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25801. 题目: Biochar-amendment-reduced Cotransport of Graphene Oxide Nanoparticles and Dimethyl Phthalate in Saturated Porous Media
文章编号: N19121406
期刊: Science of The Total Environment
作者: Lun Lu, Baoliang Chen
更新时间: 2019-12-14
摘要: Production and application of graphene oxide (GO) and biochar for water and soil treatment is steadily growing, driving the necessity to understand the cotransport behavior of contaminants and GO nanoparticles in porous media and the possible effect of biochar to reduce their cotransport. The cotransport of GO nanoparticles and dimethyl phthalate (DMP) as a model in a sand column and biochar-amended sand column (biochar column) was compared. The transport of DMP in the test columns was independent of the solution ionic strength (IS), while the transport of GO decreased with increased IS due to the enhanced aggregation of GO nanoparticles. The sand column had no retention capacity (<1%) for DMP, while the biochar column had significantly increased retention of DMP (100%). The retention of GO in the biochar column was significantly higher than that of the sand column because biochar can improve the roughness of the media and adsorb GO via π-π interactions. Under low-IS conditions, GO facilitated DMP transport by providing vehicles and adsorption sites (vehicle effect). Due to reversible adsorption-desorption, the adsorbed DMP on GO could be released, resulting in tailing during the flushing phase. The vehicle effect of GO on DMP transport was significantly weakened in the biochar columns, and DMP tailing during the flushing phase was not observed in the biochar columns, which was attributed to the strong retention/adsorption of the biochar columns for both GO and DMP, higher affinity of DMP on biochar than GO, and desorption hysteresis of DMP on biochar. These observations are important for evaluating the potential role of biochar in soil and water remediation, as well as mitigating the health risks of GO and organic contaminants in the environment.
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25802. 题目: Effect of amendment of biochar supplemented with Si on Cd mobility and rice uptake over three rice growing seasons in an acidic Cd-tainted paddy from central South China
文章编号: N19121405
期刊: Science of The Total Environment
作者: Fengfeng Sui, Jingbo Wang, Jing Zuo, Stephen Joseph, Paul Munroe, Marios Drosos, Lianqing Li, Genxing Pan
更新时间: 2019-12-14
摘要: To examine the effect of rice straw biochar and the synergism with silicon on Cd immobilization, a Cd-contaminated acidic sandy loam paddy, polluted from emissions from industrial activity, was chosen in central South China. A field trial was conducted over three rice growing seasons during 2016–2017. Rice straw biochar (BR), produced by the pyrolysis of rice straw pellets at 450 °C, was amended at 10 t/ha (BR1), 20 t/ha (BR2), and supplemented with 0.75 t/ha sodium silicate (SS) at 10 t/ha, (BR1 + SS) and 20 t/ha (BR2 + SS), compared to the control without biochar and sodium silicate (BR0). BR supplemented with Si enhanced Cd soil immobilization and decreased Cd accumulation in rice plant within three rice seasons. Compared to BR0, BR + SS reduced Cd concentrations in grains by 19.5–73.7%, higher than that of 8.6–50.2% following BR. Cd bio-concentration factor of the root was reduced by an average of 54.6% from BR + SS and by 19.0% from BR, compared to BR0 in last two rice seasons. BR + SS significantly increased soil pH and available Si, and soil CaCl₂-Cd was negatively related to soil available Si (p < 0.05). The synergistic effect of BR and Si induced liming effect and co-precipitation of Cd with Si compounds during the aging process of biochar. Thus, we suggest that an alkaline silicon supplementation is used as an amendment to BR, which could be used as a strategic approach for tackling Cd contamination in South China rice paddies.
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25803. 题目: Water extractable organic matter and iron in relation to land use and seasonal changes
文章编号: N19121404
期刊: Science of The Total Environment
作者: Susan Praise, Hiroaki Ito, Takayuki Sakuraba, Dung Viet Pham, Toru Watanabe
更新时间: 2019-12-14
摘要: The soil carbon pool is an essential part of the global carbon cycle although it is sensitive to climatic changes and the local environment. Terrestrial areas are important sources of organic matter for aquatic ecosystems and the fluctuation of different soil minerals and elements is largely influenced by land use and season changes. We studied water-extractable organic matter (WEOM) properties including iron (Fe), water extractable organic carbon (WEOC) and spectral characteristics from forests and arable soils to evaluate the effects of land use and seasonal change on WEOM and Fe in terrestrial areas. We collected soil samples randomly from arable land (AR), broadleaf (BL) and aged needle leaf forests (NL) and extracted WEOM for analysis using rainwater. Results of WEOC and Fe showed revealed similar trend seasonally and were higher in forest sample than in AR. WEOC was high in the upper layer while Fe was independent of the depth and higher in AR. On the other hand, specific ultra-violet absorbance at 254 nm (SUVA₂₅₄) and a proxy for aromaticity significantly varied with both land use and season and was on average two times higher in arable land than forests during spring and summer. Humic-like components significantly varied between the studied sites seasonally while tyrosine-like protein-like component was affected by season only. The relative abundance of both humic-like and tryptophan-like components were significantly affected by land use while [Fe]: [WEOC] ratio was also high in arable land and negatively correlated with humic-like components in forest sites. As observed from ratio and Fe oxidation rate constant, summer presented ideal conditions for WEOM interactions. The synchronized seasonal WEOC and Fe changes indicate an enhancement of Fe mobility by DOM whereas the differences observed between sites especially from the high humic- and protein-like components in NL and BL reflects the effect of land use.
