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12621. 题目: Tryptophan-like fluorescence as a measure of microbial contamination risk in groundwater
文章编号: N18072903
期刊: Science of The Total Environment
作者: Saskia Nowicki, Dan J. Lapworth, Jade S.T. Ward, Patrick Thomson, Katrina Charles
更新时间: 2018-07-29
摘要: Microbial water quality is frequently assessed with a risk indicator approach that relies on Escherichia coli. Relying exclusively on E. coli is limiting, particularly in low-resource settings, and we argue that risk assessments could be improved by a complementary parameter, tryptophan-like fluorescence (TLF). Over two campaigns (June 2016 and March 2017) we sampled 37 water points in rural Kwale County, Kenya for TLF, E. coli and thermotolerant coliforms (total n = 1082). Using three World Health Organization defined classes (very high, high, and low/intermediate), risk indicated by TLF was not significantly different from risk indicated by E. coli (p = 0.85). However, the TLF and E. coli risk classifications did show disagreement, with TLF indicating higher risk for 14% of samples and lower risk for 13% of samples. Comparisons of duplicate/replicate results demonstrated that precision is higher for TLF (average relative percent difference of duplicates = 14%) compared to culture-based methods (average RPD of duplicates ≥ 26%). Additionally, TLF sampling is more practical because it requires less time and resources. Precision and practicality make TLF well-suited to high-frequency sampling in low resource contexts. Interpretation and interference challenges are minimised when TLF is measured in groundwaters, which typically have low dissolved organic carbon, relatively consistent temperature, negligible turbidity and pH between 5 and 8. TLF cannot be used as a proxy for E. coli on an individual sample basis, but it can add value to groundwater risk assessments by improving prioritization of sampling and by increasing understanding of spatiotemporal variability.
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12622. 题目: Photocatalytic degradation of bisphenol A over a ZnFe2O4/TiO2 nanocomposite under visible light
文章编号: N18072902
期刊: Science of The Total Environment
作者: Thanh Binh Nguyen, C.P. Huang, Ruey-an Doong
更新时间: 2018-07-29
摘要: A ZnFe2O4-TiO2 nanocomposite combining p-type ZnFe2O4 and n-type TiO2 was successfully fabricated. The ZnFe2O4-TiO2 nanocomposite greatly enhanced the bisphenol A (BPA) photodegradation under visible light irradiation at 465 ± 40 nm. Loading TiO2 with 1 wt% of ZnFe2O4 produced high photocurrent and low charge transfer resistance. The photodegradation rate of BPA by ZnFe2O4-TiO2, which was highly dependent on the water chemistry including pH, anions, and humic acid, was 20.8–21.4 times higher than that of commercial TiO2 photocatalysts. Chloride and sulfate ions enhanced BPA photodegradation mostly due to the production of more radical species; whereas nitrate, dihydrogen phosphate, and bicarbonate ions decreased the photodegradation rate of BPA due to the scavenge of hydroxyl radicals. The photoactivity and recyclability of ZnFe2O4-TiO2 in lake water was also assessed. A near complete BPA removal from lake water was observed under visible light irradiation. Furthermore, >90% of photocatalytic activity toward BPA degradation was achieved in 5 cycles of continuous addition of BPA to the lake water. The BPA degradation intermediates were identified by HPLC/MS/MS and possible reaction pathways were proposed. Results clearly demonstrate the excellent visible-light-sensitive photocatalytic degradation of BPA over ZnFe2O4-TiO2 composite which has a great application potential for the decomposition of emerging contaminants in impaired waters.
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12623. 题目: Bioactivity of humic substances and water extracts from compost made by ligno-cellulose wastes from biorefinery
文章编号: N18072901
期刊: Science of The Total Environment
作者: R. Spaccini, V. Cozzolino, V. Di Meo, D. Savy, M. Drosos, A. Piccolo
更新时间: 2018-07-29
摘要: The ligno-cellulose residues from biorefinery production of bio-ethanol were used as woody structuring material within an on-farm composting system, with the aim to obtain bioactive water soluble and humic fractions from composted materials. The molecular characterization of initial biomasses and final products revealed a transformation towards more stable compounds during composting and showed the selective incorporation of specific phenolic derivatives of ligno-cellulose in both bulk samples and corresponding extracts. While the use of the stable bulk composts as organic fertilizer resulted in a decrease of nitrogen and phosphorous assimilation in maize tissues, a bio-stimulation was shown by water soluble organic compounds and humic substances in germination tests and pot experiments, respectively. The differential responses obtained in maize seedlings and plants were related to the molecular composition and concentration of the applied water extracts and humic substances, thus suggesting a role of phenols and lignin derivatives in the stimulation of maize roots and shoots and the enhancement of P uptake. The results confirm that ligno-cellulose residues may be effectively recycled as composting additives in order to enrich mature compost in aromatic and lignin compounds. A preliminary knowledge on the molecular characteristics and biological properties of composted materials is an essential requirement to select the most suitable derivatives from composted ligno-cellulose wastes in sustainable agricultural practices.
