17321. 题目: Spectral characteristics of soil dissolved organic matter: Long-term effects of exogenous organic matter on soil organic matter and spatial-temporal changes
作者: N.Y. Musadji, L. Lemée, L. Caner, G. Porel, P. Poinot, C. Geffroy-Rodier
摘要: The aim of this study was to evaluate the long-term effect of urban and green waste compost exogenous organic matter (EOM) on soil dissolved organic matter (DOM). A luvic cambisol was amended 7 years before the study. DOM was investigated along a soil profile down to 1 m depth regarding seasonal variations (autumn and spring). DOM sampled by suction cups was characterized using dissolved organic carbon (DOC) content and excitation emission matrix (EEM) fluorescence. The variability of DOM concentrations was pronounced but no major change in composition was determined. The results obtained, reinforced by statistical analysis, showed that the DOM quality was mainly influenced by soil management (organic matter amendment) whereas the quantity mainly depended on the season (heavy precipitation event). DOM humic characteristics were strongly dependent on amendment and changed with depth but was not affected by the season. Long term effect of compost organic matter was highlighted after a 7-years amendment.
17322. 题目: Competitive adsorption of tylosin, sulfamethoxazole and Cu(II) on nano-hydroxyapatitemodified biochar in water
作者: Zhen Li, Zhaoyan Wang, Xiaona Wu, Miao Li, Xiang Liu
摘要: Antibiotics and heavy metals are frequently detected simultaneously in water environment. In this study, the competitive adsorption behavior of tylosin (TYL) and sulfamethoxazole (SMX) on nano-hydroxyapatite modified biochar (nHAP@biochar) in accordance with Cu(II) in single, binary and ternary systems was investigated. The specific surface area of nHAP@biochar was 566.056 m2/g. The adsorption of TYL on nHAP@biochar reduced by 13.36%–41.04% or 9.92%–38.69% with Cu(II) and SMX in the solution, respectively. The suppression of SMX was stronger than Cu(II) on the adsorption of TYL when the SMX or Cu(II) was constant. The adsorption of SMX increased by 2.01–3.56 times in the present of Cu(II), while suppressed by TYL up to 42.30%. Due to the bridging of TYL or SMX between the nHAP@biochar and Cu(II) and destroying of bound water surrounded, the adsorption of Cu(II) increased to a greater extent. Electrostatic interaction and H-bond were the two main interactions between TYL, SMX and Cu(II) and nHAP@biochar. π-π interactions was also interaction between the SMX and nHAP@biochar.
17323. 题目: Effects of pH and gallic acid on the adsorption of two ionizable organic contaminants to rice straw-derived biochar-amended soils
期刊: Ecotoxicology and Environmental Safety
作者: Ying He, Ting Yao, Shuo Tan, Bingqi Yu, Kailin Liu, Lifeng Hu, Kun Luo, Min Liu, Xiangying Liu, Lianyang Bai
摘要: The existing form of ionizable organic contaminants (IOCs) could affect their adsorption characteristics to soil and biochar. In this study, 2 IOCs, namely, sulfadiazine and imazalil, were selected to study their adsorption by rice straw-derived biochar-amended soils, as well as the effect of pH and gallic acid on their adsorption. The results showed that the soil adsorption isotherms of the two ionizable organic contaminants could be fitted well by a linear equation and the Freundlich equation, and r2 was more than 0.80. The adsorption coefficient (Kd) in the three kinds of soil ranged from 0.262 to 4.07 L kg−1 for sulfadiazine and from 3.11 to 96.5 L kg−1 for imazalil. After the addition of biochar, the adsorption of sulfadiazine and imazalil in the soil increased. The adsorption of sulfadiazine by biochar gradually decreased with the increase in pH; the adsorption of imazalil increased when the pH increased from 2 to 5 and then gradually decreased with increasing pH. Gallic acid enhanced the adsorption of the two IOCs to pure soil and biochar-amended soil.