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25804. 题目: Seasonal variation and ecological risk assessment of dissolved organic matter in a peri-urban critical zone observatory watershed
文章编号: N19121403
期刊: Science of The Total Environment
作者: Jianfeng Tang, Wendong Wang, Lei Yang, Qianlinglin Qiu, Meixia Lin, Changli Cao, Xinhu Li
更新时间: 2019-12-14
摘要: Peri-urban ecosystems are among the most intensive areas in terms of competition between different ecosystem components. Dissolved organic matter (DOM) plays a significant role in aquatic carbon cycling. The chemical composition of DOM and associated potential ecological risks in peri-urban aquatic ecosystems are poorly understood. Herein, we used fluorescence excitation-emission matrix and parallel factor analysis (EEM-PARAFAC) to characterize DOM in a peri-urban critical zone observatory watershed in Eastern China. According to the theory of natural disaster risk formation, we calculated the ecological risk of DOM in the peri-urban watershed. Seasonal variation in DOM concentrations was observed, whereas fluorescent DOM concentrations were site-specific across four sub-watersheds. The analysis of DOM absorption properties revealed the presence of DOM components with high aromatic content and large molecular weight in the watershed. Four fluorescent components (two humic-like and two protein-like substances) were identified using the PARAFAC model. Spatial distribution analysis showed that DOM quality was mainly influenced by human activities, and the proportion of protein-like substance (C3) was strongly correlated with anthropogenic parameters. The distribution of optical indices indicated diverse sources of DOM in the watershed. Ecological risk related to DOM was greater in the dry season than the wet season. There was a slight risk in most areas, with an extreme risk in areas experiencing the most intensive human disturbance, which were also extremely or heavily vulnerable. The results emphasize the strong influence of human disturbance on the ecological risk of DOM in peri-urban aquatic ecosystems. Our study provides useful information for ecological risk assessment of DOM that is difficult to obtain using traditional chemical analysis.
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25805. 题目: Divergent responses of soil organic carbon accumulation to 14 years of nitrogen addition in two typical subtropical forests
文章编号: N19121402
期刊: Science of The Total Environment
作者: Mengxiao Yu, Ying-Ping Wang, Jeffrey A. Baldock, Jun Jiang, Jiangming Mo, Gouyi Zhou, Junhua Yan
更新时间: 2019-12-14
摘要: Developing an understanding of the response of soil organic carbon (SOC) to N addition is critical to quantify and predict the terrestrial carbon uptake under increasing N deposition in the future. However, results from field studies on the response of SOC content and composition to N addition are highly variable across different ecosystems. The interpretation of SOC responses to N addition are often complicated by the differences in climate, soil substrate and other factors. To address this question, we measured SOC and its components in adjacent broadleaved and coniferous subtropical forests after 14 years of N addition. SOC in the top 50 cm increased by 2.1 kg m⁻², 1.8 kg m⁻² and 1.2 kg m⁻² for low, medium and high rates of N addition in the broadleaved forest, but did not change significantly in the coniferous forest. Increased SOC in the broadleaved forest was contributed by the significant increases in particulate organic carbon (POC), humus organic carbon (HOC) in the 0–10 cm and 30–50 cm soil layers and resistant organic carbon (ROC) in the 0–10 cm soil layer. ¹³C nuclear magnetic resonance (NMR) spectra of coarse SOC revealed a decrease in easily decomposed carbon (C) and a shift in recalcitrant C. The increased SOC accumulation in the broadleaved forest was largely driven by altered rates of organic matter decomposition, rather than C inputs to soil. Land-history and low nutrient availability may have contributed to the lack of significant impact of N addition on SOC in the coniferous forest. Our results suggested the different controls of SOC accumulation and less sensitivity of SOC chemical composition at the molecular level to N addition in the two subtropical forest soils.
