12521. 题目: Heteroaggregation and sedimentation of graphene oxide with hematite colloids: Influence of water constituents and impact on tetracycline adsorption
期刊: Science of The Total Environment
作者: Yiping Feng, Khanh An Huynh, Zhijie Xie, Guoguang Liu, Shixiang Gao
摘要: Because the transport of graphene oxide nanosheets (GO) from water to sediments is influenced by their heteroaggregation and sedimentation with natural colloids, knowledge on the interdependence of heteroaggregation and sedimentation for GO is needed to gain a better insight on the environmental fate of these nanosheets. However, this phenomenon is still not well understood. In this study, the heteroaggregation and sedimentation behaviors of GO with hematite nanoparticles (HemNPs) were investigated at various conditions. It has been found that negatively charged GO rapidly underwent heteroaggregation with positively charged HemNPs, leading to the sedimentation of GO. Significant sedimentation occurred when the net charge of the GOHemNP mixture was close to zero. The presence of various natural organic matters suppressed the sedimentation of the heteroaggregates through various mechanisms. Specifically, adsorption of humic acid and alginate reversed HemNP surface charge from positive to negative, leading to a slow sedimentation of the GOHemNP mixtures due to the increase in nanoparticle electrostatic repulsion. Adsorption of bovine serum albumin raised steric hindrance effect between GO and HemNP, which in turn inhibited their heteroaggregation and sedimentation. At high ionic strength conditions, the sedimentation of GO and HemNP was enhanced, possibly through the combination of homo- and hetero-aggregation. At elevated pH, the heteroaggregates were partially disaggregated, probably due to the weakening of GOHemNP bonds as the surface charges of these nanomaterials became more negative. Moreover, heteroaggregation of GO with HemNP likely to occupy the adsorption sites on GO surfaces, thus greatly reduced the adsorption of tetracycline on GO. These findings highlighted the important roles of natural colloids on the fate and transport of GO, together with the importance of heteroaggregation on the adsorption of co-existing pollutants to GO in natural aquatic environments.
12522. 题目: Microbes follow Humboldt: temperature drives plant and soil microbial diversity patterns from the Amazon to the Andes
作者: Andrew T. Nottingham, Noah Fierer, Benjamin L. Turner, Jeanette Whitaker, Nick J. Ostle, Niall P. McNamara, Richard D. Bardgett, Jonathan W. Leff, Norma Salinas, Miles Silman, Loeske Kruuk, Patrick Meir
摘要: More than 200 years ago, Alexander von Humboldt reported that tropical plant species richness decreased with increasing elevation and decreasing temperature. Surprisingly, co-ordinated patterns in plant, bacterial and fungal diversity on tropical mountains are yet to be observed, despite the central role of soil microorganisms in terrestrial biogeochemistry. We studied an Andean transect traversing 3.5 km in elevation to test whether the species diversity and composition of tropical forest plants, soil bacteria and fungi follow similar biogeographical patterns with shared environmental drivers. We found co-ordinated changes with elevation in all three groups: species richness declined as elevation increased, and the compositional-dissimilarity among communities increased with increased separation in elevation, although changes in plant diversity were larger than in bacteria and fungi. Temperature was the dominant driver of these diversity gradients, with weak influences of edaphic properties, including soil pH. The gradients in microbial diversity were strongly correlated with the activities of enzymes involved in organic matter cycling, and were accompanied by a transition in microbial traits towards slower-growing, oligotrophic taxa at higher elevations. We provide the first evidence of co-ordinated temperature-driven patterns in the diversity and distribution of three major biotic groups in tropical ecosystems: soil bacteria, fungi and plants. These findings suggest that inter-related patterns of plant and microbial communities with shared environmental drivers occur across landscape scales of relatively constant soil pH, with implications for tropical forest communities under future climate change.