17324. 题目: Binding characteristics of cadmium and zinc onto soil organic matter in different water managements and rhizosphere environments
期刊: Ecotoxicology and Environmental Safety
作者: Jiajun Wen, Zhongwu Li, Ninglin Luo, Mei Huang, Xiang Ding, Xianrong Bu, Ming Chen
摘要: Soil organic matter (SOM) could immobilize most of metals, but it could promote the migration of a small part of metals in special environments. Heavy rainfall and drought makes wetlands affected by the alternation of drought and flood, altering the mobility of metals. Few studies have been conducted on the changes of binding characteristics of metals onto SOM which derived from different water conditions and rhizospheric environments. The objective of this paper was to explore the sequential differences of spectral variations of fluorescent groups and UV–Vis groups of metals onto SOM which derived from different water managements and rhizospheric environments. The method adopted was mainly two-dimensional correlation analysis (2DCOS). The results showed that flooding samples contained more aromatic substances compared to draining samples, which could promote metal binding. The binding characteristics were shown in the following: (1) Cd2+ and Zn2+ could react with aromatic substances, react with functional groups in SOM, and promote the formation of new groups such as carboxyl; (2) both Zn2+ and Cd2+ could bind with functional groups on proteins but relatively reductive environment can weaken the binding ability of Cd2+; (3) the protein-like or fulvic-like groups gave the fastest responses and then came the amide and carboxyl groups in nearly all flooding samples; (4) in flooding samples, Cd2+ was most easily to bind with fulvic-like groups, while Zn2+ was most easily to bind with protein-like groups. This work is conducive to the long-term management of heavy metal pollutants in wetlands.
17325. 题目: Are the n-alkane carbon isotopic profiles of South Australian coastal asphaltites indicative of their extent of weathering?
期刊: Organic Geochemistry
作者: David M. McKirdy, Se Gong, Alexander J. Corrick, P. Anthony Hall, Christine Trefry, Andrew S. Ross
摘要: Asphaltic bitumen (asphaltite) found on the ocean beaches of South Australia is considered to be a product of an adjacent, but as yet unlocated, submarine oil seep. Four large asphaltites recently stranded on three different beaches were sub-sampled (n = 5–6). Samples were analysed to determine if their n-alkane δ13C profiles displayed systematic variation along a transect from the centre to the outer rim of the specimen. Previously reported 13C-enrichment in n-alkanes isolated from the outer portions of similar archival asphaltites was attributed to weathering. With one notable exception, these new specimens exhibited no unidirectional enrichment from interior (fresh) to exterior (weathered), although in every instance n-alkanes in the intermediate and outermost sub-samples were for the most part isotopically heavier than the same homologues in the central interior of the specimen. To be a viable measure of the extent of weathering in a population of coastal asphaltites, and hence also their relative exposure time in the ocean, this analytical protocol requires the specimens to have remained physically intact during their transit from the parent seep to shore. Whether this requirement has been met is impossible to determine, thereby limiting the effectiveness of the method to those specimens in which there is a consistent pattern of internal variation in their n-alkane carbon isotope profiles.
17326. 题目: Exploring the upper particle size limit for field flow fractionation online with ICP-MS to address the challenges of water samples from the Taihu Lake
期刊: Analytica Chimica Acta
作者: Jingjing Yang, Ping Tan, Tianyin Huang, Volker Nischwitz
摘要: Regular algal blooms are occurring in Taihu lake, which may be triggered by resuspension of sediments containing relevant amounts of phosphorus. Therefore, our study aims at quantification of phosphorus concentrations bound to suspended particulate matter in Taihu water samples to investigate this hypothesis. A field flow fractionation (FFF) method online with ICP-MS detection was developed to achieve an overview on particulate fractions of phosphorus and related elements including Fe, Al and C from the low nanometer to the low micrometer size range. Mass balance of dissolved and particulate elemental contents was established for quality control purpose and indicated low recovery of Fe, Al and P. Complementary determination of volume based particle size distribution by dynamic imaging analysis showed a majority of particle volume and thus mass in particles with size >5 μm. In order to address this challenge, the upper particle size limit of FFF online with ICP-MS was for the first time investigated in detail using well characterised monodisperse latex particles as model for organic matter in the low micrometer size range including microalgae. The effect of pre-filtration of the sample as well as the contribution of sample introduction via three different interfaces including micromist nebuliser/spray chamber, direct injection nebulisation and APEX with heated spray chamber and solvent removal by condensation on the particulate carbon recovery was studied by ICP-MS detection. The same instrumental setup was also applied for the characterisation of particulate elemental contents in the Taihu water samples as far as possible. Significant improvement of the detected particulate fraction in Taihu water samples was achieved by increasing the membrane pore size for pre-filtration and by using the APEX for introduction of the eluate from FFF into ICP-MS.
