13221. 题目: Soil quality of an Iranian forest ecosystem after conversion to various types of land use
期刊: Environmental Monitoring and Assessment
作者: M. H. Rasouli-Sadaghiani, M. Barin, S. Siavash Moghaddam, C. A. Damalas, K. Ghodrat
摘要: The impact of land-use change on parameters of the soil was evaluated in soil samples from arable land, orchard land, and grassland in West Azerbaijan, Iran, compared with their adjacent natural forestland, using some biological indices. Microbial biomass carbon (MBC); microbial basal respiration (BR); metabolic quotient (qCO2); substrate induced respiration (SIR); carbon availability index (CAI); the microbial quotient, i.e., the ratio of microbial carbon to soil organic carbon (Cmic/Corg); and soil organic carbon (SOC) were calculated in collected soil samples. Deforestation and long-term land use showed adverse effects on soil biological properties. The spatial distribution of MBC, BR, SIR, and SOC, followed the order: forestland > grassland > orchard land > arable land. SOC showed the highest decline by 67.7% in arable land, 43.6% in orchard land, and 36.3% in grassland, with an average reduction of 49.2% compared with forestland. Similarly, BR and MBC decreased by an average reduction of 41.3 and 34.8%, respectively, compared with forestland. By contrast, the qCO2 index, the CAI index, and the Cmic/Corg ratio were not affected significantly by land use, except from a significant raise of the Cmic/Corg ratio in the arable land. Land-use change exerted a remarkable negative influence on soil quality with several soil attributes affected due to cropping compared with adjacent grassland and forestland. At the field level, proper management practices that increase SOC in the soil, e.g., effective recycling of crop residues and manures, should be considered, when land is continuously cultivated.
13222. 题目: Oceanic fronts control the distribution of dissolved barium in the Southern Ocean
期刊: Marine Chemistry
作者: Kimberley M. Pyle, Katharine R. Hendry, Robert M. Sherrell, Oliver Legge, Andrew J. Hind, Dorothee Bakker, Hugh Venables, Michael P. Meredith
摘要: The globally-observed relationship between oceanic barium and the macronutrient silicic acid results from the shared influence of large-scale ocean circulation and mixing on the two elements, and the inherent link between barium and organic matter formation and dissolution. A detailed examination of deviations from barium-silicon correlations can reveal variations in non-conservative processes within the marine barium cycle. Here, we present a high-resolution dataset of dissolved barium and macronutrients from the Drake Passage and the Scotia and Weddell Seas. Our new results highlight the influence of Southern Ocean frontal zones on barium cycling and the deviations of barium and macronutrient distributions as a result of spatial variations in phytoplankton assemblages and in barite formation processes. These new data also reinforce findings that water mass mixing and ocean circulation, in particular the location of oxygen minima, play a key role in barium distribution. Our findings have implications for the use of sedimentary barium as a proxy for export production, which may be complicated by physical water circulation changes or shifts in plankton community structure.
13223. 题目: Branched GDGT variability in sediments and soils from catchments with marked temperature seasonality
期刊: Organic Geochemistry
作者: Min Cao, Gemma Rueda, Pedro Rivas-Ruiz, M? Carmen Trapote, Mona Henriksen, Teresa Vegas-Vilarrúbia, Antoni Rosell-Melé
摘要: The distributions of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in sediments are used as a proxy measurement to infer changes in past mean annual air temperatures (MAT). When applied to high resolution sedimentary sequences, measurement of brGDGT distributions is employed to reconstruct MAT at subdecadal time scales. In addition, brGDGT proxy estimates are also sometimes purported to be seasonally biased in environments where annual brGDGT production may not be constant during a seasonal cycle. The main aim of this study was to assess the occurrence of seasonality in the production and distribution of brGDGTs and the seasonality bias of the derived temperature proxy. For this purpose, we examined brGDGT distributions and brGDGT-derived MAT estimates in surface soils and settling/suspended particulate matter over one year, from two sites located in the same latitude but at different altitudes, in the Catalan Pyrenees, as well as at one site in southern Norway. These locations have marked seasonal temperature cycles, which were expected to maximize the possibility of detecting any seasonal bias in the production and compositions of brGDGTs. The results show that brGDGT abundance is heterogeneous and increases with soil humidity. The brGDGT distributions and some of the brGDGT-derived proxy measurements in soils are relatively stable throughout the year and do not change significantly in the suspended particulate matter in the river or settling particulate matter in traps. Our study shows that the impact of the seasonality of temperature on brGDGT distribution was absent in the soils studied, regardless of altitude or latitude on a catchment/regional scale. As soils are likely to contain a brGDGT signature which is representative of average environmental conditions in the catchment at least over decades, brGDGT proxy reconstructions derived from soil sources are more suitable to infer variability in environmental parameters over the same timescales (i.e. decades or longer). On shorter timescales (i.e. annual), sediment downcore variability in brGDGTs is likely to be related to changes derived from in situ production and sediment sources.
