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24541. 题目: Tidally resolved observations of organic carbon exchange through Eastern Long Island Sound
文章编号: N19110910
期刊: Estuarine, Coastal and Shelf Science
作者: Allison L. Byrd, Penny Vlahos, Michael M. Whitney, Christina Menniti, Joseph K. Warren
更新时间: 2019-11-09
摘要: Long Island Sound (LIS), is an urban estuary on the US east coast that undergoes seasonal hypoxia in its western and central regions. Approximately 90% of the water exchange between LIS and the adjacent continental shelf, the Mid Atlantic Bight, occurs through its eastern boundary. Recent estimates of organic carbon (OC) export from LIS have shown that this value varies appreciably, both seasonally and inter-annually. In this study, the spatial, tidal, and seasonal variability were resolved by measuring dissolved and particulate organic carbon (DOC and POC) concentrations and currents at a cross-section in eastern LIS near the estuary mouth. Fluxes were extrapolated from these high-resolution observations collected in May, August, and November 2016, and August 2017. In August of 2016 (a low flow year), an OC flux of 41 × 10⁶ kg C month⁻¹ resulted from a net import of DOC and an export of POC. In August of 2017 (an average flow year), there was an OC flux of 30 × 10⁶ kg C month ⁻¹ due to both DOC and POC export, indicating significant seasonal and inter-annual variability. The seasonally weighted-average total OC flux for 2016 was −41 × 10⁶ ± 9 kg C yr⁻¹ (net import). Results show that spot sampling in tidal estuaries can lead to spatial and tidal bias in concentrations of DOC (6–15%) and POC (31–18%) under high and low river flow conditions, respectively. This uncertainty is recommended for spot sampling in future OC studies and flux estimates in LIS.

24542. 题目: The bioavailability of riverine dissolved organic matter in coastal marine waters of southern Texas
文章编号: N19110909
期刊: Estuarine, Coastal and Shelf Science
作者: Kai Wu, Kaijun Lu, Minhan Dai, Zhanfei Liu
更新时间: 2019-11-09
摘要: To examine the bioavailability of dissolved organic carbon (DOC) and nitrogen (DON) in riverine dissolved organic matter (DOM) discharged to the coastal ocean, we conducted a series of month-long (24 days) incubation experiments with filtered samples collected from five southern Texas rivers (Lavaca, San Antonio, Mission, Aransas, and Nueces) inoculated using the same natural coastal microbial assemblages during summer (June) and winter (January) in 2016. The bioavailable fractions of DOC and DON (BDOC% and BDON%) varied substantially in different rivers and seasons, ranging respectively from 6 to 11%, and 15–38% during winter, and 0–6% and 9–15% during summer. Relatively higher BDOC% and BDON% occurred in the San Antonio and Aransas Rivers, which are impacted more by human activities through discharge from wastewater treatment plants. Seasonally, the riverine DOM was more bioavailable in winter than in summer when DOM may have been extensively degraded in situ due to the low base flow (or long residence time) and the elevated temperature in river water in summer. The principal component analysis on amino acid composition further confirmed that DOM was less degraded in winter than in summer. Functional gene abundance data revealed that winter riverine DOM was relatively labile as evidenced by an increase in N-metabolism pathways and functional genes during the winter incubation, whereas the opposite pattern was observed in summer. The findings of the varying bioavailability of DOM among rivers and seasons have important implications about the fate of riverine DOM and their potential contributions to nutrient supplies as southern Texas bays and estuaries are often nitrogen limited.

24543. 题目: The Early Pliocene global expansion of C₄ grasslands: A new organic carbon-isotopic dataset from the north China plain
文章编号: N19110908
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: Jiayi Lu, Thomas J. Algeo, Guangsheng Zhuang, Jilong Yang, Guoqiao Xiao, Jiangsi Liu, Junhua Huang, Shucheng Xie
更新时间: 2019-11-09
摘要: C₄-grasslands are known to have first expanded globally in the Late Miocene, and recent research has hinted at a second expansion phase during the Early Pliocene; however, the geographic extent of this second event and its driving force are debated. In this study, we present organic carbon-isotopic evidence from a high-resolution drillcore in North China spanning the interval from ∼8.0 Ma to the present. A prominent positive δ¹³C_org shift at ∼4.1 Ma marks C₄-grassland expansion on the North China Plain, and rapid oscillations of >6‰ from ∼3.2 to 2.2 Ma imply large shifts between C₃- and C₄-dominated floras. Our δ¹³C_org profile mirrors carbon isotope shifts in loess-red clay deposits of the Chinese Loess Plateau, confirming the regional nature of this event. Furthermore, coeval carbon isotope records from Africa, North America, and South America provide evidence that the Early Pliocene C₄-grassland expansion was global in scale and temporally distinct from the Late Miocene event. Whereas the Late Miocene event may have been related to aridification and altered fire regimes, this mechanism cannot account for the Early Pliocene expansion owing to contemporaneous increases in humidity at many Northern Hemisphere sites. We hypothesize that C₄-grassland expansion in the Early Pliocene was triggered by falling atmospheric CO₂ levels, as evidenced by multiple pCO₂ proxy records and supported by quantum photosynthetic efficiency modeling.