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12624. 题目: Fluorescence Quenching and Energy Transfer Phenomena Associated with the Interactions of Terbium Ion and Humic Acid
文章编号: N18072804
期刊: Aquatic Geochemistry
作者: Mingquan Yan, Gregory V. Korshin, Marc F. Benedetti, Chi-Wang Li
更新时间: 2018-07-28
摘要: Fluorescence of the hydrophobic acid fraction (HPOA) of Suwannee River natural organic matter and Tb3+ excitation spectra were measured in tandem using the instantaneous and time-resolved emission modes. The intensity of HPOA fluorescence decreased in the presence of Tb3+, while the intensity of the emission from Tb3+ cations bound by HPOA increased by up to several orders of magnitude due to energy transfer (ET) from HPOA to Tb3+ ions. To determine intrinsic ET and fluorescence quenching (FQ) coefficients, NICA–Donnan modeling was carried. It showed that phenolic groups in HPOA dominated both the ET and FQ processes and that the binding of Tb3+ by HPOA could be described using the non-ideality parameter nTb, median binding constant log KTb for the phenolic sites and intrinsic ET and FQ coefficients (denoted as ηTbΦ and αTbΦ), and were 0.48, 8.5, 1385 and 0.12, respectively. The high value of the energy transfer coefficient of Tb3+ ions bound by the phenolic groups in HPOA is indicative of both the match between the electronic levels of the donor and acceptor, and the short distance between them. The deviation of the data of Nica–Donnan modeling of the ET and FQ dependence of versus [Tb]total for a 1.0 M ionic strength highlights the need to quantify the distribution of donor–acceptor distances in HPOA molecules in more detail.

12625. 题目: Effects of altered dry-season length and plant inputs on soluble soil carbon
文章编号: N18072803
期刊: Ecology
作者: Peter M Homyak, Joseph C Blankinship, Eric W Slessarev, Sean M Schaeffer, Stefano Manzoni, Joshua P Schimel
更新时间: 2018-07-28
摘要: Soil moisture controls microbial activity and soil carbon cycling. Because microbial activity decreases as soils dry, decomposition of soil organic matter (SOM) is thought to decrease with increasing drought length. Yet, microbial biomass and a pool of water‐extractable organic carbon (WEOC) can increase as soils dry, perhaps implying microbes may continue to break down SOM even if drought stressed. Here, we test the hypothesis that WEOC increases as soils dry because exoenzymes continue to break down litter, while their products accumulate because they cannot diffuse to microbes. To test this hypothesis we manipulated field plots by cutting‐off litter inputs and by irrigating and excluding precipitation inputs to extend or shorten the length of the dry season. We expected that the longer the soils would remain dry, the more WEOC would accumulate in the presence of litter, whereas shortening the length of the dry season, or cutting off litter inputs, would reduce WEOC accumulation. Lastly, we incubated grass roots in the laboratory and measured the concentration of reducing sugars and potential hydrolytic enzyme activities, strictly to understand the mechanisms whereby exoenzymes break down litter over the dry season. As expected, extending dry season length increased WEOC concentrations by 30% above the 108 μg C g−1 measured in untreated plots, whereas keeping soils moist prevented WEOC from accumulating. Contrary to our hypothesis, excluding plant litter inputs actually increased WEOC concentrations by 40% above the 105 μg C g−1 measured in plots with plants. Reducing sugars did not accumulate in dry senesced roots in our laboratory incubation. Potential rates of reducing sugar production by hydrolytic enzymes ranged from 0.7 to 10 μmol g−1 hr−1 and far exceeded the rates of reducing sugar accumulation (~0.001 μmol g−1 hr−1). Our observations do not support the hypothesis that exoenzymes continue to break down litter to produce WEOC in dry soils. Instead, we develop the argument that physical processes are more likely to govern short‐term WEOC dynamics via slaking of microaggregates that stabilize SOM and through WEOC redistribution when soils wet up, as well as through less understood effects of drought on the soil mineral matrix.

