenland (LRG) and Morris Jesup Rise (MJR) cores. Low productivity in the central Arctic, along with similarity in the spatial patterns of marine-derived brGDGTs and isoprenoid GDGTs, as well as terrestrial long-chain <em>n</em>-alkanes, suggests that these biomarkers are primarily transported to the central Arctic from the Siberian shelves. This spatial pattern persisted throughout MISs 3–1, suggesting continued sea ice drift during glacial periods, albeit with weakened intensities. Meanwhile, the spatiotemporal variations of the Branched Isoprenoid Tetraether (BIT) index in the region plausibly reflect the relative changes in the crenarchaeol and brGDGT production on the shelf and/or selective degradation of crenarchaeol during its transport.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"201 ","pages":"Article 104920"},"PeriodicalIF":2.6,"publicationDate":"2024-12-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143378488","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Comparing lipid extraction methods on lake sediments without dichloromethane","authors":"Aaron F Diefendorf","doi":"10.1016/j.orggeochem.2024.104919","DOIUrl":"10.1016/j.orggeochem.2024.104919","url":null,"abstract":"<div><div>This study compares different lipid extraction methods and solvents with a focus on reducing or eliminating the use of dichloromethane (DCM). DCM has high neurotoxicity and is carcinogenic. This study focuses on lake sediment extraction using accelerated solvent extraction (ASE), sonication, QuEChERS, and Soxhlet methods and compares the solvents DCM, ethyl acetate (EtOAc), methanol (MeOH), and hexanes. For ASE and sonication extractions, the replacement of DCM with EtOAc results in similar extraction efficiencies for <em>n</em>-alkanes, <em>n</em>-alkanols, and slightly lower extraction of <em>n</em>-alkanoic acids. For example, when using an ASE with recovery standards, switching from 9:1 DCM/MeOH to 9:1 EtOAc/MeOH results in a small decrease of 10% in the extraction of total hydrocarbons (mostly <em>n</em>-alkanes), the same recovery of the alcohols (mostly <em>n</em>-alkanols), and a decrease of 19% for the acids (mostly <em>n</em>-alkanoic acids). The QuEChERS method reduces the volume of DCM, but had poor recovery compared to ASE or sonication. Many labs could switch from using DCM to EtOAc with ASE or sonication and have minor to no changes in extraction efficiency. The use of 9:1 hexanes/EtOAc produced high recoveries of <em>n</em>-alkanes and <em>n</em>-alkanols with a cleaner extract that requires less post extraction cleanup. Sonication has the potential advantage of higher throughput and lower costs, although hands-on time is higher than ASE and recoveries were not always as high as with ASE. While this study focuses on the extraction of lake sediment, the results should be transferable to the extraction of soils, rocks, and other biological materials with minor method adjustments.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"202 ","pages":"Article 104919"},"PeriodicalIF":2.6,"publicationDate":"2024-12-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143386988","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Organic matter accumulation driven by land-sea interactions during the Late Cretaceous: A geochemical study of the Nenjiang Formation, Songliao Basin","authors":"Congsheng Bian ,&nbsp;Shiju Liu ,&nbsp;Wei Liu ,&nbsp;Xiong Cheng ,&nbsp;Xin Liu ,&nbsp;Jin Dong ,&nbsp;Rui Wang ,&nbsp;Yongxin Li ,&nbsp;Ming Guan ,&nbsp;Qianhui Tian ,&nbsp;Wenzhi Zhao","doi":"10.1016/j.orggeochem.2024.104901","DOIUrl":"10.1016/j.orggeochem.2024.104901","url":null,"abstract":"<div><div>The Late Cretaceous Nenjiang Formation in the Songliao Basin presents a unique setting to examine how climate change and sea-level rise influenced organic matter accumulation. This study combines TOC analysis, Rock-Eval pyrolysis, GC–MS, GC–MS-MS, and elemental geochemistry on core samples from two wells to assess organic matter deposition before and after transgressive events. TOC values range from 0.18 to 14.63 wt%, with significant variations in hydrocarbon potential and thermal maturity. Periodic warm and cool climates triggered intermittent seawater intrusions that created anoxic conditions conducive to marine diatom and lacustrine dinoflagellate proliferation. Extended warm periods, however, suppressed dinoflagellate development and reduced paleo-productivity. The activity of methanogenic bacteria further contributed to the degradation of sedimentary organic matter, hindering its accumulation. While warm climates facilitated flood events that transported terrigenous nutrients, enhancing dinoflagellate blooms and expanding the oxygen minimum zone. These findings highlight the bio-environmental interactions that governed organic matter accumulation during transgressions, offering insights for exploration in similar sedimentary environments.