24544. 题目: Tillage-induced effects on SOC through changes in aggregate stability and soil pore structure
文章编号: N19110907
期刊: Science of The Total Environment
作者: Yafei Guo, Ruqin Fan, Xiaoping Zhang, Yan Zhang, Donghui Wu, Neil McLaughlin, Shixiu Zhang, Xuewen Chen, Shuxia Jia, Aizhen Liang
更新时间: 2019-11-09
摘要: Soil structure plays a key role in soil organic carbon (SOC) dynamics. To determine how soil structure and aggregate affects SOC, we collected undisturbed soil cores of 0–5 cm layer (Typic Hapludoll) at an experimental site in Northeast China. The site had been under continuous tillage treatments of conventional tillage (CT) and no tillage (NT) for 17 years. We measured SOC by elemental analysis, aggregate size distribution by wet sieving, and soil pore parameters of pore size distribution, pore average diameter, pore numbers, pore connectivity, pore anisotropy, and pore fractal dimension by X-ray computer tomography. SOC content was significantly correlated with aggregate-associated SOC and soil water-stable aggregate content. CT with residue removal and annual plowing and cultivation increased <53 μm and 53–250 μm aggregates. CT decreased total SOC of 0–5 cm soil layer but increased aggregate-associated SOC of <53 μm. NT with greater residue input increased total SOC of 0–5 cm soil layer by 26.0% and aggregate mean weight diameter by 111.8% and increased aggregates of 250–1000 μm and >1000 μm. Soil under NT had a greater total number of micropores and greater connectivity whereas CT had a greater total number of macropores, average macropore diameter, anisotropy, and fractal dimension. Structural equation modeling showed that CT can decrease SOC of 0–5 cm soil layer by different paths, including increased anisotropy and macropore porosity, and NT can increase SOC of 0–5 cm soil layer by different paths, including increased mean weight diameter and connectivity. These results enhance our understanding of the relationship between soil structure and SOC, and could guide tillage management decisions to increase SOC.
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24545. 题目: The distribution, characteristics and ecological risks of microplastics in the mangroves of Southern China
文章编号: N19110906
期刊: Science of The Total Environment
作者: Ruili Li, Lingyun Yu, Minwei Chai, Hailun Wu, Xiaoshan Zhu
更新时间: 2019-11-09
摘要: During the production, use and disposal of plastic products, microplastics (MPs) are dispersed into the surrounding environment and have inevitable impacts on mangrove ecosystems in estuaries and offshore areas. In the mangroves of Southern China, the systematic evaluation of the distribution, characteristics and ecological risks of MPs is lacking. In this study, surface sediments (0-5 cm depth) were collected from six representative mangroves in China to explore MP contamination and its associated ecological risk. Based on the results, MP concentrations of MPs in mangrove sediments were as follows : FT (2249±747 items/kg), ZJ (736±269 items/kg), DF (649±443 items/kg), DZG (431±170 items/kg), YX (424±127 items/kg), and FCG (227±173 items/kg). The higher MP concentration in the Futian mangrove was mainly related to inputs from the Pearl River, the third largest river in China. The predominant shape, colour, and size of MPs were fibrous, white-transparent, and 500 -5,000 μm, respectively. The main MP polymer types were polypropylene, polyethylene, and polystyrene. Degradation artefacts were present on surface of MPs as well as metallic and non-metallic elements. MPs concentration in mangrove sediments increased with increasing social-economic development of surrounding districts, which indicated the clear influence of anthropogenic activity on MP pollution in these mangroves. Furthermore, total organic carbon (TOC) and silt content were positively associated with MPs (P < 0.01), indicating a facilitatory role in deposition of MPs in mangroves. Based on a comprehensive evaluation using the potential ecological risk factor (Ei), potential ecological risk (RI), polymer risk index (H) and pollution load index (PLI), MPs were found to present ecological risks in these mangroves, with the highest risk occurring in the Futian mangrove.