17327. 题目: Linkages between flow regime, biota, and ecosystem processes: Implications for river restoration
作者: Margaret Palmer, Albert Ruhi
摘要: River ecosystems are highly biodiverse, influence global biogeochemical cycles, and provide valued services. However, humans are increasingly degrading fluvial ecosystems by altering their streamflows. Effective river restoration requires advancing our mechanistic understanding of how flow regimes affect biota and ecosystem processes. Here, we review emerging advances in hydroecology relevant to this goal. Spatiotemporal variation in flow exerts direct and indirect control on the composition, structure, and dynamics of communities at local to regional scales. Streamflows also influence ecosystem processes, such as nutrient uptake and transformation, organic matter processing, and ecosystem metabolism. We are deepening our understanding of how biological processes, not just static patterns, affect and are affected by stream ecosystem processes. However, research on this nexus of flow-biota-ecosystem processes is at an early stage. We illustrate this frontier with evidence from highly altered regulated rivers and urban streams. We also identify research challenges that should be prioritized to advance process-based river restoration.
17328. 题目: Aided phytostabilisation over two years using iron sulphate and organic amendments: Effects on soil quality and rye production
作者: Teresa Fresno, Jesús M. Peñalosa, Maren Flagmeier, Eduardo Moreno-Jiménez
摘要: An outdoor macrocosm experiment using Fe-based and organic amendments over 2 years was set up to evaluate the effectiveness of aided-phytostabilisation. For that, a soil contaminated with As- and Cu-rich waste material (∼13000 mg As kg−1 and ∼500 mg Cu kg−1) was treated with combinations of iron sulphate (Fe) with lime, paper mill sludge (PS), holm-oak biochar (BC), olive mill waste compost (OMWC) or green waste compost (GWC). Rye (Secale cereale L.) was grown in the treated and non-treated soils 16 months after addition of the amendments. Arsenic and Cu dynamics in soil were assessed throughout the experiment and soil quality parameters (soil nutrients, organic matter and soil biology) were measured almost two years after addition of the amendments. All treatments resulted in a reduction of soluble and extractable Cu during the experiment and, despite the increase in soil pH (from 5 to 68) and DOC (from 10 up to 50 mg DOC L−1) provoked by the amendments, As was not significantly mobilised in the treated soils. Treatments combining Fe sulphate with the organic materials, especially biochar and both composts, resulted in an increase in soil available nutrients and enhanced rye growth. In this semi-field scale experiment, the combination of Fe sulphate with holm-oak biochar showed the most promising results in terms of soil fertility (nutrient availability), plant As and Cu uptake and soil C sequestration. Further research should focus on monitoring long-term effects of the soil amendments on crops, following repeated applications.
17329. 题目: Biochar synthesis from sweet lime peel for hexavalent chromium remediation from aqueous solution
期刊: Journal of Environmental Management
作者: Amita Shakya, Avelino Núñez-Delgado, Tripti Agarwal
摘要: Sweet lime (Citrus limetta) peel biochar was obtained by slow pyrolysis of raw biomass at 450 °C with 5 °C/min heating rate. Proximate and ultimate analysis, physico-chemical characterization of the biochar was done. Batch adsorption experiments for Cr(VI) removal were performed with varying pH, biochar dose, contact time and initial Cr(VI) concentrations. It took 8–24 h to reach the equilibrium at 30 °C for varying Cr(VI) concentrations. The biochar was found to possess higher adsorption capacity (100 mg/g) than the adsorbents reported in several previous studies. Langmuir adsorption isotherm and pseudo second order model best explained the experimental data, suggesting monolayer adsorption as the dominant mechanism. Chemical interaction, ion exchange of solute and sorbate ions and physical adsorption also contributed into Cr(VI) adsorption process. Further, Cr(VI) adsorption was found to be a multistep process. The findings suggested that sweet lime peel biochar can be utilized as a low cost and efficient alternative for Cr(VI) removal, which could be useful for aqueous solutions, as well as to promote overall protection against soil and water degradation and pollution.