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"199 ","pages":"Article 104901"},"PeriodicalIF":2.6,"publicationDate":"2024-11-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142746085","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"C/H isotope fractionation of hydrocarbon gases from hydrogenation of organic matter: Insights from hydrothermal experiments","authors":"Kun He ,&nbsp;Xiaomei Wang ,&nbsp;Chunlong Yang ,&nbsp;Linfeng Xie ,&nbsp;Shuichang Zhang","doi":"10.1016/j.orggeochem.2024.104884","DOIUrl":"10.1016/j.orggeochem.2024.104884","url":null,"abstract":"<div><div>It is widely accepted that organic–inorganic interactions involving hydrogen-rich fluids (H₂O and H₂) play a significant role in hydrocarbon (HC) generation in sedimentary basins, and the effects of hydrogenation of organic matter (OM) by H₂O/H₂ on C/H isotope fractionation remain poorly understood. This study investigates these effects through a series of pyrolysis experiments conducted at 330–420 °C and 50 MPa, encompassing three groups: (1) anhydrous pyrolysis with kerogen only (Group 1), (2) kerogen and H₂O (Group 2), and (3) kerogen, H₂O, and Fe_1-<em>_x</em>S (Group 3). Groups 2 and 3 were designed to simulate hydrogenation of OM by H₂O and H₂, respectively. Results show that HC gas yields in Group 3 experiments are 1.8 to 3.2 times of those in Group 1, while yields in Group 2 are lower than Group 1. Moreover, hydrogenation by H₂ produces HC gases with smaller ¹³C fractionation and more negative δ²H values compared to hydrogenation by H₂O. These findings suggest distinct mechanisms for HC gas generation during H₂-OM and H₂O-OM reactions. Further analysis demonstrates that the equilibrium isotope effect (EIE) governs ¹³C and ²H isotope fractionation during hydrogenation of OM by H₂. Importantly, the EIE for ²H isotope fractionation of H₂O-H₂, CH₄-H₂, and OM-H₂ is evaluated under both experimental and geological conditions. This study provides crucial insights into the significant influence of hydrogenation of OM by H₂ on the generation and C/H isotopic fractionation of HC gases, as well as the evolution and preservation of H₂ in organic-rich shales.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"199 ","pages":"Article 104884"},"PeriodicalIF":2.6,"publicationDate":"2024-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142699708","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Role of aromatic and non-protonated aromatic carbon in the stability of soil organic matter","authors":"Moazame Mesgar ,&nbsp;Seyedahmad Kia ,&nbsp;Paul R. Voroney ,&nbsp;Andy Lo ,&nbsp;Adam W. Gillespie","doi":"10.1016/j.orggeochem.2024.104897","DOIUrl":"10.1016/j.orggeochem.2024.104897","url":null,"abstract":"<div><div>Research on soil organic matter (SOM) in its natural state is vital for comprehending the mechanisms governing soil stability and carbon cycling, crucial in addressing global climate change. We utilized solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy on HF treated samples, along with a 260-day laboratory mineralization experiment and thermal analysis-programmed pyrolysis (PP) to evaluate SOM biodegradability and thermal stability. To cover the potential range of organic carbon variability, we selected samples from three land uses and soil types, featuring total organic carbon levels from 1% to 39%. Our analysis confirmed the substantial contribution of non-protonated aromatic-carbon not bonded to oxygen to SOM’s biological and thermal stability, constituting approximately 14–21% of soil organic carbon. These components exhibited a strong correlation with SOM stability matrices, such as thermal stability and oxygen index determined by PP. Samples with a higher prevalence of these components also displayed the lowest cumulative carbon mineralization. These findings enhance our understanding of the stable SOM pool, aiding in the identification of sustainable soil management practices to mitigate climate change impacts on soil health and carbon dynamics.