13224. 题目: Sedimentary records of human activity and natural environmental evolution in sensitive ecosystems: A case study of a coral nature reserve in Dongshan Bay and a mangrove forest nature reserve in Zhangjiang River estuary, Southeast China
期刊: Organic Geochemistry
作者: Dongyi Li, Yonghang Xu, Yunhai Li, Jianjun Wang, Xijie Yin, Xiang Ye, Aijun Wang, Liang Wang
摘要: Total organic carbon (TOC), total nitrogen (TN), δ13Corg, δ15N, and grain size were measured in two sediment cores from reserves adjacent to Dongshan Bay, China. The aims were to identify organic matter (OM) sources and to evaluate the combined impact of human activity and natural environmental processes over the last 100 yr. In a coral reserve far from the estuary of Zhangjiang River, the average sediment accumulation rate (SAR) was 0.51 cm/yr from ca. 1839–2015, and the values of δ13Corg and C/N (atomic ratio of TOC to total N) ranged from 21.9‰ to 23.7‰ and from 5.7 to 8.1, respectively. In a mangrove forest reserve near the estuary, SAR averaged 0.49 cm/yr from ca. 1891–1985 and 2.41 cm/yr from ca. 1985–2015, and the δ13Corg and C/N values ranged from 22.7‰ to 26.3‰ and from 9.3 to 21.7, respectively. By combining a comparison plot of C/N and δ13Corg and a binary mixing model (based on δ13Corg and Norg/Corg, respectively), the major OM sources were assigned and their sedimentary contributions estimated. The sedimentary OM in the coral reserve had mainly an offshore marine authigenic signature with an average terrigenous contribution of <27%. In the mangrove forest reserve, the sedimentary OM was a mixture of terrestrial and marine sources, with an average terrigenous contribution of >56%. While input from the Zhangjiang River declined from the 1980 s, urban development, deforestation and land reclamation contributed to an overall increase in the total mass accumulation rate (MAR). The coral was also severely damaged by the advent of poaching around the same time. These two factors collectively resulted in a rapid decrease in OM content and OC accumulation rate (CARorg ) of the sediments until the establishment of the coral reserve in 1997. Changes in terrain and climate and the construction of water conservancy facilities were traditionally the primary factors responsible for changes in the sedimentary environment of the mangrove forest reserve. Since the 1980s, however, the expansion of the mangrove forest along with human activity has led to rapid increases in MAR and CARorg ; while, protective measures and a favorable climate have also promoted the growth of the mangrove forest.
13225. 题目: The composition and radiolysis impact on aromatic hydrocarbons in sedimentary organic matter from the Mulga Rock (Australia) uranium deposit
期刊: Organic Geochemistry
作者: Paul F. Greenwood, Chao Shan, Alex I. Holman, Kliti Grice
摘要: Our interest in the effect of ionizing radiation on sedimentary organic matter (OM) has extended to the molecular distributions and stable isotopic values of aromatic hydrocarbons. Thermally immature sediments (%Ro = 0.26; Tmax < 421 °C) spanning a 173–5280 ppm radiolytic gradient from the Mulga Rock Uranium Deposit (Western Australia) contained high abundances of vascular plant sourced aromatic (and aliphatic) terpenoids. Terpenoids with 2–5 rings and various levels of aromatisation were detected in the aromatic fractions of these sediments. The extent of aromatisation increased with sedimentary U/radiolytic levels, attributed to free-radical promoted reactions including dehydrogenation and oxidation of aliphatic precursors. The sediment with the highest U content (5280 ppm) showed only diterpenoids and low MW PAHs, reflecting complete radiolytic removal of higher MW terpenoids. A larger number and variety of terpenoid products were detected from the other sediments (U ≤ 1700 ppm) from which several radiolytically promoted reaction pathways were identified. Cadinene, for instance, was subject to competing hydrogenation and dehydrogenation reactions which gave cadinane and progressively aromatised diterpenoid analogues, respectively. Pentacyclic terpane precursors were also progressively aromatised and partially converted to des-A-triterpenoid or C-ring cleaved triterpenoid (tetracyclic) products. These reactions are typical of the natural diagenetic transformation of plant terpenoids, with the main effect of the high radiolytic levels an apparent hastening of diagenetic processes. The δ13C values of several aromatised products indicated a slight 13C enrichment with increasing aromatisation, likely due to preferential abstraction of H from 12C.