12523. 题目: Variation in hydrogen isotope composition among saltmarsh plant organic compounds highlights biochemical mechanisms controlling biosynthetic fractionation
期刊: Journal of Geophysical Research: Biogeosciences
作者: Yvette Eley, Joseph White, Lorna Dawson, Michael Hren, Nikolai Pedentchouk
摘要: Hydrogen isotopes of plant‐derived biomarkers can vary by >100‰ at a single location. Isotope fractionation associated with the movement of water in plant leaves cannot account for this variability alone. Biochemical processes therefore must play a fundamental role in controlling hydrogen isotope fractionation during secondary compound biosynthesis. Different biosynthetic pathways utilize discrete hydrogen pools, and occur within distinct cell compartments. We analysed hydrogen isotope compositions of C16 and C18 fatty acids and phytol from 7 saltmarsh plants, and compared these data with: (i) leaf water and n‐alkane δ2H; (ii) leaf carbon and nitrogen contents; and (iv) nitrogen isotopes of bulk tissue, to evaluate the relationship between biochemical processes, cellular compartmentalization, and hydrogen isotope fractionation. Interspecies variation in chloroplastic fatty acids and phytol δ2H exceeds leaf water δ2H, indicating that different commitments of metabolites among species at branching points in chloroplast metabolic processes may be important determinants of lipid δ2H values. Dominant osmoregulatory strategies, in particular, show strong correlation with leaf wax n‐alkane δ2H. Species that preferentially produce nitrogenous compounds (dicots/shrubs) as protective solutes have 2H‐enriched n‐alkanes relative to species that produce mainly carbohydrates (monocots). n‐Alkane δ2H values, in combination with δ15N data and elemental (C, N) composition, together provide information about biochemical environmental adaptations exhibited by different higher plant species in response to environmental stresses. Thus, while spatial and temporal integration of biomarkers may produce an isotopic record of ecosystem function, biomarkers from individual plant or microbial remains may hold additional details into biologic function and adaptation to ancient environments.
12524. 题目: Effects of straw management and nitrogen application rate on soil organic matter fractions and microbial properties in North China Plain
期刊: Journal of Soils and Sediments
作者: Zengqiang Li, Dandan Li, Lei Ma, Yueyue Yu, Bingzi Zhao, Jiabao Zhang
摘要: Purpose: A 2-year field experiment was conducted on the North China Plain to assess the effects of two straw management practices and different nitrogen fertilizer addition levels on soil organic matter (SOM) fractions and microbial properties under a winter wheat-summer maize cropping system. Materials and methods: Eight treatments (two straw management practices and four nitrogen fertilizer input levels) were established using a randomized complete block design. The straw management practices were no straw return and straw return. Each straw management practice received nitrogen fertilizer rates at 0 (N0), 270 (N270), 360 (N360), or 450 (N450) kg N ha−1 year−1. The soil properties measured included SOM fractionation, enzyme activities, community level physiology profile (CLPP), and microbial community abundance and composition, which were represented by phospholipid fatty acid (PLFA). Results and discussion: Compared to no straw return, the addition of straw significantly increased soil total organic carbon and nitrogen, particulate organic carbon and nitrogen, and occluded particulate organic carbon and hot water extractable organic carbon by 7–29%. Invertase, protease, urease, and dehydrogenase activities increased by 22–40%. The biomasses of Gram-positive bacteria and fungi also increased. The increase in SOM fractions may be attributed to the decomposition of the added straw by more active enzymes, which may result from the shift of microbial community composition. In addition, hot-water extractable organic carbon, NO3-N, urease activity, and fungal biomass in the N270, N360, and N450 treatments significantly increased, independent of the nitrogen application rate, which indicated that N input level had a non-linear effect on soil properties in this area. Conclusions: Short-term straw return combined with a modest nitrogen fertilizer input (270 kg N ha−1 year−1) can increase SOM contents and microbial activity, which may help improve soil fertility in this region.
12525. 题目: Abundance of lipids in differently sized aggregates depends on their chemical composition
作者: Gerrit Angst, Klaas G. J. Nierop, Šárka Angst, Jan Frouz
摘要: Evidence for a vital role of soil mineral matrix interactions in lipid preservation is steadily increasing. However, it remains unclear whether solvent-extractable (‘free’) or hydrolyzable (‘bound’) lipids, including molecular proxies, e.g., for cutin and suberin, are similarly affected by different stabilization mechanisms in soil (i.e., aggregation or organo-mineral association). To provide insights into the effect of these stabilization mechanisms on lipid composition and preservation, we investigated free and bound lipids in particulate and mineral soil fractions, deriving from sand- and silt-/clay-sized aggregates from a forest subsoil. While free lipids accumulated in sand-sized aggregates, the more complex bound lipids accumulated in silt- and clay-sized aggregates, particularly in the respective mineral fractions < 6.3 µm (fine silt and clay). The presence of both, cutin and suberin markers indicated input of leaf- and root-derived organic matter to the subsoil. Yet, our cutin marker (9,10,ω-trihydroxyoctadecanoic acid) was not extracted from the mineral aggregate compartments < 6.3 µm, perhaps due to its chemical structure (i.e., cross-linking via several hydroxy groups, and thus higher ‘stability’, in macromolecular structures). Combined, these results suggest that the chemical composition of lipids (and likely also that of other soil organic matter compounds) governs interaction with their environment, such as accumulation in aggregates or association with mineral soil compartments, and thus indirectly influences their persistence in soil.
