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30081. 题目: Evolution over years of structural characteristics of humic acids in Black Soil as a function of various fertilization treatments
文章编号: N18120804
期刊: Journal of Soils and Sediments
作者: Jiuming Zhang, Tingting An, Fengqin Chi, Dan Wei, Baoku Zhou, Xiaoyu Hao, Liang Jin, Jingkuan Wang
更新时间: 2018-12-08
摘要: Purpose: Humic substances are the relatively stable and recalcitrant pool of soil organic carbon in the agricultural system. Humic acid (HA) is an active part of soil humic substances. However, little information exists on how structural characteristics of HA evolved with fertilization years in Black Soil. Materials and methods: Soil samples were collected in 1997, 2002, 2008, and 2012 from the Long-term Fertilization Station of Black Soil. The methods of ¹³C-nuclear magnetic resonance spectroscopy, elemental composition analysis, and infrared spectroscopy were employed to analyze the structure of HA. Results and discussion: Long-term fertilization had no significant (P > 0.05) effect on the ratio of O and S to C in HA. The ratio of H to C in HA increased with fertilization years after the application of organic manure (M) single or combined with chemical NPK fertilizers. The ratios of aliphatic C to aromatic C, and alkyl C to O-alkyl C in soil HA increased by 7.72% and 20.3%, respectively, in MNPK and M treatments, whereas NPK treatment declined the ratio of aliphatic C to aromatic C by 2.67% compared with CK treatment. Conclusions: The HA structure tends to become aliphatic and simplified with years of organic manure combined with NPK fertilizers. To save costs, organic manure was only applied once within the period of crop rotation and was combined with NPK every year to satisfy crop demands for soil nutrients.

30082. 题目: Effect of humic acid concentration on pharmaceutically active compounds (PhACs) Rejection by direct contact membrane distillation (DCMD)
文章编号: N18120803
期刊: Separation and Purification Technology
作者: Carolina Fonseca Couto, Míriam Cristina Santos Amaral, Liséte Celina Lange, Lucilaine Valeria de Souza Santos
更新时间: 2018-12-08
摘要: In this study, a direct contact membrane distillation process was used to achieve rejection of 25 pharmaceutically active compounds (PhACs) in water. The influence of natural organic matter (NOM), a common contaminant in waters that are used for water supply, on PhACs removal was investigated. Humic acid was used as an organic model in order to represent major constituents of NOM. Results indicated that flux decline slightly increased from 0 to 8% as HA feed concentration increased from 0 to 80 mg L^-1. Flux decline was mainly associated with membrane fouling which added hydraulic resistance to the transfer of liquid water. Pore wetting was observed when HA concentration increased, which indicated changes in the hydrophobic character of the membrane. MD process showed a rejection of ≥ 99% for the 25 assessed PhACs for all HA concentration evaluated even at high permeate recovery rate (60%), whereas, 24 PhACs presented concentrations below limit detection. The retention of PhACs by MD membrane occurs predominantly by membrane rejection which is mainly governed by volatility and, to a lesser extent, by hydrophobia. The adsorption contribution to PhACs retention was low (<8%) and was significantly associated with positively charged compounds. Although the feed side of the membrane became hydrophilic due to the HA deposit, the PhACs retention by DCMD was not affected, which reinforces the robustness of the process and the ability to produce safe water. Thus, in general, DCMD is less influenced by the feed composition than nanofiltration or reverse osmosis, implicating in higher PhACs rejections.

