14661. 题目: A mechanistic microbial underpinning for the size-reactivity continuum of dissolved organic carbon degradation
期刊: Marine Chemistry
作者: C. Arnosti, G. Reintjes, R. Amann
摘要: The reservoir of dissolved organic carbon (DOC) in the ocean is modified by multiple input and removal processes. Incubation experiments as well as measurements of oceanic DOC have demonstrated that the high molecular weight (HMW) fraction of DOC typically has a younger radiocarbon age and is more reactive biologically than the low molecular weight (LMW) fraction of DOC. These observations have been summarized as a ‘size-reactivity continuum’ of DOC reactivity, but mechanistic explanations for these observations have been lacking. Here we describe how our recent discovery of ‘selfish’ HMW organic matter uptake among bacteria in surface ocean waters may help explain the rapid removal of HMW DOC. ‘Selfish’ substrate uptake by bacteria encompasses rapid binding and partial hydrolysis of intact polysaccharides on the outer membrane of bacteria, seamlessly followed by the transport of large oligosaccharide fragments into the periplasm with little to no loss of LMW hydrolysis products. ‘Selfish’ bacteria therefore process HMW substrates in a manner distinct from bacteria that carry out extracellular hydrolysis that yields LMW hydrolysis products in the environment. Recognition of the presence and prevalence of selfish bacteria in the ocean has profound implications for carbon flow – the source and quantity of LMW substrates made available to non-extracellular-enzyme producing bacteria – as well as for efforts to model and measure bacterial interactions during organic matter degradation. This discovery also highlights the importance of targeted substrate binding and uptake as key (often understudied) factors in geochemical investigations of microbially driven carbon cycling in the ocean. We conclude with some speculative thoughts about the factors that may determine the prevalence of selfish substrate uptake in the environment.
14662. 题目: Sorption of Cu(II) by Al hydroxide organo–mineral coprecipitates: Microcalorimetry and NanoSIMS observations
期刊: Chemical Geology
作者: Huihui Du, Qiaoyun Huang, Min Zhou, Boqing Tie, Ming Lei, Xiangdong Wei, Xiaoli Liu, Yuan Yang
摘要: The Al constituents of soils and sediments play an important role in the bioavailability and fate of trace heavy metals. Pure Al precipitates rarely exist; instead, Al3+ is commonly coprecipitated with organics to produce organo–Al hydroxide composites. Herein, we replicate the Al hydroxide organo−mineral composite formation in soils and sediments by synthesizing composites using humic acid (HA) during coprecipitation with Al hydroxide (Al(OH)3). The mineralogy and morphology results indicate the formation of amorphous and nanosized pure Al(OH)3 and Al(OH)3HA composites, while HA reduces the SSA and aggregation of the pure mineral. The sorption of Cu is enhanced on the Al(OH)3HA composite over pure Al(OH)3 at pH < 6, which is attributable to the additional binding sites present in the HA molecule. The isothermal titration calorimetry (ITC) results show that Cu sorption is endothermic on Al(OH)3 and exothermic on HA, and the sorption sequence is HA > Al(OH)3. The Cu uptake by the Al(OH)3HA composite is an energy-favorable process accomplished by an increase in entropy, signifying the formation of Cu-ligand inner-sphere complexes. Nano secondary ion mass spectrometry (NanoSIMS) results demonstrate that Cu is mainly sorbed on the HA fraction of the Al(OH)3–HA composite. This study therefore has important implications for predicting the cycling of trace heavy metals in Al-rich geologic environments, and sheds light on the combined use of ITC and NanoSIMS to uncover the distribution and speciation of trace elements in complex mineral–organic composites.