12526. 题目: Influence of soil porewater properties on the fate and toxicity of silver nanoparticles to Caenorhabditis elegans
期刊: Environmental Toxicology and Chemistry
作者: Carolin L. Schultz, Elma Lahive, Alan Lawlor, Alison Crossley, Victor Puntes, Jason M. Unrine, Claus Svendsen, David J. Spurgeon
摘要: Engineered nanoparticles (NPs) entering the environment are subject to various transformations that in turn influence how particles are presented to, and taken up by, organisms. To understand the effect of soil properties on the toxicity of nanosilver to Caenorhabditis elegans, toxicity assays were performed in porewater extracts from natural soils with varying organic matter content and pH using 3–8 nm unfunctionalized silver (Ag 3–8Unf), 52‐nm polyvinylpyrrolidone (PVP)‐coated Ag NPs (Ag 52PVP), and AgNO3 as ionic Ag. Effects on NP agglomeration and stability were investigated using ultraviolet‐visible (UV‐vis) spectroscopy and asymmetric flow field‐flow fractionation (AF4); Ag+ showed greater overall toxicity than nanosilver, with little difference between the NP types. Increasing soil organic matter content significantly decreased the toxicity of Ag 3–8Unf, whereas it increased that of AgNO3. The toxicity of all Ag treatments significantly decreased with increasing porewater pH. Dissolution of both NPs in the porewater extracts was too low to have contributed to their observed toxic effects. The UV‐vis spectroscopy revealed low levels of agglomeration/aggregation independent of soil properties for Ag 3–8Unf, whereas higher organic matter as well as low pH appeared to stabilize Ag 52PVP. Overall, both soil organic matter content and pH affected NP fate as well as toxicity to C. elegans; however, there appears to be no clear connection between the measured particle characteristics and their effect. Environ Toxicol Chem 2018;9999:1–10. © 2018 SETAC
12527. 题目: Variations in river input of iron impact sedimentary phosphorus burial in an oligotrophic Baltic Sea estuary
作者: Wytze K. Lenstra, Matthias Egger, Niels A. G. M. van Helmond, Emma Kritzberg, Daniel J. Conley, and Caroline P. Slomp
摘要: Estuarine sediments are key sites for removal of phosphorus (P) from rivers and the open sea. Vivianite, an iron (Fe)(II)-P mineral, can act as a major sink for P in Fe-rich coastal sediments. In this study, we investigate the burial of P in the Öre Estuary in the northern Baltic Sea. We find much higher rates of P burial at our five study sites (up to ~0.145molm−2yr−1) when compared to more southern coastal areas in the Baltic Sea with similar rates of sedimentation. Detailed study of the sediment P forms at our site with the highest rate of sedimentation reveals a major role for P associated with Fe and the presence of vivianite crystals below the sulfate methane transition zone. By applying a reactive transport model to sediment and porewater profiles for this site, we show that vivianite may account for up to 40% of total P burial. With the model, we demonstrate that vivianite formation is promoted in sediments with a low bottom water salinity and high rates of sedimentation and Fe oxide input. While high rates of organic matter input are also required, there is an optimum rate above which vivianite formation declines. Distinct enrichments in sediment Fe and sulfur at depth in the sediment are attributed to short periods of enhanced riverine Fe and organic matter input linked to variations in rainfall on land. Most of the P associated with the Fe in the sediment is likely imported from the adjacent eutrophic Baltic Proper. Our work demonstrates that variations in land-to-sea transfer of Fe may act as a key control on burial of P in coastal sediments. Ongoing climate change is expected to lead to a decrease in bottom water salinity and contribute to continued high inputs of Fe oxides from land, further promoting P burial as vivianite in the coastal zone of the northern Baltic Sea. This may enhance the role of this oligotrophic area as a sink for P imported from eutrophic parts of the Baltic Sea.