12626. 题目: Rapid oxidation of iodide and hypoiodous acid with ferrate and no formation of iodoform and monoiodoacetic acid in the ferrate/I/HA system
文章编号: N18072802
期刊: Water Research
作者: Xianshi Wang, Yulei Liu, Zhuangsong Huang, Lu Wang, Yicheng Wang, Yanting Li, Juan Li, Jingyao Qi, Jun Ma
更新时间: 2018-07-28
摘要: Toxic and odorous iodinated disinfection byproducts (I-DBPs) could form in the chemical oxidation of iodine-containing water. A critical step for controlling the hazardous I-DBPs is to convert the iodine species into stable and harmless iodate (IO3) while inhibiting the accumulation of highly reactive hypoiodous acid (HOI). Herein, the oxidation of I and HOI with ferrate was investigated, and the formation profile of HOI during the oxidation of I was determined based on 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) coloring method through a stopped-flow spectrophotometer. The second-order rate constants (kapp) of ferrate with HOI decreased from 1.6 × 105 M−1s−1 to 8.3 × 102 M−1s−1 as the solution pH varied from 5.3 to 10.3, which were 7.5, 7.2 and 13.8 times higher than that of ferrate with I at pH 6.0, 7.0 and 8.0, respectively. Compared with other oxidants such as ozone, hypochlorous acid, chloramine and potassium permanganate, ferrate would swiftly oxidize HOI formed in the I oxidation process. For the ferrate oxidation of I-containing water, HOI was swiftly oxidized to IO3 from pH 5.0 to 9.0. Phosphate buffer promoted the oxidation of I while inhibited the oxidation of HOI with ferrate. When 5 mgC/L of humic acids (HA) existed in the solution, no formation of iodoform and monoiodoacetic acid (MIAA) was observed in the oxidation of iodide (20 μM) with ferrate (from 10 μM to 80 μM). These results have important implications for the control of I-DBPs in water treatment.
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12627. 题目: A Neolithic palaeo-catena for the Xagħra Upper Coralline Limestone plateau of Gozo, Malta, and its implications for past soil development and land use
文章编号: N18072801
期刊: CATENA
作者: Charles French, Sean Taylor, Rowan McLaughlin, Alan Cresswell, Tim Kinnaird, David Sanderson, Simon Stoddart, Caroline Malone
更新时间: 2018-07-28
摘要: Geoarchaeological survey on the island of Gozo combined with test excavations and new chronometric dating of two Neolithic temple sites at Santa Verna and Ġgantija on the Xagħra plateau have revealed well-preserved buried soils which tell a new story of soil development and change for the early-mid-Holocene period. Micromorphological analysis has suggested that the earlier Neolithic climax soil type was a thick, well-developed, humic and clay-enriched argillic brown Mediterranean soil. With human intervention on the Xagħra Upper Coralline Limestone plateau from at least the early 4th millennium BCE, the trajectory of soil development quickly changed. Radical soil change was marked by the removal of scrub woodland, then consequent poorer organic status and soil thinning, and rubefication and calcification, no doubt exacerbated by Neolithic agricultural activities and a more general longer-term aridification trend. The beginnings of this transitional brown to red Mediterranean soil change process has been observed at Santa Verna temple by the early 4th millennium BCE, and appears to be much further advanced by the time of the latter use of Ġgantija temple in the early-mid-3rd millennium BCE. There is also evidence of attempts at amending these deteriorating soils during this period and into the 2nd millennium BCE, a practice which probably underpinned the viability of later Neolithic agricultural society in the Maltese Islands. The changes observed ultimately resulted in the creation of the thin, xeric, red Mediterranean soils on the Coralline Limestone mesa plateaux which are typical of much of Gozo and Malta today.

12628. 题目: Uranium Retention in a Bioreduced Region of an Alluvial Aquifer Induced by the Influx of Dissolved Oxygen
文章编号: N18072713
期刊: Environmental Science & Technology
作者: Donald Pan, Kenneth H. Williams, Mark J. Robbins, Karrie A. Weber
更新时间: 2018-07-27
摘要: Reduced zones in the subsurface represent biogeochemically active hotspots enriched in buried organic matter and reduced metals. Within a shallow alluvial aquifer located near Rifle, CO, reduced zones control the fate and transport of uranium (U). Though an influx of dissolved oxygen (DO) would be expected to mobilize U, we report U immobilization. Groundwater U concentrations decreased following delivery of DO (21.6 mg O2/well/h). After 23 days of DO delivery, injection of oxygenated groundwater was paused and resulted in the rebound of groundwater U concentrations to preinjection levels. When DO delivery resumed (day 51), groundwater U concentrations again decreased. The injection was halted on day 82 again and resulted in a rebound of groundwater U concentrations. DO delivery rate was increased to 54 mg O2/well/h (day 95) whereby groundwater U concentrations increased. Planktonic cell abundance remained stable throughout the experiment, but virus-to-microbial cell ratio increased 1.8–3.4-fold with initial DO delivery, indicative of microbial activity in response to DO injection. Together, these results indicate that the redox-buffering capacity of reduced sediments can prevent U mobilization, but could be overcome as delivery rate or oxidant concentration increases, mobilizing U.
