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12841. 题目: Dual isotope evidence for sedimentary integration of plant wax biomarkers across an Andes-Amazon elevation transect
文章编号: N18092002
期刊: Geochimica et Cosmochimica Acta
作者: Sarah J. Feakins, Mong Sin Wu, Camilo Ponton, Valier Galy, A. Joshua West
更新时间: 2018-09-20
摘要: Tropical montane regions tend to have high rates of precipitation, biological production, erosion, and sediment export, which together move material off the landscape and toward sedimentary deposits downstream. Plant wax biomarkers can be used to investigate sourcing of organic matter and are often used as proxies to reconstruct past climate and environment in sedimentary deposits. To understand how plant waxes are sourced within a wet, tropical montane catchment, we measure the stable C and H isotope composition (δ13C and δD) of n-alkanes and n-alkanoic acids in soils along an elevation transect and from sediments within the Madre de Dios River network along the eastern flank of the Peruvian Andes, draining an area of 75,400 km2 and 6 km of elevation. Soils yield systematic trends in plant wax δ13C (+1.75 and +1.31‰ km–1, for the C29n-alkanes and C30n-alkanoic acids respectively in the mineral horizon) and δD values (–10 and -12‰ km–1, respectively) across a 3.5 km elevation transect, which approximates trends previously reported from canopy leaves, though we find offsets between δ13C values in plants and soils. River suspended sediments generally follow soil isotopic gradients defined by catchment elevations (δ13C: +1.03 and +0.99‰ km–1 and δD: –10 to –7‰ km–1, for the C29n-alkanes and C30n-alkanoic acids respectively) in the wet season, with a lowering in the dry season that is less well-constrained. In a few river suspended sediments, petrogenic contributions and depth-sorting influence the n-alkane δ13C signal. Our dual isotope, dual compound class and seasonal sampling approach reveals no Andean-dominance in plant wax export, and instead that the sourcing of plant waxes in this very wet, forested catchment approximates that expected for spatial integration of the upstream catchment, thus with a lowland dominance on areal basis, guiding paleoenvironmental reconstructions in tropical montane regions. The dual isotope approach provides cross-check on the altitudinal signals and can resolve ambiguity such as might be associated with vegetation change or aridity in paleoclimate records. Further, the altitude effect encoded within plant waxes presents a novel dual-isotope biomarker approach to paleoaltimetry.

12842. 题目: Impacts of moisture, soil respiration, and agricultural practices on methanogenesis in upland soils as measured with stable isotope pool dilution
文章编号: N18092001
期刊: Soil Biology and Biochemistry
作者: P.E. Brewer, F. Calderón, M. Vigil, J.C. von Fischer
更新时间: 2018-09-20
摘要: Anoxic microsites can alter the habitat of upland soils and host diverse anaerobic processes that affect greenhouse gas production, nitrogen dynamics, and biodiversity. Microsites that are methanogenic indicate deeply reducing conditions that may have especially strong impacts on soil function. However, there have not been controlled studies to determine the regulators of methanogenic microsite formation or persistence and most studies have been limited to tropical or high organic matter soils. We hypothesized that upland methanogenesis, as an indicator of anaerobic activity, is primarily affected by soil moisture and organic matter. To test this hypothesis, we examined relationships between soil properties, rates of methanogenesis, and biogeochemical responses in an incubation experiment that manipulated soil source (semi-arid and mesic ecosystems), agricultural practice (conventional, no-till, and organic), and moisture (10%–95% water-filled porespace) of intact soil cores. Methanogenesis was correlated with factors related to both increased O2 demand (e.g., soil respiration) and decreased O2 diffusion (e.g., water-filled porespace), and the relative importance of these different mechanisms changed over four months. While the highest rates of methanogenesis occurred above 75% water-filled porespace, we observed methanogenesis over the full range of soil moistures. These are the driest soils shown to host methanogenesis, outside of biological soil crusts. Cores from plots with organic amendments had the highest rates of methanogenesis. Comparisons of methanogenesis and N-cycling revealed new relationships in upland soils: stronger methanogenesis was associated with more soil NH4+ and higher N2O emissions but less NO3, likely due to reduced conditions causing increased denitrification and/or decreased nitrification. Our findings show that upland methanogenesis can arise from either increased O2 demand or decreased O2 diffusion, similar to wetland ecosystems, and that the presence of anoxic microsites appears to alter N-cycling. The current paradigm is that upland anaerobicity is generally a minor or moisture-related event, but we demonstrate here that it can be persistent, occur across the full range of soil moisture, and may result in significant impacts on nutrient availability. These and other anaerobic impacts on soil function and biodiversity may occur over the entire landscape of temperate ecosystems.