13226. 题目: Archaeal and bacterial glycerol dialkyl glycerol tetraether (GDGT) lipids in environmental samples by high temperature-gas chromatography with flame ionisation and time-of-flight mass spectrometry detection
期刊: Organic Geochemistry
作者: Sabine K. Lengger, Paul A. Sutton, Steven J. Rowland, Sarah J. Hurley, Ann Pearson, B. David A. Naafs, Xinyue Dang, Gordon N. Inglis, Richard D. Pancost
摘要: Archaeal isoprenoidal glycerol dibiphytanyl glycerol tetraether lipids (iGDGTs) and their non-isoprenoidal branched bacterial analogues (brGDGTs) have widespread applications in biogeochemistry and paleothermometry. Analysis of GDGTs usually involves separation using high performance liquid chromatography, typically coupled via atmospheric pressure chemical ionisation to mass spectrometric detection in selected ion-monitoring mode (HPLC–APCI-MS). However, reliable determination of ratios and, in particular, quantification by this technique, can be challenging due to differences in ionisation efficiencies of the various compounds. Quantification of GDGTs also relies on external calibration of the relative response to an internal standard with authenticated GDGTs, which are often not readily accessible. Here, we tested the suitability of high temperature gas chromatography with flame ionisation detection (HTGC-FID) for the determination of concentrations and tetraether lipid-based ratios in marine and terrestrial samples. For this, we identified GDGTs in environmental samples using HTGC coupled to time-of-flight mass spectrometry (HTGC–MS). Using a purified GDGT standard, we show we can quantify GDGT-0 in environmental samples by GC-FID. Some GDGT-based ratios measured by HTGC-FID exhibited a linear correlation (1:1) with ratios derived from HPLC–MS and weight-based ratios of mixtures of purified standards. However, ratios relying on minor isomers, such as TEX86 and MBT/CBT have many unresolved challenges for determination by HTGC. Detection limits were higher than for HPLC–MS. However, the advantages of employing HTGC-based methods include: (1) the independence from MS tuning-related differences in ionisation energies; (2) the potential for direct comparison with other, non-GDGT based biomarkers; and (3) a more complete insight into biomarker distributions in environmental samples by the extension of the temperature range. Quantitative elution of GDGTs from a HTGC column as demonstrated herein, will also enable their analysis by compound-specific isotope ratio mass spectrometry.
13227. 题目: Assessment of apolar lipids in subseafloor rocks and potential contaminants from the Atlantis Massif (IODP Expedition 357)
期刊: Organic Geochemistry
作者: Katherine A. Hickok, Tran B. Nguyen, Susan Q. Lang
摘要: International Ocean Discovery Program Expedition 357 drilled 17 boreholes across the Atlantis Massif with the goals of investigating carbon cycling and the presence of life in a zone of active serpentinization. The expedition recovered multiple lithologies including gabbros, basalts, carbonate sands, and serpentinites. A subset of contrasting lithologies were analyzed for apolar lipid content to determine if non-volatile organic molecules can be detected in the oceanic subsurface. The definitive detection and identification of abiotic and biological lipids in the subsurface of an actively serpentinizing system would be a significant step towards understanding a variety of scientific processes, including the evolution of pre-biotic chemistry, microbial habitability, and the global carbon cycle. Given the high potential for contamination during drilling, a suite of materials used in sample collection and processing were also analyzed to characterize their signatures. An n-alkane series ranging from C18 to C30 with δ13C isotopic values of 30.9‰ to 28.8‰ was present in lithologically diverse samples. Multiple lines of evidence point to the rock saw used to remove core exteriors during sample processing as the source of these compounds. Many of the other sample-handling procedures designed to reduce surface contamination were determined to be effective and could be implemented in future projects. This result highlights the value of careful prevention and characterization of contamination to allow for more accurate interpretations of complex and dynamic subsurface processes, and the importance that future reports of these compounds occurs in conjunction with thorough contamination assessments.
