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23481. 题目: The carbon: 234Thorium ratios of sinking particles in the California current ecosystem 2: Examination of a thorium sorption, desorption, and particle transport model
文章编号: N19031508
期刊: Marine Chemistry
作者: Michael R. Stukel, Thomas B. Kelly
更新时间: 2019-03-15
摘要: Thorium-234 (234Th) is a powerful tracer of particle dynamics and the biological pump in the surface ocean; however, variability in carbon: thorium ratios of sinking particles adds substantial uncertainty to estimates of organic carbon export. We coupled a mechanistic thorium sorption and desorption model to a one-dimensional particle sinking model that uses realistic particle settling velocity spectra. The model generates estimates of 238U234Th disequilibrium, particulate organic carbon concentration, and the C:234Th ratio of sinking particles, which are then compared to in situ measurements from quasi-Lagrangian studies conducted on six cruises in the California Current Ecosystem. Broad patterns observed in in situ measurements, including decreasing C:234Th ratios with depth and a strong correlation between sinking C:234Th and the ratio of vertically-integrated particulate organic carbon (POC) to vertically-integrated total water column 234Th, were accurately recovered by models assuming either a power law distribution of sinking speeds or a double log normal distribution of sinking speeds. Simulations suggested that the observed decrease in C:234Th with depth may be driven by preferential remineralization of carbon by particle-attached microbes. However, an alternate model structure featuring complete consumption and/or disaggregation of particles by mesozooplankton (e.g. no preferential remineralization of carbon) was also able to simulate decreasing C:234Th with depth (although the decrease was weaker), driven by 234Th adsorption onto slowly sinking particles. Model results also suggest that during bloom decays C:234Th ratios of sinking particles should be higher than expected (based on contemporaneous water column POC), because high settling velocities minimize carbon remineralization during sinking.
23482. 题目: Soil organic matter increases antimonate mobility in soil: An Sb(OH)6 sorption and modelling study
文章编号: N19031507
期刊: Applied Geochemistry
作者: Mieke Verbeeck, Ruben Warrinnier, Jon Petter Gustafsson, Yves Thiry, Erik Smolders
更新时间: 2019-03-15
摘要: The role of organic matter (OM) in antimonate (further denoted as Sb(OH)6) mobility in soil is unclear. The objective of this study was to evaluate Sb(OH)6–OM interaction. Antimonate solid:liquid distribution coefficients (KD) were measured at low Sb concentrations in soil samples with a natural gradient in soil organic carbon (OC) that were collected from different depths of up to 3 m in two excavated soil profiles and in a subset of four soil samples with experimentally increased OM concentration from addition of Suwannee River OM. The KD values were related to soil properties by multiple linear regression and described with the CD–MUSIC model of ferrihydrite. The KD values ranged from 12 to 2800 L kg−1 and decreased strongly with increasing OC concentrations, when normalized to the amount of iron (Fe) and aluminium (Al) in acid oxalate extracts (r = −0.69; p < 0.0001). Experimentally increasing OC by ∼1.5 g kg−1 increased soluble Sb and decreased Sb(OH)6 KD values by up to a factor of 8. The multiple regression model reveals that sorption of Sb(OH)6 to Fe and Al hydroxides decreases with increasing pH and increasing dissolved organic carbon concentration. This effect could be explained with geochemical modelling by the competitive and electrostatic effects of adsorbed humic substances on Sb(OH)6 surface complexation to the reactive surface sites of the Fe and Al hydroxides. Finally, both models could predict the in situ pore water Sb concentrations of unspiked samples, with a RMSE of 0.35 for the regression model and 0.43 for the geochemical model on the log10Sb concentrations. For these predictions, the 0.1 M Na2HPO4–extractable Sb concentration was measured and used to estimate the reversibly sorbed Sb pool. This study shows that increasing soil OM increases Sb(OH)6 mobility at low soil Sb concentration, likely due to competitive sorption on Fe and Al hydroxides and a process based, geochemical model was calibrated to describe Sb(OH)6 mobility in soil.