30083. 题目: The shelf-to-basin iron shuttle in the Black Sea revisited
文章编号: N18120802
期刊: Chemical Geology
作者: W.K. Lenstra, M. Hermans, M.J.M. Séguret, R. Witbaard, T. Behrends, N. Dijkstra, N.A.G.M. van Helmond, P. Kraal, P. Laan, M.J.A. Rijkenberg, S. Severmann, A. Teacǎ, C.P. Slomp
更新时间: 2018-12-08
摘要: Continental shelf sediments are a major source of iron (Fe) for phytoplankton in surface waters. In this study, we investigate the mechanisms that control release of Fe from shelf sediments and its lateral transport (“shuttling”) in oxic and hypoxic waters on the northwestern Black Sea shelf. We find that at two coastal stations near the outflow of the Danube river high input of organic matter drives strong reductive dissolution of Fe(oxyhydr)oxides (henceforth termed Fe oxides) in surface sediments, supporting high rates of Fe release to oxygenated bottom waters (∼0.36 mmol m⁻² d⁻¹). We suggest that bioirrigation plays a key role in the release of Fe from these sediments. At four stations further offshore organic matter deposition is lower resulting in limited mobilization of Fe²⁺ in the sediment and low benthic fluxes of Fe (<0.07 mmol m⁻² d⁻¹). Lateral transport of Fe from the coastal zone towards the deep basin mostly takes place in colloidal and/or particulate form (>0.2 μm) in the lower part of the water column, likely through repeated deposition and resuspension of Fe oxides from surface sediments. Using synchrotron-based X-ray spectroscopy and sequential chemical extractions, we demonstrate that the suspended matter and surface sediments are enriched in easily reducible Fe oxides (mostly ferrihydrite) and Fe associated with clay. The mobilization of Fe in the coastal zone and subsequent lateral transport of these Fe-bearing particles results in higher ratios of Fe/Al in surface sediments at outer shelf stations (ca. 1.2 to 2 wt.% wt.%⁻¹) than at coastal stations (ca. 0.5 to 0.9 wt.% wt.%⁻¹). However, below the sediment surface layer Fe/Al ratios are similar at all stations indicating limited burial of the laterally transported Fe. Our results highlight the critical role of organic matter input, associated biological activity and riverine Fe input as drivers of Fe shuttling on continental shelves. We also show that in shelf areas where sediments receive low inputs of organic matter, physical transport controls the ultimate fate of the shuttled Fe.This article is part of a special issue entitled: “Cycles of trace elements and isotopes in the ocean - GEOTRACES and beyond” - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.

30084. 题目: Preparation of magnetic polyimide@ Mg-Fe layered double hydroxides core-shell composite for effective removal of various organic contaminants from aqueous solution
文章编号: N18120801
期刊: Chemosphere
作者: Hanjun Wu, Huali Zhang, Weijun Zhang, Xiaofang Yang, Hong Zhou, Zhiquan Pan, Dongsheng Wang
更新时间: 2018-12-08
摘要: In this work, a novel core-shell structured magnetic polyimide@layered double oxides (LDO) composites coating a porous polyimide (PI)-coated Fe₃O₄ magnetic core and layered double hydroxide (LDH) has been successfully synthesized by solve-thermal synthesis and co-precipitation process. The magnetic PI@LDO composites were characterized by scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), thermogravimetry analysis (TGA) and magnetic properties analysis. The composite materials displayed core-shell structure with flower-like morphology. The magnetic PI@LDO composites were applied to remove tetracycline (TC), 2,4-dichlorophenol (2,4-DCP) and glyphosate (GP) from aqueous solution. The action pH value was ranged from 5 to 9 for TC and GP and 3 to 7 for 2,4-DCP, respectively. Cl⁻ showed a weak competitive adsorption effect to TC, 2, 4-DCP and GP. In addition, the presence of humic acid (HA) could slightly reduce the adsorption capacity of magnetic PI@LDO composites. The adsorption process could be well described by pseudo-second-order model for TC and GP, while pseudo-first-order model for 2,4-DCP. The experimental data of TC and 2,4-DCP could be fitted better with Freundlich model, while that of GP were fitted better with Langmuir model. The adsorptions of TC, 2,4-DCP and GP were both spontaneous and endothermic. The adsorption capacity decreased slightly after adsorption-desorption cycles repeated five times. This study demonstrated that magnetic PI@LDO exhibited great potential to be a mild and cost-effective adsorbent for the removal of various organic contaminants from wastewater.