13228. 题目: Glacial-interglacial vegetation changes in northeast China inferred from isotopic composition of pyrogenic carbon from Lake Xingkai sediments
期刊: Organic Geochemistry
作者: Weiwei Sun, Enlou Zhang, Enfeng Liu, Jie Chang, Rong Chen, Ji Shen
摘要: Understanding the changes in monsoon intensity and ecosystem response at different timescales is crucial for the well-being of humans, yet the paleoclimatic interpretation of stable carbon isotope (δ13C) values from northeast China records is debatable. In this study, reported δ13C data from 76 surface soils in northeast China are compiled, and a δ13C record of pyrogenic carbon (δ13CPyC) from Lake Xingkai in northeast China since the last interglacial period is presented. The aim was to investigate the orbital timescale environmental implication of geological δ13CPyC data for northeast China. The results showed a distinct increase in δ13C values of surface soils, which correlated with increasing temperature of the warmest month. Higher temperature favored the expansion of C4 plants, while precipitation had only a weak correlation with δ13C values of surface soils in the region. On an orbital timescale, the δ13CPyC record from Lake Xingkai generally reflected paleovegetation change, suggesting that the abundance of C4 plants was relatively high during the warm periods, changing to almost purely C3 plants during the cold periods. Both modern and geological analysis suggest that the climatic factor determining the δ13C in northeast China was temperature of the warmest month. This is similar to the situation for mid-latitudes such as the Chinese Loess Plateau, in contrast to low latitudes such as southern China.
13229. 题目: Sediment records of long chain alkyl diols in an upwelling area of the coastal northern South China Sea
期刊: Organic Geochemistry
作者: Xiaowei Zhu, Guodong Jia, Shengyi Mao, Wen Yan
摘要: Long chain alkyl diols in sediment cores were studied in the Yuedong Upwelling (YDU) area in the coastal northern South China Sea to investigate whether sea surface temperature (SST) and upwelling intensity over the last few decades can be traced by the diol-derived indices, i.e., the LDI (long chain diol index) as a proxy for SST and the DI-1 and DI-2 (diol index 1 and 2) as proxies for upwelling intensity. The influence of riverine long chain alkyl diols (e.g., 1,13- and 1,15-diols), which may affect LDI-reconstructed SSTs, was largely ruled out based on the comparison between diol distributions in suspended particulate materials in the Pearl River estuary and the core sediments. LDI-derived SSTs in downcore sediments matched well with local annual mean SSTs. The records of DI-2 changed in parallel with the local wind stress and inversely with SST at times of upwelling, suggesting that DI-2 is an effective proxy for upwelling intensity of YDU. The DI-1 showed a generally inverse variation pattern with DI-2, implying a major influence by SST, and it is thus not an applicable upwelling indicator for YDU. A negative relationship of DI-1 and a positive relationship of DI-2 with LDI-derived SST were observed. This occurrence might be attributed to El Ni o–Southern Oscillation (ENSO), because the SST and upwelling intensity were largely modulated by ENSO, showing a warm annual mean SST during the years of enhanced El Ni o and intensified summer upwelling.
13230. 题目: Variations in abundance and distribution of methyltrimethyltridecylchromans (MTTCs) in sediments from saline lacustrine settings in Cenozoic lacustrine basins, China
期刊: Organic Geochemistry
作者: Kaixi Jiang, Chunming Lin, Xia Zhang, Chunfang Cai, Fei Xiao, Wenxiang He, Li Peng
摘要: This study examines the abundance and distribution of MTTCs and biomarker compositions in samples of MTTC-rich sediments obtained from Paleogene strata in the Bohai Bay, Jianghan and Western Qaidam Basins in China. Biomarker signatures, including high C35/C34 hopane ratios, high gammacerane index values, low pristane/phytane (Pr/Ph) ratios and the presence of aryl isoprenoids, indicate saline lacustrine settings and photic zone euxinia (PZE). The distributions of MTTCs indicate significant palaeosalinity differences in the depositional environments of the three sets of samples obtained from the Bohai Bay, Jianghan and Western Qaidam Basins. These sets of samples were deposited under normal to mesosaline, meso- to hypersaline and hypersaline environments, respectively. The δ-MTTC% values are positively correlated with the values of the gammacerane index, but are negatively correlated with the Pr/Ph ratios. This result demonstrates that MTTCs do not form in the upper or lower parts of stratified water columns, but may form in the euxinic portions of photic zones. Therefore, MTTC parameters can only be used to reconstruct palaeosalinity in the euxinic portions of photic zones and are not applicable to the upper or lower parts of stratified water columns. This paper infers that variations in palaeosalinity in the euxinic portions of photic zones likely play a key role in controlling the distribution and abundance of MTTCs.
