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23201. 题目: Impact of long-term N fertilisation on CO₂ evolution from old and young SOM pools measured during the maize cropping season
文章编号: N18123004
期刊: Science of The Total Environment
作者: Muhammad Shahbaz, Lorenzo Menichetti, Thomas Kätterer, Gunnar Börjesson
更新时间: 2018-12-30
摘要: The relationship between carbon (C) inputs and nitrogen (N) fertilisation is a key element of soil organic matter (SOM) dynamics, which remains poorly resolved. In temperate climates, it is critical to investigate the interactive effect of C and N inputs on SOM stabilisation under low or high substrate availability. We measured SOM content and in situ soil respiration in a long-term field experiment in Sweden, which started in 1956. In 2000, the previous C3 crops were replaced with C4 maize, making it possible to trace old- (C3-derived) and young-C (C4-derived) sources in CO₂ and SOM under bare fallow, maize cropped with or without N-fertilisation (root C-inputs). Soil respiration and its isotopic composition were measured in the field prior to sowing, every second week during crop growth and once after harvest. During 1956–1999, the bare fallow lost 38% of its SOM, following an exponential decay trend. Despite root C inputs, total SOM content under C3 crops declined from 1.5% in 1956 to 1.4% and 1.2% C in fertilised and unfertilised treatments, respectively, in 1999. After the crop change in 2000, estimated C input increased by 5% (under fertilisation), but SOM content continued to decline (as before 2000), to 1.25% (fertilised) and 1.03% (unfertilised) in 2017. Analysis of δ¹³C revealed that 9 and 11% of young-C was retained in unfertilised and fertilised SOM, respectively. However, up to 70% of soil respiration derived from young-C. Comparing the contributions of old- and young-C to CO₂ and SOM showed that, irrespective to the time of measurement, young-C was always more available for microbial decomposition than old-C, particularly under fertilisation. We conclude that the amount of C entering the soil through root inputs was insufficient to counterbalance SOM losses over time. Moreover, soil nutrient status and recent root-C availability appear to be important for CO₂ release, and must be considered in further recommendations on maintaining/improving SOM stocks.
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23202. 题目: Fate of selenium in soil: A case study in a maize (Zea mays L.) field under two irrigation regimes and fertilized with sodium selenite
文章编号: N18123003
期刊: Science of The Total Environment
作者: M. De Feudis, R. D'Amato, D. Businelli, M. Guiducci
更新时间: 2018-12-30
摘要: Selenium (Se) is a trace element necessary for both human and livestock nutrition. To increase Se human intake, soil Se fertilizations were performed but the fate of the added Se remains unclear. The present research aims to: (1) determine the influence of Se fertilization on the fractionation of Se in soil; (2) assess the influence of water availability on the distribution of soil Se chemical fractions; and (3) monitor the Se content in soil, leachates and plants. To reach these goals, 200 g Se ha⁻¹ was applied to soil as sodium selenite in maize crops under two irrigation regimes, and the Se content in plant, soil chemical fractions and leachates were analyzed. Se application increased the total Se content of the soil, specifically it increased the Se content of the soluble, exchangeable and organic fractions with more pronounced effect in the soils with higher water availability. These differences disappeared over time likely due to the Se loss through volatilization. The hypothesis of Se volatilization is confirmed by the absence of both leachates during the maize growing season and differences among the treatments of Se content in sub-soil samples. Also, although the Se treated plants showed higher Se content than the untreated ones, overall <1% of the added Se was assimilated by plants. Hence, this study demonstrated that the addition of selenite to the soil increased the Se contents of the plants, but the Se does not accumulate in the soil because it is likely lost via volatilization. Further, leaching of Se into groundwater is avoided due to its association with both the soil organic matter and positively charged binding sites of soil, and due to its loss via volatilization. Therefore, soil Se fertilization could increase the nutritional value of plants without consequences on the environment.
