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22621. 题目: Seasonal variations in the optical characteristics of dissolved organic matter in glacial pond water
文章编号: N20111912
期刊: Science of The Total Environment
作者: D. Vione, N. Colombo, D. Said-Pullicino, D. Bocchiola, G. Confortola, F. Salerno, G. Viviano, S. Fratianni, M. Martin, D. Godone, M. Freppaz
更新时间: 2020-11-19
摘要: Large amounts of dissolved organic matter (DOM) are stored in mountain glaciers. However, few researches have analysed the optical characteristics of DOM in surface waters fed by mountain glaciers and their seasonal variations. In a pond fed by a glacier we observed simultaneous decreases in the dissolved organic carbon, and increases in both absorbance at 254 nm and specific absorption coefficient (SUVA254) during the ice-free season 2015. This behaviour differs from the typical behaviour of lake/pond water in summer, and from the trends observed in a nearby pond not fed by a glacier. The trends of DOM properties, main ions and water stable isotopes at the glacier-fed pond could be attributed to transient modifications of the subglacial hydrological system. Flushing of previously isolated pools of subglacially stored water, containing terrestrial DOM derived from glacially-overridden soil and vegetation, would be driven by intense rainfall events during the melting season. These findings suggest that heavy rainfall events during the melting season have the capability to transiently modify the characteristics of DOM in a glacial pond. These events may be further exacerbated in the future, as summer rainfall events in the Alps are predicted to increase due to global warming.

22622. 题目: Photo-ammonification in surface water samples: mechanism and influencing factors
文章编号: N20111911
期刊: Science of The Total Environment
作者: Yanwen Yang, Peizhe Sun, Lokesh P. Padhye, Ruochun Zhang
更新时间: 2020-11-19
摘要: Dissolved organic nitrogen (DON) accounts for a large proportion of the total aquatic nitrogen. Compared with dissolved inorganic nitrogen (DIN), the reactivity of DON has received limited attention. Photo-ammonification contributes significantly to the transformation of DON to DIN. However, information on the mechanism of this process is limited. This study investigated the photo-ammonification process of different natural surface water samples. The effects of seasons and rainfall on this process were explored, and the contributing factors were identified. Results showed that the seasonal effect on photo-ammonification differed for different water samples, whereas rainfall increased the rates of photo-ammonification for most of the lakes. The concentrations of reactive species, including triplet states of chromophoric dissolved organic matter (3CDOM*) and singlet oxygen (1O2), were found to be significantly correlated with water optical-parameters. Multivariable linear regression analysis (R2 = 0.617) revealed that the photo-ammonification of DON was mainly facilitated by 3CDOM* whereas 1O2 competed with 3CDOM* and showed an inhibiting effect. The components of dissolved organic matter (DOM) were identified by fluorescence excitation emission matrices coupled with parallel factor analysis and were found to be greatly influenced by the location. Allochthonous humic-like components were found to promote the production of reactive species while tryptophan-like component was found to be a reactive species consumer. This study revealed that the composition of DOM and the reactive species governed the rates of photo-ammonification.

22623. 题目: Accumulation and characteristics of fluorescent dissolved organic matter in loess soil-based subsurface wastewater infiltration system with aeration and biochar addition
文章编号: N20111910
期刊: Environmental Pollution
作者: Wen Li, Chenglong Liang, Lu Dong, Xin Zhao, Haiming Wu
更新时间: 2020-11-19
摘要: Subsurface wastewater infiltration systems (SWISs) have been widely used to treat rural domestic sewage. However, the low nitrogen removal and severe clogging problem always restrict the sustainability of SWISs for wastewater treatment. This study investigated the effects of aeration and biochar on the accumulation of nutrients and dissolved organic matter (DOM) in the substrate of loess soil-based SWISs for understanding the accumulation characteristics of DOM and the enhanced decontamination mechanism. The results showed that biochar addition could not improve the accumulation of nitrogen and phosphorus in the substrate, but could enhance denitrification (22%) via providing sufficient carbon for microorganisms. Moreover, the accumulation of organic matter in the substrate was also greatly affected. The DOM concentration of System D in the 40-60 cm layer reached 85.76 mg L-1, which indicated that biochar could release abundant DOM. Substrate DOM mainly contained humic acid-like and tryptophan-like substances. Moreover, the refractory macromolecular DOM components with high aromaticity and humification were found in the substrate below 60 cm of systems with biochar addition. This may be related to the DOM released by biochar and the extracellular polymeric substance (EPS) produced by microorganisms. It may affect the sustainability of the substrate to a certain extent, but fortunately that intermittent aeration could reduce this adverse effect. This research could provide new insights for preventing clogging and useful guidance for improving wastewater treatment performance in SWISs.