13231. 题目: Binding of heavy metals by oxidised kerogen in (palaeo)weathered black shales
期刊: Chemical Geology
作者: Arkadiusz Derkowski, Leszek Marynowski
摘要: Sub-aerial weathering of black shales drives the gradual leaching of sulphur- and organic-bound heavy metal elements, which are abundant in these rocks due to geochemical deposition conditions. The formation of oxygen functional groups in kerogen, however, can lead to an opposing mechanism, metal adsorption and binding, similar to a process common in soils. An increase in cation exchange capacity (CEC) measured previously in metal complexes in black shales oxidised under laboratory conditions implies that the same phenomenon may occur in naturally oxidised black shale. This idea was tested on a unique, well-developed and -preserved Permian palaeoweathering profile containing two neighbouring but diverse black shales from the Devonian/Carboniferous boundary in the Holy Cross Mountains (Poland). In the studied black shale beds, the oxygen groups formed in kerogen in the partially-weathered zone were found to be responsible for significant changes in adsorption properties measured using hexamminecobalt(III) and Cu(II) triethylenetetramine cations, which are common probes for CEC. Compared to a pristine part of black shales, the partially weathered zone was depleted of total organic carbon (TOC), sulphur, and sulphur- and organic-bound metals, and highly enriched in Cu, which is generally present in low levels in the nascent shales. In the partially weathered zone, where TOC content is reduced, apparent CEC values surpass the CECs predicted from the contents and structures of clay minerals and correlate linearly with the content of oxygen groups developed during weathering. The adsorption properties of carboxyl groups in oxidised kerogen are suggested as being responsible for the syn- or post-weathering enrichment in Cu caused by the remobilisation of older Cu-sulphide ores present in the area. As opposed to natural weathering, aggressive oxidation, e.g. under laboratory conditions produces a high proportion of cross-linked oxygen groups that do not participate in metal cation adsorption. The CEC values of artificially oxidised samples reached a limit corresponding to those of naturally oxidised shales.
13232. 题目: Contribution of the Excited Triplet State of Humic Acid and Superoxide Radical Anion to Generation and Elimination of Phenoxyl Radical
期刊: Environmental Science & Technology
作者: Yuan Chen, Xu Zhang, Shixiang Feng
摘要: Contributions of excited triplet state of humic acid (3HA*) and superoxide radical anion (O2 –), which is mainly generated via the reaction of O2 with HA-derived reducing intermediates (HA –), to phenol transformation were revealed using acetaminophen, 2,4,6-trimethylphenol and tyrosine as probe molecules. Phenol transformation was initiated by 3HA*, leading to the formation of the phenoxyl radical (PhO ), but the distribution of transformation intermediates was codetermined by 3HA* and HA –. The influence of HA – essentially resulted from the production of O2 –, which affected the fate of PhO . PhO could undergo dimerization, or react with O2 –, leading to either phenol peroxide formation (radical addition) or phenol regeneration (electron transfer). In addition, PhO could bind to HA or react with HA radicals, particularly in the absence of O2 and O2 –. These PhO reactions were dependent on the reduction potential and structure of PhO . This study also proved that the reaction of phenol with 1O2 and the reaction of PhO with O2 – lead to the same oxidation product. The contributions of 3HA* and its generated 1O2, HA – and its generated O2 – to phenol transformation were pH-dependent.
