Guangzhou Institute of Geochemistry
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Sedimentary responses to climatic variations and Kuroshio intrusion into the northern South China Sea since the last deglaciation
No full textThe terrigenous sediment source-to-sink processes in marginal seas are governed by intricate interactions among climate, sea level, and ocean currents. The continental slope of the northern South China Sea (SCS) provides an excellent setting to examine these processes due to its substantial terrigenous influx and continuous sedimentation. In this study, we present a high-resolution sedimentary record from the northern SCS continental slope covering the last deglaciation. Analyses of Rare Earth Elements (REEs) and Sr-Nd isotopic compositions in the NH07 core indicate that the predominant source of terrigenous sediment was Taiwan. Grain size-standard deviation analysis identified two sensitive grain size components, with the sensitive component 2 used as a marker of the Kuroshio intrusion into the northern SCS through Luzon Strait. The intensity of the Kuroshio intrusion into the northern SCS was found to be inversely related to that of the open Pacific. The Asian monsoon and El Nino- Southern Oscillation (ENSO) significantly influenced the variability of the Kuroshio Current throughout the deglaciation period. During the interval 16, 000-11, 700 cal yr BP, variations in terrigenous influx were collectively driven by sea level changes and the intensity of the Kuroshio intrusion, while chemical weathering intensity was affected by the reworking of previously exposed shelf sediments due to sea level fluctuations. During the Holocene, however, the East Asian summer monsoon intensity became the primary factor influencing variations in terrigenous influx and chemical weathering
Molecular simulation on Cs, Rb retention in Na/K-montmorillonite interlayer coupling clay swelling/collapse
No full textA key issue about radioactive waste disposal and nuclear accident contamination control is the retention of radionuclides in clay minerals. The cation (Cs+, Rb+, Na+, K+) selectivity in montmorillonite (Mt) interlayers have not been quantitatively studied. This work employs classical molecular dynamics (CMD) to systematically investigate the interlayer structure, swelling properties, diffusion dynamics, and cation exchange processes. The selectivity of alkali ions within the interlayer space coupled with clay swelling/collapse under different water activity (a(w)) and cation activity, has been quantified. Both Cs-, Rb-Mt demonstrate a monolayer hydrate configuration as the most stable state. The mobility of intercalated species, as indicated by self-diffusion coefficients, exhibits a stepwise trend with increasing water content. The cationic selectivity within the interlayer follows the order Cs+ > Rb+ > K+ > Na (+) at a(w) = 1.0. The logarithm values of the selectivity coefficients for Cs/Rb relative to Na/K are as follows: logK(c)(Cs/K) = 0.73, logK(c)(Cs/Na) = 1.62, logK(c)(Rb/K) = 0.62, and logK(c)(Rb/Na) = 1.57 at a(w) = 1.0. A model correlating selectivity coefficients with water activity has been proposed. It is noted that Cs+ and Rb+ ions tend to accumulate within the interlayer as water activity decreases, and interlayer Rb+ competes with Cs+ for exchange positions at low water activity. These results can be used to quantify cationic partitioning during the remediation of radiocesium contamination in soil and weathering processes of sediments
Microbial recruitment and microbial ecological roles in soil nutrient cycling of Populus cathayana males and females
No full textSoil nitrogen (N) availability influences plant production and soil nutrient cycling. However, how it influences sex-specific microbial community composition and rhizosphere nutrient cycling in dioecious plant species is poorly understood. We examined the rhizospheric bacterial and fungal community assemble and their influences on soil nutrient cycling under different N backgrounds in 30-year-old experimental stands and a soil microbial reshaping-controlled experiment. In comparison to male trees, female trees increased fungal community diversity, and the relative abundance of taxa related to nutrient availability; elevated phosphorus (P) mobilization by increasing acidic phosphatase activity and carboxylic acid release; and decreased the counts of denitrification nirS, nirK, and nosZ genes at high N supply. Males increased the nifH gene counts related to microbial N fixation at high N supply. Low N supply increased N fixation nifH gene counts in the rhizosphere of females. Males decreased bacterial and fungal diversity, increased enzymatic activities related to organic N and P mineralization, and elevated soil nitrate-nitrogen levels at low N supply. Our results indicate that sex-specific responses to N availability are associated with rhizospheric bacterial and fungal community composition and diversity and their effects on rhizospheric nutrient cycling, which may explain sex-specific resource utilization and niche differentiation
Iron isotopic fractionation during seafloor hydrothermal alteration of oceanic upper crust, as recorded in Geotimes lavas of Semail ophiolite, Oman