12843. 题目: A color-index based empirical algorithm for determining particulate organic carbon concentration in the ocean from satellite observations
文章编号: N18091915
期刊: Journal of Geophysical Research: Oceans
作者: Chengfeng Le, Xueying Zhou, Chuanmin Hu, Zhongping Lee, Lin Li, Dariusz Stramski
更新时间: 2018-09-19
摘要: An empirical algorithm based on color‐index approach for estimating particulate organic carbon concentration (POC) in the surface ocean from satellite observations is formulated and validated using in situ POC data and remote‐sensing reflectance (Rrs) data obtained from match‐up satellite ocean color measurements. The algorithm builds upon the band‐difference algorithm concept which was originally developed for estimating chlorophyll‐a concentration. This approach utilizes three spectral bands centered approximately at 490 nm, 550 nm, and 670 nm to determine a color index (CIPOC), from which POC can be estimated from different ocean color sensors. For comparison, the blue–green band ratio (BG) algorithm is also formulated using the same dataset of in situ POC and satellite‐derived Rrs. Results show that the statistical parameters characterizing the differences between the satellite‐derived POC and matchup in situ POC are similar when the CIPOC and BG algorithms are applied to open ocean waters where the values of CIPOC are relatively low. In coastal waters where the values of CIPOC are generally higher, the statistical parameters of algorithm performance are better for the CIPOC algorithm. In addition, because the CIPOC algorithm is less sensitive to errors and noise in the satellite‐derived Rrs, the image quality obtained with this algorithm can be improved, including the open ocean areas.

12844. 题目: Impact of seabed resuspension on oxygen and nitrogen dynamics in the northern Gulf of Mexico: A numerical modeling study
文章编号: N18091914
期刊: Journal of Geophysical Research: Oceans
作者: Julia M. Moriarty, Courtney K. Harris, Marjorie A. M. Friedrichs, Katja Fennel, Kehui Xu
更新时间: 2018-09-19
摘要: Resuspension affects water quality in coastal environments by entraining seabed organic matter into the water column, which can increase remineralization, alter seabed fluxes, decrease water clarity, and affect oxygen and nutrient dynamics. Nearly all numerical models of water column biogeochemistry, however, simplify seabed and bottom boundary layer processes and neglect resuspension. Here, we implemented HydroBioSed, a coupled hydrodynamic–sediment transport–biogeochemical model to examine the role of resuspension in regulating oxygen and nitrogen dynamics on timescales of a day to a month. The model was implemented for the northern Gulf of Mexico, where the extent of summertime hypoxia is sensitive to seabed and bottom boundary layer processes. Results indicated that particulate organic matter remineralization in the bottom water column increased by an order of magnitude during resuspension events. This increased sediment oxygen consumption and ammonium production, which were defined as the sum of seabed fluxes of oxygen and ammonium, as well as oxygen consumption and ammonium production in the water column due to resuspended organic matter. The increases in remineralization impacted biogeochemical dynamics to a greater extent than resuspension–induced seabed fluxes and oxidation of reduced chemical species. The effect of resuspension on bottom water biogeochemistry increased with particulate organic matter availability, which was modulated by sediment transport patterns. Overall, when averaged over the shelf and on timescales of a month in the numerical model, cycles of erosion and deposition accounted for about two–thirds of sediment oxygen consumption and almost all of the sediment ammonium production.

12845. 题目: Path-dependent reductions in CO2 emission budgets caused by permafrost carbon release
文章编号: N18091913
期刊: Nature Geoscience
作者: T. Gasser, M. Kechiar, P. Ciais, E. J. Burke, T. Kleinen, D. Zhu, Y. Huang, A. Ekici, M. Obersteiner
更新时间: 2018-09-19
摘要: Emission budgets are defined as the cumulative amount of anthropogenic CO2 emission compatible with a global temperature-change target. The simplicity of the concept has made it attractive to policy-makers, yet it relies on a linear approximation of the global carbon–climate system’s response to anthropogenic CO2 emissions. Here we investigate how emission budgets are impacted by the inclusion of CO2 and CH2 emissions caused by permafrost thaw, a non-linear and tipping process of the Earth system. We use the compact Earth system model OSCAR v2.2.1, in which parameterizations of permafrost thaw, soil organic matter decomposition and CO2 and CH2 emission were introduced based on four complex land surface models that specifically represent high-latitude processes. We found that permafrost carbon release makes emission budgets path dependent (that is, budgets also depend on the pathway followed to reach the target). The median remaining budget for the 2 °C target reduces by 8% (1–25%) if the target is avoided and net negative emissions prove feasible, by 13% (2–34%) if they do not prove feasible, by 16% (3–44%) if the target is overshot by 0.5 °C and by 25% (5–63%) if it is overshot by 1 °C. (Uncertainties are the minimum-to-maximum range across the permafrost models and scenarios.) For the 1.5 °C target, reductions in the median remaining budget range from ~10% to more than 100%. We conclude that the world is closer to exceeding the budget for the long-term target of the Paris Climate Agreement than previously thought.