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25806. 题目: Long-term decomposition captures key steps in microbial breakdown of seagrass litter
文章编号: N19121401
期刊: Science of The Total Environment
作者: Stacey M. Trevathan-Tackett, Thomas C. Jeffries, Peter I. Macreadie, Bojana Manojlovic, Peter Ralph
更新时间: 2019-12-14
摘要: Seagrass biomass represents an important source of organic carbon that can contribute to long-term sediment carbon stocks in coastal ecosystems. There is little empirical data on the long-term microbial decomposition of seagrass detritus, despite this process being one of the key drivers of carbon-cycling in coastal ecosystems, that is, it influences the amount and quality of carbon available for sequestration. Here, our goal was to investigate how litter quality (leaf vs. rhizome/root) and the microbial communities involved in organic matter remineralisation shift over a 2-year field decomposition study north of Sydney, Australia using the temperate seagrass Zostera muelleri. The sites varied in bulk sediment characteristics and the sediment-associated microbial communities, but these variables overall had little influence on long-term seagrass decomposition rates or seagrass-associated microbiomes. The results showed a clear succession of bacterial and archaeal communities for both tissues types from r-strategists such as α- and γ-proteobacteria to K-strategies, including δ-proteobacteria, Bacteroidia and Spirochaetes. We used a new mathematical model to capture how decay rates varied over time and found that two decomposition events occurred for some seagrass leaf samples, possibly due to exudate input from living seagrass roots growing into the litter bag. The new model also indicated that conventional single exponential models overestimate long-term decay rates, and we detected for the first time the refractory, or stable, phase of decomposition for rhizome/root biomass. The stable phase began at approximately 20% mass remaining and after 600 days, and the persistence of rhizome/root biomass was attributed to the anoxic conditions and the preservation of refractory organic matter. While we predict that rhizome/root biomass will contribute more to the long-term sediment carbon stocks, the preservation of leaf carbon may be enhanced at locations were sedimentation is high and burial in anoxic conditions is rapid and constant.
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25807. 题目: Variations in soil organic carbon decompositions of different land use patterns on the tableland of Loess Plateau
文章编号: N19121306
期刊: Environmental Science and Pollution Research
作者: Mengyun Liu, Mengmeng Liu, Peng Li, Jinghan Yang, Jing Wang, Qingrui Chang
更新时间: 2019-12-13
摘要: Land use patterns are one of the critical factors affecting soil carbon sequestration or decomposition and greenhouse gas emissions. The accurate evaluation of its change is particularly crucial for the carbon cycle of the terrestrial ecosystem and global climate change. This paper examined the dynamic soil respiration by means of the indoor airtight culture method and static box-gas chromatography under the land uses of the farmland, natural grassland, shrub forestland, arbor and shrub mixed forestland, and arbor forestland on the tableland of Loess Plateau. The results showed that soil organic carbon mineralization and soil respiration rate were influenced by the land use type. (1) The content and rate of soil mineralizable carbon in grassland were significantly higher than that in forestland and farmland, and that in forestland significantly higher than that in the farmland (P < 0.05). The trend of organic carbon mineralization was rapid in the initial stage of culture (by the rate of 30.02~238.56 mg kg⁻¹ h⁻¹ in the first 0.5 h) and slowed down in the later stage (by the rate of 1.07~1.95 mg kg⁻¹ h⁻¹ in 1575 h). In the soil of grassland, the accumulation of mineralizable organic carbon in the 0–5-cm layer was 1.20~1.64 times that in the soil of forestland and 1.82 times that of farmland. Compared with the 0–5-cm soil layer, there were decreases in the 5–20-cm soil layer under all land uses, with a decline of up to 48% in farmland. (2) The soil carbon mineralization potential of different land use types ranged from 0.81 to 2.70 mg kg⁻¹, that of grassland was significantly higher than that of farmland (P < 0.05), and the soil organic carbon decomposition rate constant (k) under shrub forestland was significantly higher than that under other land use types (P < 0.05). The highest organic carbon mineralization capacity and the lowest sequestration were in the soil of farmland, while that in grassland had the lowest organic carbon mineralization capacity and the highest sequestration. (3) The cumulative amount of soil respiration was highest under the natural grassland, followed by the shrub forestland, and lowest under the farmland. The soil respiration rate was positively correlated with soil temperature, and its correlation with soil water content was positive in the wet season (May through October) and negative in the dry season (November through April in the following year). (4) The soil respiration rate showed obvious seasonal differences. After the conversion of farmland to forestland, it would be rising in the content of soil organic carbon and labile organic carbon, and be going down in the temperature sensitivity (Q₁₀). In summary, by converting farmland to forestland or grassland, the sequestration of soil organic carbon had greatly been enhanced, and the possibility of soil greenhouse gas emissions had reduced on the tableland of Loess Plateau.