14663. 题目: Complexation and reduction of iron by phenolic substances: Implications for transport of dissolved Fe from peatlands to aquatic ecosystems and global iron cycling
期刊: Chemical Geology
作者: Xiang Wan, Wu Xiang, Neng Wan, Sen Yan, Zhengyu Bao, Yiliu Wang
摘要: Iron (Fe) is among the limiting nutrients in marine environments and mainly originates from terrigenous sources. Dissolved organic carbon (DOC), an important natural organic ligand, plays a key role in the dissolution and transport of terrestrial iron. Peat-derived DOC contains a large number of phenolics, and a systematic study of the geochemical interaction between DOC and Fe will contribute to the understanding of the global carbon and iron cycles. Phenolics, including phenolic acids, are secondary metabolites from plants and fungi. These compounds possess an aromatic ring bearing one or more hydroxyl groups and their structures may range from that of a simple phenolic molecule to that of a complex high-molecular weight polymer. Despite the extensive literature describing the biological effects of phenolic acids, the effect of phenolics on the iron cycle in peatlands is not known very well. Zoige peatland, the world's largest plateau peat wetland, was studied through field investigation and laboratory simulated experiments. The content of phenolics, filterable Fe and some physicochemical parameters in the rivers of the area were investigated. The waters are generally alkaline, with an average pH of 8.04, and aqueous Fe(III) and Fe(II) concentrations are higher than most of the common rivers in the world. The results of our experiments suggested that the high iron solubility was closely related to the phenolic content of the DOC. In particular, phenolics with catechol or galloy moieties forming complexes with iron and significantly impede the oxidation of complexed Fe(II). In addition, some phenolic substances are able to reduce ferric iron to ferrous iron. The combination of complexation and reduction in Fe by phenolics effectively increased the proportion of ferrous iron to total iron and slowed the oxidation and precipitation in the waters, maintaining a high content of “soluble iron” in the peatland. This mechanism has great implications for the effective transport of soluble iron from peatlands to aquatic ecosystems and the global coupled iron and carbon cycles.
14664. 题目: Mechanistic insights into adsorption and reduction of hexavalent chromium from water using magnetic biochar composites: Key roles of Fe3O4 and persistent free radicals
期刊: Environmental Pollution
作者: Delai Zhong, Yanrong Zhang, Linling Wang, Jing Chen, Yi Jiang, Daniel C.W. Tsang, Zezhou Zhao, Shupeng Ren, Zhenhua Liu, John C. Crittenden
摘要: Magnetic biochar (MBC) has been used to remove hexavalent chromium (Cr(VI)) from water, but the roles of Fe3O4 and persistent free radicals (PFRs) in MBC in Cr(VI) removal are still less investigated. In this work, the MBC synthesized by microwave co-pyrolysis of solid-state FeSO4 and rice husk was employed to remove Cr(VI) from water. In comparison to the rice husk biochar (BC), the MBC exhibits the 3.2- and 11.7-fold higher adsorption and reduction efficiency of Cr(VI), resulting in the higher Cr(VI) removal efficiency (84.3%) and equilibrium adsorption capacity of MBC (8.35 mg g−1) than that (26.5% and 2.63 mg g−1) of BC. Multiple characterization results revealed that the high Cr(VI) removal performance of MBC was mainly attributed to the presence of active Fe3O4 and carbon-centered PFRs in the porous and graphitic MBC. The Fe3O4 not only provided active chemisorption/reduction sites for Cr(VI) via its Fe(II)oct and Fe(III)oct coordination, but also facilitated the generation of more active electron donating carbon-centered PFRs than carbon-centered PFRs with an oxygen atom in the graphitic structure to reduce Cr(VI). The presence of Fe3O4 also elevated 36.7 m2 g−1 of BET-surface area and 0.043 cm2 g−1 of pore volume of MBC, promoting the Cr(VI) removal. The Fe3O4 and carbon-centered PFRs contributed to ∼81.8% and ∼18.2% of total Cr(III) generation, respectively. In addition, the initial solution pH was responsible for determining the relative significance of Cr(VI) adsorption and reduction. This study provides new insights into the mechanisms of Cr(VI) removal from water by the MBC.