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24546. 题目: PAEs and PAHs in the surface sediments of the East China Sea: Occurrence, distribution and influence factors
文章编号: N19110905
期刊: Science of The Total Environment
作者: Xiangai Zhao, Haiyan Jin, Zhongqiang Ji, Donghao Li, Han Yeong Kaw, Jianfang Chen, Zhiyong Xie, Tianzhen Zhang
更新时间: 2019-11-09
摘要: A total of 29 sediment samples were collected from the East China Sea (ECS), with the Yangtze River estuary and the Zhejiang costal area. These sediment samples were analyzed for 6 phthalate esters (PAEs) and 16 polycyclic aromatic hydrocarbons (PAHs): the ΣPAEs and ΣPAHs concentrations ranged between 1649.5–8451.5 ng g^–1 (mean = 3446.3 ng g^–1) and 57.5–364.5 ng g^–1 (mean = 166.2 ng g^–1), respectively. Overall, the PAEs and PAHs concentrations gradually decreasing in the offshore and southward directions: their compositions and distributions suggest they could have mainly derived from the Yangtze River. In particular, their distribution was influenced by the sources’ proximity, hydrodynamics, and sediment geochemistry (i.e., TOC content and grain size). A classical two-end member model was utilized to estimate the fraction of terrestrial organic carbon in the sediments of the ECS. When the sediment was dominated by terrestrial-derived organic matter (OM), the concentrations of PAEs and PAHs were significantly correlated to the TOC content and gran size of the sediments. In contrast, the poor correlation of TOC content and grain size with PAEs in those sediments dominated by marine-derived OM, implied that the distribution of PAEs in the ECS was mainly related to land-based inputs, (especially to that of the Yangtze River). Regardless of the origin of most of the OM contained in the sediments, we observed positive correlations between the TOC content, and grain size of those containing PAHs. These results suggest that the distribution of PAHs in the ECS was not only related to the Yangtze River input, but also to the geochemical characteristics of the sediments.
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24547. 题目: A comparison of dissolved organic matter transformation in low pressure ultraviolet (LPUV) and ultraviolet light-emitting diode (UV-LED)/chlorine processes
文章编号: N19110904
期刊: Science of The Total Environment
作者: Ze-Chen Gao, Yi-Li Lin, Bin Xu, Ying Xia, Chen-Yan Hu, Tian-Yang Zhang, Tong-Cheng Cao, Yang Pan, Nai-Yun Gao
更新时间: 2019-11-09
摘要: This study compared the degradation of dissolved organic matter (DOM) by UV/chlorine advanced oxidation processes (AOPs) with emerging ultraviolet light-emitting diode (UV-LED, 275 nm) and traditional low pressure UV (LPUV, 254 nm) as UV sources. Excitation emission matrix-parallel factor (EEM-PARAFAC) analysis and two-dimensional (2D) correlation gel permeation chromatograph were applied to explore the evolutions of DOM during oxidation processes. The degradation behaviors of DOM indicated by UV absorbance at 254 nm (UV₂₅₄), dissolved organic carbon (DOC), and fluorophores fitted the pseudo-first-order kinetics well. The removal efficiency of DOM was similar under UV-LED and LPUV irradiation alone. However, UV-LED exhibited much higher degradation rates (increased by 29–160%) than LPUV regardless of the tracking variables during UV/chlorine processes. For three PARAFAC components, humic-like fluorescences were preferentially degraded by UV/chlorine oxidation compared with protein-like fluorescence potentially due to the differences of electronic moieties and molecular weight (MW). The decline in UV₂₅₄, DOC, and fluorophores increased with increasing chlorine dosage; linear correlations between those indicators were observed during the two AOPs. Moreover, UV-LED/chlorine could achieve greater extents of MW change. Our study demonstrated that UV-LED could be a superior alternative for the future selection of UV source in the UV/chlorine process.
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24548. 题目: Microbial growth and enzyme kinetics in rhizosphere hotspots are modulated by soil organics and nutrient availability
文章编号: N19110903
期刊: Soil Biology and Biochemistry
作者: Peng Tian, Bahar S. Razavi, Xuechen Zhang, Qingkui Wang, Evgenia Blagodatskaya
更新时间: 2019-11-09
摘要: The input of labile organics by plant roots stimulates microbial activity and therefore facilitates biochemical process rates in the rhizosphere compared to bulk soil, forming microbial hotspots. However, the extent to which the functional properties of soil microorganisms are different in the hotspots formed in soils with contrasting fertility remains unclear. We identified the hotspots related to different levels of Zea mays L. root architecture by zymography of leucine aminopeptidase in two soils with contrasting fertility. The hotspots localized by tiny wet-needle approach around first- and second-order roots were compared for parameters of microbial growth and enzyme kinetics. The pattern of hotspot distribution was more dispersed and the hotspot area was one order of magnitude smaller around first- versus second-order roots. The specific microbial growth rate (μ_m) and biomass of active microorganisms were soil-specific, with no difference between the hotspots and bulk soil in the fertile soil. In contrast, in the soil poor in organic matter and nutrients, 1.2-fold higher μ_m and greater growing biomass were found in the hotspots versus bulk soil. Lower enzyme affinity (1.3-2.2 times higher K_m value) of β-glucosidase and leucine aminopeptidase to the substrate was detected in the hotspots versus bulk soil, whereas only β-glucosidase showed higher potential enzyme activity (V_max) in the hotspots, being 1.7-2.1 times greater than that in bulk soil. Notably, the activity of C-acquiring enzyme, β-glucosidase positively correlated with the biomass of actively growing microorganisms. The fertile soil, on the whole, showed greater V_max and catalytic efficiency (V_max/K_m) and an approximately 2.5 times shorter substrate turnover time as compared to the poor soil. Therefore, we conclude that i) the differences in microbial growth strategy between rhizosphere hotspots and bulk soil were dependent on soil fertility; ii) affinity of hydrolytic enzyme systems to substrate was mainly modulated by plant, whereas potential enzymatic activity was driven by both plant and soil quality.