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30085. 题目: Importance of a Coastal Artificial Lake in Methylmercury Production: A Case Study of Lake Changpo, Korea
文章编号: N18120709
期刊: Ocean Science Journal
作者: Sampa Rani Kundu, Eunhee Kim, Seunghee Han, Byeong-Gweon Lee
更新时间: 2018-12-07
摘要: Lake Changpo (LC) is an artificial freshwater lake surrounded by wetlands and farmlands, inundated with water during the wet season, on the southwest coast of Korea. To investigate the temporal and spatial distribution of total mercury (THg) and methylmercury (MeHg) in LC and adjacent Cheonggye Bay (CB), water and sediment samples were collected five times from August 2009 to August 2010. In addition, fish samples were collected to examine Hg levels. The THg concentration in the unfiltered water of LC ranged from 1.6 to 5.0 ng/L and had a positive relationship with total suspended solids (TSS). This positive relation indicates that TSS is an important source of THg in LC. The MeHg levels were highest during August and ranged from 0.03 to 0.19 ng/L in unfiltered water and from 0.01 to 0.10 ng/L in filtered water. Both the THg and MeHg levels in the sediments were significantly correlated with the organic matter content of the sediments. Overlapping of the spatial and temporal distribution patterns of MeHg and %MeHg between the water column and sediments suggests that production and diffusion of MeHg from the sediment, particularly during warm summer, was the primary source of MeHg in the water column. In addition, higher THg and MeHg concentrations were found in catfish, a bottom-dweller fish. Thus, the higher THg and MeHg concentrations in LC compared to CB demonstrate that artificial lakes could be a significant site for Hg methylation and an additional source of MeHg to coastal seas.

30086. 题目: Relating Organic Fouling in Membrane Distillation to Intermolecular Adhesion Forces and Interfacial Surface Energies
文章编号: N18120708
期刊: Environmental Science & Technology
作者: Chanhee Boo, Seungkwan Hong, Menachem Elimelech
更新时间: 2018-12-07
摘要: This study investigates the fouling mechanisms in membrane distillation, focusing on the impact of foulant type and membrane surface chemistry. Interaction forces between a surface-functionalized particle probe simulating a range of organic foulants and model surfaces, modified with different surface energy materials, were measured by atomic force microscopy. The measured interaction forces were compared to those calculated based on the experimentally determined surface energy components of the particle probe, model surface, and medium (i.e., water). Surfaces with low interfacial energy exhibited high attractive interaction forces with organic foulants, implying a higher fouling potential. In contrast, hydrophilic surfaces (i.e., surfaces with high interfacial energy) showed the lowest attractive forces with all types of foulants. We further performed fouling experiments with alginate, humic acid, and mineral oil in direct contact membrane distillation using polyvinylidene fluoride membranes modified with various materials to control membrane surface energy. The observed fouling behavior was compared to the interaction force data to better understand the underlying fouling mechanisms. A remarkable correlation was obtained between the evaluated interaction force data and the fouling behavior of the membranes with different surface energy. Membranes with low surface energy were fouled by hydrophobic, low surface tension foulants via “attractive” and subsequent “adsorptive” interaction mechanisms. Furthermore, such membranes have a higher fouling potential than membranes with high or ultralow surface energy.
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30087. 题目: Legacy and Emerging Persistent Organic Pollutants (POPs) in Terrestrial Compartments in the High Arctic: Sorption and Secondary Sources
文章编号: N18120707
期刊: Environmental Science & Technology
作者: Ana Cabrerizo, Derek C. G. Muir, Amila O. De Silva, Xiaowa Wang, Scott F. Lamoureux, Melissa J. Lafrenière
更新时间: 2018-12-07
摘要: Legacy persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), and emerging perfluoroalkyl substances (PFASs) were measured in vegetation and soil samples collected at remote lakes in the Canadian High Arctic. Field studies were carried out in 2015 and 2016 to assess concentrations of POPs, study the relevant sorbing phases, and determine whether Arctic soils were sinks or sources of legacy POPs to the atmosphere and to neighboring lakes. The patterns of legacy POPs in vegetation and soils were dominated by low molecular weight PCB congeners along with OCPs, confirming the importance of long-range atmospheric transport. Lipid and non-lipid organic matter was a key determinant of legacy POPs in Arctic vegetation. Soil organic matter was the main descriptor of hydrophobic PCBs and OCPs in soils, while soil inorganic carbon content, was an important driver of the sorption of PFASs in soils. While contaminant concentrations were low in soil and vegetation, higher PCBs and PFOS organic and inorganic carbon-normalized concentrations were found at Resolute Lake indicating the presence of local sources of contamination. Comparison of fugacities of PCBs in soil and air from Resolute Lake indicated soils as net sources of PCBs to the atmosphere.