17330. 题目: Investigation of polycyclic aromatic hydrocarbons in soils from Caserta provincial territory, southern Italy: Spatial distribution, source apportionment, and risk assessment
期刊: Journal of Hazardous Materials
作者: Pengzhi Qi, Chengkai Qu, Stefano Albanese, Annamaria Lima, Domenico Cicchella, David Hope, Pellegrino Cerino, Antonio Pizzolante, Huang Zheng, Jiji Li, Benedetto De Vivo
摘要: The concentrations of polycyclic aromatic hydrocarbons (PAHs) in soils from Caserta provincial territory, southern Italy, were systematically investigated along with their correlations with soil properties and health risk. The concentrations of ∑16PAHs ranged from 10.0 to 4191 ng/g, with a median (1 st quartile, Q1; 3rd quartile, Q3) of 28.5 (17.5–65.0) ng/g; Four-ring PAHs were the most abundant and contributed an average of ∼50.2% of the ∑16PAHs. Signiﬁcant differences in the spatial distributions of PAHs in soil were observed, with higher levels of PAH contamination found in Caserta city and the surrounding areas. According to the positive matrix factorization (PMF) model, three sources were identified: chemical production and metal smelting, vehicle emissions, and coal/biomass combustion. Soil total organic carbon was significantly correlated with the concentration of total PAHs and the concentrations of PAHs with three-, four-, and five-rings. In contrast, only the concentration of ∑4DBPs (dibenzo(a,e)pyrene, dibenzo(a,h)pyrene, dibenzo(a,i)pyrene, dibenzo(a,l)pyrene) was well correlated with population density. The soil mass inventory of ∑16PAHs was estimated to be 6.87 metric tons (geometric mean). The ecological risks posed by PAHs in the study are negligible; however, health risks of exposure to soil-borne PAHs were identified based on a probabilistic risk model.
17331. 题目: Unravelling the influences of sewer-dosed iron salts on activated sludge properties with implications on settleability, dewaterability and sludge rheology
期刊: Water Research
作者: Sohan Shrestha, Keshab Sharma, Zhongwei Chen, Zhiguo Yuan
摘要: Although the beneficial impacts of iron dosing to sewer on activated sludge unit's performance, especially in relation to phosphate removal, have been reported, the extent of impacts on different sludge properties affecting the operation and performance of the activated sludge unit are not fully understood. In this study, we investigated the influences of iron salt dosing to sewer on both settleability and dewaterability of downstream activated sludge unit. We also examined, based on the comparative assessment of different key activated sludge properties, possible underlying factors responsible for the changes in sludge settleability and dewaterability. For this, iron chloride was dosed to a sewer reactor of integrated laboratory sewer-bioreactor system. The activated sludge samples were obtained from two separate reactors, an experimental sequencing batch reactor (SBR-E) downstream of sewer reactor receiving iron dosing and a control SBR (SBR-C) downstream of a sewer reactor without any iron dosing. Iron-conditioned sludge showed improved settleability and dewaterability over the unconditioned activated sludge. Mean differences in settleability and dewaterability between two sludges were 22.5 ± 7.8 mL/g (p < 0.05) and 7.8 ± 1.2% (p < 0.05), respectively. Iron-conditioned sludge showed lower contents of soluble extracellular polymeric substances (EPS) fractions, protein and polysaccharide contents, and monovalent-to-divalent (M+/D++) cations ratio, but higher humification index as compared to the unconditioned sludge. Iron-conditioned sludge exhibited marginal increment in mean particle size (Dv50) and settleable particle size classes (100–400 μm) but reduction in supracolloidal particle size classes (1–100 μm). In terms of sludge rheology, iron-conditioned sludge exhibited relatively lower relative sludge network strength, viscosity, yield stress, elastic/viscous/complex moduli (G′/G′′/G*), and damping factor tan(δ) but increased shear compliance (J) and shear strain (%) with time.The iron-conditioned sludge therefore exhibited relatively weaker deformation resistance and sludge elasticity. Based on the foregoing results, we posit the combined synergistic effect of favourable changes to the key sludge properties, might be responsible for the observed improvement in settleability and dewaterability of iron-conditioned sludge.