12846. 题目: Size Fractionation of Dissolved Organic Nitrogen in Peatland Fluvial Systems
文章编号: N18091912
期刊: Environmental Science & Technology
作者: Donald A. Edokpa, Martin G. Evans, Stephen Boult, James J. Rothwell
更新时间: 2018-09-19
摘要: Understanding the nature and fate of nitrogen (N) in freshwater systems is crucial for assessing the risk of eutrophication. However, there is a paucity of information on the characterization of fluvial N in upland peat-dominated environments. Here, we employ a combination of field sampling and tangential flow ultrafiltration (TFU) to investigate the concentrations and fluxes of low molecular weight (LMW) and high molecular weight (HMW) dissolved organic N (DON) in a peatland stream-reservoir system in the south Pennines (UK). Our TFU results show that ∼26% of DON concentration is LMW DON and represents an estimated fluvial flux of 3.07 ± 22 kg N ha–1 during the study period. Our mass balance results reveal that the reservoir retains 71% of LMW DON input, which accounts for ∼25% retention of bioavailable (dissolved inorganic N + LMW DON) N. Our study suggests that current understanding of inorganic N as the sole source of bioavailable N with eutrophic significance in upland freshwaters requires a reappraisal. Evaluation of ecosystem response to increased loading of N needs to include a consideration of LMW DON.
图文摘要:

12847. 题目: Characteristic Regions of the Fluorescence Excitation–Emission Matrix (EEM) To Identify Hydrophobic/Hydrophilic Contents of Organic Matter in Membrane Bioreactors
文章编号: N18091911
期刊: Environmental Science & Technology
作者: Kang Xiao, Yuexiao Shen, Shuai Liang, Jihua Tan, Xiaomao Wang, Peng Liang, Xia Huang
更新时间: 2018-09-19
摘要: This study systematically investigated the correlations between fluorescence distributions characterized by the excitation–emission matrix (EEM) and hydrophobic/hydrophilic composition of dissolved organic matter (DOM) in membrane bioreactors (MBRs). On the basis of samples from 10 full-scale MBRs, we performed point-to-point comparisons among different components using an EEM fluorescence quotient (FQ) method and obtained a hydrophobic/hydrophilic fluorophore distribution map via Wilcoxon signed rank test. Hydrophobic acids/bases (HOA/HOB) concentrated in the low-wavelength region [excitation wavelength (Ex) < 235 nm], while hydrophilic substances (HIS) were enriched in the region of Ex > 235 nm [especially with emission wavelength (Em) = 300–360 nm]. Quantitatively, EEM regional contribution to whole wavelength fluorescence was found to significantly correlate with the hydrophobic/hydrophilic proportions of DOM, with Pearson’s coefficients of 0.94 and 0.78 (p < 0.01) for HOA and HIS, respectively. We established a linear regression model showing the HOA proportion as a function of the EEM regional contribution at (Ex, Em) = (200–285, 340–465 nm), with R2 = 0.876, which was validated via leave-one-out cross-validation and Monte Carlo simulation. This study shows a statistically hydrophobicity-dependent fluorescence property across different MBRs, and it might be applied to provide a quick estimation of hydrophobic/hydrophilic composition of DOM in wastewater treatment systems based on EEM monitoring.
图文摘要:

12848. 题目: Quantitative mechanisms of cadmium adsorption on rice straw- and swine manure-derived biochars
文章编号: N18091910
期刊: Environmental Science and Pollution Research
作者: Yiyi Deng, Shuang Huang, David A. Laird, Xiugui Wang, Caiqin Dong
更新时间: 2018-09-19
摘要: We quantified and investigated mechanisms for Cd2+ adsorption on biochars produced from plant residual and animal waste at various temperatures. Ten biochars were produced by pyrolysis of rice straw (RB) and swine manure (SB) at 300–700 °C and characterized. The Cd2+ adsorption isotherms, adsorption kinetics, and desorption characteristics were studied via a series of batch experiments, and Cd2+-loaded biochars were analyzed by SEM–EDS and XRD. The total Cd2+ adsorption capacity (Qc) increased with pyrolysis temperature for both biochars, however, rice straw-derived biochars had greater Qc than swine manure-derived biochars; hence, the biochar derived from rice straw at 700 °C (RB700) had the largest Qc, 64.4 mg g−1, of all studied biochars. Cadmium adsorption mechanisms in this study involved precipitation with minerals (Qcp), cation exchange (Qci), complexation with surface functional groups (Qco), and Cd-π interactions (Q). Both the pyrolysis temperature and feedstock affected the quantitative contributions of the various adsorption mechanisms. The relative percent contributions to Qc for Cd2+ adsorption by RB and SB were 32.9–72.9% and 35.0–72.5% for Qcp, 21.7–50.9% and 20.4–43.3% for Qci, 2.2–14.8% and 1.4–18.8% for Qco, and 1.4–3.1% and 3.0–5.8% for Q, respectively. For biochars produced at higher pyrolysis temperatures, the contributions of Qcp and Q to adsorption increased, while the contributions of Qci and Qco decreased. Generally, Qcp dominated Cd2+ adsorption by high-temperature biochars (700 °C) (accounting for approximately 73% of Qc), and Qci was the most prominent mechanism for low-temperature biochars (400 °C) (accounting for 43.3–50.9% of Qc). Results suggested that biochar derived from rice straw is a promising adsorbent for the Cd2+ removal from wastewater and that the low-temperature biochars may outperform the high-temperature biochars for Cd2+ immobilization in acidic water or soils.