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30088. 题目: Effects of fertiliser on phosphorus pools in soils with contrasting organic matter content: A fractionation and path analysis study
文章编号: N18120706
期刊: Geoderma
作者: J.L. González Jiménez, M.G. Healy, K. Daly
更新时间: 2018-12-07
摘要: With the intensification of agricultural production in many European countries, more marginal soils with elevated organic matter (OM) content are being brought into cultivation. However, little is known about the transformations in the constituent phosphorus (P) pools of organic soils receiving applications of P fertiliser. Soil P fractions were measured before and after receiving fertiliser in a controlled experiment to determine the change in the soil pools and path analysis was used to evaluate the relationships between P pools. In this study, P deficient soils ranging in OM content from 8 to 76%, were placed in large pots, planted with ryegrass and subjected to P fertiliser applications ranging from 10 to 145 kg ha⁻¹, and monitored over an eight-month study period. High OM soils had a diminished ability to build-up the labile pool from freshly applied P, with relatively low increases up to 200% of the initial value, compared to mineral soils in which the labile pool increased to >2500% of the initial concentration. Additionally, organic soils had higher P uptakes in the grass yield than mineral soils, indicating a higher availability of added P in the soil solution than mineral soils due to their limited sorption ability. In general, there was a reduction in the organic P pool over applications from 0 to 55 kg ha⁻¹, which was indicative of partial mineralization, but was followed by an accumulation of added P over applications from 55 to 145 kg P ha⁻¹. The residual P pools did not build-up with P additions, but data indicated the occurrence of mineralization in most of the soils with decreases of around 40% of the initial concentrations. Organic and residual pools therefore displayed potential to supply P to more labile P pools across all soils of this study. Path analysis indicated that applied P was the only source of labile P in the soil with the highest OM content, leaving it dependent on continuous P applications to supply P for productivity, whereas in the rest of the soils there were interrelations between the non-labile and labile pools. Low pH strongly immobilised the applied P and should be corrected before the initiation of any fertilisation program, even in soils deficient in plant available P. The results demonstrated that P added as fertiliser to organic soils does not accumulate as in mineral soils, which may leave them susceptible to P losses in surface runoff. Therefore, organic soils under agricultural production located in high status catchments should receive low P applications and only during periods with low probability of precipitation to minimise the possibility of P exports to receiving waters.

30089. 题目: The Influence of Natural Organic Matter on the Adsorption of Microcystin-LR by Powdered Activated Carbon
文章编号: N18120705
期刊: Environmental Science: Water Research & Technology
作者: Asnika Bajracharya, Yen-Ling Liu, John Lenhart
更新时间: 2018-12-07
摘要: In this study, microcystin-LR (MC-LR) adsorption to four different types of powdered activated carbon (PAC) was evaluated to provide insight into the use of PAC to treat water containing MC-LR. MC-LR adsorption to the four PAC types (wood, coal blend, bituminous coal, and coconut shell) was studied in equilibrium and kinetic batch experiments utilizing a model water with different natural organic matter (NOM) concentrations (0, 5 and 10 mg/L) and pH (5.2, 8.5 and 9.5). The effect of NOM type was evaluated by comparing MC-LR uptake in model water amended with Suwannee river fulvic acid or a NOM extracted from a natural water experiencing an algal bloom. The results demonstrated that the wood-based PAC removed MC-LR at the highest rate and to the greatest extent, which likely reflects that wood-based PAC typically contains a greater proportion of mesopores than the other types of PAC in this study. MC-LR removal was significantly reduced in the presence of NOM, with the impact being slightly higher for the algal-derived NOM compared to Suwannee river fulvic acid. MC-LR removal decreased with decreasing pH in the presence of NOM, but increased with decreasing pH in the absence of NOM. This suggests competition with NOM not only varies depending upon the source of NOM, but also on the solution pH as NOM interactions with PAC will vary with pH. Thus, properly determining PAC doses to treat MC-LR must account for the presence of NOM as well as the pH-dependent interactions of NOM with PAC as these interactions strongly influence MC-LR adsorption.