14665. 题目: Soil Na + concentration controls salt-affected soil organic matter components in Hetao region China
期刊: Journal of Soils and Sediments
作者: Xinliang Dong, Mozhi Li, Qimei Lin, Guitong Li, Xiaorong Zhao
摘要: Purpose: There is little knowledge on the organic matter fractions of salt-affected soil aggregates. This study aimed at investigating characteristics of salt-affected soil organic carbon components and the relationships between soil salt concentration and soil organic carbon component content. Materials and methods: Five typical salt-affected soils in Hetao region China were collected and analyzed for light (LF) and heavy fraction (HF) in different water-stable aggregates. And the soil organic carbon components were measured by Fourier transform infrared (FTIR) and pyrolysis-gas chromatography/mass spectrometer (Py–GC/MS). Results and discussion: The results showed that the salt-affected soils were dominant in 53–10-μm water-stable aggregates, 61–80% in the bulk soil, and very low in > 250-μm macro-aggregates, less than 7.06% in the bulk soil. The proportions of > 250-μm macro-aggregates and the mean weight diameter (MWD) were negatively correlated to Na+ concentration (p < 0.05). Furthermore, the macro-aggregates were generally higher in total organic carbon (TOC) and accordingly higher C/N ratio than those in micro-aggregates. Heavy fractions (HF) from both > 53 μm and < 53-μm soil aggregates accounted for 99.30–99.83% of the bulk soil and contained 89.6–98.5% lower TOC and accordingly 49.2–84.8% lower C/N ratio than those in light fractions (LF). The LFs were high in lignin (7.27–34.02% in total pyrolysis products, 19.89% on average) and alkane/alkene-derived compounds (9.51–37.21%, 23.18% on average), but low in N-containing compounds (0–3.64%, 1.71% on average), while HFs were high in both alkane/alkene (4.38–27.46%, 15.06% on average) and N-containing compounds (7.45–26.45%, 13.98% on average), but low in lignin-derived compounds (1.13–8.75%, 3.86% on average). Conclusions: The tested salt-affected soils were predominant in 53–10-μm micro-aggregates, which was caused by the Na+ dispersion effect on soil aggregates. Most SOM was stored in HF that contained high N-containing compounds and low C/N ratios. Our results suggested that the components of SOM were mainly controlled by the soil Na+ concentration.
14666. 题目: Biodegradability of thermokarst carbon in a till‐associated, glacial margin landscape: the case of the Peel Plateau, NWT, Canada
期刊: Journal of Geophysical Research: Biogeosciences
作者: Cara A. Littlefair, Suzanne E. Tank
摘要: The Peel Plateau is a characteristic glacial margin landscape, with permafrost comprised of thick, ice‐rich glacial tills deposited at the end of the Last Glacial Maximum. Unmodified tills at depth are overlain by a paleo‐active layer, created when early Holocene warming deepened regional active layers, enabling organic matter incorporation into now‐frozen soils. Ice‐rich permafrost encourages retrogressive thaw slumps (RTSs), which mobilize variable proportions of modern active layer, paleo‐active layer, and Pleistocene tills to downstream systems. Here, we investigate the biolability of thaw‐released dissolved organic carbon (DOC) on the Peel Plateau, and compare our results to previous studies from non‐till‐dominated landscapes. Similar to other Arctic regions, biolability was significantly greater for slump‐derived DOC (RTS runoff) than for DOC from paired, unimpacted locations. However, runoff source was an important control on biolability. Lability was greater for slumps releasing water with a Holocene‐like δ18O signature than for slumps with a more Pleistocene‐like signature, while a small slump, with runoff δ18O similar to the modern active layer, showed no biolability increase. Similar to other Arctic regions, biolability was strongly related to DOC aromaticity and molecular weight. However, lability also increased significantly with increasing nutrients, which has not been shown universally. Previous work has shown that DOC concentration dynamics differ sharply on the Peel Plateau when compared to other permafrost thaw landscapes. This work indicates that the lability of permafrost DOC may be relatively uniform across variable Arctic regions, although some factors – such as the importance of nutrient status – may need further exploration.
14667. 题目: Fe(II)-Catalyzed Transformation of Organic Matter–Ferrihydrite Coprecipitates: A Closer Look Using Fe Isotopes
期刊: Environmental Science & Technology
作者: Zhe Zhou, Drew E. Latta, Nadia Noor, Aaron Thompson, Thomas Borch, Michelle M. Scherer
摘要: Ferrihydrite is a common Fe mineral in soils and sediments that rapidly transforms to secondary minerals in the presence of Fe(II). Both the rate and products of Fe(II)-catalyzed ferrihydrite transformation have been shown to be significantly influenced by natural organic matter (NOM). Here, we used enriched Fe isotope experiments and 57Fe Mössbauer spectroscopy to track the formation of secondary minerals, as well as electron transfer and Fe mixing between aqueous Fe(II) and ferrihydrite coprecipitated with several types of NOM. Ferrihydrite coprecipitated with humic acids transformed primarily to goethite after reaction with Fe(II). In contrast, ferrihydrite coprecipitated with fulvic acids and Suwannee River NOM (SRNOM) resulted in no measurable formation of secondary minerals. Despite no secondary mineral transformation, Mössbauer spectra indicated electron transfer still occurred between Fe(II) and ferrihydrite coprecipitated with fulvic acid and SRNOM. In addition, isotope tracer experiments revealed that a significant fraction of structural Fe in the ferrihydrite mixed with the aqueous phase Fe(II) (∼85%). After reaction with Fe(II), Mössbauer spectroscopy indicated some subtle changes in the crystallinity, particle size, or particle interactions in the coprecipitate. Our observations suggest that ferrihydrite coprecipitated with fulvic acid and SRNOM remains a highly dynamic phase even without ferrihydrite transformation.