23483. 题目: A facile one-pot hydrothermal synthesis of hydroxyapatite/biochar nanocomposites: Adsorption behavior and mechanisms for the removal of copper(II) from aqueous media
文章编号: N19031506
期刊: Chemical Engineering Journal
作者: Kyung-Won Jung, Seon Yong Lee, Jae-Woo Choi, Young Jae Lee
更新时间: 2019-03-15
摘要: In this study, hydroxyapatite/biochar nanocomposites (HAP/BC-NCs) were synthesized through a simple one-pot hydrothermal process and utilized as an adsorbent for the removal of copper(II) from aqueous media. Characterization results revealed that rod-shaped HAP nanoparticles were successfully incorporated on the surfaces of synthesized HAP/BC-NCs. A set of systematically designed batch experiments were carried out to determine the influences of adsorbent dosage, solution pH, ionic strength, and temperature on the adsorption behavior of the HAP/BC-NCs. Overall findings from batch experiments and extended X-ray absorption fine structure analysis demonstrated that the potential mechanisms responsible for the removal of Cu(II) from aqueous media are cation exchange between Cu2+ in solution and Ca2+ in the HAP on the surfaces of the as-synthesized nanocomposites and the formation of inner-sphere surface complexes on the surfaces of the HAP/BC-NCs. Kinetic studies revealed that the adsorption process follows the pseudo-second-order model and that the overall adsorption rate is controlled by film diffusion as the dominant mechanism and intraparticle diffusion as a secondary mechanism. Adsorption isotherms were accurately represented by a Langmuir isotherm model and the maximum adsorption capacity was determined to be 99.01 mg/g at 298 K, which represents a higher efficiency for Cu(II) adsorption compared to previously reported composite materials. Thermodynamic analysis indicated that the process is thermodynamically spontaneous and endothermic process. Overall, the findings presented in this paper suggest that HAP/BC-NCs have promising applicability for the removal of heavy metals from aqueous media as an alternative, low-cost, and eco-friendly adsorbent for environmental remediation.
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23484. 题目: Comprehensive evaluation on a prospective precipitation-flotation process for metal-ions removal from wastewater simulants
文章编号: N19031505
期刊: Journal of Hazardous Materials
作者: Hongyang Wu, Wenjuan Wang, Yanfang Huang, Guihong Han, Shuzhen Yang, Shengpeng Su, Hafiza Sana, Weijun Peng, Yijun Cao, Jiongtian Liu
更新时间: 2019-03-15
摘要: Toxic metal pollutants threaten water environment. It exists undesirably metal-ion concentration limits with conventional precipitation flotation. An enhanced precipitation flotation system focusing on efficient removal for bivalent metal-ions was researched. The system involved the addition of humics and Fe3+ to generate and regulate the precipitates. The characteristics of precipitates were investigated by particle analysis, conditional stability constants and DLVO theory calculations, and SEM&TEM imaging. The results reveal that metal-ions chelate with humics at low metal-ion concentration, with generating the limited micro-size precipitates of <2.0 μm, fractal dimension of 1.60–1.80 and precipitate efficiency of <91.00%. By adding trivalent Fe3+, the macro-size precipitates are obtained with particle size of approximate 10.0 μm, fractal dimension of 1.50–1.60, and nearly-total flotation removal of precipitate. The chelating interaction of Fe3+ with humics is the mainly regulating mechanism, which could enhance the conditional stability constants and the precipitate efficiency of metal-ions at low concentration. The desired precipitate particles are finally obtained by breaking the limitations of metal-ion concentration. Finally, the flotation removal of metal-ions from single or mixed solutions is respectively 99.10 ± 0.10% for Cu2+, 99.60 ± 0.10% for Pb2+, and 94.30 ± 0.30% for Zn2+. Therefore, the enhanced precipitation flotation process is an efficient purification approach for metal-containing wastewaters.