12528. 题目: Seasonal trends in surface pCO2 and air‐sea CO2 fluxes in Apalachicola Bay, Florida from VIIRS ocean color
期刊: Journal of Geophysical Research: Biogeosciences
作者: Ishan D. Joshi, Nicholas D. Ward, Eurico J. D'Sa, Christopher L. Osburn, Thomas S. Bianchi, Diana Oviedo‐Vargas
摘要: Estuaries have been recognized as important sources of carbon dioxide (CO2) to the atmosphere; however, contributions of these systems to regional and global carbon budgets are not well constrained due to limited information on seasonal and spatial variability. In this study, we use satellite remote sensing to obtain seasonal pCO2 distribution and air‐sea CO2 fluxes in Apalachicola Bay, a national estuarine research reserve located in the northern Gulf of Mexico, that receives seasonally varying dissolved organic matter‐rich waters from the Apalachicola River. A combination of time‐series (2005–2016) and seasonal field observations (2015–2016) of pH and biophysical variables were used to develop seasonal pH–pCO2 relationships for obtaining surface pCO2 estimates and air‐sea CO2 fluxes from VIIRS ocean color data. Monthly and seasonal maps of pCO2 and air‐sea CO2 fluxes showed a general trend of higher fluxes in winter and summer corresponding to high river flow and warm water temperatures. However, CO2 fixation via photosynthesis and low water temperatures contributed to lower fluxes to the atmosphere in spring and fall, respectively. Throughout the study period, Apalachicola Bay was a net source of CO2 with large seasonal and spatial variability and a mean annual CO2 flux to the atmosphere of 3.4 ± 3.1 mol m‐2 y‐1 (9.4 ± 8.5 mmol m‐2 d‐1), consistent with fluxes reported for other estuaries. This study demonstrates the critical role that satellite observations can play to improve the estuarine contributions to the global carbon flux estimates.
12529. 题目: The Role of Ligninolytic Enzymes Laccase and a Versatile Peroxidase of the White‐Rot Fungus Lentinus tigrinus in Biotransformation of Soil Humic Matter: Comparative in vivo Study
期刊: Journal of Geophysical Research: Biogeosciences
作者: A. G. Zavarzina, A. V. Lisov, A. A. Leontievsky
摘要: Soil organic matter (SOM) turnover by ligninolytic fungi is a large‐scale process that controls organic carbon geochemistry in terrestrial ecosystems. However, the role of certain oxidative enzymes (e.g. laccase) in humus degradation remain unclear, as well as the molecular structure and recalcitrance of SOM components. In order to address these questions, the degradation of forest soil humic acid (HA) in the presence of laccase and a versatile peroxidase (VP) have been studied in the liquid culture of Lentinus tigrinus. Contrary to the evolving views on humus structure, we have found that alkali‐extractable and acid‐insoluble constituents of SOM (HA) contain true macromolecular components, stable in the presence of 0.1% sodium dodecyl sulfate but degradable/re‐synthesizable by oxidative enzymes acting on covalent linkages. The HA degradation in the presence of laccase (high N medium) occurs at slower initial rate than in the presence of VP (low N medium). However each of the enzymes caused about 60% color loss and almost complete degradation of HA into smaller molecules (gel‐filtration data) within two weeks of cultivation. Depolymerization of HA in the culture liquid in the presence of laccase was accompanied by polymerization of degradation products on mycelium. Our results show that 1) humus macromolecules are not stable to oxidative enzymes once desorbed from the mineral phase; 2) laccase of L.tigrinus is comparable by its degradation potential to VP; 3) interfacial secondary synthesis reactions occur during humus decay in the presence of laccase. Our results highlight the important role of laccases in SOM sequestration in soils.
12530. 题目: Organic matter protection by kaolinite over bio-decomposition as suggested by lignin and solvent-extractable lipid molecular markers
期刊: Science of The Total Environment
作者: Fangfang Li, Zhaofeng Chang, Kaythi Khaing, Yuwei Zhou, Haiyun Zhao, Ni Liang, Dandan Zhou, Bo Pan, Christian E.W. Steinberg
摘要: The formation of organo-mineral complexes is essential in organic matter (OM) stabilization. However, limited studies have been conducted to systematically examine the mineral influence on the decomposition of plant residuals at a molecular level. In this study, pine needles and chestnut leaves were mixed with kaolinite at the weight ratio of 5:1. The controls were plant tissues without kaolinite. All the samples were incubated in the laboratory for one year. Molecular markers, including lignin-derived phenols (e.g. Vanilly units, syringyl units and cinnamyl units) and solvent-extractable lipids (e.g. n-alkanoic acid, n-alkanols and n-alkanes), were analyzed. The concentrations of lignin-derived phenols and lipid compounds were higher in the presence of kaolinite than without kaolinite. Lower degradation indexes, such as (Ad/Al)V (ratio of vanillic acid to vanillin) and CPI (carbon preference index of n-alkanoic acid and n-alkanes), were found in the kaolinite system. These results indicate that kaolinite reduced the OM decomposition. The addition of kaolinite also stabilized some carbohydrates from plants. Furthermore, the degradation of OM led to the generation of persistent free radicals, indicated by electron paramagnetic resonance (EPR) signals. The EPR signals were higher with than without kaolinite. We hypothesize that the adsorption of semiquinone or quinone radicals on kaolinite may limit their reaction with other OM moieties and thus extended their lifetimes. In addition to embedding OM in soil aggregates, our results provide direct evidence of another mineral protective mechanism of soil OM.