No full textThe Semail ophiolite in Oman features a crustal stratigraphy akin to a fast-spreading modern oceanic lithosphere. Its Geotimes pillow lavas, the stratigraphically oldest extrusive sequence at the bottom, share geochemical traits with contemporary mid-ocean ridge basalts, offering a unique opportunity to examine iron (Fe) isotopic fractionation during hydrothermal alteration under varied redox conditions. Significant alteration transformed primary minerals, evidenced by the dissolution of clinopyroxene, plagioclase, and ilmenite, alongside the precipitation of chlorite, albite, and magnetite-hematite. The 87Sr/88Sr ratios of 18 basalt subsamples from altered pillow lava range from 0.705110 to 0.705680, indicating extensive seawater interaction. The delta 56Fe values show systematic variations at a centimeter scale (0.037-0.291 parts per thousand), primarily resulting from hydrothermal processes rather than source inheritance. Notably, the pillow lava's core displays higher delta 56Fe values, suggesting the initial dissolution of Fe-bearing minerals under reduced conditions. In contrast, the edges show lower delta 56Fe values akin to mean mid-ocean ridge basalt, indicating that strong oxidation conditions minimally affected these isotopic values. In conclusion, this study reveals the complex variations of the Fe concentrations and Fe isotopic compositions of altered basalt that suffered hydrothermal alteration during the various redox conditions
Examining the reliability of current micro-and nano-indentation-based rock mechanical upscaling schemes: a comprehensive comparison with uniaxial/triaxial macroscopic mechanical testing
No full textShale and marlstone are two typical rocks for gas reservoirs and caprocks for the underground storage of carbon dioxide. Accurately estimating their mechanical properties is challenging due to these rocks' multiphase and multiscale structures. In this study, we conducted triaxial compressive, microindentation, and nanoindentation tests on samples collected in a borehole to investigate Young's modulus at different scales. To upscale the mechanical properties, we utilized existing homogenization models, namely Mori-Tanaka (MT), Self-Consistent (SC), and Voigt-Reuss-Hill average (VRH), and compared the moduli upscaled from the nanoindentation technique and rock mineralogical method with those measured from microindentation and triaxial compressive tests. Results showed that the rock mineralogy-based MT and SC methods produced higher moduli than the nanoindentation-based MT method, and all of these were significantly larger than those obtained from the triaxial compressive tests. Additionally, the nanoindentation-based VRH method and the microindentation test yielded close moduli but still exhibited a certain gap compared to the macroscopic mechanical test results. This suggests that the current indentation-based mechanical upgrading method cannot accurately estimate the rock mechanics at the macroscale. Nevertheless, in the absence of a better solution, the above two methods can still be considered. The difference between the moduli measured by the compressive test and those upscaled through these homogenization models was attributed to the underestimation caused by the low elastic stiffness of pores, fractures, and grain contacts in the rocks. Therefore, more advanced methods are required to develop to make mechanical upscaling closer to the real situation of rocks
Green remediation of REEs-contaminated soil by biodegradable chelators with optimization and risk assessment
No full textThe omnipresence of rare earth elements (REEs) in the environment, driven by their extensive industrial applications and common occurrence in some weathered crusts, has raised significant concerns as emerging pollutants. Soil washing has been recognized as an effective approach to remediate REEs-contaminated soils. However, traditional washing agents frequently lead to soil acidification and salinization, adversely affecting soil microbial communities and plant growth. This study explored the use of biodegradable chelators (BCs)-specifically N,N-bis(carboxymethyl)-L-glutamic acid (GLDA), iminodisuccinic acid (ISA), and polyaspartic acid (PASP)-as alternatives for removing REEs from contaminated agricultural soils. Our findings demonstrated that the removal efficiency of REEs positively correlates with BCs concentration, liquid-to-solid ratio, and washing time, while showing a negative correlation with solution pH. Through response surface analysis, we determined the optimal parameters for the washing process, revealing that GLDA, ISA, and PASP achieved total REEs removal efficiencies of 50.8%, 40.5%, and 23.2%, respectively. Statistical analysis confirmed that the concentration of BCs was the primary factor influencing washing effectiveness. Moreover, washing with BCs significantly removed reducible REEs-those bound to iron/manganese oxides-thereby decreasing the mobility and bioavailability of REEs in soil. The reduction in bioavailable REEs significantly lowered the environmental risk associated with contaminated soil. Notably, the activity of soil enzymes improved post-washing with BCs, indicating a positive impact on soil health. This study provides valuable insights into the remediation of REEscontaminated soils using BCs, with GLDA emerging as a particularly effective agent
Generation characteristics of polybrominated and polychlorinated dibenzo-<i>p</i>-dioxins/furans (PBDD/Fs and PCDD/Fs) under varying incineration conditions of municipal solid waste