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23485. 题目: Linking solids retention time to the composition, structure, and hydraulic resistance of biofilms developed on support materials in dynamic membrane bioreactors
文章编号: N19031504
期刊: Journal of Membrane Science
作者: Ju Huang, Xianwei Wu, Donglong Cai, Gaofeng Chen, Deyong Li, Yang Yu, Leslie F. Petrik, Guoqiang Liu
更新时间: 2019-03-15
摘要: Biofilms have permeable structures, which can be used as membranes for solids separation, e.g., dynamic membrane bioreactors (DMBRs) that relied on the biofilm developed on the support material with large apertures for filtration. This study found that the biofilm formed on the support material in DMBRs under different solids retention time (SRTs) had diverse structures, which in turn determined the hydraulic resistance and filtration performance. At 5-day SRT, a thin but compact gel-like biofilm layer (porosity = 27.5%) was formed on the support materials, which had a higher hydraulic resistance of approximately 4.9 × 1011 m−1. As a result, the transmembrane pressure (TMP) rose dramatically every 20–40 days' operation. A thick but porous biofilm layer (porosity > 60% and hydraulic resistance < 2.5 × 109 m−1) was formed at longer SRTs of 20 and 40 days and the TMP could keep consistently low (<20 Pa) for more than 180 days. Therefore, a longer SRT could facilitate the formation of a porous biofilm layer on the support material, which was of critical importance for achieving long-term and low-pressure filtration. The biofilm porosity was negatively correlated with the protein/polysaccharide ratio of its extracellular polymeric substance (EPS). Extending SRT would reduce the Live/Dead cell ratio of biofilm, thus lowering EPS production while increasing the porosity. Moreover, extending SRT promoted the growth of protozoa (e.g., Euglypha) that inhabited the biofilm, which could maintain the biofilm porous and mitigate the support layer biofouling though feeding and movement.
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23486. 题目: Selenium translocation in the soil-rice system in the Enshi seleniferous area, Central China
文章编号: N19031503
期刊: Science of The Total Environment
作者: Chuanyu Chang, Runsheng Yin, Xun Wang, Shuxun Shao, Chongying Chen, Hua Zhang
更新时间: 2019-03-15
摘要: Rice is an important source of selenium (Se) exposure; however, the transformation and translocation of Se in the soil-rice system remain poorly understood. Here, we investigated the speciation of Se in Se-rich soils from Enshi, Central China and assessed which Se species is bioavailable for rice grown in Enshi. Extremely high Se concentrations (0.85 to 11.46 mg/kg) were observed in the soils. The soil Se fractions, which include water-soluble Se (0.2 to 3.4%), ligand-exchangeable Se (4.5 to 15.0%), organically bound Se (57.8 to 80.0%) and residual Se (6.1 to 32.9%), are largely controlled by soil organic matter (SOM) levels. Decomposition of SOM promotes the transformation of organically bound Se to water-soluble Se and ligand-exchangeable Se, thereby increasing the bioavailability of Se. The bioaccumulation factors (BAFs) of Se decrease in the following order: roots (0.84 ± 0.30) > bran (0.33 ± 0.17) > leaves (0.18 ± 0.09) > polished rice (0.14 ± 0.07) > stems (0.12 ± 0.07) > husks (0.11 ± 0.07). Selenium levels in rice plants are affected by multiple soil Se fractions in the soil. Water-soluble, ligand-exchangeable and organically bound Se fractions are the major sources of Se in rice tissues.
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23487. 题目: Fate and transport of nanoplastics in complex natural aquifer media: Effect of particle size and surface functionalization
文章编号: N19031502
期刊: Science of The Total Environment
作者: Zefeng Song, Xinyao Yang, Fangmin Chen, Fangyuan Zhao, Ying Zhao, Lili Ruan, Yinggang Wang, Yuesuo Yang
更新时间: 2019-03-15
摘要: Environmental processes of nanoplastics in heterogeneous natural groundwater systems remain unclear. In this study, the control of particle size and surface functional groups on the fate and transport of nanoplastics in an organic matter (OM) rich aquifer was explored using batch and column tests. The carboxyl-modified 200 nm (200CNP), carboxyl-modified 50 nm (50CNP), and amino-modified 50 nm (50ANP) polystyrene latex beads were used as surrogates for nanoplastics of contrasting sizes and surface functional groups. Aquifer sand and natural groundwater sampled from an agriculture-impacted shallow sandy aquifer were processed to obtain granule beds with/out surface minerals and groundwater containing different-sized fractions of OM. Results show that particle size controlled the hetero-aggregation rate of nanoplastics with OM and Ca2+: a larger size resulting in a lower reaction rate led to a higher stability of 200CNP than 50CNP and 50ANP. Meanwhile, surface functional groups appeared to affect the affinity of OM and Ca2+ to nanoplastics, i.e. the amino group allowed the adsorption of dissolved OM on the particle but inhibited the adsorption of Ca2+ and suspended OM, while the carboxyl group allowed adsorption of the all. The resulting variable OM coatings formed on the different nanoplastics played a critical role in determining the particle stability and mobility, i.e. the suspended OM increased both the particle stability and mobility while the dissolved OM reduced both. These findings suggest that: 1. Depending on the OM properties, the influence of particle size and surface group on the nanoplastic processes might be secondary to the OM impact; 2. In evaluating the OM impact, not only the OM concentration but also the size and surface physiochemistry of the OM should be characterized. The insight gained is important to predict the concentration evolution pattern of weathered nanoplastics in OM-impacted sandy aquifers.