24549. 题目: Direct measurement of the in situ decomposition of microbial-derived soil organic matter
文章编号: N19110902
期刊: Soil Biology and Biochemistry
作者: Yuntao Hu, Qing Zheng, Lisa Noll, Shasha Zhang, Wolfgang Wanek
更新时间: 2019-11-09
摘要: Soil organic matter (SOM) is the dominant reservoir of terrestrial organic carbon and nitrogen, and microbial necromass represents a primary input to it. However, knowledge of stabilization mechanisms and direct measurements of the decomposition of microbial-derived SOM are lacking. Here we report a novel ¹⁵N isotope pool dilution approach using labeled amino sugars and muropeptides as tracers to quantify the decomposition of proteins and microbial cell walls, which allows to estimate in situ decomposition rates of microbial-derived SOM. Our results demonstrate that microbial cell walls are as recalcitrant as soil protein, exhibiting comparable turnover times across various ecosystems. The bacterial peptidoglycan in soils was primarily decomposed to muropeptides which can be directly utilized by microbes without being further depolymerized to free amino compounds. Moreover, bacterial peptidoglycan decomposition was correlated with soil microbial biomass while fungal chitin and soil protein decomposition were correlated with high soil pH and fine soil texture. This approach thereby provides new insights into the decomposition pathways and stabilization mechanisms of microbial-derived SOM constituents pertaining to SOM persistence.

24550. 题目: The role of ¹⁵N in tracing N dynamics in agro-ecosystems under alternative systems of tillage management: A review
文章编号: N19110901
期刊: Soil and Tillage Research
作者: Christopher J. Smith, Phillip M. Chalk
更新时间: 2019-11-09
摘要: Cultivation has led to a substantial loss of soil organic matter in the surface soil layers. The use of no-till (or zero-till) has been promoted as a practice that maximises the retention on organic residues to reverse or slow the loss of soil organic matter. However, the terms are misnomers because sowing the crop disturbs the soil. The definitions of conservation tillage systems should be used, including quantifying the mass of residue return to the system. Over 116 research papers that used ¹⁵N natural abundance, ¹⁵N depleted or ¹⁵N enriched isotopic techniques were reviewed to quantify the impact of tillage, especially no-till, on the N dynamics of cropping systems. The negative effects of no-till on crop yields at low fertiliser N applications were reported in numerous studies that had operated for short periods, with a few conducted on a long-term basis (>10-15 years). Based on the cumulative research, we concluded that no-till had little impact on ¹⁵N fertiliser recovery, or the accumulation of N released from the mineralisation of “native” soil organic matter. In most studies, the impact of no-till on N dynamics is confounded by soil water and soil temperature differences. Often the positive response to no-till was attributed to greater plant available water during the growing season. Soil moisture was the main determinant of the gross N transformation rate and the potential for N mineralisation was not different between conventional and no-till systems. The effect of no-till is restricted to the surface soil. Although differences exist in the surface soil, we were unable to confirm from the ¹⁵N studies that no-till increased organic N sequestration. Net N mineralisation of the large unlabelled soil organic N pool in the root zone dilutes the effect of increased organic N accumulation and N mineralised in the surface layers of no-till systems. Tillage systems did affect the percentage of legume N derived from the atmosphere. Nitrogen fixation was greater under no-till compared to conventional cultivation when (i) mineral N was lower, and (ii) plant available water status was better due to suppression of weeds.