13233. 题目: Influence of pO2 on Iron Redox Cycling and Anaerobic Organic Carbon Mineralization in a Humid Tropical Forest Soil
期刊: Environmental Science & Technology
作者: Chunmei Chen, Christof Meile, Jared Wilmoth, Diego Barcellos, Aaron Thompson
摘要: Ferrous iron (FeII) oxidation is an important pathway for generating reactive FeIII phases in soils, which can affect organic carbon (OC) persistence/decomposition. We explored how pO2 concentration influences FeII oxidation rates and FeIII mineral composition, and how this impacts the subsequent FeIII reduction and anaerobic OC mineralization following a transition from oxic to anoxic conditions. We conducted batch soil slurry experiments within a humid tropical forest soil amended with isotopically labeled 57FeII. The slurries were oxidized with either 21% or 1% pO2 for 9 days and then incubated for 20 days under anoxic conditions. Exposure to 21% pO2 led to faster FeII oxidation rates and greater partitioning of the amended 57Fe into low-crystallinity FeIII-(oxyhydr)oxides (based on M ssbauer analysis) than exposure to 1% pO2. During the subsequent anoxic period, low-crystallinity FeIII-(oxyhydr)oxides were preferentially reduced relative to more crystalline forms with higher net rates of anoxic FeII and CO2 production—which were well correlated—following exposure to 21% pO2 than to 1% pO2. This study illustrates that in redox-dynamic systems, the magnitude of O2 fluctuations can influence the coupled iron and organic carbon cycling in soils and more broadly, that reaction rates during periods of anoxia depend on the characteristics of prior oxidation events.
13234. 题目: Overlooked Risks of Biochars: Persistent Free Radicals trigger Neurotoxicity in Caenorhabditis elegans
期刊: Environmental Science & Technology
作者: Thora Lieke, Xuchao Zhang, Christian E.W. Steinberg, and Bo Pan
摘要: In recent years, biochars have gained increasing interest in mitigating climate changes and revitalizing contaminated or drained soil. Studies determining their impact on the ecosystem, especially on soil invertebrates, however, are still scarce and the neurotoxic potential of biochars has never been evaluated before. Using the model organism Caenorhabditis elegans we determined the neurotoxic effect of biochar produced from rice straw by pyrolysis at 500 °C at concentrations ranging from 0 to 2000 mg C·L–1. Biochar had a hormetic effect on locomotion behavior. Furthermore, high concentrations impaired defecation as well as the recognition and response to a chemical attractant. None of the potential toxic chemicals in the biochar had sufficient high concentrations to explain the detected neurotoxic effect. Using electron paramagnetic resonance (EPR) spectroscopy, we detected free radicals in the biochar. Detrimental reaction of free radicals with biotic macromolecules can induce oxidative stress responses and are a potential reason for the evaluated neurotoxic effect of biochar. Overall, we were able to prove that biochars have the potential to act as weak neurotoxins to soil organisms and effects of persistent free radicals should be investigated further.
13235. 题目: δ13C of aromatic compounds in sediments, oils and atmospheric emissions: A review
期刊: Organic Geochemistry
作者: Alex I. Holman, Kliti Grice
摘要: This review discusses major applications of stable carbon isotopic measurements of aromatic compounds, along with some specific technical aspects including purification of aromatic fractions for baseline separation. δ 13C measurements of organic matter (OM) in sediments and oils are routine in all fields of organic geochemistry, but they are predominantly done on saturated compounds. Aromatic compounds are important contributors to sedimentary organic matter, and provide indication of diagenetic processes, OM source, and thermal maturity. Studies have found evidence for a small 13C-enrichment during diagenetic aromatisation of approximately 1–2‰, but the formation of polycyclic aromatic hydrocarbons (PAHs) from combustion and hydrothermal processes seems to produce no effect. Likewise, maturation and biodegradation also produce only small isotopic effects. An early application of δ 13C of aromatic compounds was in the classification of oil families by source. Bulk measurements have had some success in differentiating marine and terrigenous oils, but were not accurate in all settings. Compound-specific analyses measure certain aromatics with strong links to source, therefore allowing more accurate source identification. δ 13C measurements of individual aromatic compounds also allow identification of higher plant input in ancient sediments, even after severe diagenetic alteration or combustion to PAHs. Perylene, a PAH with a historically contentious origin, was assigned a source from wood-degrading fungi on the basis of its isotopic composition. Stable carbon isotopic measurements are also important in the analysis of organic matter from Chlorobiaceae, which is an important indicator of photic zone euxinic conditions in ancient sediments. A large range of aromatic products are formed from the carotenoid pigments of Chlorobiaceae, with an enriched carbon isotopic composition characteristic of the reverse tricarboxylic acid photosynthetic pathway employed by this family of organisms. In future, site-specific isotope analysis using techniques such as nuclear magnetic resonance spectrometry and high-resolution isotope ratio mass spectrometry may reveal more information about isotopic effects associated with aromatisation processes and maturation.