30090. 题目: Heterotrophic metabolism of C1 and C2 low molecular weight compounds in northern Gulf of Mexico sediments: controlling factors and implications for organic carbon degradation
文章编号: N18120704
期刊: Geochimica et Cosmochimica Acta
作者: Guang-Chao Zhuang, Andrew Montgomery, Samantha B. Joye
更新时间: 2018-12-07
摘要: Low molecular weight (LMW) compounds are key intermediates in organic matter degradation and their metabolism supports a diverse microbial community in anoxic sediments. Much remains to be learned about the metabolic pathways and turnover rates of LMW compounds as well as the factors that influence their metabolism in the environment. We studied the microbial metabolism of acetate, methanol and methylamine in sediments from Northern Gulf of Mexico to elucidate their role as energy and carbon sources for microorganisms mediating terminal metabolic processes and to constrain the importance of C1 and C2 metabolism in the sedimentary carbon cycle. In terms of carbon flow, methanogenesis was a minor process in sulfate-rich sediments; acetate and methanol were oxidized primarily by non-methanogenic heterotrophs as an energy source. A large fraction of utilized acetate (20%−76%) was assimilated into biomass, suggesting that acetate was a significant biomass-building source. Results from direct metabolic rate assays were generally consistent with in situ thermodynamic predictions and the results of inhibitor experiments employing 2-bromoethanesulfonate and molybdate. Methylamine, by contrast, was utilized for methane production (up to 100%), but its utilization was not limited to methanogens. At organic-poor deep-sea sites, elevated acetate and methanol oxidation rates in the absence of sulfate-reducing and methanogenic activity indicated that metabolism of LMW compounds was coupled to other electron accepting processes, such as denitrification. Heterotrophic carbon assimilation was an important pathway for generating biomass at this site, as evidenced by comparable rates of acetate assimilation and dark bicarbonate incorporation. Microbial activity generally decreased with depth, following the trend of organic carbon degradation rates. Environmental factors, such as temperature but not pressure, affected the metabolism of LMW compounds. In seep sediments, the oxidation of acetate and methanol accounted for 5% and 0.9%, respectively, of the total organic carbon oxidation. Collectively, this assessment of C1 and C2 LMW compound utilization shows that they serve as energetic substrates to fuel methanogens, sulfate reducers and other microbes.

30091. 题目: Shallow convective mixing promotes massive Noctiluca scintillans bloom in the northeastern Arabian Sea
文章编号: N18120703
期刊: Marine Pollution Bulletin
作者: V.V.S.S. Sarma, J.S. Patil, D. Shankar, A.C. Anil
更新时间: 2018-12-07
摘要: The northeastern Arabian Sea (NEAS) experiences convective mixing during winter, but this mixing does not reach up to the silicicline, resulting in the limited supply of silicate (Si) compared to nitrate (N) and phosphate (P) to the mixed layer (ML) and formation of non-diatom blooms. The poleward advection of waters of low surface salinity by the West India Coastal Current (WICC) to the NEAS weakens the vertical mixing and reduces the Si input to the mixed layer, resulting in occurrence of Noctiluca scintillans blooms. The saturation of dissolved oxygen in the NEAS varied between 88 and 98%, suggesting N. scintillans blooms occur in oxic conditions. Enhanced cell abundance of N. scintillans was observed in the bloom region in the upper 10 m. Phytoplankton pigments data revealed higher contribution of Chlorophytes, Prasinophytes, Prymnesiophytes and Prochlorophytes in the bloom than non-bloom region. The isotopic composition of nitrogen and carbon of particulate organic matter indicated that natural and in situ processes contributed to both nutrients and organic carbon pool in the NEAS in supporting the massive occurrence of N. scintillans blooms than hitherto hypothesized to anthropogenic sources. This study further suggests that the effect of anthropogenic pollutants released into the NEAS from the mega-cities is limited to the neighbourhood of these cities and does not affect the open ocean.