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12629. 题目: Effects of anthropogenic nitrogen deposition on soil nitrogen mineralization and immobilization in grassland soil under semiarid climatic conditions
文章编号: N18072712
期刊: Environmental Monitoring and Assessment
作者: Ambreen Bhatti, Jawad Ahmad, Muhammad Qasim, Muhammad Riaz, Malcolm S. Cresser
更新时间: 2018-07-27
摘要: Earlier studies by the authors on English soils under grassland strongly supported their hypothesis that soil/plant systems have naturally evolved to conserve nitrogen (N) by having a close match between the dynamics of mineral-N production in soils and the dynamics of plant N requirements. Thus, maximum mineral-N production in soils occurred in spring when plant N requirements were greatest and were very low in mid to late summer. Low temperature and a high C:N ratio of senescing material helped to conserve N in winter, but mobile N was associated with pollution inputs. We test the hypothesis that under the much more arid conditions of Pakistan, soil/plant systems naturally have evolved to conserve mineral-N, especially over the very dry and cooler months between October and February. When soils from a grassland site were incubated at ambient temperatures after removal of plant roots and exclusion of atmospheric N inputs, there was consistent evidence of immobilization of nitrate and immobilization and possibly volatilization of ammonia/ammonium. In the wetter months of July and August, the soil at 0–10 cm depth showed no evidence of significant ammonium-N production in July and only small ammonium production at 10–20 cm depth in August, but was associated with significant nitrate-N immobilization in August. Nitrate leaching only appeared likely towards the end of the rainy season in September. The results strongly suggest that, under grass, the retention of atmospheric N inputs over the long dry periods is regulating the pools of available N in the soils, rather than the N produced by mineralization of soil organic matter.

12630. 题目: Phytolith content in Vietnamese paddy soils in relation to soil properties
文章编号: N18072711
期刊: Geoderma
作者: Minh N. Nguyen, Stefan Dultz, Andrew Meharg, Quang V. Pham, Anh N. Hoang, Than T.N. Dam, Van T. Nguyen, Khai M. Nguyen, Huan X. Nguyen, Nghia T. Nguyen
更新时间: 2018-07-27
摘要: Understanding of the fate of phytolith in soils is important because of its role as an agronomical nutrient resource and for carbon sequestration. Accumulation of phytolith derived silica occurs in paddy soils when phytolith input, here through straw incorporation, is higher than silica removal through crop offtake, dissolution and leaching. Phytolith dissolution is thought to be the main reason for diminishing of phytolith derived silica in soil, with this dissolution being highly dependent on soil chemical properties. In this study, phytolith content from 78 paddy soils sampled in the Red River (RRD) and Mekong River (MRD) Deltas, Vietnam, were quantified and related to pH, electrical conductivity (EC), oxalate-extractable Al and Fe (Alox and Feox), organic carbon (OC) and clay content. Average phytolith contents within the topsoil (0–20 cm) were 4.8 ± 1.98 and 7.74 ± 2.97 mg g−1 for the RRD and MRD, respectively. Positive correlation coefficients obtained for Alox, OC, clay content and EC, implying that these parameters might enhance phytolith resistance to dissolution. Soil pH had a negative correlation coefficient with phytolith content. Lower pH and higher Alox content explained the predominance of the phytolith in the MRD compared to the RRD. Soil pH adjustment can be proposed as an active management strategy to maintain phytolith added Si, source for crops and for carbon sequestration.
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12631. 题目: Evaluation of the anaerobic biodegradation of linear alkylbenzene sulfonates (las) using oecd 308 water/sediment systems
文章编号: N18072710
期刊: Journal of Hazardous Materials
作者: Carmen Corada-Fernández, Eduardo González-Mazo, Pablo A. Lara-Martín
更新时间: 2018-07-27
摘要: Linear alkylbenzene sulfonates (LAS) are the most widely used anionic surfactants in household detergents and cleaning products. We have evaluated LAS anaerobic degradation in sediments following OECD 308 guidelines. Four different classes of sediments were collected from non-polluted areas and tested to check the influence of: fine and coarse texture, low and high organic carbon content, and freshwater and marine origin. The concentrations of LAS and possible degradation metabolites in sediment and water phases were monitored by high resolution mass spectrometry over an incubation period of 160 days. LAS removal was between 0 and 63%, depending on the sediment used, and it was accompanied by formation of sulfophenyl carboxylic acids (SPCs). The best results were observed for marine sediments having low organic carbon and silt + clay contents (0.5% and 13%, respectively), whereas degradation was negligible in freshwater sediments. The large differences in degradation observed across the sediments tested were attributed to their physicochemical properties influencing LAS bioavailability and the heterogeneity of microbial communities. Further research is also needed to address some shortcomings observed during the application of the OECD 308 and to ensure that test results obtained with these guidelines model anaerobic biodegradation under realistic environmental conditions.