22624. 题目: Relationship Between Dissolved Organic Matter and Phytoplankton Community Dynamics in a Human-impacted Subtropical River
文章编号: N20111909
期刊: Journal of Cleaner Production
作者: Qi Liu, Yulu Tian, Yang Liu, Ming Yu, Zhaojiang Hou, Kejian He, Hui Xu, Baoshan Cui, Yuan Jiang
更新时间: 2020-11-19
摘要: Dissolved organic matter (DOM) is closely related to phytoplankton blooms, one of the most concerning environmental problems globally. DOM originates from phytoplankton production and metabolic activity and, in turn, can influence phytoplankton biomass and community structure. Therefore, clarifying the relationship between phytoplankton community dynamics and DOM has implications for bloom prevention and control as well as for aquatic ecosystem management. To understand this relationship further, we investigated phytoplankton communities at 110 sites in the dry and rainy seasons within the Dongjiang River basin, China, which is known for high rates of urbanization, industrialization, and agricultural intensification. The interaction between DOM (two humic-like DOM [C1 and C2] and two protein-like DOM [C3 and C4]) and phytoplankton community dynamics was investigated. Phytoplankton biomass and taxonomic composition were significantly related to C2, C3, and C4. The effect of C3 and C4 on phytoplankton taxonomic composition was prominent. C2 originating from agricultural wastewater increased phytoplankton biomass and changed phytoplankton taxonomic composition, whereas C1, originating from terrestrial soils and plants, did not stimulate phytoplankton biomass in rivers. There were clear change points, where phytoplankton abundance rapidly increased or decreased with changes in the concentrations of DOM components. Results suggested that DOM controls phytoplankton community dynamics and their relationship changes with variations in DOM chemical composition. DOM generated by anthropogenic activities may act as a potential warning of phytoplankton blooms.

22625. 题目: Absorption properties and forcing efficiency of light-absorbing water-soluble organic aerosols: seasonal and spatial variability
文章编号: N20111908
期刊: Environmental Pollution
作者: Vikram Choudhary, Prashant Rajput, Tarun Gupta
更新时间: 2020-11-19
摘要: Light-absorbing organic aerosols, also known as brown carbon (BrC), enhance the warming effect of the Earth's atmosphere. The seasonal and spatial variability of BrC absorption properties is poorly constrained and accounted for in the climate models resulting in a substantial underestimation of their radiative forcing estimates. This study reports seasonal and spatial variability of absorption properties and simple forcing efficiency of light-absorbing water-soluble organic carbon (WSOC, SFEWSOC) by utilizing current and previous field-based measurements reported mostly from Asia along with a few observations from Europe, the USA, and the Amazon rainforest. The absorption coefficient of WSOC at 365 nm (babs-365) and the concentrations of carbonaceous species at Kanpur were about an order of magnitude higher during winter than in the monsoon season owing to differences in the boundary layer height, active sources and their strengths, and amount of wet precipitation. The WSOC aerosols during winter exhibited ∼1.6 times higher light absorption capacity than in the monsoon season at Kanpur site. The assessment of spatial variability of the imaginary component of the refractive index spectrum (kλ) across South Asia has revealed that it varies from ∼1 to 2 orders of magnitude and light absorption capacity of WSOC ranges from 3 to 21 W/g. The light absorption capacity of WSOC aerosols exhibited less spatial variability across East Asia (5 to 13 W/g) when compared to that in South Asia. The photochemical aging of WSOC aerosols, indicated by the enhancement in WSOC/OC ratio, was linked to degradation in their light absorption capacity, whereas the absorption Ångström exponent (AAE) remained unaffected. This study recommends the adoption of refined climate models where sampling regime specific absorption properties are calculated separately, such that these inputs can better constrain the model estimates of the global effects of BrC.