No full textMunicipal solid waste incinerators (MSWIs) are deemed important sources of polychlorinated and polybrominated dibenzo-p-dioxin/furans (PCDD/Fs and PBDD/Fs). However, compared to PCDD/Fs, the emission characteristics of MSWI-derived PBDD/Fs have been rarely studied. Here we selected a long-term operating MSWI, investigated the generation of PBDD/Fs under varying incineration conditions within the normal range, and compared them to those of PCDD/Fs. Generally, PBDD/Fs exhibited mass-based emission factors (mass-EFs) one order of magnitude higher than those of PCDD/Fs and were predominantly released via slag, as were PCDD/ Fs, though at lower percentages. Both PBDD/Fs and PCDD/Fs showed significant changes in emissions with the variations in waste load, O2 content, and waste composition, particularly PBDD/Fs. Comparatively, furnacederived PBDD/Fs demonstrated heightened sensitivity to waste load and composition, whereas PCDD/Fs were primarily influenced by O2 levels, followed by waste composition; PCDD/Fs consistently exhibited increasing mass-EFs under unconventional conditions and PCDD/Fs in filtered fly ash were highly sensitive to all the three variables, while filtered PBDD/Fs remained insensitive to these conditions. Data comparison between raw flue gas and filtered fly ash indicated secondary generation of PBDD/Fs and PCDD/Fs during gas purification, as well as the insufficient dioxin-trapping efficiency of bag filters, particularly for PBDD/Fs. Therefore, MSWI-derived PBDD/Fs and dioxins in slag and other MSWI-derived wastes warrant significant attention
Microwave Digestion for Re-Os Isotope Measurements in Geological Samples
No full textIn this study, we present the novel use of a microwave digestion system (CEM BLADE) to digest geological materials for Re-Os isotopic analysis. This technique employs quartz digestion vessels that are easy to clean and reusable, avoid the complicated steps of opening and sealing, and enable complete digestion of the samples within 30 min at high temperature (max. 310 degrees C) and pressure (max. 700 psi). The microwave digestion system was used to digest samples of four ultramafic rock reference materials (GBW07101, GBW07102, GBW07291, and WPR-1a), one basalt reference material (BIR-1a), and one black shale reference material (SGR-1b). The Re-Os isotope measurement results for GBW07291, BIR-1a, and SGR-1b were in agreement with previously published values, and we are the first to report Re-Os isotopes for GBW07101, GBW07102, and WPR-1a. Therefore, this new microwave digestion system is a simple, efficient, reliable, and safe sample digestion method for prospective applications in Re-Os isotopic analysis
A comparative study on the formation of nitrogen-containing organic compounds in cloudd roplets and aerosolp articles
No full textNitrogen-containing organic compounds (NOCs)maypotentiallycontributetoaqueoussec-ondaryorganicaerosols,yet the different formationofNOCsinaerosolparticlesand clouddropletsremainsunclear. With the in-situmeasurementsperformedatamountainsite(1690ma.s.l.)in southernChina,weinvestigatedtheformationofNOCsintheclouddropletsandthecloud-freeparticles,basedontheirmixingstateinformationofNOCs-containingparticlesbysingleparticlemassspectrometry.TherelativeabundanceofNOCsinthecloud-freeparticleswassignificantlyhigherthanthoseincloudresidual(cloudRES)particles.NOCswerehighlycorrelatedwithcarbonylcompounds(includingglyoxalateandmethylglyoxal)inthecloud-freeparticles,however,limitedcorrelationwasobservedforcloudRESparticles.AnalysisoftheirmixingstateandtemporalvariationshighlightsthatNOCswasmainlyformedfromthecarbonylcompoundsandammoniuminthecloud-freeparticles,ratherthaninthecloud RES particles.Theresultssupportthattheformation of NOCsfromcarbonylcompoundsisfacilitatedinconcentratedsolutionsinwetaerosols,ratherthanclouddroplets.In addition,we have identified the transport of biomass burnin
Size-segregated nitrated aromatic compounds in PM10 and potential health risks in Guangzhou, South China
No full textNitrated aromatic compounds (NACs) are toxic, light-absorbing components of particulate matter, impacting both human health and climate. This study conducted a 14-day field campaign at an urban site in Guangzhou, southern China, collecting size-segregated aerosol samples at cutting points of 0.49, 0.95, 1.5, 3.0, 7.2, and 10 mu m, to analyze NAC size distribution, light absorption, and toxicity. Nearly 90% of NACs were concentrated in particulate matters with aerodynamic diameter smaller than 1.5 mu m (PM1.5). Their concentrations on polluted days strongly correlated with molecular markers from primary emissions, especially from coal combustion. Backward trajectory analysis indicated that northern coal-fired sources significantly contributed to pollution levels. Filter-based light absorption measurements showed that over 90% of brown carbon (BrC) were concen- trated in PM0.95. Despite lower mass concentrations of the 9 toxic NACs compared to the 16 USEPA priority polycyclic aromatic hydrocarbons (PAHs), their Benzo[a]pyrene toxic equivalency quotients (TEQBaP) were substantially higher, with 1,6-dinitropyrene, 1,8-dinitropyrene, and 6-nitroperylene accounting for 95% of the TEQBaP. 1,6-dinitropyrene was the dominant contributor to NACs' TEQBaP on both clean and polluted days. The TEQBaP of NACs exceeded 1.0 ng m-3, indicating substantial health risks associated with exposure. These findings highlight the urgent need for emission control to mitigate the health impact of NACs