12632. 题目: Interpreting the effects of natural organic matter on antimicrobial activity of Ag2S nanoparticles with soft particle theory
文章编号: N18072709
期刊: Water Research
作者: Yulei Liu, Tao Yang, Lu Wang, Zhuangsong Huang, Juan Li, Haijun Cheng, Jin Jiang, Suyan Pang, Jingyao Qi, Jun Ma
更新时间: 2018-07-27
摘要: Natural organic matter (NOM) ubiquitously exists in natural waters and would adsorb onto the particle surface. Previous studies showed that NOM would alleviate the toxicity of nanomaterials, while the mechanism is seldom quantitatively interpreted. Herein, the effects of humic substances [Suwannee River fulvic acid (SRFA) and Suwannee River humic acid (SRHA)] and biomacromolecules [alginate and bovine serum albumin (BSA)] on the aggregation and antimicrobial effects of silver sulfide nanoparticles (Ag2S-NPs) were investigated. The aggregation kinetics of Ag2S-NPs in electrolyte solutions were in agreement with the results based on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The dynamic light scattering (DLS) results showed that the SRFA, SRHA, alginate and BSA molecules coated on the Ag2S-NPs surfaces. The NOM coating layer prevented salt-induced coagulation of Ag2S-NPs, and the effects of BSA and SRHA on Ag2S-NPs stabilizing were more obvious than that of SRFA and alginate. Flow cytometry results showed that BSA and SRHA were more effective on alleviating the Ag2S-NPs induced cell (Escherichia coli) membrane damage than SRFA and alginate. After interpreting the electrophoretic mobility (EPM) data of the NOM coated Ag2S-NPs by Ohshima's soft particle theory, it was found that the thickness of the NOM coating layers followed the orders of BSA > SRHA > alginate > SRFA. The E.coli cell membrane damage level was negatively correlated with the thickness and softness of the coating layer. NOM coating may physically alleviate the contact between NPs and E. coli cells and thus attenuate the extent of cell membrane damage caused by the NP-cell interaction. This work provides a new perspective for quantitatively interpreting the influence of NOM on the environmental behaviors and risks of nanomaterials.
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12633. 题目: Dissolved organic matter binding with Pb(II) as characterized by differential spectra and 2D UV–FTIR heterospectral correlation analysis
文章编号: N18072708
期刊: Water Research
作者: Huacheng Xu, Mingquan Yan, Wentao Li, Helong Jiang, Laodong Guo
更新时间: 2018-07-27
摘要: Dissolved organic matter (DOM) in aquatic environment significantly influences the behavior and fate of heavy metals via binding, complexation and thus changes the metal speciation; however detailed interfacial processes and mechanisms are still unclear. Here, differential absorbance and fluorescence spectra and two dimensional UV–FTIR heterospectral correlation analysis were applied to probe into the Pb(II)–DOM interaction at a wide range of pH and ionic strength (IS). The absorbance of DOM molecules under all conditions increased with metal addition, while the different extents of absorbance variations along the wavelength range in the differential zero-order and log-transformed absorbance spectra indicated the site heterogeneity within the DOM pool for metal binding. Spectral parameters, namely differential fluorescent components 1 and 2 (DFC1 and DFC2) and differential slopes of log-transformed absorbance in the range of wavelength 350–400 nm (DSlope350–400) were found to be highly correlated with the total amounts of DOM-bound Pb(II) predicted by the NICA-Donnan model, while the differential absorbance spectra at 235 nm (DA235) was related to the extent of Pb(II) bound by carboxylic groups. Thus, these parameters are an indicator or proxy for the in situ Pb(II)–DOM interaction extent. Aryl C–H gave the fastest response to Pb(II) binding at lower pH and IS (e.g., pH 4.7 and IS = 0.01 M), followed by carboxyl C=O and polysaccharide C–OH and then chromophoric groups at 265 nm (CDOM265). However, the CDOM265 bound to Pb(II) prior to aryl C–H and polysaccharide C–OH groups at higher pH and IS (6.0 and 0.1 M, respectively), showing that the binding sequences were highly dependent on solution chemistry. Differential spectra combined with two dimensional UV–FTIR heterospectral correlation analysis can be used as a promising approach to elucidate metal–DOM interaction processes, including site heterogeneity, binding sensitivity and sequence at the functional group level.