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23488. 题目: Biochar impacts on phosphorus cycling in rice ecosystem
文章编号: N19031501
期刊: Chemosphere
作者: Min Xu, Peng Gao, Zhijun Yang, Linlin Su, Jun Wu, Gang Yang, Xiaohong Zhang, Jing Ma, Hong Peng, Yinlong Xiao
更新时间: 2019-03-15
摘要: Biochar can affect the phosphorus (P) cycle in the rice ecosystem through various pathways. Pot experiments were conducted to investigate the risk of P contamination and the P supply rate to crops with the application of maize straw-derived biochar (BM) and P fertilizer. The biochar increased 18.3% and 8.45% total phosphorus (TP) concentration in the low-P level and high-P level soils, respectively. The addition of biochar increased the phosphorus activation coefficient (PAC) by 9.00% at low-P levels, while the PAC was reduced by 10.4% at high-P levels. The results suggested that biochar could serve as either a source or a sink for P. The P concentration in the dithionite-citrate-bicarbonate (DCB) extracts on the root surfaces in biochar-treated soils increased by 467.1% and 46.1% in the low-P level and high-P level soils, respectively. It may cause by the acidification of soils near the root and the increase in Fe plaque. The results also showed the addition of biochar increased the DCB-P concentration and subsequently promoted rice growth. The biochar additions enhanced bacterial community richness and diversity, while the P supplementations inhibited bacterial growth. Redundancy analysis (RDA) showed that available nitrogen (AN), Fe-P, Ca-P, P uptake and, DCB extracted Fe (DCB-Fe) were significantly correlated with microbial community composition and explained 46.8%, 37.1%, 38.0%, 37.5% and 36.7% of the total community variability, respectively. This study provided evidence that biochar might affect the P cycle by impacting the microbial community composition and the Fe-reducing processes in the rice ecosystem.
23489. 题目: Temporal variations in groundwater nitrogen under intensive groundwater/surface-water interaction
文章编号: N19031411
期刊: Hydrogeology Journal
作者: Shuai Shen, Teng Ma, Yao Du, Kewen Luo, Yamin Deng, Zongjie Lu
更新时间: 2019-03-14
摘要: Nitrogen (N) pollution in shallow groundwater within the Jianghan Plain—a depositional basin along the Yangtze River in China—is a serious issue affecting the local water supply. There is little concern regarding temporal variation patterns of groundwater N in regions with intensive groundwater/surface-water interactions thus far. In this study, a 2-year field monitoring program and a set of incubation experiments were jointly applied to characterize the seasonal variation mechanisms of groundwater N. Groundwater monitoring suggested that temporal N variations in monitoring wells of 25 and 10-m depth were correlated with fluctuations in water levels, with lower NH4-N and higher NO3−-N concentrations corresponding to groundwater discharge during the dry season, and with higher NH4-N and lower NO3−-N concentrations corresponding to groundwater recharge during the wet season. Batch sediment incubation experiments showed that buried organic carbon in sediments from the field site could not promote NH4-N release, but exogenous organic carbon and oxidant input could catalyze organic N mineralization, resulting in NH4-N release. Nevertheless, NO3−-N release was limited in all incubations. Thus, the temporal variation patterns could be divided into (1) groundwater N in type-1 wells (25 and 10 m), controlled by the annual reversal of groundwater flow gradient, which determined whether there was input of exogenous organic carbon or oxidants, ultimately affecting organic N mineralization, denitrification and other transformation processes, and (2) groundwater N in type-2 wells (<4 m depth), which showed no significant seasonal variation, implying the process is mainly controlled by surface inputs in the shallower subsurface.