24551. 题目: Soil Organic Matter and Phosphate Sorption on Natural and Synthetic Fe Oxides under in Situ Conditions
文章编号: N19110816
期刊: Environmental Science & Technology
作者: Kristof Dorau, Lydia Pohl, Christopher Just, Carmen Höschen, Kristian Ufer, Tim Mansfeldt, Carsten W. Mueller
更新时间: 2019-11-08
摘要: Iron (Fe) oxides in soils are strong sorbents for environmentally important compounds like soil organic matter (SOM) or phosphate, while sorption under field conditions is still poorly understood. We installed polyvinyl chloride plastic bars which have been coated either with synthetic Fe or manganese (Mn) oxides for 30 days in a redoximorphic soil. A previous study revealed the formation of newly formed (natural) Fe oxides along the Mn oxide coatings. This enables us to differentiate between sorption occurring onto the surfaces of synthetic versus natural Fe oxides. After removal of the bars, they were analyzed by nanoscale secondary ion mass spectrometry (NanoSIMS) to study the distribution of Fe (56Fe16O–), SOM (12C14N–), and phosphorus (31P16O2–) at the microscale. Image analysis of individual Fe oxide particles revealed a close association of Fe, SOM, and P resulting in coverage values up to 71%. Furthermore, ion ratios between sorbent (56Fe16O–) and sorbate (12C14N– and 31P16O2–) were smaller along the natural oxides when compared with those for synthetic Fe oxides. We conclude that both natural and synthetic Fe oxides rapidly sequester SOM and P (i.e., within 30 days) but that newly, natural formed Fe oxides sorbe more SOM and P than synthetic Fe oxides.

24552. 题目: Mineralogical control on the fate of continentally derived organic matter in the ocean
文章编号: N19110815
期刊: Science
作者: T. M. Blattmann, Z. Liu, Y. Zhang, Y. Zhao, N. Haghipour, D. B. Montluçon, M. Plötze, T. I. Eglinton
更新时间: 2019-11-08
摘要: First-order relationships between organic matter content and mineral surface area have been widely reported and are implicated in stabilization and long-term preservation of organic matter. However, the nature and stability of organomineral interactions and their connection with mineralogical composition have remained uncertain. In this study, we find that continentally derived organic matter of pedogenic origin is stripped from smectite mineral surfaces upon discharge, dispersal, and sedimentation in distal ocean settings. In contrast, organic matter sourced from ancient rocks that is tightly associated with mica and chlorite endures in the marine realm. These results imply that the persistence of continentally derived organic matter in ocean sediments is controlled to a first order by phyllosilicate mineralogy.

24553. 题目: Distribution character of localized iron microniche in lake sediment microzone revealed by chemical image
文章编号: N19110814
期刊: Environmental Science and Pollution Research
作者: Zhihao Wu, Shengrui Wang, Ningning Ji
更新时间: 2019-11-08
摘要: DGT (diffusive gradients in thin films) technique and LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) for heterogeneous distribution of the soluble labile iron (Fe) at submillimeter resolution in lake sediment porewater are reported. The soluble labile Fe species include ion and labile organic complexes. The chemical images in two dimensions (2D) for DGT concentration of Fe (C_DGT(Fe)) are investigated for Fe remobilization character. There are 902 C_DGT(Fe) values between 1000 and 2000 μg L⁻¹, 463 values between 2000 and 3000 μg L⁻¹, and 112 values over 3000 μg L⁻¹ in all chemical maps. Based on the linear correlation relationships between C_DGT (Fe) and total Fe (TFe), total organic carbon (TOC), acid-volatile sulfide (AVS), Eh, concentrations of the soluble reactive phosphorus (P) (SRP), and soluble labile trace metals (Zn, Cu, Pb, and Zn) in a vertical 1D profile of sediment or porewater, Fe release mechanisms are mainly due to the reductive Fe release from iron oxyhydroxides and the decomposition of organic matter in algae biomass and deep sediment layer. It can be used to explain the formation mechanisms of Fe microniches in chemical maps with heterogeneous character to a great extent. C_DGT(Fe) peak flux in the center of Fe microniche and the low C_DGT (Fe) at the edge of a microniche are due to the formation of the insoluble iron sulfide and the abundant acid-volatile sulfide (AVS) in sediment. The verified co-remobilization of the soluble labile Fe and trace metals or SRP in sediment porewater can be used to predict their simultaneous release from Fe microniches with the large C_DGT (Fe) peaks. The different kinds of Fe microniche zones and hot spots from sediment/water interface (SWI) to deep sediment correspond to the formation mechanisms of microniches mentioned above. Moreover, some narrow Fe microniche zones with the large C_DGT (Fe) across chemical maps are due to the desorption of Fe(II) from the freshly formed oxide on Myriophyllum verticiilatur roots, which are located at sites of microniche zones.