14668. 题目: Dissolved Carbon Dynamics in Meltwaters From the Russell Glacier, Greenland Ice Sheet
期刊: Journal of Geophysical Research: Biogeosciences
作者: M. Grace Andrews, Andrew D. Jacobson, Magdalena R. Osburn, Theodore M. Flynn
摘要: Melting of the Greenland Ice Sheet (GrIS) has accelerated in recent decades. Given the close association between the water and carbon (C) cycles, melting of the GrIS may also drive local and global C cycle feedback. However, few studies have quantified such feedback, which may have important implications for predicting future climate or understanding linkages between ice sheet destabilization and climate change in the geologic past. Here we investigate seasonal and interannual dissolved C cycling at the margin of the Russell Glacier, west Greenland. By synthesizing isotopic analyses of water (δ18O) and C (δ13C and Δ14C) with geomicrobiological observations, we present evidence for previously unknown connections between the GrIS's supraglacial and subglacial dissolved C cycles. Supraglacial streams have variable concentrations of dissolved organic carbon (DOC) and are the dominant source of DOC in subglacial discharge. Supraglacial stream dissolved inorganic carbon (DIC) concentrations are uniform and sourced from a spatially and temporally constant mixture of organic C (~25%) respired by aerobic heterotrophs inhabiting the GrIS surface and dissolved atmospheric C (~75%). Supraglacial inputs account for ~50% of subglacial discharge DIC. The remaining subglacial DIC derives from carbonate weathering and microbial CO2 production, with the latter attributable to abundant anaerobic heterotrophic communities observed in subglacial discharge. Furthermore, we find that supraglacial streams deliver young DOC to the subglacial environment during snowmelt and rain events. These pulses of organic C may drive heterotrophic microbial respiration, with the cumulative effect being a seasonal shift in the source of basal DIC, from microbial‐ to carbonate‐dominated.
14669. 题目: The enigmatic structure of the crenarchaeol isomer
期刊: Organic Geochemistry
作者: Jaap S. Sinninghe Damsté, W. Irene C. Rijpstra, Ellen C. Hopmans, Mimi J. den Uijl, Johan W.H. Weijers, Stefan Schouten
摘要: Isolation of crenarchaeol and its isomer from marine surface sediments, followed by ether cleavage and GC–MS characterization using supersonic molecular beam (SMB) ionization of the biphytanes formed, revealed that the crenarchaeol isomer comprises a tricyclic biphytane that is stereochemically different from the tricyclic biphytane of crenarchaeol. This isomeric tricyclic biphytane was also released from the crenarchaeol isomer in extant Thaumarchaeotal biomass. Reinterpretation of previously obtained 13C NMR data of the crenarchaeol isomer suggested that the cyclopentane moiety adjacent to the cyclohexyl moiety of the tricyclic biphytane of the crenarcheaol isomers possesses the unusual cis stereochemistry in comparison to the trans stereochemistry of all cyclopentane moieties in crenarchaeol. This stereochemical difference likely affects the packing of lipid membranes of Thaumarchaeota and therefore provides a biophysical explanation for the role of the crenarchaeol isomer in the TEX86 palaeothermometer based on fossilized Thaumarcheotal lipids.