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12634. 题目: Comparative evaluation of influence of aging, soil properties and structural characteristics on bioaccessibility of polychlorinated biphenyls in soil
文章编号: N18072707
期刊: Chemosphere
作者: Qingqing Ti, Chenggang Gu, Chang Liu, Jun Cai, Yongrong Bian, Xinglun Yang, Yang Song, Fang Wang, Cheng Sun, Xin Jiang
更新时间: 2018-07-27
摘要: Though bioaccessibility commonly recognized as a guideline for risk assessment is closely related with pollution occurrence and chemical species of compounds, the mechanistic links are barely evaluated particularly for widespread polychlorinated biphenyls (PCBs) in soil. With the biomimetic extraction of hydroxypropyl-β-cyclodextrin (β-HPCD), the temporal and spatial influences of soil properties, aging and structural characteristics, e.g. polarity of PCB congeners on bioaccessibility were investigated for PCBs. Sensitive variation of bioaccessibility with aging, soil organic matter (SOM), particle size and soil moisture were clearly evidenced for different PCB congeners. Due to aging, the bioaccessibility decreased in the long term after stabilization for 36 h. In concert with the first-order kinetics, the decay rates of bioaccessibility were shown with congener-specificity and were well correlated with dipoles of PCBs. The increment of SOM diminished the bioaccessibility for the strengthened adsorption while the increased particle size and soil moisture elevated it possibly due to the less adsorption on soil particles and more accommodation of PCBs in soil pore water. Except the positive correlations with particle size, soil moisture and dipole moment, the greater dependency on aging and SOM was highlighted for bioaccessibility by partial least squares (PLS) analysis. The mutual relationship with influential factors was quantitatively formulated for accelerative prediction of bioaccessibility, and the comparative evaluation and detailed insights into the mechanistic links would thus help enhance the precise determination of bioaccessibility and risk assessment of PCBs in soil.

12635. 题目: Seagrass community-level controls over organic carbon storage are constrained by geophysical attributes within meadows of Zanzibar, Tanzania
文章编号: N18072706
期刊: Biogeosciences
作者: Elizabeth Fay Belshe, Dieuwke Hoeijmakers, Natalia Herran, Matern Mtolera, and Mirta Teichberg
更新时间: 2018-07-27
摘要: The aim of this work was to explore the feasibility of using plant functional traits to identify differences in sediment organic carbon (OC) storage within seagrass meadows. At 19 sites within three seagrass meadows in the coastal waters of Zanzibar, Tanzania, species cover was estimated along with three community traits hypothesized to influence sediment OC storage (above and belowground biomass, seagrass tissue nitrogen content, and shoot density). Sediments within four biogeographic zones (fore reef, reef flat, tidal channel, and seagrass meadow) of the landscape were characterized, and sediment cores were collected within seagrass meadows to quantify OC storage in the top 25cm and top meter of the sediment. We identified five distinct seagrass communities that had notable differences in the plant traits, which were all residing within a thin veneer (ranging from 19 to 78cm thick) of poorly sorted, medium to coarsely grained carbonate sands on top of carbonate rock. One community (B), dominated by Thalassodendron ciliatum, contained high amounts of above (972±74gDWm−2) and belowground (682±392gDWm−2) biomass composed of low-elemental-quality tissues (leaf C:N = 24.5; rhizome C:N = 97). While another community (C), dominated by small-bodied ephemeral seagrass species, had significantly higher shoot density (4178 shootsm−2). However, these traits did not translate into differences in sediment OC storage and across all communities the percentage of OC within sediments was similar and low (ranging from 0.15% to 0.75%), as was the estimated OC storage in the top 25cm (14.1±2.2Mg Cha−1) and top meter (33.9±7.7Mg Cha−1) of sediment. These stock estimates are considerably lower than the global average (194.2±20.2Mg Cha−1) reported for other seagrass ecosystems and are on the lower end of the range of estimates reported for the tropical Indo-Pacific bioregion (1.9 to 293Mg Cha−1). The uniformly low OC storage across communities, despite large inputs of low-quality belowground tissues in community B, indicates that the geophysical conditions of the coarse, shallow sediments at our sites were not conducive to OC stabilization and outweighed any variation in the quantity or quality of seagrass litter inputs. These results add to a growing body of evidence showing that geophysical conditions of the sediment modulate the importance of plant traits in regards to retention of OC within blue carbon ecosystems and cautions against the use of plant traits as a proxy for sediment OC storage across all seagrass ecosystems.