25808. 题目: Spatial variability of sediment methane production and methanogen communities within a eutrophic reservoir: Importance of organic matter source and quantity
文章编号: N19121305
期刊: Limnology and Oceanography
作者: Megan E. Berberich, Jake J. Beaulieu, Trinity L. Hamilton, Sarah Waldo, Ishi Buffam
更新时间: 2019-12-13
摘要: Freshwater reservoirs are an important source of the greenhouse gas methane (CH₄) to the atmosphere, but global emission estimates are poorly constrained (13.3–52.5 Tg C yr⁻¹), partially due to extreme spatial variability in emission rates within and among reservoirs. Spatial heterogeneity in the availability of organic matter (OM) for biological CH₄ production by methanogenic archaea may be an important contributor to this variation. To investigate this, we measured sediment CH₄ potential production rates, OM source and quantity, and methanogen community composition at 15 sites within a eutrophic reservoir in Ohio, USA. CH₄ production rates were highest in the shallow riverine inlet zone of the reservoir, even when rates were normalized to OM quantity, indicating that OM was more readily utilized by methanogens in the riverine zone than in the transitional or lacustrine zones. Sediment stable isotopes and C:N indicated a greater proportion of terrestrial OM in the particulate sediment of this zone. Methanogens were present at all sites, but the riverine zone contained a higher relative abundance of methanogens capable of acetoclastic and methylotrophic methanogenesis, likely reflecting differences in decomposition processes or OM quality. While we found that methane potential production rates were negatively correlated with autochthonous carbon in particulate sediment OM, rates were positively correlated with indicators of autochthonous carbon in the porewater dissolved OM. It is likely that both dissolved and particulate sediment OM affect CH₄ production rates, and that both terrestrial and aquatic OM sources are important in the riverine methane production hot spot.

25809. 题目: Variations in stable carbon and nitrogen isotopes of particulate organic matter in surface waters of water-receiving area of Eastern Route of South-to-North Water Transfer Project, China
文章编号: N19121304
期刊: Environmental Science and Pollution Research
作者: Wei Hou, Shaohua Sun, Mingquan Wang, Binhe Gu, Xiang Li, Chengxiao Zhang, Ruibao Jia
更新时间: 2019-12-13
摘要: The purpose of this study was to assess the water quality and variations in stable carbon and nitrogen isotopes of particulate organic matter (δ¹³C_POM and δ¹⁵N_POM), as well as to evaluate the sources of carbon and nitrogen that contribute to the POM pools in lakes and reservoirs located in the water-receiving area of the Eastern Route of South-to-North Water Transfer Project (SNWTP) in Northern China. During each season from October 2013 to July 2014, samples of POM from 14 lakes and reservoirs in Northern China were collected. The lakes and reservoirs were meso-eutrophic with considerably high brackish ions (SO₄²⁻, 173 mg/L; Cl⁻, 296 mg/L) in Yangtze River lake, and high total nitrogen: total phosphorus ratio (averaged with 772) or dissolved inorganic nitrogen: soluble reactive phosphorus molar ratios (averaged with 1077) in mountainous reservoirs. The δ¹³C_POM, δ¹⁵N_POM, carbon to nitrogen (C/N) ratios showed significant seasonal variation, with ranges of − 32.5 to − 17.4‰, − 3.6 to 13.5‰, and 5.1–13.2, respectively, while they were hard to be distinguished among types of water sources. Principal component analysis (PCA) indicated that brackish ions, nutrients, and their molar ratios were the main factors influencing variations in δ¹³C_POM and δ¹⁵N_POM. δ¹³C_POM and C/N ratios suggested autochthonous primary production mainly contributed to POM during from April to October, while exogenous organic matter might mainly contribute these carbon pools in January. The low values of δ¹⁵N_POM (< 0‰) and negative correlation between δ¹⁵N_POM and TN suggested discharge of agricultural waste water (e.g., fertilizers, irrigation tailwater) in Bailanghe, Xinan, and Taihe Reservoir during the fertilization season, while higher values indicated domestic sewage input to waterbodies (e.g., Mishan, Gengjing, Donghai Reservoir). Our results suggested that the aquatic ecosystem in water-receiving area of SNWTP would be potentially affected by the inter-basin water diversion, and thus, ecosystem-based strategies were also presented accordingly.

25810. 题目: Influence of humic acid and its different molecular weight fractions on sedimentation of nanoscale zero-valent iron
文章编号: N19121303
期刊: Environmental Science and Pollution Research
作者: Yanan Wu, Haoran Dong, Lin Tang, Long Li, Yaoyao Wang, Qin Ning, Bin Wang, Guangming Zeng
更新时间: 2019-12-13
摘要: The effects of humic acid (HA) and its different molecular weight (MW) fractions on the sedimentation of nanoscale zero-valent iron (NZVI) in the absence and presence of cations (i.e., Na⁺/Mg²⁺/Ca²⁺) were investigated. Ultrafiltration (UF) was used as the method of fractionation to obtain four different MW fractions (separated by ultrafiltration membranes of 10 kDa, 50 kDa, and 100 kDa). Differing sedimentation behavior was observed for NZVI with different MW fractions of HA. Generally, the degree of settling of NZVI particles in the presence of high MW fractions of HA was lower than that of low MW fractions of HA and that without HA. The results were mainly attributed to the steric stabilization provided by the high MW fractions of HA. The presence of Na⁺/Mg²⁺/Ca²⁺ alone had insignificant influence on the settling of NZVI, but both Mg²⁺ and Ca²⁺ exerted an obvious influence on the settling of NZVI in the co-presence of HA. The settling behavior of NZVI was further examined in the co-presence of different MW fractions of HA and Ca²⁺. The co-presence of low MW HA fractions and Ca²⁺ led to a lower settling of NZVI. This might be due to the formation of a layer of HA-Ca²⁺ complex on the particle surface, providing stronger steric stabilization. Nevertheless, in the co-presence of high MW HA fractions and Ca²⁺, the settling of NZVI was initially reduced but accelerated with time, which might be due to the gradual aggregation of NZVI with time resulted from the bridging effect of HA-Ca²⁺ complex.