22626. 题目: Design and fabrication of exfoliated Mg/Al layered double hydroxides on biochar support
文章编号: N20111907
期刊: Journal of Cleaner Production
作者: Yutao Peng, Yuqing Sun, Daniel C.W. Tsang, Aamir Hanif, Jin Shang, Zhengtao Shen, Deyi Hou, Yaoyu Zhou, Qing Chen, Yong Sik Ok
更新时间: 2020-11-19
摘要: Tailored design and fabrication of biochar-based adsorbents with high porosity and well dispersion is a critical process for enhancing their environmental applications. To elucidate the material structure-performance relationship, this study synthesized and compared corn straw biochar-supported Mg/Al layered double hydroxides composites (LDHs-BCs) using conventional co-precipitation or aqueous miscible organic solvent treatment (AMOST) methods under various pyrolysis temperatures (350, 550, 750, and 950 °C) and metal loadings (5 and 15 wt.%). The comprehensive surface characterization demonstrated enlarged interlayer spacing, increased specific surface area, and smaller crystal size of LDHs as well as lowered intensities of O-containing functional groups in LDHs-BCs. These results suggested that, in comparison to conventional co-precipitation method, AMOST method can serve as a simple, cost-effective, and robust method to induce exfoliation, higher dispersion, and more stable attachment of LDHs on the biochar surface. The Langmuir adsorption isotherms further demonstrated that the AMOST-derived composites prepared at higher temperatures (i.e., 750 and 950 °C) and lower metal loading (i.e., 5 wt.%) exhibited superior contaminant removal capacities (280.7−286.2 mg PO43−/g and 92.5−94.7 mg Cu(II)/g at pH 5.0−6.0). The synergistic effect was attributed to coupled functionalization of LDHs and biochar under customized synthesis conditions. These results provide valuable insights into fabricating high-performance and environmentally friendly LDHs-BCs for green remediation and sustainable development.

22627. 题目: Impacts of red mud on lignin depolymerization and humic substance formation mediated by laccase-producing bacterial community during composting
文章编号: N20111906
期刊: Journal of Hazardous Materials
作者: Zhiwei Jiang, Xintian Li, Mingqi Li, Qiuhui Zhu, Gen Li, Chaofan Ma, Qingyun Li, Jianzong Meng, Youyan Liu, Qunliang Li
更新时间: 2020-11-19
摘要: The aim of this study was to investigate the impacts of red mud on lignin degradation, humic substance formation and laccase-producing bacterial community in composting to better improve composting performances. The results indicated that the organic matter contents of final compost products in the treatment group with red mud (T) decreased by 25.74%, which was more than the control group without red mud (CK) (12.09%). The final lignin degradation ratio and humic substance concentration of the T were 18.67% and 22.80% higher than that of the CK, respectively. The final C/N values of compost in the CK and T were 11.32 and 10.66, respectively, which were both less than 15, suggesting that compost reached maturity. Redundancy analysis showed that temperature was the main factors driving the variation of laccase-producing bacterial community. Pearson analysis suggested that Pseudomonas, Phenylobacterium, and Caulobacter were the most significantly correlated with lignin degradation and humification in the T.

22628. 题目: Quenching of an Aniline Radical Cation by Dissolved Organic Matter and Phenols: A Laser Flash Photolysis Study
文章编号: N20111905
期刊: Environmental Science & Technology
作者: Frank Leresche, Lucie Ludvíková, Dominik Heger, Urs von Gunten, Silvio Canonica
更新时间: 2020-11-19
摘要: Aromatic amines are relevant aquatic organic contaminants whose photochemical transformation is affected by dissolved organic matter (DOM). The goal of this study is to elucidate the underlying mechanism of the inhibitory effect of DOM on such reactions. The selected model aromatic amine, 4-(dimethylamino)benzonitrile (DMABN), was subjected to laser flash photolysis in the presence and absence of various model photosensitizers. The produced radical cation (DMABN•+) was observed to react with several phenols and different types of DOM on a time scale of ∼100 μs. The determined second-order rate constants for the quenching of DMABN•+ by phenols were in the range of (1.4–26) × 108 M–1 s–1 and increased with increasing electron donor character of the aromatic ring substituent. For DOM, quenching rate constants increased with the phenolic content of the DOM. These results indicate the reduction of DMABN•+ to re-form its parent compound as the basic reaction governing the inhibitory effect. In addition, the photosensitized oxidation of the sulfonamide antibiotic sulfadiazine (SDZ) was studied. The observed radical intermediate of SDZ was quenched by 4-methoxyphenol less effectively than DMABN•+, which was attributed to the lower reduction potential of the SDZ-derived radical compared to DMABN•+.

22629. 题目: Distribution characteristics of low molecular weight organic acids in seawater of the Changjiang Estuary and its adjacent East China Sea: Implications for regional environmental conditions
文章编号: N20111904
期刊: Marine Pollution Bulletin
作者: Lina Lyu, Kejing Fang, Hong Jin, Gui-Peng Yang, Haorui Liang, Haibing Ding
更新时间: 2020-11-19
摘要: In this study, components, concentrations, distribution characteristics and sources of low molecular weight organic acids (LMWOAs) in seawater of the Changjiang Estuary and its adjacent East China Sea were investigated in March 2015. Lactic, acetic and formic acids were identified with their concentration range of 0–16.7, 0–42.7 and 0–6.7 μmol·L−1, respectively. In the surface seawater, high concentrations of LMWOAs appeared in the sea area close to the estuary and along the coast. LMWOAs were important fractions of dissolved organic carbon and acetic acid was dominant component of LMWOAs. Riverine, terrestrial input, phytoplankton and sediment release were important sources for the LMWOAs, and human activities were considered as dominant sources for them in sampling period. The consistency of regions with high concentrations of LMWOAs, eutrophication, seasonal hypoxia and frequent red tide occurrence suggested LMWOAs as potential indicators for evaluating pollution status in coastal areas.