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23203. 题目: Enhanced coagulation of low-turbidity micro-polluted surface water: Properties and optimization
文章编号: N18123002
期刊: Journal of Environmental Management
作者: Zhouzhou Liu, Hua Wei, Aimin Li, Hu Yang
更新时间: 2018-12-30
摘要: Micro-polluted surface water with low turbidity and low content of dissolved organic matter (DOM) is usually inefficiently purified. In this work, a combined technique for the enhanced coagulation of this surface water was proposed and investigated using cationic grafted starch (St-G) and polyaluminum chloride (PACl) as co-coagulants, followed by a magnetic ion-exchange resin (MIER). St-G was fed before PACl, and this procedure not only efficiently removes turbidity but also largely reduces the doses of the two coagulants. MIER remarkably removed DOM, and raw water was effectively purified. The entire coagulation process was further optimized through response surface methodology based on a central composite design by using the doses of St-G, PACl, and MIER as input variables. The dose effects of the three chemicals on the coagulation performance for turbidity and DOM removal were examined, and the coagulation mechanisms, including the interactive effect among various chemicals, were discussed in detail. This work provided a new strategy for the efficient treatment of low-turbidity micro-polluted surface water by utilizing organic and inorganic co-coagulants with magnetic ion-exchange resin in practical applications.
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23204. 题目: Biogeochemistry of soil organic matter in agroecosystems & environmental implications
文章编号: N18123001
期刊: Science of The Total Environment
作者: Gabrijel Ondrasek, Helena Bakić Begić, Monika Zovko, Lana Filipović, Cristian Meriño-Gergichevich, Radovan Savić, Zed Rengel
更新时间: 2018-12-30
摘要: The biogeochemistry of soil organic matter (SOM), as a highly complex and dynamic soil property, is of vital importance for the health and ecological functioning of ecosystems, including managed and natural ones. Dominantly composed of carbon (C), SOM functions in global C cycling, including C sequestration and emission (e.g. soil respiration). Mediterranean agroecosystems especially, due to favourable climate conditions for mineralisation of SOM, are expected to go through enhanced SOM decomposition (i.e. C emission) under the ongoing global warming and related climatic change and variability (frequent heat waves, fires and extreme water disturbances). The relatively stable (humified) SOM components, especially in the organically-enriched topsoil layers, due to their specific physical chemistry (strongly charged interface) may have a significant role in biogeochemistry of charged (in)organic nutrients and/or contaminants such as toxic metal ions and persistent organic pollutants. The recent studies show that some natural vulnerabilities of Mediterranean regions (such as high risk of the erosion-driven processes) can increase movement of some hazardous pedospheric constituents (e.g. pesticides) to water bodies and/or into the air, thus influencing the whole ecosystem health. A majority of recent surveys confirm depletion of SOM and spatially variable distribution of metal contamination in the Mediterranean topsoils. Using the advanced geochemical prediction approaches in combination with the relevant soil databases, we characterised organo-mineral and organo-metal complexation and its effect on speciation and sorption of trace metals in karstified Mediterranean agroecosystems. Metal biogeochemistry was found to vary markedly under relatively constant pedosphere conditions, depending on organo-mineral soil components and pH, which may significantly impact metal mobility/availability in the soil-plant continuum. The knowledge of the SOM spatial distribution and dynamics and its interactions with other pedovariables is essential for sustainable management of SOM and control of contaminant mobility to avoid degradation processes in (agro)ecosystems.
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23205. 题目: Toxicity of sulfide-modified nanoscale zero-valent iron to Escherichia coli in aqueous solutions
文章编号: N18122907
期刊: Chemosphere
作者: Yujun Cheng, Haoran Dong, Yue Lu, Kunjie Hou, Yaoyao Wang, Qin Ning, Long Li, Bin Wang, Lihua Zhang, Guangming Zeng
更新时间: 2018-12-29
摘要: Sulfide-modified nanoscale zero-valent iron (S/nZVI) has been widely studied for groundwater remediation, but the potential environmental risks are poorly understood. This study examined the toxicity of S/nZVI to Escherichia coli in aqueous solutions. The sulfidation could reduce toxicity of nZVI, and S/nZVI exhibited a weaker toxicity at lower Fe/S molar ratio, resulting from the lower Fe⁰ content and higher sulfate and iron oxide. The toxicity of S/nZVI was significantly alleviated in the presence of N-Acetyl-L-cysteine (a scavenger for reactive oxygen species (ROS)), revealing that the ROS-induced oxidative stress was the principal mechanism. Moreover, Transmission Electron Microscopy images elucidated that the membranes of S/nZVI-treated cells were disrupted and S/nZVI existed on E. coli surface and in the cytoplasm. S/nZVI might have interacted with the amine, carboxyl, and ester groups on E. coli cell surface, as demonstrated by Fourier Transform Infrared Spectroscopy analysis. However, the presence of individual groundwater component (e.g., Ca²⁺, SO₄²⁻, HCO₃⁻ and humic acid) could more or less alleviate the toxicity of S/nZVI. Furthermore, S/nZVI only exhibited slight toxic effect (<0.15-log after 1 h) in the presence of the mixed components. The same faint toxicity was observed for the aged S/nZVI, indicating that S/nZVI could lose its toxicity over time.