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12636. 题目: Temperature sensitivity of extracellular enzymes differs with peat depth but not with season in an ombrotrophic bog
文章编号: N18072705
期刊: Soil Biology and Biochemistry
作者: J. Megan Steinweg, Joel E. Kostka, Paul J. Hanson, Christopher W. Schadt
更新时间: 2018-07-27
摘要: Peatlands contain a large portion of Earth's terrestrial soil organic matter in part due to a reduction in decomposition rates. Organic matter decomposition is initially mediated by extracellular enzyme activity, which is in turn controlled by temperature, moisture, and substrate availability; and all are subject to seasonal variation. As depth increases in peatlands, temperature variability and labile carbon inputs decrease. We hypothesized that the more stable recalcitrant subsurface would contain a smaller less diverse enzyme pool, that is better adapted to a narrow temperature range. Thus temperature dependence would be diminished at depth compared to superficial peat. Potential enzyme activity rates were determined across seasons and with depth in peat samples collected from the Marcell Experimental Forest in northern Minnesota, USA. The temperature dependence, assessed by activation energy, was quantified for three hydrolytic enzymes involved in nutrient cycling at up to 15 temperature points ranging from 2 °C to 65 °C. Potential enzyme activity decreased with peat depth as expected and corresponded with changes in peat composition and microbial biomass from the acrotelm to the catotelm. In an environmentally relevant temperature range (2–23 °C), activation energy decreased with depth for β-glucosidase as predicted and leucine amino peptidase activation energy was the lowest of all enzymes. Stable temperatures at depth appear to result in a microbial community containing enzymes that have lower sensitivity to temperature increases. Surprisingly, there was no significant seasonal effect on enzyme temperature dependence observed in our study. Based on these results, and without shifts in microbial community composition, warming of peat could result in increased carbon and phosphorus cycling at the surface but little change at depth. Additionally differences in enzyme temperature sensitivity suggest nitrogen cycling could remain constant with warming, potentially resulting in proteolytic nitrogen cycling being decoupled from carbon and phosphorus cycling.

12637. 题目: Labile soil organic carbon for assessing soil quality: influence of management practices and edaphic conditions
文章编号: N18072704
期刊: CATENA
作者: Matias E. Duval, Juan A. Galantini, Juan M. Martínez, Fabiana Limbozzi
更新时间: 2018-07-27
摘要: Soil organic carbon (SOC) is a complex set of pools, and to understand its dynamics it is necessary to know which of these pools are sensitive to the edaphic and climatic conditions or the agricultural practices, or to both. The objectives of this study were to evaluate the relationships between permanganate oxidizable C (POX-C) and various soil organic carbon fractions in different land-uses and soil types, and to examine whether the POX-C fraction is sensitive to different agricultural management practices in soils under no-tillage. Three treatments were identified at four sites located in the Argentine Pampas region: two different agricultural scenarios in terms of crop rotation, fertilizers and use of agrochemicals (Good Agricultural Practices and Poor Agricultural Practices, GAP and PAP, respectively) and an undisturbed natural (NE) environment adjacent to the agricultural sites as the control treatment. The following organic fractions were quantified: SOC, coarse and fine particulate organic carbon (POCc and POCf, respectively), hot water and acid extractable organic carbon (HWC and HAC, respectively) and POX-C. Soil POC values ranged from 0.46 to 7.29 g kg−1, HAC values ranged from 1.50 to 6.73 g kg−1, HWC values ranged from 0.20 to 1.10 g kg−1 and POX-C values ranged from 0.41 to 1.04 g kg−1 soil, POCc being the most variable fraction (CV = 72%) and POX-C the least (CV = 22%). Soil POCc and POCf at 0–10 cm, and POCc at 10–20 cm were largely explained by management practices with a component of variance >50%. The relationship between POX-C and SOC was generally stronger (R2 = 0.76–0.92) than POX-C with other organic fractions and where depth and site factors have a greater influence on this relationship than management practices. Among the labile fractions, the most sensitive indicators of soil quality in agricultural soils were POCf and HWC, which displayed the highest F-statistic values. Despite the dilute solution used (0.02 mol L−1 KMnO4) the POX-C demonstrated limited sensitivity to different agricultural practices. However, this methodology could be used to estimate SOC regarding site conditions and depths. The POCf was the fraction most affected by agricultural practices, indicated by high relationships with both the soil physical attributes (macroporosity, bulk density, and density, volume and stability of aggregates) and the agronomic parameters (soybean and maize yields).