25811. 题目: Compositional dynamics of suspended sediment in the Rhine River: sources and controls
文章编号: N19121302
期刊: Journal of Soils and Sediments
作者: Marcel van der Perk, Alvaro Espinoza Vilches
更新时间: 2019-12-13
摘要: Purpose: Information on the geochemical composition of suspended sediments in rivers is crucial to identify sediment source type or area. In large river basins, however, the relation between sediment composition and its controlling factors is often obscured. This study aims to assess and improve the conceptual understanding on the factors and mechanisms that control the composition of suspended sediments in the River Rhine, one of the large European rivers, and to identify the dominant source types of elements. Materials and methods: We performed log-linear regression analysis and principal component analysis (PCA) on bi-weekly monitoring data of suspended sediment composition, supplemented with daily measurements of suspended sediment concentrations (SSC) and discharge at the Lobith monitoring station near the German-Dutch border for the period 2011–2016. Results and discussion: The statistical analyses show a consistent grouping of elements that display contrasting temporal variation or different responses to increased discharge. The contrasting behaviour also becomes manifest in the results from the PCA. A first component that explains about the half of the total variance in the entire dataset reflects the variation in clay content in the suspended sediment. A second component reflects anthropogenic pollution and explains about a quarter of the total variance. A third component probably reflects variation in sediment provenance. Conclusions: The majority of the temporal variation in suspended sediment composition can be attributed to variations in grain size (clay content), organic matter content, and anthropogenic pollution. Only a minority of the variation can be attributed to variations in the contributions from different upstream source areas. This variation represented by the third and higher components from the PCA can potentially be used for sediment provenance analysis.

25812. 题目: Impacts of anthropogenic forcing on source variability of sedimentary organic matter in the Yellow River estuary over the past 60 years
文章编号: N19121301
期刊: Marine Pollution Bulletin
作者: Rui Xiao, Xiuning Wu, Jinzhou Du, Bing Deng, Lei Xing
更新时间: 2019-12-13
摘要: To evaluate changes in the source of sedimentary organic matter (OM) in the Yellow River estuary, a sediment core collected in eastern Laizhou Bay was analyzed for total organic carbon (TOC), stable carbon isotopes of TOC, and biomarkers. The results showed a decreasing trend in terrestrial OM (TOM), but an increasing trend in marine OM (MOM) over the past 60 years. TOM was subdivided into soil OM and plant OM in a three end-member mixing model. The soil OM gradually decreased over the past 60 years, with a significant decline since the 1980s, while the plant OM gradually increased. This reveals that the reduction in TOM was caused mainly by the decreased input of soil OM. The reduced TOM contribution can be attributed primarily to dam construction and a decline in precipitation, whereas the elevated MOM contribution was caused by enhanced marine productivity driven by a rise in nutrient inputs.

25813. 题目: Fundamental drivers of dissolved organic matter composition across an Arctic effective precipitation gradient
文章编号: N19121212
期刊: Limnology and Oceanography
作者: Anne M. Kellerman, Ana Arellano, David C. Podgorski, Ellen E. Martin, Jonathan B. Martin, Kelly M. Deuerling, Thomas S. Bianchi, Robert G. M. Spencer
更新时间: 2019-12-12
摘要: The standard model for aquatic ecosystems is to link hydrologic connectivity to dissolved organic carbon (DOC) concentration and dissolved organic matter (DOM) composition and, ultimately, reactivity. Studies across effective precipitation gradients have been suggested as models for predicting how carbon cycling will change in Arctic aquatic ecosystems with projected drying (i.e., reduced hydrologic connectivity). To evaluate links between DOM dynamics and hydrologic connectivity, 41 stream samples from Greenland were analyzed across an effective precipitation gradient for DOM optical properties and elemental composition using ultrahigh‐resolution mass spectrometry. Sites with negative effective precipitation and decreased hydrologic connectivity exhibited elevated specific conductivity (SpC) and DOC concentrations as well as DOM composition indicative of decreased hydrologic connectivity, for example, lower aromaticity, assessed using carbon‐specific UV absorbance at 254 nm, decreased relative abundances of polyphenolic and condensed aromatic compounds, and increased relative abundances of highly unsaturated and phenolic compounds. Allochthonous inputs decreased as the summer progressed as exhibited by decreases in aromatic compounds. A decrease in molecular richness and N‐containing compounds coincided with the decrease in allochthonous inputs. DOC concentrations increased over the summer but more slowly than SpC, suggesting degradation processes outweighed combined evapoconcentration and production. The patterns in DOM composition suggest evapoconcentration and photodegradation are dominant controls. However, when hydrologic connectivity was high, regardless of effective precipitation, DOM reflected allochthonous sources such as snowmelt‐fed wetlands. These results highlight the challenges of modeling carbon cycling in aquatic ecosystems across effective precipitation gradients, particularly those with strong seasonality and regional variability in hydrologic inputs.