22630. 题目: The effects of management practices on soil organic carbon stocks of oil palm plantations in Sumatra, Indonesia
文章编号: N20111903
期刊: Journal of Environmental Management
作者: Niharika Rahman, Ken E. Giller, Andreas de Neergaard, Jakob Magid, Gerrie van de Ven, Thilde Bech Bruun
更新时间: 2020-11-19
摘要: The rapid increase in global production of and demand for palm oil has resulted in large-scale expansion of oil palm monoculture in the world's tropical regions, particularly in Indonesia. This expansion has led to the conversion of carbon-rich land-use types to oil palm plantations with a range of negative environmental impacts, including loss of carbon from aboveground biomass and soil. Sequestration of soil organic carbon (SOC) in existing oil palm plantations is an important strategy to limit carbon losses. The aim of this study was to investigate SOC stocks of oil palm plantations under different management systems. Soil samples were collected from three different management systems (best management practices (BMP), current management practices typical of large plantations (CMP) and smallholder management practices (SHMP)) in north Sumatra, Indonesia. Plantations were divided into four management zones that were sampled separately with four replicate profiles in the weeded circle, frond stack, harvesting path and interrow zones. All the soil samples were collected from five (0–5, 5–15, 15–30, 30–50 and 50–70 cm) soil depths. Soil samples were analysed for concentration of SOC, soil texture, soil bulk density and pH. Calculations of SOC stocks in the soils were undertaken according to the fixed-depth and equivalent soil mass approaches. Results showed that SOC stocks of plantations under BMP (68 t ha−1) were 31% and 18% higher than under CMP (57 t ha−1) and SHMP (46 t ha−1) respectively. In the BMP system, soils under the interrow zone that received enriched mulch and frond stack positions stored significantly more SOC than the harvesting path of the BMP system (77, 73 and 57 t ha−1 respectively). BMP also had a 33% higher fresh fruit bunch yield compared to the SHMP system. This study shows that residue incorporation or retention as a part of BMP could be an effective strategy for increasing SOC stocks of oil palm plantations and confirms that these management practices could improve yields from SHMP systems.

22631. 题目: Spatial heterogeneity of biochar (segregation) in biochar-amended media: An overlooked phenomenon, and its impact on saturated hydraulic conductivity
文章编号: N20111902
期刊: Journal of Environmental Management
作者: Seyyed Ali Akbar Nakhli, Sydney Goy, Kalehiwot Nega Manahiloh, Paul Thomas Imhoff
更新时间: 2020-11-19
摘要: While the use of biochar as a soil amendment is gaining popularity for environmental and agricultural purposes, spatial heterogeneity of biochar (segregation) in biochar-amended media and its underlying causes have been overlooked. In this study, for the first time particle segregation in biochar-amended media and its impact on the media's saturated hydraulic conductivity (Ksat) were investigated. Two uniformly graded media were amended with different sizes of a wood-based biochar under dry and wet conditions. While the intended biochar volume fraction (bf) was 17.5%, in dry-packed columns biochar was often segregated and the measured bf ranged from 7.5 ± 0.8 SE% (SE = standard error) to 23.6 ± 1.8 SE% across all spatial locations. If, however, 20% water (volume of water/bulk volume of packed media) was added to the mixtures during mixing, homogeneous packings were achieved. In dry-packing, segregation was governed by the difference in the physical properties of the media and the biochar: particle size, density, and shape. In wet-packing, segregation was prevented due to the inter-particle adhesion forces associated with water. Although X-ray computed tomography images showed that the presence of segregation altered particle distributions and pore morphologies, the Ksat for wet-packed and dry-packed columns were statistically identical. The results of this study suggest that laboratory methods for packing biochar-amended media should include moisturizing the mixture to inhibit particle segregation. Mixing under wet conditions is recommended for any type of soil and biochar and for any scale of application, in both the laboratory and field.