13236. 题目: Impact of dissolved organic matter on Zn extractability and transfer in calcareous soil with maize straw amendment
期刊: Journal of Soils and Sediments
作者: Yanlong Chen, Jianglan Shi, Xiaohong Tian, Zhou Jia, Shaoxia Wang, Juan Chen, Wenling Zhu
摘要: Purpose: Crop straw return into arable land is a common method of disposing of excess straw in China and can improve soil dissolved organic matter (DOM) that is known to modify soil zinc (Zn) extractability and mobility. Materials and methods: We conducted a soil box (internal dimensions, 160 × 140 × 80 mm3) experiment to evaluate the response of Zn extractability and transfer by diffusion to DOM after maize straw amendment (St, 0 and 15 g kg 1) in calcareous soil treated with ZnSO4·7H2O (Zn, 0 and 20 mg kg 1). Soil treated with St0Zn0 (control), St15Zn0, St0Zn20, or St15Zn20 was isolated in the 10-mm center of the box, and untreated soil was placed in compartments at either side. Results and discussion: Results revealed that addition of St0Zn20 or St15Zn20 increased the concentration of Zn extracted with diethylenetriaminepentaacetic acid (DTPA-extractable Zn) in the central layer compared with control or addition of St15Zn0. Over the course of 45 days, transfer of DTPA-extractable Zn into the adjacent untreated soil was detected at 15–20 mm in soil with St15Zn20 but at 10–15 mm with St0Zn20 and only 0–5 mm with St15Zn0. Additionally, a higher amount of DTPA-extractable Zn transfer into the adjacent untreated soil also occurred in St15Zn20. This increased DTPA-extractable Zn transfer may be associated with the formation of Zn-fulvic acid complexes with the provision of DOM derived from straw. Conclusions: Soluble Zn combined with straw return may be a promising strategy for improving both Zn mobility and extractability in calcareous soil.
13237. 题目: Scrutiny of interference effect of ions and organic matters on water treatment using supported nanoscale zero-valent iron
期刊: Environmental Earth Sciences
作者: Ahmed M. E. Khalil, Osama Eljamal, Tareq W. M. Amen, Yuji Sugihara, Nobuhiro Matsunaga
摘要: Nanoscale zero-valent iron (nZVI) supported on heat-modified activated charcoal (nFe(0)/AC) can improve nitrate reduction and phosphate adsorption regarding reaction conversion, adsorption capacity, and kinetics. It is more effective in terms of mobility and stability than bare nZVI. Both nZVI and its supported type were synthesized, characterized, and examined in interference studies for applications in environmental remediation technologies. Solutions of 45.18 mg nitrate–N/L, 50 mg phosphorus/L, and a mixture of them were treated using nZVI and nFe(0)/AC in municipal wastewater body and also deionized water body in the coexistence of anions (phosphate and sulfate), cations (cuprous and cupric), organic matters (humic acid), and hardness (calcium carbonates) at different concentrations. Results showed the significant impact of interference on nitrate reduction and superiority of nFe(0)/AC by ca. 27% to ca. 183% increase in treatment efficiency over nZVI. Anions were easily attracted to the surface of nano-iron particles resulting in a negative intervening effect. Hardness and contaminants of municipal wastewater provided a negative impact and significantly interfered with nitrate removal, while organic matters had a lower negative interference compared to others. On the contrary, copper cations could improve removal efficiency until complete elimination of nitrate. The experimental data were best-fitted to a kinetic rate model that combined the pseudo-first-order rate with the deactivation rate arising from the passivation of interfering substances on the surface of nZVI-based materials. The value of parameters of this rate equation could estimate the degree and type of interference occurring during nitrate decontamination.