24554. 题目: TEMPERATURE SENSITIVITY OF DECOMPOSITION OF SOIL ORGANIC MATTER FRACTIONS INCREASES WITH THEIR TURNOVER TIME
文章编号: N19110813
期刊: Land Degradation & Development
作者: Yufu Jia, Yakov Kuzyakov, Guoan Wang, Wenbing Tan, Biao Zhu, Xiajuan Feng
更新时间: 2019-11-08
摘要: Soil organic carbon (SOC) is an indicator of soil fertility. Global warming accelerates SOC decomposition, consequently, resulting in land degradation. Characterization of the response of SOC decomposition to temperature is important for predicting land development. A simulation model based on temperature sensitivity (Q₁₀) of SOC decomposition has been used to predict SOC response to climate warming. However, uncertain Q₁₀ leads to substantial uncertainties in the predictions. A major uncertainty comes from the interference of rainfall. To minimize this interference, we sampled surface (0‐5cm) soils along an isohyet across a temperature gradient in the Qinghai‐Tibet Plateau. The Q₁₀ of bulk soil and the four soil fractions: Light fraction (LightF), particulate organic matter (POM), hydrolyzable fraction (HydrolysF), and recalcitrant fraction (RecalcitF), was studied by ¹⁴C dating. Turnover time (TT) follows the order: LightF < POM < bulk soil < HydrolysF < RecalcitF. The Q₁₀ follows the order: LightF (1.0) = POM (1.0) < HydrolysF (3.63) < bulk soil (5.93) < RecalcitF (7.46). This indicates that stable fractions are much more sensitive to temperature than labile fractions. We also suggest that protection mechanisms rather than molecular composition regulate SOC turnover. A new concept ‘protection sensitivity’ of SOC decomposition was proposed. Protection sensitivity relates to protection type and primarily controls Q₁₀ variation. A simulation model based on the Q₁₀ of individual fractions predicted SOC change and land development in the Qinghai‐Tibet Plateau in the next 100 years much effectively as compared to simulations based on one‐pool model (Q₁₀ = 2) or bulk soil (Q₁₀ = 5.93).

24555. 题目: A Global Analysis on the Impact of No‐Tillage on Soil Physical Condition and Organic Carbon Content, and Plant Root Response
文章编号: N19110812
期刊: Land Degradation & Development
作者: Surajit Mondal, Debashis Chakraborty, K.K. Bandyopadhyay, Pramila Aggarwal, D.S. Rana
更新时间: 2019-11-08
摘要: Food security involves the sustainable utilization of soil and land resources. No‐tillage (NT) practice is a proponent of better resource utilization, to improve soil physical condition, and a potential sink to atmospheric carbon. However, the impact varies across climates, over the NT history, cropping systems and soil depths. A meta‐analysis was performed, based on 4131 paired data from 522 studies spread globally, to evaluate the effect of NT in comparison to conventional tillage (CT), on soil physical condition (bulk density, BD; mean weight diameter of aggregates, MWD; field capacity water content, FC; and steady‐state infiltration rate, IR), soil organic carbon (SOC) content, and the root response (root length density, RLD). No‐tillage significantly improved MWD and FC at surface and sub‐surface layers by 19‐58% and 6‐16% respectively, and resulted in no change in BD in either of the layers, but IR increased by 66%. Surface 0‐5 and 5‐10 cm layers had significantly higher SOC content under NT, while in other layers, the SOC content either reduced or did not change, resulting in a small and insignificant variation in the SOC stock (~1.1%) in favour of NT. The RLD improved by ~35% in NT only at 0‐ to 5‐cm soil depth. Effect of climate, soil type or cropping system could not be broadly recognized, but the impact of NT certainly increased over time. Improvements in soil aggregation and hydraulic properties are highly convincing with the adoption of NT, and therefore this practice leads to the better and sustainable use of soil resources.

24556. 题目: Effect of forest land use change on carbohydrates, physical soil quality and carbon stocks in Moroccan cedar area
文章编号: N19110811
期刊: Journal of Environmental Management
作者: Hafida Zaher, Mohamed Sabir, Hassan Benjelloun, Hounzandji Paul-Igor
更新时间: 2019-11-08
摘要: The present work was conducted to evaluate the carbon storage potential of Moroccan cedar forest and its vulnerability to transformations through deforestation and overgrazing. The present study took place in the Middle Atlas where is the most beautiful of Moroccan cedar forest (Cedrus atlantica). We considered three levels of degradation (Natural cedar, degraded cedar and cleared area). For each land use, we estimated carbon stocks in four reservoirs, i.e., aboveground biomass (trees, shrubs and herbaceous plants), belowground biomass (roots), necromass (litter and deadwood) and the soil. Various physico-biochemical characteristics (structural stability, bulk density, soil organic carbon and carbohydrates (neutral and uronic sugars)) were also evaluated. Carbon stocks were 395.37 Mg ha⁻¹ for the natural cedar and 76.05 Mg ha⁻¹ for the cleared area. Analysis of the ecosystem carbon stock distribution revealed that soil was the largest reservoir. The soil carbon stock varies from 46.4% to 93.5%, that of the biomass (aboveground and belowground) fluctuate between 4.3% and 52.7% and in the necromass it is between 0.8 and 2.2%. The conversion of natural forest into cleared area resulted in a deterioration of the soil physical quality (decrease of the percentage of water-stable aggregate by 36% and increase of bulk density by 57%). Also, natural forests have 25% and 50% more neutral sugars and uronic sugars respectively than the cleared area. The correlations established between carbohydrates and carbon stocks of the different reservoirs considered showed that the increase in neutral sugars is more explained by the aboveground biomass (R² = 79%, P = 0.0013) and necromass (R² = 85%, P = 0.0004). Otherwise, the soil carbon stock explained the most increase in uronic sugars (R² = 99%, P = 0.0001). Neutral sugar can be an indicator of soil physical quality. Neutral sugars were responsible for 85% of the highly significant increase in soil structural stability and over 79% of the highly significant decrease in bulk density. Moreover, uronic sugars appear to be a good indicator of the richness in organic carbon of soils sampled since the increase of these sugars justified more than 90% of the increase in the soil organic carbon content.