12849. 题目: Mass transfer affects reactor performance, microbial morphology, and community succession in the methane-dependent denitrification and anaerobic ammonium oxidation co-culture
文章编号: N18091909
期刊: Science of The Total Environment
作者: Liang Fu, Fang Zhang, Ya-Nan Bai, Yong-Ze Lu, Jing Ding, Dandan Zhou, Yue Liu, Raymond Jianxiong Zeng
更新时间: 2018-09-19
摘要: Denitrifying anaerobic methane oxidation (DAMO) combining anaerobic ammonium oxidation (Anammox) process is a novel nitrogen removal technology. However, the roles of methane transfer (gas phase) and nitrogen transfer (liquid phase) in the heterogeneous process remain unclear. In this study, granular DAMO and Anammox co-cultures were inoculated from a hollow-fiber membrane bioreactor into a sequence batch reactor (SBR). Since the methane transfer became limited in SBR, the nitrate removal rate first decreased and then increased to 10 mg/(L∙day), while the ammonium removal rate did not recover and was around 2 mg/(L∙day). The activity of DAMO archaea and Anammox bacteria decreased noticeably. Furthermore, granular aggregates dispersed into small granules and ultimately became flocs with poor settleability in SBR. The content of extracellular polymeric substances decreased, especially that of proteins and humics. DAMO archaea decreased by 94.6% and Anammox bacteria decreased by 72%. In summary, the limitation of methane transfer affected DAMO and Anammox processes more notably than nitrogen transfer, resulting in lower nitrogen removal, granule disruption, and microbial community succession.
图文摘要:

12850. 题目: Photochemistry Illuminates Ubiquitous Organic Matter Fluorescence Spectra
文章编号: N18091908
期刊: Environmental Science & Technology
作者: K. R. Murphy, S. A. Timko, M. Gonsior, L. C. Powers, U. J. Wünsch, C. A. Stedmon
更新时间: 2018-09-19
摘要: Dissolved organic matter (DOM) in aquatic environments forms a vast reservoir of carbon present as a complex supermixture of compounds. An efficient approach to tracking the production and removal of specific DOM fractions is needed across disciplines, for purposes that range from improving global carbon budgets to optimizing water treatment in engineered systems. Although widely used to study DOM, fluorescence spectroscopy has yet to deliver specific fractions with known spectral properties and predictable distributions. Here, we mathematically isolate four visible-wavelength fluorescent fractions in samples from contrasting lake, river, and ocean environments. Using parallel factor analysis (PARAFAC), we show that most measured fluorescence in environmental samples can be explained by ubiquitous spectra with nearly stable optical properties and photodegradation behaviors over environmental pH gradients. Sample extraction changed bulk fluorescence spectra but not the number or shape of underlying PARAFAC components, while photobleaching preferentially removed the two longest-wavelength components. New approaches to analyzing fluorescence data sets incorporating these findings should improve the interpretation of DOM fluorescence and increase its utility for tracing organic matter biogeochemistry in aquatic systems.
图文摘要:

12851. 题目: Theoretical study on gas-phase reactions of nitrate radicals with methoxyphenols: Mechanism, kinetic and toxicity assessment
文章编号: N18091907
期刊: Environmental Pollution
作者: Bo Wei, Jianfei Sun, Qiong Mei, Maoxia He
更新时间: 2018-09-19
摘要: Creosol and 4-ethylguaiacol are two important methoxyphenols, lignin pyrolysis products, which are discharge into the atmosphere in large quantities. In this work, theoretical calculations of the reaction mechanism towards the two compounds with NO3 radicals was performed using DFT method. The rate constants and toxicity assessment were also investigated. The atmospheric lifetime for creosol and 4-ethylguaiacol were 0.82 and 0.19 h, respectively. A new reaction pathway was proposed for the transformation of methoxyl into hydroxyl, which has not yet been clarified in previous studies. The toxicity of methoxyphenols and their degradation products is closely related to their hydrophobicity. Although most degradation products are less toxic, they also should be pay more attention, especially for nitro-substituents.A new reaction pathway was proposed for the transformation of methoxyl into hydroxyl. The toxicity is closely related to their hydrophobicity.
图文摘要:

12852. 题目: Using multi-medium factors analysis to assess heavy metal health risks along the Yangtze River in Nanjing, Southeast China
文章编号: N18091906
期刊: Environmental Pollution
作者: Huifeng Wang, Qiumei Wu, Wenyou Hu, Biao Huang, Lurui Dong, Gang Liu
更新时间: 2018-09-19
摘要: In the environmental ecosystem, there are no absolutely isolated risks. Each risk might be influenced by multiple environmental factors and the factors’ interaction within the specific system. Hence, health risk assessments of heavy metal contamination must consider multiple environmental media and their transfer processes from one medium to another. Integrated assessments provide a new perspective for evaluating many factors, such as the potential ecological risks of soils, sediments, plants, and the transportation of heavy metals in these media, which influences the health risks. In this study, the main influencing factors for human health risk from heavy metals along the Yangtze River in Nanjing, Southeast China, were explored. The contents of five heavy metals were measured in sediment-soil-plant, including cadmium (Cd), lead (Pb), copper (Cu), zinc (Zn), and chromium (Cr). The Cd displayed the highest potential ecological risk in soils and sediments, as it possessed high bioaccessibility (BA; 0.17 ± 0.211) and bioaccumulation factor (BCF; 0.35 ± 0.33). The 5.97% of the target hazard quotient (THQ) of Cd were higher than 1, indicating a potential health risk in plant consumption. Based on the geodetector model, determinant power (DP) valves for factors influencing health risk strongly suggest that plant types (0.479) has a highest effect, followed by soil organic matter (SOM; 0.292), and the BA of heavy metals (0.107). The results also indicate that pollution from the upper reaches of the river, and agricultural activities, had a greater impact on health risk than did industrial activities in the study area. Thus, regular monitoring and source control for Cd, along with integrated agricultural management practices should be implemented to control and reduce heavy metal inputs and improve the safety of cultivated plants.
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12853. 题目: Oxidative potential of fine ambient particles in various environments
文章编号: N18091905
期刊: Environmental Pollution
作者: Lucille Joanna S. Borlaza, Enrique Mikhael R. Cosep, Seojong Kim, Kwangyul Lee, Hungsoo Joo, Minhan Park, Daphne Bate, Mylene G. Cayetano, Kihong Park
更新时间: 2018-09-19
摘要: The oxidative potential (OP) and chemical characteristics of fine particles collected from urban, roadside, rural, and industrial sites in Korea during spring, summer, fall, and winter seasons and an urban site in the Philippines during dry and wet seasons were examined. Significant differences in the OP of fine particles among sites and seasons were found. The industrial site yielded the highest OP activity (both mass and volume-normalized OP) among the sites, suggesting the strongest reactive oxygen species (ROS)-generating capability of industry source-dominant PM2.5. Seasonal data show that OP activities increased during the spring and summer possibly due to increased heavy metals caused by dust events and secondary organic aerosols formed by strong photochemical activity, respectively. The strength of the OP association with the chemical components highlights the influence of organic carbon and transition metals on the OP of ambient fine particles. The two OP assays (dithiothreitol (DTT) and electron spin resonance (ESR)) having different ROS-generating mechanisms were found to have different sensitivities to the chemical components facilitating a complementary analysis of the OP of ambient fine particles. Multiple linear regression model equations (OP as a function of chemical components) which were dependent on the sites were derived. A comparison of the daily OP and hazard index (HI) (the ratio of the measured mass concentration to the reference mass concentration of fine particles) suggests that the HI may not be sufficient to accurately estimate the health effects of fine particles, and a direct or indirect measurement of toxicity such as OP should be required in addition to the concentration level.
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12854. 题目: Insights into the formation mechanism of vaterite mediated by a deep-sea bacterium Shewanella piezotolerans WP3
文章编号: N18091904
期刊: Geochimica et Cosmochimica Acta
作者: Han Li, Qi-Zhi Yao, Feng-Ping Wang, Ya-Rong Huang, Sheng-Quan Fu, Gen-Tao Zhou
更新时间: 2018-09-19
摘要: Microbially mediated carbonate mineralization plays a crucial role in biogeochemical cycling of carbon, as microbes can efficiently transform atmospheric CO2 and organic carbon into carbonate cements which represent a significant sink in the global carbon cycle. It is well established that diverse bacteria from various natural habitats can induce the precipitation of calcium carbonate, and an increasing number of bacteria were found to be able to mediate the mineralization of vaterite. However, the precise mechanisms for the formation of bacterial vaterite are not fully understood. To better understand the effect of bacterial activity on vaterite formation, Shewanella piezotolerans WP3 was selected as a model microbe to induce calcium carbonate mineralization. A combination of bacterial and biomimetic mineralization experiments was adopted. Different bacterial components including native cells, EPS-free cells, cell-bound EPS, soluble EPS, and small molecule organics were isolated from the cultures and used to influence calcium carbonate crystallization and growth. The identification and characterization of the mineralized products were done using field emission scanning electron microscopy (FESEM), X-ray powder diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), thermogravimetry and differential thermal analysis (TG-DTA), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Bacterial in situ mineralization experiments demonstrate that S. piezotolerans WP3 can not only promote the mineralization of calcium carbonate, but also mediate polymorph selection of vaterite. Biomimetic mineralization experiments involving individual bacterial components reveal that different bacterial components have different effects on calcium carbonate polymorphism, and low molecular-weight amino acids secreted by the bacteria play a dominant role on vaterite formation and stabilization. Our observations also suggest that soluble EPS can induce the formation of aragonite while bound EPS facilitate calcite erosion. Current results can provide a deeper insight into bacterially mediated mineralization of vaterite and calcium carbonate polymorphism problem, and help evaluate the significance of biogenic carbonate in the diagenetic carbonate sinks.