12531. 题目: Fe–colloid cotransport through saturated porous media under different hydrochemical and hydrodynamic conditions
期刊: Science of The Total Environment
作者: Xiaofei Li, Wenjing Zhang, Yunqi Qin, Tianyi Ma, Jingjing Zhou, Shanghai Du
摘要: To investigate the effect of different colloids on Fe migration in saturated porous media under different hydrochemical and hydrodynamic conditions, experiments were performed using colloidal silicon (inorganic) and colloidal humic acid (HA, organic), which are representative of the colloids in groundwater. Transport of Fe with and without colloid was investigated by column experiments using various porous media, colloid concentrations, ionic strengths (ISs), cation valences, and flow rates. The results show that colloidal silicon promotes and colloidal HA inhibits Fe transport, which is mainly because of their different bonding ratio, bonding modes with Fe and opposite surface charges between Fe–colloidal silicon and Fe–colloidal HA. Almost 100% of HA binds to Fe through the deprotonated functional groups, whereas only 13.3% of colloidal silicon binds to Fe, which is by electrostatic forces. Cotransport is also dependent on the hydrochemical and hydrodynamic conditions. For the Fe–colloidal silicon system, increasing the colloid concentration and flow rate, and decreasing the IS enhances Fe transport. Compared with colloidal silicon concentration = 10 mg/L, flow rate = 0.25 mL/min, and IS = 0.05 with CaCl2, a higher colloidal silicon concentration (20 mg/L), a higher flow rate (0.50 mL/min), and a lower IS (<0.0005 M) increase Fe recovery by 1.69%, 94.49% and 38.92%, respectively. Fe migration is also different in different porous media. For the Fe–colloidal HA system, Fe recovery decreases by 81.46% as the colloidal HA concentration increases from 0 to 20 mg/L. The type of porous medium and flow rate conditions have the same effects on Fe–colloidal HA transport as for colloidal silicon, although the electrical conditions have the opposite effect. With increasing IS, Fe–colloidal HA transport is enhanced because of competitive adsorption of the cations and Fe to colloidal HA and the porous medium.
12532. 题目: Comparative characterization of surface sludge deposits from fourteen French Vertical Flow Constructed Wetlands sewage treatment plants using biological, chemical and thermal indices
期刊: Science of The Total Environment
作者: M. Kania, M. Gautier, A. Imig, P. Michel, R. Gourdon
摘要: Due to their design and mode of operation, French Vertical Flow Constructed Wetlands (VFCWs) accumulate suspended solids from the inflow wastewater in the form of a sludge layer at the surface of the first filter. In order to maintain the treatment performance over the long term, the characteristics of the sludge deposits and their evolution have to be well described. In this objective, a panel of sludge deposit samples taken from 14 French VFCW sewage treatment plants was investigated. Elemental composition and organic matter content, nature and reactivity were analyzed. Results clearly revealed two categories of sludge deposits, namely the “young-age plants” type (1 year of operation and less) and the “mature plants” type (3 years of operation and more). Sludge deposits from the “mature plants” exhibited same biological, physical and chemical properties. Their organic matter was globally less abundant, more humified and less biodegradable than in the young-age plants type. Their overall contents in trace metals were also higher, although in a limited manner. The effect of additional treatments, particularly FeCl3 injection for phosphorus precipitation, was observable in the “young-age plants” group. Finally, the sludge deposits sampled from one particular plant with specific operating conditions were found to exhibit very different characteristics from those of either groups identified. This observation underlined the influence of local conditions on the typology of the sludge deposits.