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"201 ","pages":"Article 104897"},"PeriodicalIF":2.6,"publicationDate":"2024-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143145023","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characteristics of carbazole compounds in ultra-deep marine oil from Fuman oilfield, Tarim Basin: Significance for thermal maturity assessment of crude oil","authors":"Zhongdeng Lu ,&nbsp;Hongwei Ping ,&nbsp;Honghan Chen ,&nbsp;Zulin Chen ,&nbsp;Yanqiu Zhang ,&nbsp;Zhou Xie ,&nbsp;Yintao Zhang ,&nbsp;Xu Chen","doi":"10.1016/j.orggeochem.2024.104895","DOIUrl":"10.1016/j.orggeochem.2024.104895","url":null,"abstract":"<div><div>Carbazoles in Ordovician ultra-deep marine oil from the F_I17 fault zone in Fuman oilfield (Tarim Basin) were separated using a recently proposed silica gel column chromatographic method and the enriched fractions were analyzed by GC–MS. Biomarker and carbon isotope signatures revealed that all oil in the study area was produced from the same source rock and that compositional differences can be attributed to thermal maturation. The convergent ratios of N-H shielded isomers/N-H half shielded isomers and benzo[<em>a</em>]carbazole/(benzo[<em>a</em>]carbazole + benzo[<em>c</em>]carbazole) suggested that carbazoles in crude oil had not been affected by vertical migration. Therefore, thermal maturity was identified as the main controlling factor affecting chages of carbazole concentrations and ratios in crude oil. The concentrations of the total carbazole and its three isomers (N-H shielded isomers, N-H half shielded isomers and exposed isomers) in crude oil decreased sharply with increasing maturity. The 1,8-dimethylcarbazole/carbazole (1,8-MCa/Ca) and 1,8-dimethylcarbazole/2,4-dimethylcarbazole (1,8-MCa/2,4-MCa) ratios showed significant correlation with maturity expressed as %<em>VRE</em> (the vitrinite reflectance equivalent converted from MPI₁ and MPR) when %<em>VRE</em> is &lt;1.2 %. Similar trends were observed in the 1-methylcarbazole/3-methylcarbazole (1-MCa/3-MCa) as well as 1,8-dimethylcarbazole/2,6- dimethylcarbazole (1,8-DMCa/2,6-DMCa), (1,5- dimethylcarbazole + 3-ethylcarbazole)/2, 6-dimethylcarbazole ((1, 5-DMCa + 3-ECa)/2, 6-DMCa), and (1, 4-dimethylcarbazole + 4-ethylcarbazole)/2, 6-dimethylcarbazole ((1, 4-DMCa + 4-ECa)/2, 6-DMCa) when the %<em>VRE</em> of crude oil exceeds 1.0 %. This indicated that the concentrations and ratios of carbazole can be used to qualitatively evaluate crude oil maturity. The ratio of 1,8-dimethylcarbazole/1-ethylcarbazole (1,8-DMCa/1-ECa) showed a strict linear relationship with %<em>VRE</em>. The maturity of marine oil can be calculated using the formulas <em>%R</em>c (the vitrinite reflectance equivalent calculated from MPI₁) = −0.0335(1, 8-DMCa/1-ECa) + 1.2902 or <em>%R</em>c₁ (the vitrinite reflectance equivalent calculated from MPR) = −0.0405 (1, 8-DMCa/1-ECa) + 1.3418. The study can be helpful for exploring ultra-deep hydrocarbons and restoring the thermal history of source rocks in the Tarim Basin.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"198 ","pages":"Article 104895"},"PeriodicalIF":2.6,"publicationDate":"2024-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652441","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hydrogen isotope fractionation during aromatization to form alkylnaphthalene: Insights from pyrolysis experiments of 1-n-butyldecalin","authors":"Bin Cheng ,&nbsp;Zhiwei Wei ,&nbsp;Yiman Zhang ,&nbsp;Hanyu Deng ,&nbsp;Yuxian Li ,&nbsp;Haozhe Wang ,&nbsp;Zewen Liao","doi":"10.1016/j.orggeochem.2024.104881","DOIUrl":"10.1016/j.orggeochem.2024.104881","url":null,"abstract":"<div><div>Alkylnaphthalene homologues are important components of aromatic fraction in sedimentary organic matter and contain significantly geochemical information relative to formation and evolution of the host organic matter. They mainly originate from hydrocarbon aromatization reaction which involves the dehydrogenation of aliphatic rings resulting in the fractionation of stable hydrogen isotopes between aromatic hydrocarbons and their precursors. To examine these processes, this study thermally pyrolysed 1-<em>n</em>-butyldecalin (BD) at different time intervals under 360 °C/50 MPa to study the aromatization and hydrogen