23490. 题目: Dissolved organic nitrogen production and export by meridional overturning in the eastern subpolar North Atlantic
文章编号: N19031410
期刊: Geophysical Research Letters
作者: Bieito Fernández‐Castro, Marta Álvarez, Mar Nieto‐Cid, Patricia Zunino, Herlé Mercier, Xosé Antón Álvarez‐Salgado
更新时间: 2019-03-14
摘要: Dissolved organic matter (DOM) is produced in the surface and exported towards the deep ocean, adding ∼2 PgC yr−1 to the global carbon export. Due to its central role in the Meridional Overturning Circulation (MOC), the eastern subpolar North Atlantic (eSPNA) contributes largely to this export. Here we quantify the transport and budget of dissolved organic nitrogen (DON) in the eSPNA, in a box delimited by the OVIDE 2002 section and the Greenland‐Iceland‐Scotland sills. The MOC exports >15.9 TgN yr−1 of DON downwards and, contrary to the extended view that these are materials of subtropical origin, up to 33% of the vertical flux derives from a net local DON production of 7.1 ± 2.6 TgN yr−1. The low C:N molar ratio of DOM production (7.4 ± 4.1) and the relatively short‐transit times in the eSPNA (3 ± 1 yr) suggest that local biogeochemical transformations result in the injection of fresh bioavailable DOM to the deep ocean.
23491. 题目: Mode of action and fate of microcystins in the complex soil-plant ecosystems
文章编号: N19031409
期刊: Chemosphere
作者: El Mahdi Redouane, Soukaina El Amrani Zerrifi, Fatima El Khalloufi, Khalid Oufdou, Brahim Oudra, Majida Lahrouni, Alexandre Campos, Vitor Vasconcelos
更新时间: 2019-03-14
摘要: Over the last decades, global warming has increasingly stimulated the expansion of cyanobacterial blooms in freshwater ecosystems worldwide, in which toxic cyanobacteria produce various congeners of cyanotoxins, mainly dominated by microcystins (MCs). MCs introduced into agricultural soils have deleterious effects on the germination, growth and development of plants and their associated microbiota, leading to remarkable yield losses. Phytotoxicity of MCs may refer to the inhibition of phosphatases activity, generating deleterious reactive oxygen species, altering gene functioning and phytohormones translocation within the plant. It is also known that MCs can pass through the root membrane barrier, translocate within plant tissues and accumulate into different organs, including edible ones. Also, MCs impact the microbial activity in soil via altering plant-bacterial symbioses and decreasing bacterial growth rate of rhizospheric microbiota. Moreover, MCs can persist in agricultural soils through adsorption to clay-humic acid particles and results in a long-term contact with the plant-microflora complex. However, their bioavailability to plants and half-life in soil seem to be influenced by biodegradation process and soil physicochemical properties. This review reports the latest and most relevant information regarding MCs-phytotoxicity and impact on soil microbiota, the persistence in soil, the degradation by native microflora and the bioaccumulation within plant tissues.
23492. 题目: Elucidation of desferrioxamine B on the liberation of chromium from schwertmannite
文章编号: N19031408
期刊: Chemical Geology
作者: Yingying Xie, Xiaoyun Yi, Kinjal J. Shah, John R. Reinfelder, Han Ye, Pen-Chi Chiang, Zhenqing Shi, Zhi Dang, Guining Lu
更新时间: 2019-03-14
摘要: Schwertmannite is a ferric oxyhydroxy-sulfate mineral, which is commonly found in acid sulfate systems. In this study, the liberation of chromium from Cr(VI)-substituted schwertmannite in the presence of the siderophore desferrioxamine B was studied. In addition, mineral transformation was examined using X-ray diffraction, scanning electron microscopy, and X-ray absorption spectroscopy. Based on solid phase analyses, the transformation of schwertmannite incubated at pH 6.5 in the presence of 100 mg/L desferrioxamine B proceeded through a ligand-reductive induced pathway that released dissolved sulfate, Fe(III), and Cr(III), and generated goethite. Results of XAFS showed that CrO42− substituted for SO42− in the schwertmannite framework. Kinetic analysis using the Kabai and shrinking core models showed that Cr suppressed the transformation of schwertmannite into goethite and the liberation of Cr was controlled by diffusion through the secondary mineral's layer of dissolution. The information provided in this study will be useful in predicting the effects of the interaction between dissolved organic matter and minerals on the mobilization of Cr in acid mine drainage systems.