25814. 题目: Linking stream microbial community functional genes to dissolved organic matter and inorganic nutrients
文章编号: N19121211
期刊: Limnology and Oceanography
作者: Christina Fasching, Christian Akotoye, Mina Bižić, Jeremy Fonvielle, Danny Ionescu, Sabateeshan Mathavarajah, Luca Zoccarato, David A. Walsh, Hans‐Peter Grossart, Marguerite A. Xenopoulos
更新时间: 2019-12-12
摘要: There is now increasing evidence for the importance of microbial regulation of biogeochemical cycling in streams. Resource availability shapes microbial community structure, but less is known about how landscape‐mediated availability of nutrients and carbon can control microbial functions in streams. Using comparative metagenomics, we examined the relationship between microbial functional genes and composition of dissolved organic matter (DOM), nutrients, and suspended microbial communities in 11 streams, divided into three groups based on the predominant land cover category (agriculture, forested, or wetland). Using weighted gene co‐occurrence network analysis, we identified clusters of functions related to DOM composition, agricultural land use, and/or wetland and forest land cover. Wetland‐dominated streams were characterized by functions related to nitrogen metabolism and processing of aromatic carbon compounds, with strong positive correlations with dissolved organic carbon concentration and DOM aromaticity. Forested streams were characterized by metabolic functions related to monomer uptake and carbohydrates, such as mannose and fructose metabolism. In agricultural streams, microbial functions were correlated with more labile, protein‐like DOM, PO₄, and NO₃, likely reflecting functional adaptation to labile DOM and higher nutrient concentrations. Distinct changes in the functional composition and loss of functional diversity of microorganisms became evident when comparing natural to agricultural catchments. Although all streams showed signs of functional redundancy, loss of species richness per function in agricultural catchments suggests that microbial functions in natural catchments may be more resilient to disturbance. Our results provide new insight into microbial community functions involved in nutrient and carbon biogeochemical cycles and their dependence on specific environmental settings.

25815. 题目: Carbonization of Plant Residues Decreased their Capability of Reducing Hexavalent Chromium in Soils
文章编号: N19121210
期刊: Water, Air, & Soil Pollution
作者: Bo Li, Junxing Yang, Wentao Sun, Yibing Ma
更新时间: 2019-12-12
摘要: The mechanism of Cr(VI) immobilization in soils by organic substances are not well understood. In the present study, two crop residues (maize stalk and peanut shell) and their biochars obtained at various pyrolysis temperatures were prepared to investigate their influences on the immobilization of Cr(VI) in two contaminated soils via an incubation test and a bioassay. The results showed that Cr(VI) immobilization in soils was ascribed to dominant reduction (52–99%) coupled with secondary surface adsorption (1.2–48%) by organic substances. The maximum reduction capacity (Y_m, 238 mg/kg) was found in an acidic brown soil with maize stalk amendment, secondly, with peanut shell amendment (Y_m, 231 mg/kg). Their biochars presented a weaker capacity in reducing Cr(VI) to Cr(III) of soils than raw crop residues since carbonization accelerated the decomposition of oxygen-containing functional groups of organic substances. Soil properties, mainly soil pH, were negatively related to Cr(VI) reduction in soils remarkably, while concomitant anions in soils mainly the phosphate could compete with Cr(VI) for surfaces of soil particles and decrease Cr(VI) adsorption and subsequent reduction. The bioassay in pots with wheat seedlings further validated that maize stalk was a better organic substance for Cr(VI) immobilization and subsequent decrease of its bioavailability in contaminated soils than its biochar according to the results of wheat biomass and Cr contents in shoots and roots. Accordingly, to develop a cost-effective method for immobilizing Cr(VI) in contaminated soils, the raw maize stalk is more advantageous than the carbonaceous counterparts because no pyrolysis is required for the application.