17332. 题目: Optical properties, source apportionment and redox activity of humic-like substances (HULIS) in airborne fine particulates in Hong Kong
期刊: Environmental Pollution
作者: Yiqiu Ma, Yubo Cheng, Xinghua Qiu, Gang Cao, Binyu Kuang, Jian Zhen Yu, Di Hu
摘要: Humic-like substances (HULIS) account for a considerable fraction of water-soluble organic matter (WSOM) in ambient fine particulates (PM2.5) over the world. However, systemic studies regarding the chemical characteristics, sources and redox activity of HULIS are still limited. In this study, the mass concentration, optical properties, and reactive oxygen species (ROS)-generation potential of HULIS were investigated in PM2.5 samples collected in Hong Kong during 2011–2012, and they all showed higher levels on days under regional pollution than on days under long range transport (LRT) pollution and local emissions. Positive matrix factorization (PMF) analysis was conducted regarding the mass concentration and dithiothreitol (DTT) activity of HULIS. Four primary sources (i.e. marine vessels, industrial exhaust, biomass burning, and vehicle emissions), and two secondary sources (i.e. secondary organic aerosol formation and secondary sulfate) were identified. Most sources showed higher contributions to both the mass concentration and DTT activity of HULIS on regional days than on LRT and local days, except that marine vessels had a higher contribution on local days than the other two synoptic conditions. Secondary processes were the major contributor to HULIS (54.9%) throughout the year, followed by biomass burning (27.4%) and industrial exhaust (14.7%). As for the DTT activity of HULIS, biomass burning (62.9%) and secondary processes (25.4%) were found to be the top two contributors. Intrinsic ROS-generation potential of HULIS was also investigated by normalizing the DTT activity by HULIS mass in each source. HULIS from biomass burning were the most DTT-active, followed by marine vessels; while HULIS formed through secondary processes were the least DTT-active. For the optical properties of HULIS, multiple linear regression model was adopted to evaluate the contributions of various sources to the light absorbing ability of HULIS. Biomass burning was found to be the only source significantly associated with the light absorbing property of HULIS.
17333. 题目: Nutrients and heavy metals mediate the distribution of microbial community in the marine sediments of the Bohai Sea, China
期刊: Environmental Pollution
作者: Meiqing Lu, Xin Luo, Jiu Jimmy Jiao, Hailong Li, Xuejing Wang, Jingyan Gao, Xiaolang Zhang, Kai Xiao
摘要: The Bohai Sea, one of the largest marginal seas in China, is extensively influenced by human and industrial activities. The pollutant loads from anthropogenic activities have induced severe ecological problems. The study investigates the physicochemical characteristics of seawater and sediments in Bohai Bay and Laizhou Bay of the Bohai Sea. The diversity and composition of microbial community in sediments are analyzed by 16S rRNA gene amplicon sequencing. The sequencing results present 16 phyla and 31 classes from the samples. Proteobacteria constituted a dominant phylum, of which the classes of Gamma-, Delta-, and Epsilon-are predominant sub-divisions. Nitrogen, phosphorus, and sulfur cycling related microbes present high abundance in both bays. The metabolism of organic matters is the main factor that influences the distribution of microbial communities in Bohai Bay, while the inflow of Yellow River is the dominant factor that influences the distribution of microbial communities in Laizhou Bay. Sulfur oxidizing process is expected to be positively influenced by heavy metals, while ammonia (NH4+) oxidizing process is prone to be negatively affected by heavy metals in both bays. Microbial communities in the offshore sediments of Laizhou Bay and the majority microbial communities in Bohai Bay sediments are subject to similar predominant controlling factors. This phenomenon is likely ascribed to ocean circulation. The results of this study can provide constructive guidelines on ecosystem management of marginal seas in Bohai and elsewhere.
17334. 题目: Adsorption and fractionation of Pt, Pd and Rh onto inorganic microparticles and the effects of macromolecular organic compounds in seawater
期刊: Environmental Pollution
作者: Kai Liu, Xuelu Gao
摘要: Adsorption and fractionation of Pt, Pd and Rh (defined here as platinum group elements, PGEs) onto the representative inorganic microparticles, including Fe2O3, MnO2, CaCO3, SiO2, Al2O3 and kaolinite in seawater were investigated. The effects of macromolecular organic compounds (MOCs) as the representatives of organic matter, including humic acids (HA), bovine serum albumin (BSA) and carrageenan, on the adsorption were also studied considering that organic matter is ubiquitous in seawater and indispensable to marine biogeochemical cycles. In the absence of MOCs, the representative mineral particles Fe2O3 and MnO2 had the strongest interaction with PGEs. The adsorption of PGEs onto the representative biogenic particles SiO2 and CaCO3 and lithogenic particles Al2O3 and kaolinite was similar or weaker than onto the mineral particles. MOCs inhibited the interaction between PGEs and the particles except for Pt and Pd onto the biogenic particles in artificial seawater. This impediment may be closely related to the interaction between particles, MOCs and elements. The partition coefficient (log Kd) of Pt was similar (∼4.0) in the presence of MOCs, indicating that the complexation between Pt and MOCs was less important than hydrolysis or adsorption onto the acid oxide particle surface. Rh tended to fractionate onto the mineral and lithogenic particles in the presence of HA and carrageenan, while Pd was more likely to fractionate onto the biogenic particles. However, BSA enhanced the fractionation tendency of Pd onto the mineral particles. The results indicate that the adsorption behavior of Pd onto inorganic particles was significantly affected by the composition or the type of MOCs. Hence, the interaction between PGEs and inorganic particles may be greatly affected by the macromolecular organic matter in the ocean.