12533. 题目: Duxite - fossil resin of Miocene age
期刊: Organic Geochemistry
作者: Martina Havelcová, Vladimír Machovič, Ivana Sýkorová, Ladislav Lapčák, Alexandra Špaldoňová, Karel Mach, Zdeněk Dvořák
摘要: A series of Miocene fossil resin from the northwest part of the Czech Republic, called duxite, has been analyzed by elemental, microscopic, gas chromatography (GC/MS), pyrolysis-gas chromatography, Fourier Transform infrared (FTIR), and Raman techniques. The set of samples consisted of museum, contemporary and artificially altered samples. The results of GC/MS revealed fine variances in chemical structure among the samples, which could be attributed to the geologic paleosituation during resin deposition, as was verified by alteration of a sample under different conditions. Sesquiterpenes, including α-cedrene and cuparene, were identified in sample extracts and sample pyrolysates together with diterpenoid members abietanes, pimaranes, and dehydroabietanes. The distribution and intensity of functional groups of FTIR spectra also confirmed that the duxite samples were fossilised exudates from a member of the Cupressaceae conifer family. Raman spectra supported this record indicating aromatic character of duxite and higher maturity of the samples.. The chemical composition indicated that duxite is a member of Class IV resins of the fossil resin classification system. Members of this group do not have a polymeric structure. This nonpolymerizable behaviour was confirmed by their excellent solubility in an organic solvent and the low softening point of the material. Our results therefore provide a valuable insight into the duxite-producing process and its potential for evaluating the geological environment and diagenetic conditions.
12534. 题目: Influence of biochars on the accessibility of organochlorine pesticides and microbial community in contaminated soils
期刊: Science of The Total Environment
作者: Neelum Ali, Sardar Khan, Yaying Li, Ningguo Zheng, Huaiying Yao
摘要: Biochar can be used as a promising potential substance to reduce the availability of toxic elements and compounds in contaminated soils but its effects on the accessibility of pesticides and microbiological interactions still remain unclear. Here, 65 day incubation experiments were conducted to investigate the efficacy of biochars on the accessibility of 21 different organochlorine pesticides (OCPs), and also to evaluate their influence on soil microbial community. The tested soil was collected from an agricultural field, containing loamy sand texture, and historically contaminated with high concentrations of OCPs. The soil was amended with four different kinds of biochars: sewage sludge biochar (SSBC), peanut shells biochar (PNBC), rice straw biochar (RSBC), and soybean straw biochar (SBBC). The results indicated that biochar-amendments had strong effects upon OCP accessibility over time and can act as super sorbent. Despite greater persistence of OCPs in soil, the application of selected biochars significantly (p < 0.01) reduced the accessibility of ∑OCPs in the amended soil in the order of SSBC (8–69%), PNBC (11–75%), RSBC (6–67%), and SBBC (14–86%), as compared to the control soil during 0–65 d incubation period. Moreover, the findings from total phospholipid acid (PLFA) and Illumina next-generation sequencing revealed that the incorporation of biochar have altered the soil microbial community structure over time. Higher abundances of Proteobacteria, firmicutes, Gemmatimonadetes, and Actinobacteria were found in biochar amendments. However, the relative abundances of Acidobacteria and Chloroflexi decreased, following biochar addition. The findings of these experiments suggest that biochar addition to soil at the rate of 3% (w/w) could be advantageous for decreasing accessibility of OCPs, enhancing the soil microbial communities, and their subsequent risk to environment and food chain contamination.
12535. 题目: The use of calcium carbonate-enriched clay minerals and diammonium phosphate as novel immobilization agents for mercury remediation: Spectral investigations and field applications
期刊: Science of The Total Environment
作者: Jianxu Wang, Ying Xing, Yuanyan Xie, Yong Meng, Jicheng Xia, Xinbin Feng
摘要: We used calcium carbonate-enriched clay minerals (CECM) and diammonium phosphate (DAP) as immobilization agents for mercury (Hg) immobilization. The effects of CECM, DAP, or both in different amounts and ratios, as well as pH and initial Hg concentrations, on Hg removal from solutions were investigated. The removal mechanism was revealed using transmission electron microscope with energy-dispersive X-ray (TEM-EDX) spectroscopy, and extended X-ray absorption fine structure spectroscopy (EXAFS). The performance of CECM and DAP under field conditions was also studied. The results showed that application of CECM and DAP at a ratio of 50:1 (w/w) removed over 90% of Hg from solutions containing 1.8 μM Hg2+, which was 9- or 2.6-fold higher than solely DAP (<10%) or CECM (34%<), respectively. Mercury removal by CECM and DAP was weakly affected by pH values between 4 and 10, and their maximum Hg removal capacity was 37 mg g−1. Both TEM-EDX and EXAFS results showed that the precipitate of Hg with phosphorus-associated minerals might be the primary mechanism of Hg removal by CECM and DAP. Results from the field trial showed that application of CECM and DAP decreased soil bioavailable Hg contents, but did not affect contents of organic matter bound Hg or residual Hg fractions, as compared with control and initial soils. Application of CECM and DAP resulted in dramatic reductions (40%–53%) of Hg in the edible tissues of Brassica chinensis and Raphanus raphanistrum in comparison to the non-treated control. We conclude that CECM and DAP offer a promising method for in situ remediation of Hg-contaminated farmlands in southwest of China.