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23206. 题目: Shifts in microbial community and carbon sequestration in farmland soil under long-term conservation tillage and straw returning
文章编号: N18122906
期刊: Applied Soil Ecology
作者: Minmin Hao, Hengyu Hu, Zhen Liu, Qingling Dong, Kai Sun, Yupeng Feng, Geng Li, Tangyuan Ning
更新时间: 2018-12-29
摘要: Soil microorganisms participate in soil carbon cycling and they are affected by tillage and straw returning. In this experiment, a split-plot design was adopted beginning in 2002. The whole-plot treatment had three tillage modes, conventional tillage (CT), subsoil tillage (ST) and rotary tillage (RT), and the split-plot treatment had two levels of maize straw returning, full straw returning (F) and no straw returning (0). The soil organic carbon (SOC) contents during 2012–2017 were measured, whereas the microbial community function and structure were assessed by Biolog EcoPlates® and Illumina sequencing technology. The results showed that the SOC increased under all treatments from 2012 to 2017. However, the growth rate for SOC content under STF was the highest. Subsoil tillage and full straw returning significantly increased the metabolic function and metabolic diversity of the soil microbial carbon sources. A principal component analysis (PCA) showed that except for CT0 and RT0, the microbial metabolic functions under the various treatments were different. Amino acids and amines were the main carbon sources that caused changes in the soil microbial communities. A redundancy analysis (RDA) showed that the soil water content, bulk density, total nitrogen (TN) content, SOC and pH significantly accounted for the variance in the microbial community function and structure; however, the bulk density was not conducive to variation in the microbial communities. Subsoil tillage with full straw returning could increase the gene abundances in the metabolic pathways for CO₂ fixation and organic acids but decrease the gene abundance in the di- and oligosaccharide metabolic pathway. In conclusion, a combination of subsoil tillage and full straw returning improve the basic soil physicochemical and biological properties, affect soil microbial communities, and promote an increase in the SOC content, which can eventually resolve soil degradation issues.

23207. 题目: Soil-applied biochar increases microbial diversity and wheat plant performance under herbicide fomesafen stress
文章编号: N18122905
期刊: Ecotoxicology and Environmental Safety
作者: Lulu Meng, Tong Sun, Mengyao Li, Muhammad Saleem, Qingming Zhang, Caixia Wang
更新时间: 2018-12-29
摘要: The herbicide “fomesafen” causes phytotoxicity to the rotational wheat crop and may reduce its yield. Considering that biochar may improve remediation and biophysical conditions of the contaminated soil environments to benefit plant growth. Here, we investigated the impacts of three levels of the wheat straw-derived biochar (1%, 2%, and 4% (w/w)) on growth, physiological properties, and rhizosphere microbial communities of the wheat (Triticum aestivum) seedlings under the fomesafen stress using high-throughput sequencing. The results showed that biochar amended into soil significantly reduced the uptake of wheat to fomesafen and thereby eliminate its toxicity to wheat seedlings. Moreover, biochar increased the abundance and diversity of plant beneficial bacterial and fungal taxa in the rhizosphere of wheat seedlings. Compared with the three addition amounts, amendment with 2% of biochar has the best effects to reduce the toxicity of fomesafen on wheat seedlings and maintain the balance of soil microbial community structure in soil contaminated with fomesafen (1.0 mg kg⁻¹). Overall, our results suggest that the level of biochar application influences the structure and diversity of soil microbiome (and mycobiome) and plant performance under abiotic stress conditions.