22632. 题目: Batch and Continuous Design of a Full‐Scale Treatment Facility for Removing Dissolved Natural Organic Matter
文章编号: N20111901
期刊: Clean - Soil, Air, Water
作者: Bulent Sari, Ali Erdem Oztas, Olcayto Keskinkan, Cagatayhan Bekir Ersu
更新时间: 2020-11-19
摘要: In this study, batch and continuous flow adsorption experiments were carried out and the design of a full‐scale facility (with an operating capacity of 2.5 × 105 m3/day) for removing dissolved natural organic matter (DNOM) from lake (Catalan Dam Lake) water was demonstrated. The adsorption efficiency was proportional to the temperature and the amount of adsorbent unlike pH increase. The highest DNOM removal rate was obtained at 35°C, pH 4, and an adsorbent amount of 0.8 g/L. Optimum contact time for batch studies was 60 min at equilibrium. Correlation constants (r) of Langmuir and Freundlich isotherms were 0.8905 and 0.9739, respectively. Based on the Freundlich isotherm, the highest adsorption capacity (qmax) obtained was 2.44 and 6.01 mg DNOM/g GAC for raw and enriched water, respectively. At a further stage, the effects of adsorbent amount, bed depth, empty bed contact time, and organic loading on removal performance were investigated in the rapid small‐scale column test (RSSCT) columns. 53 and 78% DNOM removal rates in raw water and enriched water, respectively, were sufficient to meet the targeted effluent concentration of 1 mg DNOM/L in GAC adsorption columns. It was determined that 15 adsorption columns with dimensions of 7 m height, 4.33 m diameter, and 22 days of operation cycle were required to remove DNOM from raw water at the design capacity of the facility. This article is protected by copyright. All rights reserved

22633. 题目: Assessing microbial residues in soil as a potential carbon sink and moderator of carbon use efficiency
文章编号: N20111811
期刊: Biogeochemistry
作者: Kevin Geyer, Jörg Schnecker, A. Stuart Grandy, Andreas Richter, Serita Frey
更新时间: 2020-11-18
摘要: A longstanding assumption of glucose tracing experiments is that all glucose is microbially utilized during short incubations of ≤2 days to become microbial biomass or carbon dioxide. Carbon use efficiency (CUE) estimates have consequently ignored the formation of residues (non-living microbial products) although such materials could represent an important sink of glucose that is prone to stabilization as soil organic matter. We examined the dynamics of microbial residue formation from a short tracer experiment with frequent samplings over 72 h, and conducted a meta-analysis of previously published glucose tracing studies to assess the generality of these experimental results. Both our experiment and meta-analysis indicated 30–34% of amended glucose-C ( 13 C or 14 C) was in the form of residues within the first 6 h of substrate addition. We expand the conventional efficiency calculation to include residues in both the numerator and denominator of efficiency, thereby deriving a novel metric of the potential persistence of glucose-C in soil as living microbial biomass plus residues (‘carbon stabilization efficiency’). This new metric indicates nearly 40% of amended glucose-C persists in soil 180 days after amendment, the majority as non-biomass residues. Starting microbial biomass and clay content emerge as critical factors that positively promote such long term stabilization of labile C. Rapid residue production supports the conclusion that non-growth maintenance activity can illicit high demands for C in soil, perhaps equaling that directed towards growth, and that residues may have an underestimated role in the cycling and sequestration potential of C in soil.

22634. 题目: Using loose nanofiltration membrane for lake water treatment: A pilot study
文章编号: N20111810
期刊: Frontiers of Environmental Science & Engineering
作者: Danyang Liu, Johny Cabrera, Lijuan Zhong, Wenjing Wang, Dingyuan Duan, Xiaomao Wang, Shuming Liu, Yuefeng F. Xie
更新时间: 2020-11-18
摘要: Nanofiltration (NF) using loose membranes has a high application potential for advanced treatment of drinking water by selectively removing contaminants from the water, while membrane fouling remains one of the biggest problems of the process. This paper reported a seven-month pilot study of using a loose NF membrane to treat a sand filtration effluent which had a relatively high turbidity (∼0.4 NTU) and high concentrations of organic matter (up to 5 mg/L as TOC), hardness and sulfate. Results showed that the membrane demonstrated a high rejection of TOC (by<90%) and a moderately high rejection of two pesticides (54%–82%) while a moderate rejection of both calcium and magnesium (∼45%) and a low rejection of total dissolved solids (∼27%). The membrane elements suffered from severe membrane fouling, with the membrane permeance decreased by 70% after 85 days operation. The membrane fouling was dominated by organic fouling, while biological fouling was moderate. Inorganic fouling was mainly caused by deposition of aluminum-bearing substances. Though inorganic foulants were minor contents on membrane, their contribution to overall membrane fouling was substantial. Membrane fouling was not uniform on membrane. While contents of organic and inorganic foulants were the highest at the inlet and outlet region, respectively, the severity of membrane fouling increased from the inlet to the outlet region of membrane element with a difference higher than 30%. While alkaline cleaning was not effective in removing the membrane foulants, the use of ethylenediamine tetraacetate (EDTA) at alkaline conditions could effectively restore the membrane permeance.