14670. 题目: Linking the geochemistry of crude oils and petroleum inclusions in the Ubarana and Lorena oilfields, Potiguar Basin, Brazilian Equatorial Margin
期刊: Organic Geochemistry
作者: André Luiz Silva Pestilho, Lena Virgínia Soares Monteiro, Carlos Alberto Carbonezi, Sandra Brandão Jorge, Eugênio V. Santos Neto
摘要: A study of petroleum inclusions based on ultraviolet fluorescence petrography, microspectrophotometry and biomarker analyses was carried out on samples from two wells of the onshore Lorena and the offshore Ubarana oilfields, Potiguar Basin, Brazil. This study aimed to evaluate the contribution and compositional variability of oils associated with different source rocks through the geochemical correlation of petroleum inclusions and crude oils. Three groups of inclusions were identified: (i) a group from the Lorena reservoir (Pendência Formation); (ii) a second from the Ubarana siliciclastic reservoir (Açu Formation); and (iii) a third from the carbonates adjacent to the Ubarana reservoir (Ponta do Mel Formation, PML). Fluorescence microspectrophotometry shows that the three groups of inclusions have different API gravity oils, variable proportion of saturate, aromatic, resins and asphaltenes and are not biodegraded. Moreover, Pendência and PML inclusions suggest multiple pulses of hydrocarbon migration, while Açu inclusions record a homogeneous pulse. Biomarkers indicate that the Pendência and Açu inclusion oils correlate with reservoir oil extracts. The Pendência inclusion oils are similar to the lacustrine oils of the Umbuzeiro graben (Pendência Formation), whereas the Açu inclusion oil displays closer biomarker signature to the Areia Branca trend of mixed oils (Alagamar Formation source rock). However, the oil from fluid inclusions of the PML has characteristics of the Alagamar Formation lacustrine organic facies. The absence of mixed oils in the PML suggests an earlier lacustrine oil migration through the carbonate fractures prior to the main infill of mixed oils in the Ubarana oilfield.
14671. 题目: Assessing biomarker syngeneity: An in situ approach using monoclonal antibodies
期刊: Organic Geochemistry
作者: Fernando Medina Ferrer, Jake V. Bailey, Frank Corsetti, J. Michael Moldowan, Silvana M. Barbanti, David Caron, Joe Bryant-Huppert
摘要: Lipid biomarkers preserved in ancient rocks have the potential to reveal much about ancient ecosystems. However, establishing that the compounds of interest are syngenetic has proven to be an analytically challenging task. Traditional biomarker analyses rely on extraction of large quantities of powdered rock, making the association of molecules with sedimentary fabrics difficult, if not impossible. As an alternative approach, here we show that monoclonal antibodies that bind specifically to geolipids can be used as molecular probes for in situ detection and localization of such compounds. Monoclonal antibodies that bind to squalene and cross-react with the biomarker squalane were evaluated for labeling sediment-associated hydrocarbons. The anti-squalene antibodies were shown by dot immunoblotting with composed standards to cross-react also with other isoprenoids, such as phytol and its diagenetic products, suggesting reactivity towards acyclic isoprenoids. Then, the anti-squalene antibodies were shown to react with naturally occurring crude oils and, via an immunofluorescence-labeling approach, to bind to isolated organic-rich laminae in rocks from the Eocene Green River Formation known to contain squalane among other linear isoprenoids. These results suggest that squalane, or structurally similar organic biomarkers that cross-react with the antibodies, are confined to discrete organo-sedimentary fabrics within those rocks, providing evidence for their syngeneity. Depending on the specificity and sensitivity of the antibody/geolipid pair, an in situ antibody detection approach may be useful for establishing biomarker syngeneity in older rocks.
14672. 题目: Change in carbon flux (1960–2015) of the Red River (Vietnam)
期刊: Environmental Earth Sciences
作者: Thi Phuong Quynh Le, Nhu Da Le, Viet Nga Dao, Emma Rochelle-Newall, Thi Mai Huong Nguyen, Cyril Marchand, Thi Thuy Duong, Thi Xuan Binh Phung
摘要: Global riverine carbon concentrations and fluxes have been impacted by climate and human-induced changes for many decades. This paper aims to reconstruct the longterm carbon concentrations and carbon fluxes of the Red River, a system under the coupled pressures of environmental change and human activity. Based on (1) the relationships between particulate and dissolved organic carbon (POC, DOC) or dissolved inorganic carbon (DIC), and suspended sediments (TSS) or river water discharge and on (2) the available detailed historical records of river discharge and TSS concentration, the variations of the Red River carbon concentration and flux were estimated for the period 1960–2015. The results show that total carbon flux of the Red River averaged 2555 ± 639 kton C year−1. DIC fluxes dominated total carbon fluxes, representing 64% of total, reflecting a strong weathering process from carbonate rocks in the upstream basin. Total carbon fluxes significantly decreased from 2816 kton C year−1 during the 1960s to 1372 kton C year−1 during the 2010s and showed clear seasonal and spatial variations. Organic carbon flux decreased in both quantity and proportion of the total carbon flux from 40.9% in 1960s to 14.9% in 2010s, reflecting the important impact of dam impoundment. DIC flux was also reduced over this period potentially as a consequence of carbonate precipitation in the irrigated, agricultural land and the reduction of the Red River water discharge toward the sea. These decreases in TSS and carbon fluxes are probably partially responsible for different negatives impacts observed in the coastal zone.