25816. 题目: Biochar applied to consolidated land increased the quality of an acid surface soil and tobacco crop in Southern China
文章编号: N19121209
期刊: Journal of Soils and Sediments
作者: Jiuquan Zhang, Yilan Huang, Jianqi Lin, Xue Chen, Caibin Li, Jiguang Zhang
更新时间: 2019-12-12
摘要: Purpose: Soil needs to be ameliorated after land consolidation because this process might decrease soil fertility, soil physical properties, and the growth of microbes, and the application of biochar is one of the soil amelioration methods. However, up to date, no relevant study has been conducted by any field experiment. The objective of this study was to investigate the biochar effect on soil improvement and crop quality. Materials and methods: A field experiment with 5 corn stover biochar application rates (0, 1, 5, 10, 20 Mg ha⁻¹) was conducted in an acid soil (Kandiudult soil in US taxonomy) with flue-cured tobacco as representative crop. Results and discussion: The results showed that in comparison with 0 Mg ha⁻¹ biochar treatment, the application of biochar decreased the soil bulk density by 13.22%, increased the > 2-mm water-stable soil aggregates by 27.38%, and the 0.25 to 2.00-mm soil aggregates by 45.57% at most. The soil pH, organic carbon, labile organic carbon, and exchangeable Ca and Mg contents increased with increasing biochar application rate. The application of biochar was also beneficial for soil microbial activities. For example, the abundance of actinomyces increased with the biochar application rate, and the maximum increase of 342.28% was recorded at the biochar application rate of 20 Mg ha⁻¹. The application of biochar decreased the total sugar and reducing sugar contents and increased the leaf K content, thus greatly improving the leaf quality of flue-cured tobacco. Conclusions: Biochar applied to consolidated acid soil can play a positive role in flue-cured tobacco production and soil amelioration with regard to soil physical properties and soil nutrient supply capacity. On consolidated land, this is the first study about the effect of biochar application on quality of acid soil and crop, which strengthens the understanding about the role of biochar in soil improvement on consolidated land.

25817. 题目: Impacts of agricultural land use change on soil aggregate stability and physical protection of organic C
文章编号: N19121208
期刊: Science of The Total Environment
作者: Lingke Guo, Jie Shen, Bing Li, Qiquan Li, Changquan Wang, Yu Guan, Luigi P. D'Acqui, Youlin Luo, Qi Tao, Qiang Xu, Huanxiu Li, Juan Yang, Xiaoyan Tang
更新时间: 2019-12-12
摘要: Soil aggregate stability and soil organic carbon (SOC) physical sequestration is essential to regulation of anthropogenic climate change. However, relative knowledge remains elusive. The total SOC stock, aggregate stability, capacity of physically protected C, structure of macroaggregates and Al/Fe oxides under rice-wheat rotation (RW), rice-vegetable rotation (RV) and afforested land (AL) were analysed. We chose 1–2 mm macroaggregates for low-temperature ashing (LTA) treatment to mimic natural oxidation to assess the capacity of physically protected C. Using scanning electron microscopy, the N adsorption method, and energy dispersive spectroscopy, we explored the internal structure of macroaggregates under different land use types. All land use types could physically protect over 50% of SOC. AL showed the strongest capacity of C sequestration, followed by RW, which preserved 67.1% and 59.6% of SOC, respectively. After 5 h of LTA treatment, the amount of SOC removed from the macropores in cropland (RW and RV) was higher than that in AL. In micropores with further oxidation, AL and RW both lost only 5% of SOC. Fe oxides were more correlated with C dynamics than Al oxides. Free Fe oxides were associated with the easily oxidised organic matter. Soil aggregate stability significantly correlated with Al/Fe oxides (p < 0.05). The RW and AL had a greater soil aggregate stability than the RV owing to the relatively higher content of Al/Fe oxides. In conclusion, the conversion of RW to RV reduced the mechanical stability of soil aggregates and the capacity of C physical sequestration, while the conversion of RW to AL increased these two properties. Land use change affected C physical sequestration mainly via changes in surface area, pore development and the content of Fe oxides in macroaggregates.
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25818. 题目: Changing riverine organic C:N ratios along the Pearl River: Implications for estuarine and coastal carbon cycles
文章编号: N19121207
期刊: Science of The Total Environment
作者: Qinyu Liu, Yingtong Liang, Wei-Jun Cai, Kuo Wang, Juying Wang, Kedong Yin
更新时间: 2019-12-12
摘要: In the traditional view, riverine organic matter typically has a higher C:N ratio than marine phytoplankton 6.7:1 and has therefore been thought to be a carbon source in estuaries and coastal waters. Thus, a decrease in the riverine organic C:N ratio to <6.7:1 would potentially switch riverine organic matter from a coastal carbon source to sink. However, few studies have paid an attention to such a change. Our field investigation showed that organic C:N ratio was 11.8:1 in the pristine upstream section of a natural reserve, but decreased after the river passed through several urban cities, reaching 5.0:1 in near the Pearl River estuary. Along the river, dissolved inorganic nitrogen, total organic carbon and nitrogen all increased and they were highly negatively correlated with organic C:N ratios. The observation has a great implication that organic matter with a decreased C:N ratio from the Pearl River would potentially switch from a coastal carbon source of 2.8 × 10¹¹ g C/year to a sink of 2.2 × 10¹¹ g C/year. This carbon sink (2.2 × 10¹¹ g C/year) contributes to 56% of the previous estimate of the Pearl River estuarine-coastal net carbon sink. Such a decrease in organic C:N ratio also occurs in some other large rivers, which should be considered in the assessment of global coastal carbon budgets and metabolic balance.