17335. 题目: Microbial sulfidogenesis of arsenic in naturally contaminated wetland soil
期刊: Geochimica et Cosmochimica Acta
作者: Magdaléna Knappová, Petr Drahota, Lukáš Falteisek, Adam Culka, Vít Penížek, Jakub Trubač, Martin Mihaljevič, Tomáš Matoušek
摘要: Microbial sulfidogenesis plays a potentially important role in As biogeochemistry within wetland soils, sediments, and aquifers. This study investigated the effects of microbial sulfidogenesis on As mineralogy in the As-enriched wetland soil found at the natural geochemical anomaly of the Smolotely-Líšnice (Czech Republic) historical gold district. The distribution and speciation of As as a function of soil depth, and the metabolic properties of microbial communities in different sulfidogenic domains were examined by bulk soil as well as pore water analyses, selective chemical extractions, S isotopes, and DNA extractions. Total solid-phase analyses and selective extractions of the soil samples below ∼40 cm showed that As (up to 1.16 g kg–1) and Fe(II) are coupled to S and TOC, and had accumulated to a considerable extent in the exterior parts of NOM fragments (up to 19 wt.% As). Microscale imaging and Raman spectroscopy revealed that As speciation in the NOM exteriors is a combination of realgar (α-As4S4), bonazziite (β-As4S4) and arsenian Fe sulfides, primarily greigite (Fe3S4) and framboidal pyrite (FeS2). The sulfide phases were depleted in the 34S isotope by 6.3-29.4‰ relative to pore water SO42–; thus implying their biologically induced formation. Microbial communities associated with sulfidogenic environments in NOM and bulk soil had variable compositions, although the dissimilative SO42– reduction was usually the main metabolic trait. Relatively low isotopic fractionation in sulfide-rich NOM fragments (6.3-11.6‰) compared to bulk soil (down to -26.1‰) revealed a reservoir effect that developed probably at mm-scales. This indicates formation of sulfide phases in highly localized environments depleted in aqueous SO42– due to strong microbial sulfidogenesis when compared to the transfer rate of the solutes. The very high proportion of fermenting microorganisms in sulfide-rich NOM fragments provided further evidence of strongly reducing conditions, which are a prerequisite for sulfide phase precipitation. We have shown that by the development of suitable conditions for sulfidogenesis, NOM fragments play an active role in As immobilization in an As-enriched wetland soil. Regarding the effectiveness of As sulfidogenesis in shallow wetland soils to remediate groundwater, our findings imply that As contamination may either be limited by the low content of labile organic matter or by the fast transfer of solutes (groundwater flow).
17336. 题目: Calculating 14C mean residence times of inorganic carbon derived from oxidation of organic carbon in groundwater using the principles of 87Sr/86Sr and cation ratio mixing
期刊: Geochimica et Cosmochimica Acta
作者: Daniel Magnone, Laura A. Richards, Bart E. van Dongen, Charlotte Bryant, Jane A. Evans, David A. Polya
摘要: The model radiocarbon age of inorganic carbon (IC) in groundwater is a key parameter for understanding groundwater chemical history and physical parameters such as groundwater residence times and flow rates. Current interpretations are based on the principle that bulk IC derives from multiple sources such as oxidation of organic carbon (OC), carbonate dissolution, and soil zone processes as well as from rainwater. Using this principle, multiple adjustment methods have been developed to calculate rainwater-related recharge ages. Of further interest, however, is the radiocarbon age of oxidised OC. This is a key measurement given that OC oxidation controls the mobility of many important geochemical components such as Fe, As, Mn and U. In this instance, conventional approaches tacitly assume that the majority of IC comes from the oxidation of OC and that other sources have a negligible effect on the bulk age. In reality, however, there are multiple source of IC which can all effect bulk radiocarbon ages. We present a new approach to calculate the age of IC derived from a specific source. This approach uses strontium isotopes (87Sr/86Sr) coupled with elemental ratios to trace and quantify the mixing of different sources of IC. We demonstrate the approach by calculating the model radiocarbon age of IC from the oxidation of OC for a case study of an aquifer in the Cambodian lowlands located adjacent to the Mekong river south of Phnom Penh. The results show that, although bulk IC is younger and more isotopically depleted than bulk organic carbon (OC), IC derived from oxidation of OC, has a similar age and isotopic signature to bulk OC. Furthermore, at our site the age of the IC formed from the oxidation of organic carbon predates modelled groundwater flow by at least a millennium indicating that in-aquifer oxidation is an important process, something previously questioned at the site. This highlights the utility of the new approach to disentangling the origin of the sources of bulk IC, so critical to the interpretation of its model radiocarbon age and isotopic signature.