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23208. 题目: Multiple regression analysis to assess the spatial distribution and speciation of mercury in surface sediments of a contaminated lagoon
文章编号: N18122904
期刊: Journal of Hazardous Materials
作者: T. Stoichev, E. Tessier, J.P. Coelho, M.G. Lobos Valenzuela, M.E. Pereira, D. Amouroux
更新时间: 2018-12-29
摘要: The concentrations of inorganic mercury (IHg) and methylmercury (MeHg) in surface sediments from the contaminated Aveiro Lagoon (Portugal) were determined by species-specific isotope dilution analysis. Different behaviour of IHg and MeHg was observed based upon multiple regression analysis, including geochemical characteristics of the surface sediments (fine fraction, concentrations of organic matter and metals) and non-Euclidean distances between sampling points. This data treatment method was valid over the entire concentration range of IHg and MeHg, allowing robust quantitative evaluation with respect to extrapolation. For IHg, there was statistical separation of the dispersion away from the contamination source and of Al concentration in the sediments. The MeHg concentrations followed those of IHg at high concentrations. The geochemical variables, such as concentrations of Ca (marine influence proxy), Mn and organic matter, were necessary to describe the behaviour of MeHg across the whole concentration range. The models for MeHg demonstrated that, close to the mouth of the lagoon, net production of MeHg was higher. In future, multiple regression analysis could be applied to separate and to evaluate quantitatively the effects of geochemistry and dispersion away from the contamination source in sediments contaminated with other substances.
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23209. 题目: High resolution bio- and chemostratigraphic framework at the Frasnian-Famennian boundary: Implications for regional stratigraphic correlation between different sedimentary facies in South China
文章编号: N18122903
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: Jieqiong Chang, Zhiqiang Bai, Yuanlin Sun, Yongbo Peng, Shujian Qin, Bing Shen
更新时间: 2018-12-29
摘要: As one of the “Big Five” mass extinctions in Phanerozoic, the Frasnian-Famennian (F-F) boundary event records the extinction of 40 % of marine invertebrate genera. The F-F boundary is defined by the first appearance of conodont Palmatolepis subperlobata as well as the abundant occurrences of Pa. ultima at the base of the Lower Pa. triangularis Zone. The F-F boundary is also broadly coincident with a positive excursion in carbon isotopes, suggesting the possible linkage between the perturbation of marine carbon cycle and the biotic crisis. However, the correlation between conodont biostratigraphy and carbon isotope chemostratigraphy has not been established yet, preventing the high-resolution regional stratigraphic correlation among different sedimentary facies. In this study, we studied the conodont biostratigraphy and analyzed carbonate carbon (δ¹³C_carb) and organic carbon (δ¹³C_org) isotopes of the Baisha section in the Guangxi Province, South China. The first appearance of index conodont fossil Pa. subperlobata for the Lower Pa. triangularis Zone, i.e. the F-F boundary, is coincident with the onset of a 3‰ positive excursion in δ¹³C_carb, while Pa. triangularis and Pa. subperlobata occur nearly simultaneously, but predate the disappearances of Pa. linguiformis and other typical Frasnian elements. In addition, a positive excursion in δ¹³C_org is associated with the decline of δ¹³C_carb near the base of the Middle Pa. triangularis Zone, which is marked by the first appearance of Pa. delicatula. Another important Famenian element Pa. minuta, the index fossil for the Upper Pa. triangularis Zone, first appears when δ¹³C_org starts to decline. The offset between δ¹³C_org and δ¹³C_carb excursions could be attributed to the oceanic anoxia (the Kellwasser Event) near the F-F boundary, followed by the mixing of surface and deep water in earliest Famenian. The high resolution bio- and chemostratigraphic framework can be used as the standard for regional stratigraphic correlation and identification of the F-F boundary in different depositional environments in South China. We propose that the F-F boundary can be identified from a conodont-poor carbonate section by the onset of the positive excursion in δ¹³C_carb, whereas the F-F boundary in a non-fossiliferous siliciclastic section might be placed slightly below the positive excursion in δ¹³C_org.

23210. 题目: Modeling kinetics of heavy metal release from field-contaminated soils: Roles of soil adsorbents and binding sites
文章编号: N18122902
期刊: Chemical Geology
作者: Paiyu Liu, Pei Wang, Yang Lu, Yang Ding, Guining Lu, Zhi Dang, Zhenqing Shi
更新时间: 2018-12-29
摘要: Release of heavy metals from soils affects the dynamic behavior of metals in the field, but quantitative models for predicting the rates of heavy metal release from field-contaminated soils are lacking. We studied heavy metal release from several field-contaminated soils with a stirred-flow method, and developed a multiple component kinetics model for the kinetic behavior of metal adsorption/desorption on field-contaminated soil. The fraction of heavy metals extracted with 0.43 M HNO₃ accounted for the heavy metal desorption from the field-contaminated soils and WHAM 7 reasonably predicted the initial metal distribution among various soil adsorbents and soil organic matter (SOM) binding sites. In our kinetics model, the nonlinear binding of metals to multiple heterogeneous binding sites of soil adsorbents and dissolved organic matter was simultaneously considered. Overall, our model fit experimental data well under varying reaction conditions. Model calculations showed that SOM was dominant in controlling the release behavior of Cd, Cu, and Zn, but iron oxides were significant for controlling Pb release. The bidentate sites were the most important SOM binding sites controlling metal release from soils for all four metals. The release rates of all four metals from the field-contaminated soils were smaller than the release rates from the laboratory metal-spiked soils as reported previously. Our model is able to accurately describe the adsorption/desorption kinetics of heavy metals in field-contaminated soils and contributes to predicting the fate of metals in soil environments.