22635. 题目: Testing the reliable proxies to understand the mid-Holocene climate variability records from Chandratal lake, Western Himalayas
文章编号: N20111809
期刊: Quaternary International
作者: Monica Sharma Shamurailatpam, Om Kumar, A.L. Ramanathan
更新时间: 2020-11-18
摘要: Chandratal lake (32°28′30.65″ N 77°37′1.42″ E) located at the junction of Indian Summer Monsoon and Westerlies give an opportunity to investigate the relationship between monsoon, Amino acids, Biogenic silica and Organic carbon. Here, we used multi-proxy (Amino acids, Biogenic silica, grain size and total organic carbon) to reconstruct mid-Holocene climate variability. Our proxy records well capture the changes in monsoon patterns, linking with Holocene climate optimum (HCO) during the ∼6344- 5821 cal BP. The sediment profile begins with a wetter and moist climate mostly from the terrestrial environment inputs, corresponding to the warm Holocene Climate Optimum (HCO) period (∼6344 - 5821 cal yr BP). A stable condition of the geochemical proxies during ∼5821–3780 cal yr BP reveals a shifting of a moisture source, catchment stability and cold/dry climate in correspondence with reduced precipitation. The period from ∼3780 to 2129 cal yr BP, follows a gradual increase of organic matter deposition and supported with an elevated atomic C/N ratio of 13.1 (mean value). Further association of organic matter with the coarser grain particles, suggesting a wetter climate from increasing runoff which is in correlation with the reinforcement of the precipitation during this time interval. From ∼2129 to 696 cal yr BP, reduced precipitation/dry condition was observed with a shift in the autochthonous production of organic matter (C/N ratio of 8.91). Increase in BSi content suggests an ameliorated climate at this interval; however, the lower organic matter content (mean, 1.79%) and shift in the correlation of organic matter from coarse grains to finer grain size, suggesting little contributions from the terrestrial activities favouring the dry environment and abundant diatoms growth. The paleoenvironmental variations illustrate in the study is comparable to other findings recorded in the Himalayan region.

22636. 题目: Rates and Dynamics of Mercury Isotope Exchange between Dissolved Elemental Hg(0) and Hg(II) Bound to Organic and Inorganic Ligands
文章编号: N20111808
期刊: Environmental Science & Technology
作者: Quanying Wang, Lijie Zhang, Xujun Liang, Xiangping Yin, Yaoling Zhang, Wang Zheng, Eric M. Pierce, Baohua Gu
更新时间: 2020-11-18
摘要: Mercury (Hg) isotope exchange is a common process in biogeochemical transformations of Hg in the environment, but it is unclear whether and at what rates dissolved elemental Hg(0)aq may exchange with divalent Hg(II) bound to various organic and inorganic ligands in water. Using enriched stable isotopes, we investigated the rates and dynamics of isotope exchange between 202Hg(0)aq and 201Hg(II) bound to organic and inorganic ligands with varying chemical structures and binding affinities. Time-dependent exchange reactions were followed by isotope compositional changes using both inductively coupled plasma mass spectrometry and Zeeman cold vapor atomic absorption spectrometry. Rapid, spontaneous isotope exchange (<1 h) was observed between 202Hg(0)aq and 201Hg(II) bound to chloride (Cl–), ethylenediaminetetraacetate (EDTA), and thiols, such as cysteine (CYS), glutathione (GSH), and 2,3-dimercaptopropanesulfonic acid (DMPS) at a thiol ligand-to-Hg(II) molar ratio of 1:1. Without external reductants or oxidants, the exchange resulted in transfer of two electrons and redistribution of Hg isotopes bound to the ligand but no net changes of chemical species in the system. However, an increase in the ligand-to-Hg(II) ratio decreased the exchange rates due to the formation of 2:1 or higher thiol:Hg(II) chelated complexes, but had no effects on exchange rates with 201Hg(II) bound to EDTA or Cl–. The exchange between 202Hg(0)aq and 201Hg(II) bound to dissolved organic matter (DOM) showed an initially rapid followed by a slower exchange rate, likely resulting from Hg(II) complexation with both low- and high-affinity binding functional groups on DOM (e.g., carboxylates vs bidentate thiolates). These results demonstrate that Hg(0)aq readily exchanges with Hg(II) bound to various ligands and highlight the importance of considering exchange reactions in experimental enriched Hg isotope tracer studies or in natural abundance Hg isotope studies in environmental matrices. The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.est.0c06229. ICP-MS quantification of Hg isotopes; Zeeman CVAAS analysis of purgeable Hg(0); certified purities and impurities of the enriched Hg isotopes 201Hg and 202Hg; elemental composition and characteristics of dissolved organic matter (DOM); list of experiments and experimental conditions used in isotope exchange reactions; QA/QC summary for Hg analyses by ICP-MS; molecular structure of organic ligands and their binding stability constants with Hg(II); speciation calculations of Hg(II) complexes with thiol ligands in 10 mM NaCl; determination of potential oxidation of 202Hg(0)aq or reduction of 201Hg(II) in 10 mM NaCl; determination of potential interactions between 202Hg(0)aq and thiol ligands or DOM; determination of purgeable Hg(0) isotopes following isotope exchange reactions between 202Hg(0)aq and 201Hg(II) bound to thiol ligands; recovery and mass balance analyses during isotope exchange reactions between 202Hg(0)aq and 201Hg(II) bound to thiol ligands; ICP-MS determination of nonpurgeable Hg(II) in solution following isotope exchange reactions between 202Hg(0)aq (12.5 nM) and 201Hg(II) (25 nM) bound to organic or inorganic ligands; determination of purgeable Hg(0) isotope concentrations, Hg recovery, and mass balance following isotope exchange reactions between 202Hg(0)aq and 201Hg(II) bound to thiol ligands and EDTA; and determination of purgeable Hg(0) isotope concentrations (nM), Hg recovery, and mass balance following isotope exchange reactions between 202Hg(0)aq and 201Hg(II) bound to SR-DOM or EFPC–DOM (PDF) This article has not yet been cited by other publications.