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24557. 题目: New insights into CO₂ sorption on biochar/Fe oxyhydroxide composites: Kinetics, mechanisms, and in situ characterization
文章编号: N19110810
期刊: Chemical Engineering Journal
作者: Xiaoyun Xu, Zibo Xu, Bin Gao, Ling Zhao, Yulin Zheng, Jinsheng Huang, Daniel C.W. Tsang, Yong Sik Ok, Xinde Cao
更新时间: 2019-11-08
摘要: Despite its importance, chemical process has been often overlooked in CO₂ sorption on carbon based oxyhydroxide composites. In this study, pristine and ball-milled biochar/Fe oxyhydroxide composites were fabricated for CO₂ sorption at 25 °C. The composites, particularly the ones with high Fe content, were effective sorbents for CO₂ with the capacities of up to 160 mg g⁻¹. The primary mechanism of CO₂ sorption on biochar composites with low Fe content was physical adsorption. When the Fe content increased, biochar/Fe oxyhydroxide composites showed enhanced CO₂ sorption capacities, but the sorption kinetics became slower. This is because the governing CO₂ sorption mechanism was shifted from physical adsorption to chemical reaction between Fe oxyhydroxides and CO₂. The formed (oxy)hydroxycarbonate could be decomposed at a temperature between 50 and 125 °C. Furthermore, ball milling could speed up CO₂ mineralization rate on the composites, especially for those with high Fe content, to favor the relative significance of chemical sorption. Both physical and chemical CO₂ sorption mechanisms were verified by different characterization methods including in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Findings of this study not only demonstrate the importance of chemical sorption, but also provide new insights on CO₂ capture by low-cost and environmentally benign biochar/Fe oxyhydroxide composites. Besides, the low regeneration temperature of chemically-sorbed CO₂ gives biochar/Fe oxyhydroxide composite a competitive edge over other CO₂ sorbents, which often need a high regeneration temperature or are not regenerable.
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24558. 题目: Interfacial oxygen nanobubbles reduce methylmercury production ability of sediments in eutrophic waters
文章编号: N19110809
期刊: Ecotoxicology and Environmental Safety
作者: Xiaonan Ji, Chengbin Liu, Gang Pan
更新时间: 2019-11-08
摘要: Eutrophication can induce hypoxia/anoxia and rich organic matter at the sediment-water interface in surface waters. When eutrophic waters are impacted with mercury (Hg) pollution, methylmercury (MeHg) production ability (MPA) of surface sediment would increase and more MeHg might be produced. To tackle this risk, this study firstly collected samples of surface sediment and overlying water from a typical eutrophic lake—Taihu Lake. Then from a sediment-water simulation system, we demonstrated that eutrophic waters were able to methylate Hg spontaneously, and that sediment is the major Hg sink in the system. After the addition of HgCl₂ solution (approximately 1 mg L⁻¹ in the slurry), MeHg concentrations in the sediment increased by 11.7 times after 48 h. The subsequent column experiments proved that O₂ nanobubbles could significantly decrease the MPA of surface sediment, by up to 48%. Furthermore, we found that O₂ nanobubbles could remediate anoxia mainly by increasing dissolved oxygen (from 0 to 2.1 mg L⁻¹), oxidation-reduction potentials (by 37% on average), and sulfate (by 31% on average) in the overlying water. In addition, O₂ nanobubbles could also help decrease organic matter concentration, as was revealed by the decline of dissolved organic carbon in the overlying water (by up to 57%) and total organic carbon in surface sediment (by up to 37%). The remediation of anoxia and reduction of organic matter could contribute to the decrease of hgcA gene abundance (by up to 86%), and thus result in the reduction of MPA after the addition of O₂ nanobubbles. This study revealed the risk of MeHg production in case Hg pollution occurs in eutrophic waters and proposed a feasible solution for MeHg remediation.