23211. 题目: Disparate effects of DOM extracted from coastal seawaters and freshwaters on photodegradation of 2,4-Dihydroxybenzophenone
文章编号: N18122901
期刊: Water Research
作者: Jieqiong Wang, Jingwen Chen, Xianliang Qiao, Ya-nan Zhang, Misbah Uddin, Zhongyu Guo
更新时间: 2018-12-29
摘要: Dissolved organic matter (DOM) plays an important role in degradation of organic pollutants by photochemically-produced reactive intermediates (RIs), such as excited triplet-states of DOM (³DOM*), singlet oxygen (¹O₂) and hydroxyl radical (·OH). However, it is not clear whether DOM extracted from coastal seawaters (CS-DOM) and DOM derived from freshwaters (FW-DOM) exhibit similar effects on photodegradation of organic micropollutants. Herein, 2,4-dihydroxybenzophenone (BP-1) was adopted as a model compound to probe the effects of different DOM on photodegradation kinetics of organic micropollutants. Results show that the CS-DOM promotes the photodegradation of BP-1 mainly via the pathway involving ³DOM*; while ³DOM*, ¹O₂ and ·OH are responsible for BP-1 photodegradation in the presence of the FW-DOM. Compared with the FW-DOM, the CS-DOM undergoes more photobleaching, and contains less aromatic C=C and C=O functional groups. Although ³DOM* formation quantum yields for the CS-DOM are relatively higher than those for the FW-DOM, the CS-DOM has lower rates of light absorption, leading to lower steady-state RI concentrations for the CS-DOM. BP-1 photodegradation in the presence of the CS-DOM is faster than in the presence of the FW-DOM, due to higher second-order reaction rate constants between BP-1 and CS-³DOM* and fewer antioxidants contained in the CS-DOM.
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23212. 题目: Relative sea‐level change regulates organic carbon accumulation in coastal habitats
文章编号: N18122814
期刊: Global Change Biology
作者: Kenta Watanabe, Koji Seike, Rumiko Kajihara, Shigeru Montani, Tomohiro Kuwae
更新时间: 2018-12-28
摘要: Because coastal habitats store large amounts of organic carbon (C_org), the conservation and restoration of these habitats are considered to be important measures for mitigating global climate change. Although future sea‐level rise is predicted to change the characteristics of these habitats, its impact on their rate of C_org sequestration is highly uncertain. Here we used historical depositional records to show that relative sea‐level (RSL) changes regulated C_org accumulation rates in boreal contiguous seagrass–saltmarsh habitats. Age–depth modelling and geological and biogeochemical approaches indicated that C_org accumulation rates varied as a function of changes in depositional environments and habitat relocations. In particular, C_org accumulation rates were enhanced in subtidal seagrass meadows during times of RSL rise, which were caused by post‐seismic land subsidence and climate change. Our findings identify historical analogues for the future impact of RSL rise driven by global climate change on rates of C_org sequestration in coastal habitats.

23213. 题目: Soil organic carbon and total nitrogen stocks in alpine ecosystems of Altun Mountain National Nature Reserve in dry China
文章编号: N18122813
期刊: Environmental Monitoring and Assessment
作者: Zhenzhen Zhao, Xiangfeng Zhang, Shikui Dong, Yu Wu, Shiliang Liu, Xukun Su, Xuexia Wang, Yong Zhang, Lin Tang
更新时间: 2018-12-28
摘要: The Altun Mountain National Nature Reserve (AMNNR), characterized by complex topography, is located on the northern edge of the Qinghai–Tibetan Plateau. The stocks of soil organic carbon (SOC) and total nitrogen (TN) are critically important for carbon and nitrogen sequestration in dry alpine ecosystems of the AMNNR, which is a “natural laboratory” for assessing the carbon and nitrogen storage without human disturbance. We explored the stocks of SOC and TN in soils of different dry alpine ecosystems by sampling 23 sites across the AMNNR during 2013. The results showed that the SOC and TN stocks of AMNNR varied significantly with ecosystem types. The SOC stocks of 0–15 cm were highest in the alpine wet meadow (7.96 kg/m²), followed by alpine steppe (2.63 kg/m²). The stocks of SOC and TN in 0–5 and 5–10 cm soils of alpine wet meadow were significantly (P < 0.05) higher than those in the soils of other dry alpine ecosystems. In the whole AMNNR, total storage of SOC and TN were approximately 80.97 and 4.48 Tg, 34.25% of SOC and 24.01% of TN were stored in the alpine steppe, 21.51% of SOC and 26.01% of TN were stored in the alpine scrub, the largest ecosystem in the AMNNR. Our findings suggested it is important to protect the soil and vegetation of the dry alpine ecosystems, particularly the alpine wet meadow and alpine scrub to promote the carbon storage.