22637. 题目: Variation in concentration and sources of black carbon in a megacity of China during the COVID‐19 pandemic
文章编号: N20111807
期刊: Geophysical Research Letters
作者: Liang Xu, Jian Zhang, Xin Sun, Shengchen Xu, Meng Shan, Qi Yuan, Lei Liu, Zhenhong Du, Dantong Liu, Da Xu, Congbo Song, Bowen Liu, Gongda Lu, Zongbo Shi, Weijun Li
更新时间: 2020-11-18
摘要: Black carbon (BC) not only warms the atmosphere but also affects human health. The nationwide lockdown due to the COVID‐19 pandemic led to a major reduction in human activity during the past thirty years. Here, the concentration of BC in the urban, urban‐industry, suburb, and rural areas of a megacity Hangzhou were monitored using a multi‐wavelength Aethalometer to estimate the impact of the COVID‐19 lockdown on BC emissions. The citywide BC decreased by 44% from 2.30 μg/m3 to 1.29 μg/m3 following the COVID‐19 lockdown period. The source apportionment based on the Aethalometer model shows that vehicle emission reduction responded to BC decline in the urban area and biomass burning in rural areas around the megacity had a regional contribution of BC. We highlight that the emission controls of vehicles in urban areas and biomass burning in rural areas should be more efficient in reducing BC in the megacity Hangzhou.

22638. 题目: Dissolved organic nitrogen cycling in the South China Sea from an isotopic perspective
文章编号: N20111806
期刊: Global Biogeochemical Cycles
作者: Run Zhang, Xingchen T. Wang, Haojia Ren, Jie Huang, Min Chen, Daniel M. Sigman
更新时间: 2020-11-18
摘要: Dissolved organic nitrogen (DON) is the dominant form of fixed nitrogen in most of the low and mid‐latitude ocean surface. Here, we report measurements of DON isotopic composition (δ15N) from the west South China Sea, with the goal of providing new insight into DON cycling. The concentration of DON in the surface ocean is correlated (r=0.70, p<0.0001) with chlorophyll a concentration, indicating DON production in these surface waters. The concentration and δ15N of DON fall in a relatively narrow range in the surface ocean (4.6±0.1 μM and 4.3±0.2‰ vs. air, respectively; ±SD), similar to other ocean regions. The mean DON δ15N above 50 m (4.5±0.3‰) is similar to the δ15N of nitrate in the shallow subsurface (i.e. immediately below the euphotic zone; 4.6±0.2‰) but is higher than the δ15N of suspended particles in the surface ocean (~2.3‰). This set of isotopic relationships has been observed previously (e.g., in the oligotrophic North Atlantic and North Pacific) and can be explained by the cycling of N between PON, DON, and ammonium, in which an isotope effect associated with DON degradation preferentially concentrates 15N in DON. Consistent with this view, a negative correlation (r=0.70) between the concentration and the δ15N of DON is observed in the upper 75 m, suggesting an isotope effect of ~4.9±0.4‰ for DON degradation. Comparing the DON δ15N data from the SCS with other regions, we find that the δ15N difference between euphotic zone DON and shallow subsurface nitrate δ15N (Δδ15N(DON‐NO3)) rises from ocean regions of inferred net DON production to regions of net DON consumption, with the SCS representing an intermediate case.