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23493. 题目: Changes of topsoil under Fagus sylvatica along a small latitudinal-altitudinal gradient
文章编号: N19031407
期刊: Geoderma
作者: Valeria Cardelli, Mauro De Feudis, Flavio Fornasier, Luisa Massaccesi, Stefania Cocco, Alberto Agnelli, David C. Weindorf, Giuseppe Corti
更新时间: 2019-03-14
摘要: This study evaluated soil properties along a small transect in the Apennines chain (central Italy). Using latitude and altitude as surrogates for temperature differences, three locations at different latitudes were selected for the study. At each location, two altitudes were selected (800 and 1000 m). The study was conducted by contrasting chemical and biochemical parameters [microbial biomass-C content, amount of CO2 evolved during basal respiration (ΣCO2–C), and potential enzyme activities] of topsoils (O and A horizons) supporting European beech (Fagus sylvatica L.) forests at different scales of investigation: horizons, altitude, and latitude. Along the topsoil, the trend of all investigated properties was unique to each O and A horizon according to its level of organic matter degradation, availability of substrates, and nutrients. Contrasting the altitudes, the difference of 1 °C of temperature between 800 and 1000 m significantly affected some of the chemical parameters and both microbial and enzyme activities mainly in the mineral horizons, although glucuronidase and phosphodiesterase activities appeared to be mainly controlled by TOC content. Generally, the different enzyme activities were more clearly highlighted when they were expressed per organic C unit, rather than on a soil mass basis. Latitudinal sensitivity was recorded for total N, ΣCO2–C, and some enzyme activities, although no difference in mean annual air temperature occurred along the latitudinal transect. In this case, it is plausible that the summer-winter thermal excursion, which was lower for the southernmost location and increased going north, might have indirectly affected these parameters through changes in the plant-soil relationships, composition of the macro- and mesofauna population, and microbial activity. Considering all the investigated aspects, an increase of 1 °C in mean annual air temperature (in the range 9–10 °C) and/or the alteration of summer-winter thermal excursion might affect the actual soil-plant balance in temperate beech forests, with possible greater mineralization of the topsoil organic matter and a major release of CO2 in the atmosphere.
23494. 题目: Three-year rice grain yield responses to coastal mudflat soil properties amended with straw biochar
文章编号: N19031406
期刊: Journal of Environmental Management
作者: Jining Zhang, Sheng Zhou, Huifeng Sun, Fan Lü, Pinjing He
更新时间: 2019-03-14
摘要: Biochar application is a promising management strategy for enhancing soil fertility and carbon sequestration. A 3-year pot trial was conducted to demonstrate the relationship between rice grain yield and biochar-amended soil properties together with carbon storage in the Yangtze River estuary, China. Straw biochar was incorporated once into soil in pots at five different rates: 0%, 5%, 10%, 15%, and 20% (dry biochar weight/wet soil weight). Compared to yields from the control treatment with no biochar, rice grain yield was improved by 29.1–34.2% in the treatments with 10–15% biochar in the first year following biochar application. In the second year following biochar application, the rice yield was increased by 51.8–96.0% in the treatments with 15–20% biochar. However, compared to the control treatment, hardly any yield increase occurred in any of the biochar treatments in the third year following biochar application. Higher amounts of added biochar increased the soil organic carbon (SOC) and total nitrogen (TN). SOC contents were invariable and increased nearly 60–250% annually in the biochar treatments compared with the control. Biochar increased soil TN 22.9–75.3%, 24.0–60.9% and 13.8–51.2%, respectively, in each of three consecutive years. Biochar increased the mean concentrations of EC, RAP, RAK and DOC by 8.8–44.8%, 10.0–61.1%, 65.6–310.1% and 9.1–20.0%, respectively, during the three rice-growing seasons. The addition of 10–15% straw biochar to soil and regular annual biochar supplements for agronomic purposes is a potentially sustainable management technology to enhance coastal mudflat soil properties and improve rice yields therefrom.
23495. 题目: Variability of organic nitrogen and its role in regulating phytoplankton in the eastern Arabian Sea
文章编号: N19031405
期刊: Marine Pollution Bulletin
作者: Suhas S. Shetye, Siby Kurian, Hema Naik, Mangesh Gauns, A.V. Chndrasekhararao, Ashwini Kumar, Bhagyashri Naik
更新时间: 2019-03-14
摘要: The relative importance of organic nitrogen (ON) and inorganic nitrogen (IN) as nitrogen sources for the phytoplankton communities were studied through a seasonal time series of nitrogen species in the eastern Arabian Sea. Seasonal data on nitrogen species showed that ON dominates the system throughout the year and account for >90% of the total nitrogen (TN) during north east monsoon (NEM). The average ON concentration in the study region was 11.5 μM during NEM as compared to 7.2 μM during south west monsoon (SWM). The contribution of picoplankton to the total phytoplankton pool (fpico) increased from 19% during SWM to 36% in NEM. Along with cyanobacteria, the diatoms Thalassionema nitzchoides and Thalassiosira sp. and among the dinoflagellates Pronoctiluca sp. were found to proliferate in ON rich waters. We suggest atmospheric deposition, riverine-input, resuspension of bottom sediment and ground water intrusion as the possible sources of ON in the study region.