23214. 题目: Morphological response to salinity, temperature, and pH changes by marine fungus Epicoccum nigrum
文章编号: N18122812
期刊: Environmental Monitoring and Assessment
作者: Ramón Ahumada-Rudolph, Vanessa Novoa, José Becerra
更新时间: 2018-12-28
摘要: Epicoccum nigrum (strain LQRA39-P) was isolated from sediments collected in Chilean Patagonian fjords using microscopy and molecular techniques. We analyzed adaptive responses of cell wall morphology to salinity, temperature, and pH in order to explain the ability of E. nigrum to co-inhabit both marine and freshwater environments. For this purpose, E. nigrum was cultured in a series of media with variations in salinity (freshwater and seawater), pH (acidic, neutral, and basic), and temperature (5 to 25 °C). Changes were observed through transmission electron microscopy. A direct correlation between increased salinity and cell wall thickening (> 0.2 μm) was observed, along with a significant relationship between pH and the presence of extracellular polymeric substances (EPS) on the outside of the cell wall. The observed morphological changes could confirm that an ubiquitous fungus such as E. nigrum requires adaptive responses to co-inhabit freshwater, marine, and terrestrial substrates.

23215. 题目: Decoding the mechanism of formation in marineooids: A review
文章编号: N18122811
期刊: Earth-Science Reviews
作者: Mara R. Diaz, Gregor P. Eberli
更新时间: 2018-12-28
摘要: Ooid shoals, sedimentary structures consisting of carbonate grains, are often used as proxies to explore changes in seawater chemistry over Earth history. Despite their importance as contributors to the global carbonate budget and as paleo-environmental indicators for water depth, pH, temperature and water energy, the mechanism of formation of these concentric, sub-spherical concretions of tangentially or radially arranged aragonite or calcite crystals is still the subject of intense debate. Unlike oncoids, whose microbial origins are well acknowledged, ooids are traditionally viewed as abiotic grains, mainly produced in suspension by agitated, warm waters that are supersaturated with respect to CaCO₃. Yet, there is considerable evidence, including geochemical bio-signatures and detection of viable microbes capable of mineralization and biofilm production and degradation, to suggest otherwise. The emergence of new and sophisticated technologies reveals that the level of microbial diversity of these sedimentary grains exceeds that of some microbialite systems. These findings have refined our understanding of ooid genesis and ooid accretion processes and argue toward microbial mediation both as a direct result of metabolic activities inducing changes in the environment conducive to precipitation and by a passive mechanism, in which mucilaginous extracellular polymeric substances (EPS) act as a template for mineral nucleation. Furthermore, new developments in the field indicate that carbonate mineralization in marine ooids occurs through sequential precipitations that involve an amorphous calcium carbonate phase (ACC), which some argue are of biotic origins. Herein, we discuss the most relevant theories of ooid formation, including some of the early pioneering studies that laid the groundwork for new theories attempting to decode the origins of these controversial grains.