14673. 题目: In vitro cellular toxicity induced by extractable organic fractions of particles exhausted from urban combustion sources - Role of PAHs
期刊: Environmental Pollution
作者: Ekaterini Velali, Eleni Papachristou, Anastasia Pantazaki, Athanasios Besis, Constantini Samara, Christos Labrianidis, Theodore Lialiaris
摘要: The bioactivity of the extractable organic matter (EOM) of particulate matter (PM) exhausted from major urban combustion sources, including residential heating installations (wood-burning fireplace and oil-fired boiler) and vehicular exhaust from gasoline and diesel cars), was investigated in vitro by employing multiple complementary cellular and bacterial assays. Cytotoxic responses were investigated by applying the MTT ((3-(4, 5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide)) bioassay and the lactate dehydrogenase (LDH) release bioassay on human lung cells (MRC-5). Sister Chromatids Exchange (SCE) genotoxicity was measured on human peripheral lymphocytes. Lipid peroxidation potential via reactive oxygen species (ROS) was evaluated on E. coli bacterial cells by measuring the malondialdehyde (MDA) end product. Furthermore, the DNA damage induced by the organic PM fractions was evaluated by the reporter (β-galactosidase) gene expression assay in the bacterial cells, and, by examining the fragmentation of chromosomal DNA on agarose gel electrophoresis. The correlations between the source PM-induced biological endpoints and the PM content in polycyclic aromatic hydrocarbons (PAHs), as typical molecular markers of combustion, were investigated. Fireplace wood smoke particles exhibited by far the highest content in total and carcinogenic PAHs followed by oil boilers, diesel and gasoline emissions. However, in all bioassays, the total EOM-induced toxicity, normalized to PM mass, was highest for diesel cars equipped with Diesel Particle Filter (DPF). No correlation between the toxicological endpoints and the PAHs content was observed suggesting that cytotoxicity and genotoxicity are probably driven by other extractable organic compounds than the commonly measured unsubstituted PAHs. Clearly, further research is needed to elucidate the role of PAHs in the biological effects induced by both, combustion emissions, and ambient air particles.
14674. 题目: Environmental behavior and associated plant accumulation of silver nanoparticles in the presence of dissolved humic and fulvic acid
期刊: Environmental Pollution
作者: Yong Li, Haiyan Chen, Fei Wang, Furong Zhao, Xiaomin Han, Huanhuan Geng, Ling Gao, Huilun Chen, Rongfang Yuan, Jun Yao
摘要: This work investigated the role of natural organic matter (NOM) in the environmental processes of silver nanoparticles (AgNP) and the uptake and accumulation of AgNP in wheat. Different NOMs (Suwannee River humic acids [SRHA], fulvic acid [FA]) and Ag elements (Ag(0) and Ag+) were incubated in a hydroponic media for 15 days. The results showed that the NOM (10 mg C L−1) altered the dissolution, stabilization, uptake and accumulation of AgNP. The dissolution of AgNP declined in the presence of NOM. Compared with FA, the dissolved Ag+ decreased much more from 0.30 mg L−1 to 0.10 mg L−1 in the presence of SRHA. The fluorescence quenching results indicated that SRHA exhibited stronger binding to Ag+ than that of FA, and the quenching constants Ksv were 0.1309 (SRHA) and 0.0074 (FA), respectively. C-O, C-H, C-O-C, and Me-OH were involved in the interaction between NOM and AgNP. The NOM decreased the accumulated content of Ag in wheat. Hence, NOM alleviated the inhibition of AgNP to wheat growth. SRHA reduced the Ag content of wheat roots approximately 3-fold. These results clearly indicated the importance of NOM on altering the behavior, fate and toxicity of AgNP in an environment.