23496. 题目: Chernozem relics in the Hellweg Loess Belt (Westphalia, NW Germany) – Natural or man-made?
文章编号: N19031404
期刊: Quaternary International
作者: Till Kasielke, Rosa M. Poch, Katja Wiedner
更新时间: 2019-03-14
摘要: Chernozems and Chernozem-like soils are widespread e.g. in Central Germany but its formation is still controversially discussed. Clustered findings of Luvic Phaeozems and buried dark soil horizons in the Westphalian Hellweg Loess Belt (North Rhine-Westphalia) are traditionally interpreted as relics of early Holocene Chernozems. More recent research raised the question whether these soils are of (pre-) historic anthropogenic origin.Field observations in the east of Dortmund revealed the existence of buried black horizons in hillslope hollows. The underlying Stagnic Luvisol was penetrated by darkish clay illuviation veins forming a polygonal pattern. This feature was also found below the plough horizon in Luvisols beyond the hillslope hollows. A multi-analytical approach was used in order to clarify whether the black soil horizons are natural relics or man-made. In order to identify fire-derived black carbon (microcharcoal), benzenepolycarboxylic acids were used as molecular markers.Beside the position of the fossil black horizons on top of a well-developed Stagnic Luvisol, micromorphological thin section analysis confirmed the colluvial origin of the black horizons. Total organic carbon contents of the black horizons were only ∼1%, whereas high black carbon concentrations indicate large amounts of fire derived organic matter. High concentrations of black carbon were also found in the clay illuviation veins, testifying to a formerly more widespread occurrence of black carbon enriched soils.Radiocarbon ages of charcoal particles from the black horizons prove fire activities during the late Neolithic and Bronze Age (e.g. slash-and-burn). Finally, our results strongly indicate that the Chernozem-like soils in the study area are man-made and natural Chernozem formation can be excluded.
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23497. 题目: Stratification of dissolved organic matter in the upper 2000 m water column at the Mariana Trench
文章编号: N19031403
期刊: Science of The Total Environment
作者: Penghui Li, Jianchang Tao, Jian Lin, Chen He, Quan Shi, Xinxin Li, Chuanlun Zhang
更新时间: 2019-03-14
摘要: Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and absorbance spectroscopy were utilized to investigate the molecular composition of marine dissolved organic matter (DOM) from the upper 2000 m water column at the Mariana Trench. Molecular indices, calculated based on the relative abundance of 4699 formulas assigned from FT-ICR MS data, showed depth stratification. The degradation index (IDEG) varied from 0.610 to 0.663 (0.645 ± 0.014) in the surface layer to 0.668–0.754 (0.722 ± 0.021) in the deep ocean (below 500 m), indicating that the DOM in the deep layer was more refractory than that of the surface layer. This was confirmed by an increase of modified aromaticity index (AImod) from 0.196 to 0.207 (0.200 ± 0.003) in the surface layer to 0.213–0.225 (0.220 ± 0.003) at depth. Multivariate analysis based on both bulk molecular parameters and relative abundance of individual formulas showed that the molecular composition of DOM was highly stratified and could be well separated into three groups: the upper layer (5–75 m), the middle layer (200 m) and the deep layer (500–2000 m). In addition, surface-enriched and deep-enriched formulas were identified based on Spearman correlation between relative abundance of individual formulas and depth. The surface-enriched formulas were characterized by higher H/C and lower AImod, while deep-enriched formulas showed lower H/C and higher AImod. Variations in AImod and H/C for these formulas indicated that extracellular release (mainly from primary production) and photochemical processes strongly affected the DOM composition in euphotic zone, while microbial processes likely exerted a tremendous influence on the DOM composition at all depths. Moreover, strong correlations between spectroscopic indices (a325, S275–295 and S280–400) and FT- ICR MS derived proxies indicated these two approaches can be integrated to provide valuable information on the molecular characterization of open ocean DOM.