12855. 题目: Stimulatory effect of magnetite on the syntrophic metabolism of Geobacter co-cultures: Influences of surface coating
文章编号: N18091903
期刊: Geochimica et Cosmochimica Acta
作者: Yunshen You, Shiling Zheng, Hongmei Zang, Feng Liu, Fanghua Liu, Juan Liu
更新时间: 2018-09-19
摘要: Magnetite-mediated direct interspecies electron transfer (DIET) can facilitate syntrophic metabolism in natural microbial communities and also promote the performance of the engineered systems based on syntrophic interactions. In this study, the stimulatory effect of bare synthetic magnetite (Mt), humic acid coated magnetite, and SiO2 coated magnetite (Mt-SiO2) on DIET in defined co-cultures of Geobacter metallireducens/Geobacter sulfurreducens were studied. Magnetite coated with Aldrich humic acid (HA) and Elliott Soil humic acid (HAES), respectively, were prepared, and the two kinds of humic acid influenced the ability of Mt to promote syntrophic metabolism of the co-cultures in a similar way. When weight concentration was the same, pure humic acid presented the stimulatory effect on DIET similar to bare magnetite. However, the presence of HA coating on magnetite surface caused 50% and 61%, respectively, decrease in the rates of ethanol consumption (Re) and succinate production (Rs) in DIET processes. Pure HA in the same weight concentration as the HA coating in Mt-HA induced the similar metabolism rates as Mt-HA. In the Mt-HA mediated DIET, most electrons from ethanol metabolism were transferred to G. sulfurreducens selectively through the HA coating, and magnetite core hardly contributed to DIET processes. The SiO2 coating on magnetite resulted in 81% and 89%, respectively, decreases in Re and Rs, mainly because the non-conductive SiO2 layer hindered electron transfer between magnetite core and bacteria. After eight-day incubation with the co-cultures, bare magnetite nanoparticles formed relatively larger and more compact aggregates with cells than Mt-HA and Mt-SiO2, due to the different surface charge between bare and coated Mt. The generation of dissolved Fe(II) and HCl-extractable Fe(II) due to microbial reduction of magnetite by G. metallireducens and vivianite formation were observed along with DIET processes in all DIET experiments. Based on these results, different pathways of electron transfer in defined co-cultures of Geobacters with bare and coated magnetite nanoparticles were proposed. The findings in this study demonstrate the significant effects of surface properties on the ability of magnetite to stimulate DIET, which needs to be considered in order to comprehensively understand the role and mechanisms of mineral-mediated DIET in natural and engineered systems.