14675. 题目: Correlating fluorescence spectral properties with DOM molecular weight and size distribution in wastewater treatment systems
期刊: Environmental Science: Water Research & Technology
作者: Kang Xiao, Yuexiao Shen, Jian-yu Sun, Shuai Liang, Huiju Fan, Jihua Tan, Xiaomao Wang, Xia Huang, David Waite
摘要: This study explores the potential of fluorescence excitation-emission matrix (EEM) for indication of DOM molecular weight/size (MW) levels in wastewater treatment systems by systematically investigating the correlations between various fluorescence spectral properties and MW levels. Three types of DOM from a membrane bioreactor and an oxidation ditch were fractionated into nine grades with apparent MW cut-offs (MWCOs) of 0.7, 0.22 and 0.05 μm and 100, 30, 10, 3, 1 and 0.5 kDa. The EEM overall fluorescence intensity per unit total organic carbon (FI/TOC) and the overall FI per unit UV absorbance (FI/UVA), which represent the gross fluorescence efficiency and apparent quantum yield respectively, were found to increase significantly as MWCO decreased from 0.7 μm to 1 kDa. Further elaboration of the excitation (Ex) and emission (Em) spectra revealed that the smaller- and larger-MW fractions tend to occur in the lower-wavelength (Ex < 300 nm, Em < 280 nm) and higher-wavelength (Em > 400 nm) regions, respectively. EEM spectra in these responsible regions produced highly significant relationships between the relative intensity and log-MWCO (from 0.7 μm to 1 kDa) with R2 > 0.83 at specific Ex/Em positions. The optimal Ex/Em positions for the relationships differed according to source of the DOM that varies with process type (e.g. membrane bioreactor vs. oxidation ditch) and process stage (e.g. sludge mixed liquor vs. membrane effluent). The results of this study provide new insights with regard to the possible use of fluorescence spectroscopy for qualitative or quasi-quantitative indication of DOM MW in wastewater treatment systems.
14676. 题目: Sources and distribution of sedimentary organic matter in the Beibu Gulf, China: Application of multiple proxies
期刊: Marine Chemistry
作者: Weisen Liao, Jianfang Hu, Haoda Zhou, Jianhua Hu, Ping'an Peng, Wenfeng Deng
摘要: Geochemical and biomarker methods were combined to investigate the sources of sedimentary organic matter (OM) and their spatial distribution in the Beibu Gulf, a subtropical estuary in southern China. We measured the total organic carbon (TOC) and total nitrogen (TN) content, the glycerol dialkyl glycerol tetraethers (GDGTs) concentration, as well as the isotopic composition of sedimentary OM (δ13Corg and δ15N) in surface sediments collected from the Beibu Gulf. The spatial distribution of the bulk organic parameters (TOC, TN, C/N ratio, δ13Corg, and δ15N) revealed a generally decreasing trend in terrestrial OM from the Maowei Sea to the outer Qinzhou Bay, and from the tributary rivers to the outer bay. The BIT (branched/isoprenoid tetraether) indices also decreased seaward from the Maowei Sea to the Qinzhou Bay, and from rivers to the outer bay, showing that soil OM was mainly delivered to the bay by rivers. The spatial patterns of these bulk parameters suggest that the terrigenous OC is constrained to the coast and adjacent regions. The relatively high GDGT-0/Crenarchaeol ratios and increasing δ15N values along the coast of the Maowei Sea indicate the anthropogenic nitrogen in the Beibu Gulf. Our results show how important a multiproxy approach can be to fully understand and quantify the relative contributions of terrestrial and marine OC components and the biogeochemical processes in the Beibu Gulf, especially in the context of growing anthropogenic activities.
14677. 题目: Dual isotope evidence for sedimentary integration of plant wax biomarkers across an Andes-Amazon elevation transect
期刊: Geochimica et Cosmochimica Acta
作者: Sarah J. Feakins, Mong Sin Wu, Camilo Ponton, Valier Galy, A. Joshua West
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.
14678. 题目: Impacts of moisture, soil respiration, and agricultural practices on methanogenesis in upland soils as measured with stable isotope pool dilution
期刊: Soil Biology and Biochemistry
作者: P.E. Brewer, F. Calderón, M. Vigil, J.C. von Fischer
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.
14679. 题目: A color-index based empirical algorithm for determining particulate organic carbon concentration in the ocean from satellite observations
期刊: Journal of Geophysical Research: Oceans
作者: Chengfeng Le, Xueying Zhou, Chuanmin Hu, Zhongping Lee, Lin Li, Dariusz Stramski
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.
14680. 题目: Impact of seabed resuspension on oxygen and nitrogen dynamics in the northern Gulf of Mexico: A numerical modeling study
期刊: Journal of Geophysical Research: Oceans
作者: Julia M. Moriarty, Courtney K. Harris, Marjorie A. M. Friedrichs, Katja Fennel, Kehui Xu
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.