12536. 题目: Influence of consecutive integrated rice-crayfish culture on phosphorus fertility of paddy soils
期刊: Land Degradation & Development
作者: Qingman Li, Lei Xu, Lijing Xu, Yiguang Qian, Yang Jiao, Yonghong Bi, Tanglin Zhang, Wen Zhang, Yanjie Liu
摘要: China has experienced an increase in integrated rice‐crayfish (Procambarus clarkii) culture (IRCC) in rice paddies. However, whether the current regime degrades phosphorus (P) fertility in rice paddies remains unclear. To assess changes in P fertility, the surface soil (0‐20cm) of high‐yield rice paddies with 3, 6 and 10 consecutive years of IRCC were sampled in Honghu County in the Jianghan Plain region, China. Adjacent fields planted with long‐term rotations of rice and dry‐season crops (RRD) were also sampled. Total P (TP), available P (Pa), organic P (Po) compounds and P fractions in soils were intensively assessed using chemical digestion, NaHCO3 extraction, 31P nuclear magnetic resonance (31PNMR) and sequential chemical extraction (SEDEX). IRCC significantly increased organic matter, total nitrogen, TP, Fe (II) and S2− contents of rice paddy soils and nutrient concentrations in in the surface water, with a distinct decrease in total Fe and pH. Consecutive IRCC greatly influenced P fertility. Continuous P accumulation in paddy soils accelerated greatly, with a mean increase of ca. 43 mg·kg−1·y −1. Compared to RRD, Pa was 67% higher after 3 years of IRCC but 78% lower after 10 years. Consecutive IRCC induced a decrease in Po compounds, with a mean decrease in TPo of ca. 20 mg·kg−1·y−1. Long‐term consecutive IRCC increased transformation of Pa, Fe (II)‐P and Po into Ca‐P and Fe (III)‐P, increasing mean Ca‐P and Fe (III)‐P concentrations by ca. 69 and 7 mg·kg−1·y−1, respectively. Our results suggested that long‐term consecutive IRCC degrades P fertility in rice paddies, and implementing IRCC in high‐yield rice paddies is not recommended.
12537. 题目: Phenanthrene adsorption on soils from the Yangtze River Delta region under different pH and temperature conditions
期刊: Environmental Geochemistry and Health
作者: Lifeng Ping, Yongming Luo
摘要: The phenanthrene (PHE) adsorption on soils from the Yangtze River Delta region under different pH and temperature conditions was studied in the laboratory. Results showed that the sorption of PHE on all soils was nonlinear and fitted to the Freundlich isotherm. The PHE adsorption on the soils is related to the content of organic carbons and the environmental conditions. There was a positive correlation (the correlation coefficient was 0.956) between the PHE adsorption and the soil organic carbon content. Adsorption on the soils at 15 °C ambient temperature was higher than at 25 °C, which was related to PHE solubility enthalpy. Adsorption on the soils in background solution at pH 5.0 was higher than in those at pH 6.2 and 7.5, which may be related to alteration of the hydrophobic character of humic substances. This study showed that intrinsic organic carbons influenced the adsorption of PHE, which was affected by environmental conditions, such as pH and temperature. Therefore, the characteristics of soil organic carbon should be considered first for implementing effective schemes for the remediation of contaminated soils and in the formulation of soil environmental quality standards.