13238. 题目: Soil erosion and chemical weathering in a region with typical karst topography
期刊: Environmental Earth Sciences
作者: Kai Xiong, Chuan Yin, Hongbing Ji
摘要: Soil erosion is a global environmental issue that can lead to the loss of nutrient-rich topsoil and even soil desertification, which is more severe in vulnerable and sensitive karst areas. Currently, it is imperative to explore the soil erosion mechanism and the weathering process to help prevent soil degradation in the karst area. In this study, we estimated the soil erosion rate of a representative karst slope in Shilin area of China by 137Cs tracer method. We also analyzed the changes of soil total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) along the soil profiles. The results show that there is mild to moderate intensity erosion in this area, and erosion rates in different locations of slope are in the following order: hilltop > hillside > bottom. The 137Cs content has a certain correlation with TOC, TN and TP content in the soil profile, which indicates they may have similar loss pathways. Furthermore, the chemical index of alteration (CIA), Na/K value and their relation with soil erosion are analyzed and reveal that the studied area is seriously affected by physical erosion and chemical weathering under a hot and humid environment area.
13239. 题目: Efficient capture of aqueous humic acid using a functionalized stereoscopic porous activated carbon based on poly(acrylic acid)/food-waste hydrogel
期刊: Journal of Environmental Sciences
作者: Tao Zhou, Xin Zhao, Shuya Wu, Lianghu Su, Youcai Zhao
摘要: Stereoscopic porous carbons have shown good potential in humic acid (HA) removal. In this work, a novel stereoscopic porous activated carbon (SPAC) was designed and synthesized via the self-assembly of a hydrogel based on food waste during in-situ polymerization, vacuum drying, carbonization, and activation. Then, the SPAC was functionalized with 3-aminopropyltriethoxysilane (APTES) and the adsorption behavior of the modified SPAC (SPAC-NH2) was studied systematically. The effects of pH, contact time, initial concentration of HA, and adsorbent dose were investigated, showing that optimal HA removal efficiency (>98.0%) could be achieved at an initial HA concentration of 100 mg/L. The experimental adsorption isotherm data was fitted to the Langmuir model with a maximum adsorption capacity of 156.0 mg HA/g SPAC-NH2. Analysis of the mechanism indicated that the removal of HA was mainly realized through the amidization reaction between the COOH groups of HA and the NH2 groups of APTES. All of the above results showed that SPAC-NH2 powder is an efficient, eco-friendly, and reusable adsorbent which is suitable for the removal of HA from wastewater.
13240. 题目: Carbon dynamics and inconstant porewater input in a mangrove tidal creek over contrasting seasons and tidal amplitudes
期刊: Geochimica et Cosmochimica Acta
作者: Pierre Taillardat, Alan D. Ziegler, Daniel A. Friess, David Widory, Vinh Truong Van, Frank David, Nguy?n Thành-Nho, Cyril Marchand
摘要: Constraining the contribution of mangrove-derived carbon in tidal creeks is fundamental to understanding the fate of mangrove primary production and the role of mangroves as coastal carbon sinks. Porewater measurements and 24-h time series in a mangrove tidal creek were conducted during the dry and wet season, and over contrasting tidal ranges at the Can Gio Biosphere Reserve, Vietnam. Surface water carbon concentrations (dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), partial pressure of carbon dioxide (pCO2)) and their respective δ13C values were correlated with radon, suggesting that porewater input drives mangrove-derived carbon in the tidal creek. Based on three complementary mixing models, porewater input contributed to about 30% of the water volume and 46% to 100% of DOC and DIC pools in the tidal creek at low tide, with variabilities between seasons and tidal amplitudes. The creek carbon pool was 88% DIC, 6% DOC, and 6% particulate organic carbon (POC). The pCO2 values during the wet season (2973–16,495 μatm) were on average 5-fold higher than during the dry season (584–2946 μatm). This was explained by a potential greater mineralization attributed to higher organic matter availability and residual humidity that stimulate bacterial activity, and by a potential tidal dilution changing the pCO2/DIC ratio as suggested by the Revelle factor. Consequently, average CO2 evasion from the creek was estimated at 327–427 mmolC m 2 d 1 during the wet season and 92–213 mmolC m 2 d 1 during the dry season, using two independent approaches. Tidal amplitude seemed to influence porewater input and its carbon loads, with a higher contribution during frequent and high tidal amplitudes (symmetric). However, the highest input occurred in a tidal cycle which was preceded by tidal cycle of low amplitude (asymmetric). We explain this ambiguity by the influence of both, rapid water turnover intensifying porewater exchange, and long water residence time enhancing carbon load in porewater.