12856. 题目: Effects of tillage on CO2 fluxes in a typical karst calcareous soil
文章编号: N18091902
期刊: Geoderma
作者: Dan Xiao, Yingying Ye, Shuangshuang Xiao, Wei Zhang, Xunyang He, Kelin Wang
更新时间: 2018-09-19
摘要: It is widely believed that soil disturbance by tillage was the primary cause of historical soil organic carbon (SOC) loss and high carbon dioxide (CO2) emission levels in the calcareous karst region. Nevertheless, the mechanisms underlying CO2 fluxes resulting from the soil property changes caused by tillage are poorly understood. A one-year simulation experiment using different tillage frequencies was conducted to quantify the impacts of tillage and soil property changes on CO2 flux. Treatments included conservation tillage (T0), semiannual tillage (T1), tillage every four months (T2), bimonthly tillage (T3), and monthly tillage (T4). The effects of tillage on soil CO2 flux had a strong seasonal pattern. CO2 fluxes in higher tillage frequencies of T3 and T4 were significantly higher than those of other treatments in spring, summer, and autumn. For viable tillage management, CO2 fluxes in T1 and T2 were significantly higher than those in T0 in spring and autumn. No significant differences in CO2 flux were found among treatments in winter. Tillage also had a significant influence on soil biogeochemical properties. Aggregate stability, dissolved organic carbon (DOC), and microbial biomass carbon (MBC) significantly decreased in T2, T3, and T4, whereas SOC significantly decreased just in T3 and T4 after 1 year. A structural equation model analysis showed that the annual cumulative soil CO2 flux was directly affected by annual changes in SOC (∆SOC), DOC (∆DOC), and MBC (∆MBC). Tillage frequency directly influenced annual changes in large macroaggregates (∆AG) and ∆MBC. These results indicated that tillage practice indirectly lowered SOC by reducing large macroaggregates and microbial biomass, which in turn, enhanced CO2 flux. Our results suggested that tillage disturbance in the karst soil significantly increased SOC loss through enhanced CO2 flux compared with that in the non-karst soil in a similar climate. In contrast, reducing or eliminating tillage in the wet-hot season could lower CO2 flux rate by minimizing large macroaggregate disturbance and, by extension, microbial access to mobile carbon sources.
图文摘要:

12857. 题目: Protection of extractable lipid and lignin: Differences in undisturbed and cultivated soils detected by molecular markers
文章编号: N18091901
期刊: Chemosphere
作者: Fangfang Li, Ni Liang, Pengchao Zhang, Yan Xu, Zhaofeng Chang, Min Wu, Wenyan Duan, Christian E.W. Steinberg, Bo Pan
更新时间: 2018-09-19
摘要: Understanding formation of organo-mineral association is crucial for soil organic matter (SOM) stabilization. To remove reactive minerals from un-disturbed natural soil (NS) and two cultivated soils (dry-farming soil, TD, and terrace paddy soil, TP), a 10% HF/1M HCl treatment was applied. The mineral protection of different molecular SOM structures before and after cultivation was compared by using markers for lipid and lignin. The removal of reactive mineral increased the lipid extractability in TD and NS similarly, indicating that the cultivation did not reduce the mineral protection; this is attributable to fertilizer application and amorphous Fe oxide enrichment. In TP, the extent of lipid protection was lower than in TD, demonstrating that the protection depends on the type of cultivation. In contrast to lipids, lignin-derived phenols decreased over 80% after acid treatment. Furthermore, the ratios of acid to aldehyde in vanillyl ((Ad/Al)V) of TD and TP were much higher than in NS, indicating an increased oxidation of lignin in cultivated soils. During acid treatment, two distinct layers of soil particles were identified: an organic matter (OM)-enriched layer (LOM), and a non-reactive mineral-enriched layer (LNR) with hardly detectable OC content. However, up to 50% of lipids were detected in LNR, indicating that lipids did not selectively interact with reactive mineral particles. In TD and TP, (Ad/Al)V values were higher in LOM than in LNR, indicating a strong interaction of oxidized lignin in LOM. Therefore, the protection of lignin, especially highly oxidized lignin, can depend more on reactive minerals than lipid. Promoting the formation of organo-mineral complexes is the primary strategy for soil management, especially for highly oxidized OM.
图文摘要:

12858. 题目: Living in a browning environment: Effects on Daphnia’s growth and fatty acid pattern
文章编号: N18091815
期刊: Limnology and Oceanography
作者: Clarice Casa Nova, Reinaldo Luiz Bozelli, Alejandro Spitzy, Dörthe Müller‐Navarra
更新时间: 2018-09-18
摘要: To assess whether different concentrations of dissolved organic matter (DOM) rich in humic substances (HS) affect growth rates, reproduction and fatty acids (FA) composition of Daphnia pulex under bright light, we performed microcosms controlled laboratory trials. Experiments were run using two microalgae as food source, Cryptomonas erosa and Scenedesmus acutus at four DOM additions (0 mg C L−1, 15 mg C L−1, 30 mg C L−1, and 60 mg C L−1) under unlimited food concentrations. Results show that daphnids’ growth rates were significantly higher feeding on Scenedesmus than on Cryptomonas, but were not significantly affected by the HS‐rich‐DOM concentrations. In contrast, clutch sizes increased with increasing concentrations of HS‐rich‐DOM, with nonsignificant differences between both food treatments. As expected, FA in daphnids were mainly impacted by the food. Irrespectively of food, the content of total FA and especially saturated FA were lower in the treatments with the highest addition of HS‐rich‐DOM. In the Scenedesmus trial, certain highly unsaturated FA (HUFA) susceptible to UV degradation could only be observed in the treatments with higher concentrations of HS‐rich‐DOM (e.g., eicosapentaenoic acid [EPA] and arachidonic acid [ARA] at 30, and EPA, ARA and docosahexaenoic acid [DHA] only at 60 mg L−1). In the Cryptomonas trial, DHA levels increased with increasing concentrations of HS‐rich‐DOM. Our results show that FA mediated food quality impacted how HS‐rich‐DOM affected Daphnias’ growth. As the high dietary content in HUFA probably caused daphnids lower growth rates under UV exposure, there seems to be a trade‐off between beneficial and potential detrimental effects of feeding on a diet rich in HUFA.