30092. 题目: Novel high-throughput approach to determine key processes of soil organic nitrogen cycling: Gross protein depolymerization and microbial amino acid uptake
文章编号: N18120702
期刊: Soil Biology and Biochemistry
作者: Lisa Noll, Shasha Zhang, Wolfgang Wanek
更新时间: 2018-12-07
摘要: Proteins comprise the largest soil N reservoir but cannot be taken up directly by microorganisms and plants due to size constraints and stabilization of proteins in organo-mineral associations. Therefore the cleavage of this high molecular weight organic N to smaller soluble compounds as amino acids is a key step in the terrestrial N cycle. In the last years two isotope pool dilution approaches have been successfully established to measure gross rates of protein depolymerization and microbial amino acid uptake in soils. However, both require laborious sample preparation and analyses, which limits sample throughput. Therefore, we here present a novel isotope pool dilution approach based on the addition of ¹⁵N-labeled amino acids to soils and subsequent concentration and ¹⁵N analysis by the oxidation of α-amino groups to NO₂⁻ and further reduction to N₂O, followed by purge-and-trap isotope ratio mass spectrometry (PT-IRMS). We applied this method in mesocosm experiments with forest and meadow soils as well as with a cropland soil amended with either organic C (cellulose) or organic N (bovine serum albumin). To measure direct organic N mineralization to NH₄⁺, the latter was captured in acid traps and analyzed by an elemental analyzer coupled to an isotope ratio mass spectrometer (EA-IRMS). Our results demonstrate that the proposed method provides fast and precise measurements of at%¹⁵N even at low amino acid concentrations, allows high sample throughput and enables parallel estimations of instantaneous organic N mineralization rates.

30093. 题目: Lower mineralizability of soil carbon with higher legacy soil moisture
文章编号: N18120701
期刊: Soil Biology and Biochemistry
作者: Srabani Das, Brian K. Richards, Kelly L. Hanley, Leilah Krounbi, M.F. Walter, M. Todd Walter, Tammo S. Steenhuis, Johannes Lehmann
更新时间: 2018-12-07
摘要: The effect of long-term versus short-term water content on soil organic carbon (SOC) mineralizability was evaluated in a six-week incubation trial. Soils were sampled from field sites in upstate New York used for rain-fed bioenergy crop production: nitrogen (N)- fertilized reed canarygrass, switchgrass, switchgrass + N, as well as a broadleaf-grass fallow. Within each cropping system, natural moisture gradients due to topography and subsoil structure allowed us to sample across regions with high (0.5 g g⁻¹), mid (0.4 g g⁻¹) and low (0.3 g g⁻¹) water content. Moisture of the laboratory incubations was adjusted mimicking the three average field moisture levels in a full factorial design. Increasing laboratory moisture in the incubations increased cumulative carbon mineralization per unit soil (C mineralization) and cumulative C mineralization per unit SOC (C mineralizability) (main effect p < 0.0001), indicating that lower average moisture as found at this site on average limited mineralization but higher average moisture did not. C mineralizability at high field moisture was 31% lower than at low field moisture across all cropping systems, regardless of moisture adjustment in the incubation. The mean slow C pool size of soils from high field moisture sites (997.1 ± 0.1 mg C g⁻¹ C) was 0.2% greater than that of soils from low field moisture sites (p < 0.0001), obtained by fitting a double-exponential model. The mean residence time of the slow mineralizing C pool for soils from low field moisture sites was 5.5 ± 0.1 years, in comparison to 8.0 ± 0.1 years for soils