17337. 题目: Ocean acidification and hypoxia alter organic carbon fluxes in marine soft sediments
期刊: Global Change Biology
作者: Chiara Ravaglioli, Fabio Bulleri, Saskia Rühl, Sophie J. McCoy, Helen S. Findlay, Stephen Widdicombe, Ana M. Queirós
摘要: Anthropogenic stressors can alter the structure and functioning of infaunal communities, which are key drivers of the carbon cycle in marine soft sediments. Nonetheless, the compounded effects of anthropogenic stressors on carbon fluxes in soft benthic systems remain largely unknown. Here, we investigated the cumulative effects of ocean acidification (OA) and hypoxia on the organic carbon fate in marine sediments, through a mesocosm experiment. Isotopically labelled macroalgal detritus (13C) was used as a tracer to assess carbon incorporation in faunal tissue and in sediments under different experimental conditions. In addition, labelled macroalgae (13C), previously exposed to elevated CO2, were also used to assess the organic carbon uptake by fauna and sediments, when both sources and consumers were exposed to elevated CO2. At elevated CO2, infauna increased the uptake of carbon, likely as compensatory response to the higher energetic costs faced under adverse environmental conditions. By contrast, there was no increase in carbon uptake by fauna exposed to both stressors in combination, indicating that even a short‐term hypoxic event may weaken the ability of marine invertebrates to withstand elevated CO2 conditions. In addition, both hypoxia and elevated CO2 increased organic carbon burial in the sediment, potentially affecting sediment biogeochemical processes. Since hypoxia and OA are predicted to increase in the face of climate change, our results suggest that local reduction of hypoxic events may mitigate the impacts of global climate change on marine soft‐sediment systems.
17338. 题目: Changes of composition and content of tricyclic terpane, hopane, sterane, and aromatic biomarkers throughout the oil window: A detailed study on maturity parameters of Lower Toarcian Posidonia Shale of the Hils Syncline, NW Germany
期刊: Organic Geochemistry
作者: Ronghui Fang, Ralf Littke, Laura Zieger, Alireza Baniasad, Meijun Li, Jan Schwarzbauer
摘要: A total of 30 core samples of organic matter-rich Lower Toarcian shale (Posidonia Shale) were geochemically analyzed to study systematic changes in the quantitative and qualitative composition of specific biomarkers at different thermal maturities ranging from 0.48 to 1.45% vitrinite reflectance (VRr). The samples are derived from 5 wells (Hils Syncline, NW Germany) each representing a different level of maturation (0.48, 0.68, 0.73, 0.88, 1.45 %VRr). In NW Germany, Posidonia Shale was deposited under marine, oxygen-deficient bottom water containing initially high amounts of TOC (above 10%) and marine type I-II kerogen. Upon maturation, organic carbon has been lost and hydrogen index values have decreased. Biomarker ratios reflecting this maturation very well include ratios of short over long-chain n-alkanes, ratios of pristane and phytane over nC17 and nC18, Ts/(Ts+Tm), C29Ts/(C29Ts+C29H), ratios based on DMDBTs, and TA(I)/TA(I+II) ratios (triaromatic steroids). The evolution of different steroid-, hopane-, naphthalene-, phenanthrene- and dibenzothiophene-related parameters is documented and compared to literature.Concentrations of individual hydrocarbons were measured in order to obtain quantitative data on biomarker abundance and their evolution upon maturation. Whereas there is a general trend of increasing biomarker content from immature (0.48 %VRr) to early mature (0.68 %VRr) conditions and of decreasing biomarker content with maturation from 0.68 to 0.88 %VRr, there are some exceptions from this trend, especially at low levels of maturity. Almost no polycyclic biomarkers were detected at the highest maturity level of 1.45 %VRr in well Haddessen, where n-alkanes and aromatic hydrocarbons are predominant. The overall pattern of polycyclic biomarker abundance is not only determined by isomerization and aromatization processes, but mainly by preferential degradation of thermally less stable biomarkers leading to the observed modifications of biomarker maturity parameters.Furthermore, outer and inner sections from the 10 cm wide cores were compared in order to find out, whether 40 years of dry storage in a core repository affected the biomarker parameters. No significant and systematic differences have been observed, with exception of the most mature Haddessen well, where low molecular weight n-alkanes (<nC21) are more abundant in the outer part.