12638. 题目: Effect of different components of single superphosphate on organic matter degradation and maturity during pig manure composting
文章编号: N18072703
期刊: Science of The Total Environment
作者: Juan Wu, Aiguo Zhang, Guoxue Li, Yuquan Wei, Shengzhou He, Zhong Lin, Xiufang Shen, Qiuju Wang
更新时间: 2018-07-27
摘要: Single superphosphate (SSP) as an additive could improve phosphorus availability and reduce nitrogen loss for composts, but few studies have explored the influence of SSP on the transformation of carbon fractions in composting. The aim of this work was to assess the effect of different components of SSP, including calcium dihydrogen phosphate (CDP), calcium sulfate (CS) and free acid (FA) on organic matter degradation and maturity during pig manure composting. The results showed that CDP had significantly negative effects on the duration of thermophilic phase and organic matter degradation, but lengthened the curing phase for the transformation of organic matter. FA could intensify the inhibiting effect of CDP and postpone the biodegradation process of composting, but CS could buffer the effect of CDP on the degradation of organic carbon fractions by controlling pH. The study reveals the roles of different components of SSP to the transformation of organic carbon fractions, which lays a foundation for regulating the effects of chemical additives during composting. Regulating the content of CDP in SSP or applying SSP with other chemical additives to control the biotoxicity of excess phosphate on microbial activity should be concerned for complete and efficient composting in further study.
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12639. 题目: Sorption of organic compounds to two diesel soot black carbons in water evaluated by liquid chromatography and polyparameter linear solvation energy relationship
文章编号: N18072702
期刊: Water Research
作者: Po-Hsin Su, Dave Ta Fu Kuo, Yang-hsin Shih, Chih-yu Chen
更新时间: 2018-07-27
摘要: Substantial variability in sorption capacity of black carbon (BC) has been a major challenge for accurate fate and risk assessment of organic pollutants in soils and sediments. 16 model organic sorbates (logKOW = 0.38–4.21) encompassing diverse chemical functionalities were used to probe the sorption capacity of two diesel soot samples representative of graphitic BC (BC1, specific surface area (SSA) = 87 m2/g) and amorphous, oxygenated BC (BC2; SSA = 3.6 m2/g). The BC-water sorption coefficients (logKBC) of the model sorbates were determined using reversed-phase liquid chromatography (RP-LC) on soot-filled columns. It was found that mass-based logKBC's of BC1 (1.64–3.66 L/kgBC) exceeded those of BC2 (0.68–3.48 L/kgBC) consistently for all model sorbates. However, area-normalized logKBC's of BC2 were larger than those of BC1, suggesting that the overall sorption was more favored on the oxygenated sorbent per area basis. Linear solvation energy relationships (LSERs) for sorption onto BC1 and BC2 were found to be logKBC = (2.49 ± 0.65)E + (−2.71 ± 0.88)S + (1.17 ± 0.46)A + (2.52 ± 0.34)V and logKBC = (1.12 ± 0.39)E + (−1.68 ± 0.32)S + (−3.70 ± 0.57)B + (4.37 ± 0.38)V + (−1.51 ± 0.22), respectively. The LSERs indicated that sorption onto soot was generally enhanced with increasing non-specific van der Waals and decreasing cavitation cost (i.e., eE, sS, and vV terms). The logKBC difference between BC1 and BC2, ΔlogKBC, appeared to be correlated with the H-bonding capacity of the sorbates but not logKOW. Analysis of literature and experimental logKBC's revealed that logKBC and logSSA across different types of BC (i.e., soot, char, charcoal, activated carbon) were linearly correlated for benzene and toluene (r2 = 0.88–0.91). This work illustrates the utility of RP-LC in determining the sorption coefficients of high-capacity sorbents and suggests the possibility of a unified sorption model for the continuum of black carbon.

12640. 题目: A simple approach to estimate daily loads of total, refractory, and labile organic carbon from their seasonal loads in a watershed
文章编号: N18072701
期刊: Environmental Science and Pollution Research
作者: Ying Ouyang, Johnny M. Grace, Wayne C. Zipperer, Jeff Hatten, Janet Dewey
更新时间: 2018-07-27
摘要: Loads of naturally occurring total organic carbons (TOC), refractory organic carbon (ROC), and labile organic carbon (LOC) in streams control the availability of nutrients and the solubility and toxicity of contaminants and affect biological activities through absorption of light and complex metals with production of carcinogenic compounds. Although computer models have become increasingly popular in understanding and management of TOC, ROC, and LOC loads in streams, the usefulness of these models hinges on the availability of daily data for model calibration and validation. Unfortunately, these daily data are usually insufficient and/or unavailable for most watersheds due to a variety of reasons, such as budget and time constraints. A simple approach was developed here to calculate daily loads of TOC, ROC, and LOC in streams based on their seasonal loads. We concluded that the predictions from our approach adequately match field measurements based on statistical comparisons between model calculations and field measurements. Our approach demonstrates that an increase in stream discharge results in increased stream TOC, ROC, and LOC concentrations and loads, although high peak discharge did not necessarily result in high peaks of TOC, ROC, and LOC concentrations and loads. The approach developed herein is a useful tool to convert seasonal loads of TOC, ROC, and LOC into daily loads in the absence of measured daily load data.

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