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23498. 题目: Local-scale variation of soil bacterial communities in ice-free regions of maritime Antarctica
文章编号: N19031402
期刊: Soil Biology and Biochemistry
作者: Mincheol Kim, Hyun-Soo Lim, Chang-Uk Hyun, Ahnna Cho, Hyun-Ju Noh, Soon Gyu Hong, Ok-Sun Kim
更新时间: 2019-03-14
摘要: The majority of biogeographic studies in Antarctic terrestrial ecosystems have focused on macroscopic eukaryote taxa. In contrast, microbial taxa have been almost neglected or examined without sufficient spatial coverage. Here, we examined the spatial distribution of soil bacterial communities and their relation to local environmental gradients in ice-free regions of the maritime Antarctic. Soils in this region were dominated by Actinobacteria and Proteobacteria, which are typically found in Antarctic soils. Notably, candidate divisions AD3 and WPS-2, which rarely occur in other biomes, were found in high abundance in acidic surface soils. Soil pH and total organic carbon (TOC) were the primary drivers of the bacterial community structure and various geochemical variables also played important roles in structuring bacterial community composition. Bacterial communities were significantly correlated to measured environmental variables, most of which are spatially structured at the local spatial scale (0.5–8 km). This suggests that spatial heterogeneity of environmental factors is an important driver of shifts in bacterial communities. Although various sets of environmental variables were related to bacterial communities, a large proportion of community variation remained unexplained. This indicates that bacterial communities in Antarctic soils may be governed by other biotic or abiotic factors which are not typically measured in other biome studies.
23499. 题目: Impact of ecohydrological fluctuations on iron-redox cycling
文章编号: N19031401
期刊: Soil Biology and Biochemistry
作者: Salvatore Calabrese, Amilcare Porporato
更新时间: 2019-03-14
摘要: Because of its interaction with plants, carbon decomposition, and soil properties, soil iron cycle has been recognized as an important player in the carbon and other biogeochemical cycles. The impact of the hydrologic cycle and plants, however, remains largely unexplored. Here we focus on terrestrial ecosystems and develop a dynamical system to analyze the coupling between iron and carbon dynamics in the soil root zone as driven by fluctuations in soil moisture. Particular emphasis is placed on the modeling of the soil organic matter, the Fe-reducing population, the iron Fe2+-Fe3+ cycling, and the soil moisture level, which controls the redox rates. Informed by laboratory and field measurements from a tropical forest, our results suggest that soil moisture and litterfall rates are the primary drivers of iron fluctuations at daily-to-seasonal scales and reveal an emerging relationship between the reduction rate and the soil moisture level. We also quantify the fundamental role in the soil-iron cycle of plants, which are responsible for taking up ≈ 25% of the total iron losses.
23500. 题目: Redistribution of soil organic carbon induced by soil erosion in the nine river basins of China
文章编号: N19031310
期刊: Journal of Geophysical Research: Biogeosciences
作者: Xiaoyuan Wang, Timothy A. Quine, Haicheng Zhang, Guangjin Tian, Wenping Yuan
更新时间: 2019-03-13
摘要: Global soil erosion redistributes a large amount of soil organic carbon (SOC), and is potential to significantly change the terrestrial carbon budget. However, there are large uncertainties in the redistribution of SOC within the terrestrial and aquatic ecosystems. Based on two national survey datasets on soil erosion and sediment measurements from hydrological stations, this study estimated the redistribution of sediment and SOC in the nine river basins of China during 1995–1996 and 2010–2012. Over these two periods, 3.55–4.50 Pg of soil and 68.42–77.32 Tg C of SOC were eroded each year. For the SOC budget, on average 57% and 47% of the eroded SOC was deposited over land, 25% and 44% was deposited in the channel, and 18% and 8% was delivered into the sea during 1995–1996 and 2010–2012, respectively. Compared with the corresponding magnitudes during 1995–1996, the eroded SOC, the SOC deposited over land and the SOC discharged into the sea decreased during 2010–2012, and only the SOC deposited into the river channel increased (from 19.5 to 30.1 Tg C yr‐1). The changes in SOC deposition in the channel of the Yangtze River and the Yellow River basins demonstrate that the influence of human activities is extensive. Our results show that the erosion‐induced redistribution of SOC alters the carbon budget of China.