17339. 题目: Iron Isotope Fractionation during Bio- and Photodegradation of Organoferric Colloids in Boreal Humic Waters
期刊: Environmental Science & Technology
作者: Olga V. Oleinikova, Franck Poitrasson, Olga Yu Drozdova, Liudmila S. Shirokova, Sergey A. Lapitskiy, Oleg S Pokrovsky
摘要: Biodegradation and photolysis of dissolved organic matter (DOM) in boreal high-latitude waters are the two main factors controlling not only the aquatic fluxes and residence time of carbon but also metal nutrients associated with DOM such as Fe. The DOM is usually present in the form of organic and organomineral colloids, which also account for the majority of dissolved Fe. Here, we use the stable Fe isotope approach to unravel the processes controlling Fe behavior during bio- and photodegradation of colloids in boreal Fe- and DOM-rich humic waters (a stream and a fen). The adsorption of Fe colloids onto heterotrophic bacteria Pseudomonas aureofaciens produced enrichment in +0.4‰ (δ57Fe) in the heavier isotopes of the cell surface relative to the remaining solution. In contrast, long-term assimilation of Fe by live cells yielded preferential incorporation of lighter isotopes into the cells (−0.7‰ relative to aqueous solution). The sunlight-induced oxidation of Fe(II) in fen water led to the removal of heavier Fe isotopes (+1.5 to +2.5‰) from solution, consistent with Fe(III) hydroxide precipitation from Fe(II)-bearing solution. Altogether, bio- and photodegradation of organoferric colloids, occurring within a few days of exposure time, can produce several per mil isotopic excursions in shallow lentic and lothic inland waters of high-latitude boreal regions. Considerable daily scale variations of Fe isotopic composition should therefore be taken into account during the interpretation of the riverine flux of Fe isotopes to the ocean or tracing weathering processes using Fe isotopes in surface waters at high latitudes.
17340. 题目: Land use, not stream order, controls N2O concentration and flux in the upper Mara River basin, Kenya
期刊: Journal of Geophysical Research: Biogeosciences
作者: R.M. Mwanake, G.M. Gettel, K.S. Aho, D.W. Namwaya, F.O. Masese, K. Butterbach‐Bahl, P.A. Raymond
摘要: Anthropogenic activities have led to increases in nitrous oxide (N2O) emissions from river systems, but there are large uncertainties in estimates due to lack of data in tropical rivers and rapid increase in human activity. We assessed the effects of land use and river size on N2O flux and concentration in 46 stream sites in the Mara River, Kenya during the transition from the wet (short rains) to dry season, Nov. 2017 – Jan. 2018. Flux estimates were similar to other studies in tropical and temperate systems, but in contrast to other studies, land‐use was more related to N2O concentration and flux than stream size. Agricultural stream sites had the highest fluxes (26.38 ± 5.37 N2O‐N μg m‐2 h‐1) compared to both forest and livestock sites (5.66 ± 1.38 N2O‐N μg m‐2h‐1 and 6.95 ± 2.96 N2O‐N μg m‐2h‐1, respectively). N2O concentrations in forest and agriculture streams were positively correlated to stream carbon dioxide (CO2‐C(aq)) but showed a negative correlation with dissolved organic carbon (DOC), and the DOC:DIN ratio. N2O concentration in the livestock sites had a negative relationship with CO2‐C(aq) and a higher number of negative fluxes. We concluded that in‐stream chemoautotrophic nitrification was likely the main biogeochemical process driving N2O production in agricultural and forest streams, whereas complete denitrification led to the consumption of N2O in the livestock stream sites. These results point to the need to better understand the relative importance of nitrification and denitrification in different habitats in producing N2O and for process‐based studies.