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25819. 题目: Source apportionment of fine particulate matter in a Middle Eastern Metropolis, Tehran-Iran, using PMF with organic and inorganic markers
文章编号: N19121206
期刊: Science of The Total Environment
作者: Sepideh Esmaeilirad, Alexandra Lai, Gülcin Abbaszade, Jürgen Schnelle-Kreis, Ralf Zimmermann, Gaëlle Uzu, Kaspar Daellenbach, Francesco Canonaco, Hossein Hassankhany, Mohammad Arhami, Urs Baltensperger, André S.H. Prévôt, James J. Schauer, Jean-Luc Jaffrezo, Vahid Hosseini, Imad El Haddad
更新时间: 2019-12-12
摘要: With over 8 million inhabitants and 4 million motor vehicles on the streets, Tehran is one of the most crowded and polluted cities in the Middle East. Frequent exceedances of national daily PM_2.5 limit have been reported in this city during the last decade, yet, the chemical composition and sources of fine particles are poorly determined. In the present study, 24-hour PM_2.5 samples were collected at two urban sites during two separate campaigns, a one-year period from 2014 to 2015 and another three-month period at the beginning of 2017. Concentrations of organic carbon (OC), elemental carbon (EC), inorganic ions, trace metals and specific organic molecular markers were measured by chemical analysis of filter samples. The dominant mass components were organic matter (OM), sulfate and EC. With a 20% water-soluble organic carbon (WSOC) fraction, the predominance of primary anthropogenic sources (i.e. fossil fuel combustion) was anticipated. A positive matrix factorization (PMF) analysis using the ME-2 (Multilinear Engine-2) solver was then applied to this dataset. 5 factors were identified by Marker-PMF, named as traffic exhaust (TE), biomass burning (BB), industries (Ind.), nitrate-rich and sulfate-rich. Another 4 factors were identified by Metal-PMF, including, dust, vehicles (traffic non-exhaust, TNE), industries (Ind.) and heavy fuel combustion (HFC). Traffic exhaust was the dominant source with 44.5% contribution to total quantified PM_2.5 mass. Sulfate-rich (24.2%) and nitrate-rich (18.4%) factors were the next major contributing sources. Dust (4.4%) and biomass burning (6.7%) also had small contributions while the total share of all other factors was < 2%. Investigating the correlations of different factors between the two sampling sites showed that traffic emissions and biomass burning were local, whereas dust, heavy fuel combustion and industrial sources were regional. Results of this study indicate that gas- and particle-phase pollutants emitted from fossil fuel combustion (mobile and stationary) are the principal origin of both primary and secondary fine aerosols in Tehran.
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25820. 题目: Organic carbon stabilized by iron during slump deformation on the Qinghai-Tibetan Plateau
文章编号: N19121205
期刊: CATENA
作者: Cuicui Mu, Feng Zhang, Mei Mu, Xu Chen, Zhilong Li, Tingjun Zhang
更新时间: 2019-12-12
摘要: Soil organic carbon (SOC) associated with iron (Fe-OC) can be recognized as an important component of the stabilized carbon pool. In permafrost regions, slump deformation can expose soil organic carbon and alter moisture conditions, which change the Fe-OC distribution. We measured the top 30 cm of soils in five slump deformation landscapes under three vegetation types on the middle and eastern Qinghai-Tibetan Plateau. Three stages of slump deformation were defined according to their microtopography. In the slump deformation areas, the SOC and total nitrogen (TN) contents in the surface 30 cm of soils were all lower than the soils without slump deformation in wet meadow (22% and 26%), meadow (16% and 29%), and steppe (14% and 20%) areas. The contents of Fe-OC in wet meadow were 4.1% and 12.5% in the soils without and with slump deformation, respectively, whereas these contents in the meadow and steppe soils were 25.6% and 17.2%, respectively. Slump deformation greatly changed the physiochemical soil variables and affected the Fe-OC% based on different vegetation types. Fe-OC was correlated with factors such as soil moisture, pH and C/Fe ratio. The study shows that slump deformation greatly affected the SOC and TN distribution and SOC stabilization processes in areas with slump deformation features.