12538. 题目: Soil Conditions Following Hydrologic Restoration in Cypress Dome Wetlands
作者: Megan K. Bartholomew, Christopher J. Anderson, Jacob Berkowitz
摘要: Soil characteristics and decomposition rates were investigated in 12 geographically isolated wetlands (cypress domes) across a gradient of hydrologic alteration (altered, marginally altered and least altered sites) seven years after passive recovery from historic groundwater withdrawals. Above- and belowground decomposition rates were determined in transition (seasonally flooded) and outer deep (semi-permanently) hydrologic zones. Flood duration, frequency, redox conditions, pH, and soil organic matter were measured to potentially explain patterns across the alteration gradient. Despite the reduction in groundwater withdrawals, altered sites exhibited fewer days of inundation in transition and outer deep zones compared to marginally altered and least altered wetlands. Over a 56 week period, altered wetlands displayed greater decomposition in the aboveground outer deep zone (73.3 ± 4.0% mass remaining) and in the belowground transition zone (62.0 ± 4.5% mass remaining) compared to marginally and least altered sites. Analyses indicated that marginally altered wetlands were more comparable to least altered wetlands however differences in altered wetland soils (including decomposition) persist. Although wetland hydrology has been partially restored, additional time and/or further site augmentation may be needed for altered sites to be functionally equivalent to least altered wetlands and in some cases (e.g., excessive subsidence) the degree of past alteration may limit restoration potential.
12539. 题目: Improved methane production from waste activated sludge by combining free ammonia with heat pretreatment: Performance, mechanisms and applications
期刊: Bioresource Technology
作者: Xuran Liu, Qiuxiang Xu, Dongbo Wang, Jianwei Zhao, Yanxin Wu, Yiwen Liu, Bing-Jie Ni, Qilin Wang, Guangming Zeng, Xiaoming Li, Qi Yang
摘要: Anaerobic digestion of waste activated sludge (WAS) is often limited by low hydrolysis efficiencies and poor methane potentials. This work presents a novel pretreatment technology for WAS anaerobic digestion, i.e., combining free ammonia with heat pretreatment (CFHP). Experimental results showed that compared with control, solo free ammonia (135.4 mg NH3-N/L) and solo heat (70 °C) pretreatment, the combined free ammonia and heat (135.4 mg NH3-N/L with 70 °C) obtained 52.2%, 25.5% and 30.2% faster in hydrolysis rate and 25.2%, 17.9% and 16.5% higher in biochemical methane potential, respectively. Mechanism investigations showed that the combined pretreatment not only largely facilitated the disintegration of WAS but also increased the proportion of biodegradable organic matters, thereby providing better contract between biodegradable organics and the anaerobic microbes for methane production. Considering its effectiveness and renewability, the combined pretreatment is an attractive technology for the application in real-world situations.
12540. 题目: A microscopic simulation of particle flux in ocean waters: application to radioactive pair disequilibrium
期刊: Geochimica et Cosmochimica Acta
作者: F. De Soto, E. Ceballos-Romero, M. Villa-Alfageme
摘要: The biological carbon pump, a fundamental component of the global carbon cycle, is a mechanism comprised of biological processes that transfer large amounts of organic carbon from the upper ocean to the ocean’s interior. It sequesters CO2 for weeks to hundreds or even millions of years through the sinking of a complex mix of biogeo-chemical material. As particles sink the flux of particulate organic carbon attenuates and only a fraction of the flux reaches the ocean’s depth. Quantifying the attenuation of sinking particulate carbon flux is key to assess the amount of carbon sequestered in the twilight zone. Current knowledge of the particle flux attenuation relies on a reduced number of direct measurements, usually fitted to a power law, that tries to describe the result of a large variety of biological, physical and chemical processes involved. We present a stochastic simulation for particle production, sinking and degradation in the oceans that includes most of the essential ingredients to ultimately describe the sinking carbon flux in the ocean and where all the complex biogeochemical behavior is captured by macroscopic parameters. The algorithm proposed interprets these phenomena probabilistically and is an ideal framework to describe the observed patterns of particle flux attenuation in depth. Particles are randomly produced and degraded with depth-dependent functions, which reproduces the variability of these processes in nature. Hence, the simulation proposed provides a suitable approach to analyse sinking carbon when different particle sizes or speeds are used. Furthermore, production and degradation phenomena are time-dependent, this way their seasonal evolution can be additionally explored and the simulation results in an ideal test-bed for the assessment of both steady and non-steady state situations. In addition, the theoretical formulation proposed provides a simple frame to include particle-metals interactions through adsorption and desorption processes. In this paper we relate typical parametrizations of the flux attenuation curve to their corresponding degradation rate and propose an alternative parametrization to model the flux degradation function which is negligible at very large depths, therefore producing a constant residual flux, and remains finite in the euphotic zone. This degradation function is implemented in the simulation and applied to estimate the scavenging of the naturally occurring radioisotopes 234Th and 210Po. We use the results to estimate effective adsorption and desorption rate constants for both isotopes. We found that the degradation rate, rather than the half-life, controls the depth at which the parent and daughter reach equilibrium. Thus, this depth is ruled by a combination of the degradation rate and the particle sinking velocity.