22639. 题目: Coastal hypoxia and eutrophication as key controls on benthic release and water column dynamics of iron and manganese
文章编号: N20111805
期刊: Limnology and Oceanography
作者: Wytze K. Lenstra, Martijn Hermans, Marie J.M. Séguret, Rob Witbaard, Silke Severmann, Thilo Behrends, Caroline P. Slomp
更新时间: 2020-11-18
摘要: Continental shelves are a major source of iron (Fe) and manganese (Mn) to marine waters. Here, we investigate controls on benthic release of Fe and Mn and the impact on the water column in the Baltic Sea. We find high in situ benthic release rates of dissolved Fe and Mn at seasonally hypoxic sites (bottom water oxygen between 0–63 μmol L−1) receiving high inputs of organic matter. We find that benthic Fe and Mn release is sensitive to bottom water oxygen concentrations. Benthic Fe release is likely additionally controlled by Fe–sulfur redox chemistry in the surface sediment. For Mn, benthic release correlates positively with Mn oxide availability in the surface sediment. Benthic release contributes to high dissolved Fe and Mn concentrations in the water column and is amplified by repeated cycling of Fe and Mn between the sediment and overlying water through benthic release, oxidation in the water column, deposition as metal oxides, followed by reductive dissolution. Most water column Fe (∼ 80%) is present in particulate form near the seafloor. In contrast to Fe, a large percentage of the Mn remains dissolved (∼ 50%). We show that easily reducible Fe and Mn oxides are key forms of particulate Fe and Mn in suspended matter. The Baltic Sea represents a highly eutrophic, low oxygen end‐member when compared to other modern coastal systems. Our results imply that, upon continued eutrophication and deoxygenation of the coastal ocean, benthic release of dissolved Fe and Mn from continental shelves could become greater than previously thought.

22640. 题目: Dispersed Ground Ice of Permafrost Peatlands: Potential Unaccounted Carbon, Nutrient and Metal Sources
文章编号: N20111804
期刊: Chemosphere
作者: Artem G. Lim, Sergey V. Loiko, Daria M. Kuzmina, Ivan V. Krickov, Liudmila S. Shirokova, Sergey P. Kulizhsky, Sergey N. Vorobyev, Oleg S. Pokrovsky
更新时间: 2020-11-18
摘要: The physical and chemical consequences of massive ground ice (wedges) melt upon permafrost thaw is one of the central issues of environmental research linked to climate warming in the Arctic. Little is known about the chemical properties of dispersed ground ice abundant throughout permafrost peatlands that can easily melt with increasing active layer thickness (ALT). This is especially pertinent in continental lowlands, that account for sizeable areas of the Arctic, and contain high amount of organic carbon in both solid (peat) and liquid (porewater) phases. Here we studied 8 peat cores (0-130 cm depth)—comprised of porewater from the active layer (0-45 cm) as well as ice dispersed in frozen peat (40-130 cm)—across a latitudinal profile of Western Siberia Lowland (WSL) extending from discontinuous into continuous permafrost zones. Dissolved Organic Carbon (DOC), alkali and alkaline-earth metals (Ca, Mg, Sr, Ba, Li, Rb, Cs), sulfate, phosphorus, some trace elements (Al, Fe, Mn, Zn, Ni, Co, V, As, Y, REE, Zr, Hf, U) were sizably [more than 3 times] enriched in peat ice compared to peat porewaters from the active layer. In most sampled cores, there was a local maximum of strong enrichment (up to factors between 14 and 58) in DOC, P, Ca, Mg, Mn, Fe, Sr, As located 30-50 cm below the active layer. This maximum likely occurred due to solute concentration during full freezing of the soil column during winter. There was a sizable correlation between DOC, Al, Fe and other major and trace element concentrations that suggests strong control of organic complexes and organo-mineral (Al, Fe) colloids on element migration throughout the peat profile. The pool of C, major cations and trace metals in peat ice (40-130 cm) was approximately 3 to 55 times higher than the pool of these elements in porewaters from the active layer (0-40 cm). A 1-m increase of the ALT over the next 100 years is capable of mobilizing 58±38 Tg of DOC from soil ice into the rivers and lakes of the WSL latitudinal belt (63-67 °N). This fast lateral export of C (3.7±2.7 t C km-2 y-1) may double current C yields in WSL rivers (3.4±1.3 t C km-2 y-1). A strong increase (150 to 200 %) in riverine export of Zn, P and Cs may also occur while other micronutrients (Fe, Ni, Co, Ba, Mo, Rb) and toxicants (Cd, As, Al) may be affected to a lesser degree (20 to 30 % increase). We propose a global peat ice inventory in permafrost regions is essential for assessing the consequenaces of permafrost thaw on surface aquatic systems.