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24559. 题目: Quantification of different silicon fractions in broadleaf and conifer forests of northern China and consequent implications for biogeochemical Si cycling
文章编号: N19110808
期刊: Geoderma
作者: Xiaomin Yang, Zhaoliang Song, Changxun Yu, Fan Ding
更新时间: 2019-11-08
摘要: The terrestrial biogeochemical silicon (Si) cycle significantly contributes to maintaining the functions and sustainability of terrestrial ecosystems. Over the short term, the biogeochemical Si cycle can be strongly influenced by dissolved Si, organic bound Si, Si adsorbed to pedogenic oxides/hydroxides, and biogenic and pedogenic amorphous Si. However, quantitative studies about these relatively soluble Si fractions are rare. In this study, we quantified different Si fractions in the 0–10 cm, 10–20 cm, 20–30 cm, 30–40 cm and 40–50 cm soil layers of broadleaf forests (Betula forest and Quercus forest) and conifer forests (Larix forest and Pinus forest) in northern China using a sequential chemical extraction scheme optimized for these Si fractions. The results showed that the total Si (Si_t) in the soil layers consisted of 97.7–98.5% crystalline Si (Si_cry) and 1.5–2.3% non-crystalline Si (Si_noncry) fractions. Within the Si_noncry fraction, the proportions of dissolved Si (Si_dis), organic matter bound Si (Si_org), pedogenic oxides/hydroxides chemisorbed Si (Si_sorb), and amorphous Si (Si_amor) were 3.4–6.7%, 5.5–8.9%, 6.3–8.5%, and 77.7–84.8%, respectively. Although the Si_dis fraction was the least abundant component, it is at the center of the interconversion processes among the different Si_noncry fractions. The Si_amor fraction was the largest component of Si_noncry and was composed of 37.7–71.9% biogenic amorphous Si (Si_bio-amor) and 28.1–62.3% pedogenic amorphous Si (Si_ped-amor). Our study indicated that i) Si_ped-amor fraction is more easily influenced by soil pH comparing to Si_bio-amor fraction; ii) the Si_bio-amor fraction contributes more to the biogeochemical Si cycle in broadleaf forests, whereas the Si_ped-amor fraction contributes more in conifer forests; and iii) soil pH, soil organic matter, and plant community differences can influence the vertical distribution of the different Si_noncry fractions and thus affect the multiple transformation processes among these Si fractions in studied forests.

24560. 题目: Land‐use change with pasture and short‐rotation eucalypts impacts the soil C emissions and organic C stocks in the Cerrado biome
文章编号: N19110807
期刊: Land Degradation & Development
作者: Rafael da Silva Teixeira, Ricardo Cardoso Fialho, Daniela Cristina Costa, Rodrigo Nogueira de Sousa, Rafael Silva Santos, Ana Paula Mendes Teixeira, Thalles Guimarães Reis, Ivo Ribeiro da Silva
更新时间: 2019-11-08
摘要: The expansion of short‐rotation eucalypt plantations in low soil organic matter (SOM) sandy soils may offers an alternative to improve soil C sequestration. The goal of this study was to estimate the changes in C stocks and emissions in different SOM fractions following conversion of the native Cerrado to pasture and then to eucalypt plantation. Therefore, we studied soils under native Cerrado, planted pasture (cultivated for 34‐years following the clearing of the Cerrado) and eucalypt plantation (4‐years). The C and N stocks in particulate organic matter (POM) and mineral‐associated organic matter (MAOM) were determined 4‐years after eucalypt planting. Soil CO₂‐C, CH₄‐C fluxes and CO₂‐C concentrations in soil profile were measured in different seasons over four years. Variation in the natural abundance of ¹³C was used to partition the SOM‐C. The soil CO₂‐C and CH₄‐C fluxes were influenced by soil surface moisture (r = 0.185^o and r = 0.430^**, respectively), while only the soil CH₄‐C fluxes correlated with soil surface temperature (r = 0.355^**). The highest soil CO₂‐C flux in soil under eucalypt occurred after 4‐years of eucalypt planting (2.5 kg ha^‐1 h^‐1, approximately 70%). The pasture soil acted as a CH₄‐C source to the atmosphere. The pasture MAOM‐C losses in the 0.0‐1.0‐m soil layers were not compensated by the new eucalypt C inputs (MAOM‐C lost ~ 9.6 Mg ha^‐1). In summary, the recent worldwide expansion of short‐rotation eucalypt plantations should be carefully considered, particularly under pasture degraded soil sandy soils, since land‐uses able to increase SOM are priorities.