12859. 题目: Residues of endosulfan in cotton growing area of Vehari, Pakistan: an assessment of knowledge and awareness of pesticide use and health risks
文章编号: N18091814
期刊: Environmental Science and Pollution Research
作者: Ashfaq Ahmad, Muhammad Shahid, Sana Khalid, Habiba Zaffar, Tatheer Naqvi, Arshid Pervez, Muhammad Bilal, Muhammad Arif Ali, Ghulam Abbas, Wajid Nasim
更新时间: 2018-09-18
摘要: This study is based on self-reported information collected from selected farmers of Vehari District, Punjab, Pakistan, to determine their technical knowledge and awareness about pesticide use and associated environmental and health risks. Moreover, soil contamination by routinely used persistent organochlorine pesticide, endosulfan, was also evaluated. Survey data revealed very low literacy rate (on an average 9th grade education) and technical knowledge (almost missing) of the farmers in Vehari District. The farmers are unable to fully read and understand the instructions about the use of pesticide marked on the containers. They are not fully aware of pesticide persistence and toxicity (73%), unable to identify cotton pests and diseases (86%), and do not know which crop to grow in cotton adjacent fields (100%). Data also revealed that the farmers (100%) do not follow safety measure during pesticide application and are unaware of pesticide toxicity symptoms in human as well as the basic first-aid practices (89%). Poor literacy rate and lack of technical knowledge of farmers in Vehari regarding pesticide use and handling are posing serious environmental and health risks among the local inhabitants, particularly among farmers. Soil analysis results showed that concentration of α- and β-endosulfan ranged from 0–14 to 0–14.64 μg/mg, respectively. Principal component analysis showed that soil organic matter is the key soil parameter controlling the occurrence and fate of endosulfan under sandy loam soil conditions of Vehari District. There is a serious need of improving technical and environmental knowledge of farmer about pesticide risks on human health in the studied area, in particular, and the entire country in general. Findings are of great use for policymaking in Pakistan to minimize pesticide risks in Pakistan.

12860. 题目: Seasonal and geographic variation in dissolved carbon biogeochemistry of rivers draining to the Canadian Arctic Ocean and Hudson Bay
文章编号: N18091813
期刊: Journal of Geophysical Research: Biogeosciences
作者: Joanna Y. S. Li Yung Lung, Suzanne E. Tank, Christopher Spence, Daqing Yang, Barrie Bonsal, James W. McClelland, Robert M. Holmes
更新时间: 2018-09-18
摘要: The chemical composition of river water can be used to diagnose change on land, while playing a determining role in the ecology and biogeochemistry of riverine‐influenced ocean waters. Despite this, little is known about the seasonal and geographic variability of riverine chemistry throughout much of the Canadian north. Here, we assess the chemical composition of a broad suite of rivers draining to the Canadian Arctic Ocean and Hudson Bay using previously unpublished government data. We focus on inorganic and organic carbon (alkalinity and dissolved organic carbon [DOC]), using paired chemistry and discharge measurement to assess constituent flux. Concentrations and area‐normalized yields vary substantially across the northern Canadian landscape, with DOC typically highest in rivers draining the Hudson Bay Lowland, alkalinity highest in rivers draining Cordillera and Plains terrains, and the ratio of organic to inorganic species highest in rivers draining the Canadian Shield. Yields of major weathering ions show that carbonate weathering – much of which appears to be driven by sulfide oxidation – dominates inorganic carbon delivery from the rivers we assess. Despite the reasonably diverse coverage of the dataset, we find that clear gaps exist, including a lack of data through to the present‐day for many rivers, and a dearth of measurements from the Arctic Archipelago and eastern shores of Hudson Bay. We therefore use a modeling approach to extrapolate fluxes to the full Canadian Arctic drainage basin. Region‐specific differences between our results and previous models reinforce the need for targeted river water chemistry measures throughout the Canadian Arctic domain.

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