isotope fractionation during alkylnaphthalene formation and evolution. The relative content of aromatic products, such as naphthalene (N) and 1-methylnaphthalene (1-MN), increases with increasing aromatization. Sulfur enhanced the degree of aromatization during BD thermal evolution, resulting in greater N and 1-MN formation. For the compounds with the same carbon skeleton, i.e. <em>tran</em>-1-methyldecalin (1-MD), 5-methyltetraline (5-MT) and 1-MN, the ²H enrichment follows the order δ²H_1-MD &lt; δ²H_5-MT &lt; δ²H_1-MN during the low thermal conversion of BD. However, the order was subsequently destroyed with increasing aromatization. The results indicate that hydrocarbon aromatization can enrich aromatic hydrocarbon in ²H, resulting in a higher δ²H value of higher aromatic-ring-number hydrocarbon than that of a lower aromatic-ring-number at low aromatization. However, ²H enrichment will decrease and even result in a reverse order with enhanced aromatization. Our findings are beneficial for understanding genetic mechanism and hydrogen isotope fractionation effect during the formation and evolution of aromatic hydrocarbons.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"198 ","pages":"Article 104881"},"PeriodicalIF":2.6,"publicationDate":"2024-11-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652442","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Porphyrin protonation induces decoupling of trace metals in petroleum","authors":"Jingkun Zhang ,&nbsp;Jian Cao ,&nbsp;Wenjun He","doi":"10.1016/j.orggeochem.2024.104878","DOIUrl":"10.1016/j.orggeochem.2024.104878","url":null,"abstract":"<div><div>The mechanism of migration of trace metals in petroleum systems is poorly understood, which limits our understanding of organic–inorganic interactions and their application in tracing oil sources. Based on a molecular model of metalloporphyrin, numerical simulations involving density functional theory have revealed that porphyrin protonation is associated with trace-metal decoupling in petroleum. Trace metals readily form covalent bonds with weakly protonated porphyrin N to form stable compounds. However, the metals may be decoupled at lower fluid pH owing to increased N protonation, which activates the formation of ionic bonds with O²⁻. The released metals may then be fixed in authigenic calcite cement (ACC) reservoirs through substitution of Ca. For Mg, Mn, and Fe, the decoupling order is Mg &gt; Fe &gt; Mn, whereas that for the substitution of Ca is Mn &gt; Fe &gt; Mg, reflecting the complexity of organic–inorganic interactions and indicating the potential application of metals in fingerprinting oil sources. This case study of the southern Junggar Basin, China, revealed that Mn, Fe, and Mg enrichment of ACC may provide indications of Paleozoic, Mesozoic, and Cenozoic petroleum systems, respectively, providing a potential new approach for the tracing of oil sources in petroleum basins.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"198 ","pages":"Article 104878"},"PeriodicalIF":2.6,"publicationDate":"2024-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652438","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Influencing factors of hydrogen isotopic fractionation of light hydrocarbons during evaporation and implications","authors":"Wenna Liu ,&nbsp;Wanglu Jia ,&nbsp;Qiang Wang ,&nbsp;Jian Chen ,&nbsp;Jinbu Li ,&nbsp;Ping’an Peng","doi":"10.1016/j.orggeochem.2024.104894","DOIUrl":"10.1016/j.orggeochem.2024.104894","url":null,"abstract":"<div><div>The isotopic fractionation of organic compounds during evaporation is one of the most critical issues in the field of stable isotopes. The hydrogen (H) isotopic compositions of light hydrocarbons (LHs) in oil have gained increasing interest in the research of oil genesis in recent years. However, compared to carbon (C) isotopes, our understanding of H isotopic fractionation patterns and influences for various types of LHs during evaporation is limited. In this study, we performed evaporation experiments at a constant temperature on LHs in three systems: single compound, alkane mixture, and light oil. We assessed the contents and H isotopic compositions of individual LHs in the residual liquid phase. The degree of H isotopic fractionation and influencing factors are studied combined with C isotopes. The H isotopic fractionation of LHs exhibits “inverse isotope fractionation” characteristics (a depletion in D in the residual LHs) with progressive evaporation, which is opposite to the C isotopic fractionation. The degree of isotopic fractionation is influenced by the evaporation system, the compounds’ molecular weight, and their structure. (1) The isotopic fractionation degree of H and C decreases in the following order: light oil &gt; alkane mixture &gt; single compound system. This difference may be related to the unsaturation level of the evaporative system and the evaporation matrix. (2) For LHs with the similar structure in the same evaporation system, the degree of H isotopic fractionation increases with increasing molecular weight due to the buffering effect of the sample pool, while the magnitude of C isotopic fractionation decreases. (3) For LHs with the same C number, methylcyclohexane (MCH) has a lower evaporation rate and less isotopic fractionation than the other C₇ compounds like 3-methylhexane (3-MH), <em>n</em>-heptane (<em>n</em>C₇), and toluene (Tol).</div><div>The distinctive fractionation characteristics of H isotopes make them very useful in geological applications. Combining H and C isotopic compositions of the same compound with the commonly used molecular ratios of LHs (e.g., <em>n</em>C₇/MCH, Tol/<em>n</em>C₇) enables full differentiation of three critical processes controlling oil formation: evaporation, thermal maturation, and biodegradation. Furthermore, the differences in H isotopic compositions between C₇ LHs (3-MH, <em>n</em>C₇, and Tol) may be changed by evaporation, but the variation range is much smaller than that caused by source differences. Therefore, combining H and C isotopes may have great potential for oil source characterizations.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"198 ","pages":"Article 104894"},"PeriodicalIF":2.6,"publicationDate":"2024-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142572988","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Characterisation of dissolved organic matter in two contrasting arsenic-prone sites in Kandal Province, Cambodia","authors":"Oliver C. Moore ,&nbsp;Amy D. Holt ,&nbsp;Laura A. Richards ,&nbsp;Amy M. McKenna ,&nbsp;Robert G.M. Spencer ,&nbsp;Dan J. Lapworth ,&nbsp;David A. Polya ,&nbsp;Jonathan R. Lloyd ,&nbsp;Bart E. van Dongen","doi":"10.1016/j.orggeochem.2024.104886","DOIUrl":"10.1016/j.orggeochem.2024.104886","url":null,"abstract":"<div><div>Aquifers throughout Asia are impacted by the release of geogenic arsenic (As) into groundwater by microbial reduction of As-bearing Fe(III) (oxy)hydroxide minerals, severely impacting water quality. Groundwater dissolved organic matter (DOM) is likely key to As release, mainly as electron donor or electron shuttles. This study used optical analyses and ultra-high resolution mass spectrometry to examine the sources and composition of groundwater DOM in the As-prone aquifers of Kandal Province, Cambodia, at boreholes with differing host lithology (clay- and sand-dominated). Groundwater and surface water DOM composition were related to As concentrations, to infer the potential role of DOM in promoting As release. Optical and molecular-level analyses indicated an overall dominance of terrestrial-derived DOM in the groundwater samples, with higher freshness index and relative abundance (RA) of aliphatic compounds in clay compared to sand-dominated lithology. Compared to surface water, groundwater DOM had relatively lower O/C ratios and nominal oxidation state of carbon (−0.19 to −0.13 compared to 0.04 for ground and surface water, respectively), with a lower %RA of aliphatic compounds and higher %RA of carboxyl-rich alicyclic molecules, suggesting microbial processing of DOM since percolation into the aquifer. Concentrations of As across both sites were negatively correlated with DOM tryptophan:fulvic-like fluorescence and the %RA of aliphatics, potentially indicating microbial degradation of biolabile DOM in connection with As release, which is consistent with its role as an electron donor source. Together these data support DOM composition as an important control on microbial mediated As release.</div></div>","PeriodicalId":400,"journal":{"name":"Organic Geochemistry","volume":"198 ","pages":"Article 104886"},"PeriodicalIF":2.6,"publicationDate":"2024-10-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142652445","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}