23216. 题目: Tight trophic association between benthic diatom blooms and shallow-water megabenthic communities in a rapidly deglaciated Antarctic fjord
文章编号: N18122810
期刊: Estuarine, Coastal and Shelf Science
作者: Sun-Yong Ha, In-Young Ahn, Hye-Won Moon, Bohyung Choi, Kyung-Hoon Shin
更新时间: 2018-12-28
摘要: This study reports isotopic evidence of a unique and highly efficient trophic structure based on a rarely reported benthic diatom species in a rapidly warming Antarctic fjord (Marian Cove; MC). Recent surveys of MC revealed a very conspicuous feature, an intense, persistent benthic diatom bloom (‘benthic diatom bush’) overgrowing a variety of common megabenthic fauna, primarily filter feeders (bivalves, ascidians, and demosponges), which occurred widely at shallow depths. To ascertain if the benthic diatom bloom is consumed as a primary food source, δ¹³C and δ¹⁵N were analyzed in the associated filter feeders and other herbivores, as well as in the diatom bush and other potential food sources (microphytobenthos, sedimentary organic matter and macroalgae). The analysis showed that the δ¹³C values of all filter feeders (−23.5 to −25.2‰) were very similar to those of the diatom bush (−23.1 to −23.6‰), strongly suggesting that these benthic diatoms are the principal diet of the associated filter feeders. The isotopic signatures of the other food sources were very close to those of the diatom bush, indicating that the organic matter had the same origin, namely benthic diatoms. Given its quality, quantity and availability, the diatom bush could be regarded as the primary food source. The benthic diatom bush was predominated by the chain-forming centric diatom Paralia sp., which occurs in shallow coastal waters with a wide range of salinity in various geographic localities. Thus, the Paralia sp. bloom in this rapidly warming fjord also indicates its potential utility as an indicator of climate-induced environmental changes. Additional isotopic analysis of other common fauna showed that the benthic food web in this fjord comprised up to four trophic levels of consumers, with starfish and isopods at the apex. Given that filter feeders comprise the largest trophic group in the cove and many other Antarctic coastal waters, the results of this study strongly suggest that benthic diatoms are of prime importance in supporting the benthic food web in MC, and possibly other nearshore Antarctic waters. Further studies on the mechanism underlying benthic diatom blooms and their relevance to climate-induced processes would provide better project future scenarios for rapidly warming fjord ecosystems.

23217. 题目: Origin of hydroxyl GDGTs and regular isoprenoid GDGTs in suspended particulate matter of Yangtze River Estuary
文章编号: N18122809
期刊: Organic Geochemistry
作者: Xiaoxia Lü, Jiali Chen, Tianwei Han, Huan Yang, Weichao Wu, Weihua Ding, Kai-Uwe Hinrichs
更新时间: 2018-12-28
摘要: Hydroxylated isoprenoid glycerol dialkyl glycerol tetraethers (OH-GDGTs) were found having the potential to track past sea surface temperatures (SST), in analogy to the TEX₈₆ - a paleothermometer based on isoprenoid GDGTs (iGDGTs). Especially in estuarine regions with high terrestrial input, the ring index of OH-GDGTs (RI-OH) was more robust to trace the summer SST than TEX₈₆. In order to clarify the potential sources of sedimentary GDGTs and to further elucidate the potential of OH-GDGTs as SST proxy, we investigated the seasonal distribution of core OH-GDGTs and iGDGTs in the suspended particulate matter in a transition section in Yangtze River Estuary. The concentrations of OH-GDGTs and iGDGTs were higher in the estuary than those in the lower Yangtze River, which suggested the OH-GDGTs and iGDGTs in estuarine sediment mainly came from marine autochthonous organisms, whereas the terrestrial contribution was relatively low. The higher content of OH-GDGTs and iGDGTs in summer than in winter indicated that sedimentary OH-GDGTs and iGDGTs mainly originated from the summer SPM deposition. In addition, the ratio of OH-GDGTs versus iGDGTs suggested that OH-GDGTs were relatively abundant in the upper water layer compared to iGDGTs, regardless of season. Furthermore, the distributions of iGDGTs and OH-GDGTs were found to be influenced by hydrodynamics. The increasing warm bias of iGDGT and OH-GDGT reconstructed temperatures with water depth suggested that either GDGTs in deeper waters derive mainly from surface water or GDGTs cyclization in deeper waters was influenced by reduced ammonium oxidation rates in response to the limited supply of ammonium and oxygen, especially in summer.

23218. 题目: Tropical soil profiles reveal the fate of plant wax biomarkers during soil storage
文章编号: N18122808
期刊: Organic Geochemistry
作者: Mong Sin Wu, A. Joshua West, Sarah J. Feakins
更新时间: 2018-12-28
摘要: The waxy coating that protects the leaves and other soft tissues of plants includes n-alkane and n-alkanoic acid compounds that are commonly used as biomarkers to reconstruct past environment. Plant waxes have geological relevance given their persistence in soils and paleosols, as well as in lake and marine sediments, yet diagenesis may alter their molecular and isotopic signatures from synthesis to deposition. This study seeks to understand the fate of plant wax biomarkers in soils after leaf-fall as characterized by a series of tropical soil profiles. We investigate the changes in abundance, molecular distributions, and hydrogen (δD) and carbon isotopic compositions (δ¹³C) of plant waxes (n-alkanes and n-alkanoic acids) in six litter-to-soil profiles along a 2740 m elevation transect from the eastern flank of the Andes mountains down to the lowland Amazon floodplain in Peru. From litter to soil, we find acid/alkane ratios increase, while absolute abundances decrease. In contrast, within each soil, acid/alkane ratios are roughly constant and we find an equivalent exponential decline in concentration in both compound classes with depth; with molecular distributions indicating some new production. We observe a 4 – 6‰ ¹³C-enrichment from litter to deeper soils for both C₂₉n-alkanes and C₃₀n-alkanoic acids; of which the Suess effect accounts for ≤ 2‰. We infer that microbial degradation and production (or ‘turnover’) processes influence the δ¹³C of plant waxes that survive in soils; in contrast, no systematic change in δD values is observed. The plant wax signal in soils includes averaging of inputs and diagenetic effects, so this signature is particularly relevant for the interpretation of plant waxes archives in paleosols and the plant waxes eroded from soils and exported to downstream sedimentary archives. We show that soils represent the major stock of plant wax under living ecosystems, suggesting that soils may be a quantitatively-important source of plant waxes available for fluvial erosion, with implications for studies of carbon cycling and paleoenvironmental reconstructions from downstream geological archives.

23219. 题目: Transformation of dissolved organic matter during advanced coal liquefaction wastewater treatment and analysis of its molecular characteristics
文章编号: N18122807
期刊: Science of The Total Environment
作者: Li Zhang, Yongzhen Peng, Jiachun Yang
更新时间: 2018-12-28
摘要: Coal liquefaction wastewater (CLW) contains numerous toxic and biorefractory organics. A series of advanced treatment processes were designed to remove the dissolved organic matter (DOM) from CLW. Here, the reactivity and state of the DOM in the treatment train were studied in relation to its chemical composition by a Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) analysis. Within an isobaric group, the raw CLW possessed a high average double-bond equivalent (DBE_wa) and low H/C_wa values with the N- and S-containing compounds accounting for approximately 77% of the raw CLW, which represented lignin (73.6%) and condensed aromatic structures (19.8%). In addition, the flotation process removed some hydrophobic DOM compounds with highly unsaturated states, which were biorefractory compounds. Ozonation and catalytic oxidation processes preferentially removed the highly unsaturated compounds and produced more oxidized molecules. The biofiltration process impacted the organics composition by consuming oxygen-rich substances, whereas the anoxic/oxic (A/O) process converted the reactive compounds into newly formed compounds through the loss of hydrogen (unsaturation) from the original compounds. The membrane bioreactor (MBR) process was more efficient in removing the N-containing compounds with higher unsaturated states. The compounds resistant to the applied CLW treatment processes were characterized by lower molecular weights (approximately 250–350 Da), higher oxidation states (O/S > 6), numerous carboxylic groups, and non-biodegradable features.
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23220. 题目: Rapid and efficient activated sludge treatment by electro-Fenton oxidation
文章编号: N18122806
期刊: Water Research
作者: Yasong Chen, Huiping Chen, Jie Li, Lin Xiao
更新时间: 2018-12-28
摘要: Advanced oxidation process is one of the important process to improve the efficiency of activated sludge dewatering and digestion. In this study, electro-Fenton (EF) was investigated as a pretreatment method for improving activated sludge dewatering and disintegration in terms of specific resistance to filtration, volatile suspended solids removal and release of soluble organics. The morphology of sludge flocs and properties of extracellular polymeric substance (EPS) were investigated to understand the involved mechanisms. The results showed that EF could increase the dewaterability of activated sludge effectively in 40 - 60 minutes. The size of sludge flocs decreased after EF treatment, but zeta potential was elevated to near zero and floc structure became coarser with bigger holes. EF could enhance the sludge floc disintegration, released protein and polysaccharide to soluble EPS fraction, and promote the humification process. The kinetic analysis further indicated that EF increased the pseudo first-order EPS solubilization rate. EF had high operational stability by retaining over 90 % initial activity even after five repeated use of dewatering filtrate. This study provides a rapid and efficient solution for improving sludge dewaterability by electro-Fenton.
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