from high field moisture sites (p < 0.0001). While permanganate-oxidizable carbon (POXC) per unit SOC (r = 0.1) was positively correlated to C mineralizability, wet aggregate stability (r = −0.2) was negatively correlated to C mineralizability. Above-ground biomass did not affect C mineralizability (p > 0.05) and root biomass marginally influenced (p = 0.05) C mineralizability after correcting for soil texture variations. Additionally, after correcting for soil texture variations and biomass inputs, C mineralizability significantly decreased with higher field moisture (p = 0.02), indicating possible stabilization mechanisms through mineral interactions of SOC under high water content. Bulk contents of pedogenic iron and aluminum determined by oxalate extraction did not clearly explain differences in mineralizability. However, exchangeable calcium and magnesium contents were significantly (p < 0.0001) greater in high moisture soils than soils with lower moisture. Additionally, cumulative C mineralizability at 6 weeks was negatively correlated to calcium (r = −0.7) and magnesium (r = −0.6) and mean residence time of the modeled slow pool correlated positively with calcium (r = 0.4). Therefore, cation bridging by retained or illuviated base ions was more important than redox changes of iron as a stabilization mechanism in this experiment.

30094. 题目: VARIATIONS IN CARBON‐DECOMPOSITION ENZYME ACTIVITIES RESPOND DIFFERENTLY TO LAND USE CHANGE IN CENTRAL CHINA
文章编号: N18120613
期刊: Land Degradation & Development
作者: Qian Zhang, Jiao Feng, Junjun Wu, Dandan Zhang, Qiong Chen, Qianxi Li, Chunyang Long, Adugna Feyissa, Xiaoli Cheng
更新时间: 2018-12-06
摘要: The turnover of soil organic carbon (SOC) is primarily regulated by extracellular enzymes secreted by the microorganism. However, how soil C‐decomposition enzymes respond to different land use change remains unclear. Here we conducted a study to explore seasonal variations in C‐decomposition enzyme activities including hydrolases (α‐glucosidase, β‐glucosidase, cellobiohydrolase, and β‐xylosidase) and oxidases (polyphenol oxidase and peroxidase) in woodland, shrubland, cropland and adjacent uncultivated soils in central China. Soil dissolved organic C (DOC), SOC, labile C (LC), recalcitrant C (RC), soil C recalcitrance index (RIC: RC/SOC ratio), pH, soil moisture and temperature were also investigated. Both afforested and cropland averaged higher hydrolase and oxidase activities compared to the uncultivated land, with higher levels of enzyme activities in top soils than deep soils. By comparing with the uncultivated land, higher hydrolytic enzyme activities in afforested soils were mainly attributed to higher DOC and LC contents, whereas higher hydrolase activities in cropland soils were possibly due to lower C: nitrogen (N) ratios and agricultural disturbance (i.e. fertilization and tillage). In contrast, two oxidases activities were the highest in the cropland, which might be attributed to higher RIC and lower C: N ratio. Cropland soils also averaged higher specific enzyme activities (i.e. enzyme activities per unit of SOC) compared to the afforested land, indicating fast C turnover rates in cropland. Seasonal variations in soil enzyme activities were primarily driven by soil temperature and pH. Overall, our results reveal the different underlying mechanisms between hydrolases and oxidases in response to types of land use change.

30095. 题目: Effects of topography on soil organic carbon stocks in grasslands of a semiarid alpine region, northwestern China
文章编号: N18120612
期刊: Journal of Soils and Sediments
作者: Meng Zhu, Qi Feng, Mengxu Zhang, Wei Liu, Yanyan Qin, Ravinesh C. Deo, Chengqi Zhang
更新时间: 2018-12-06
摘要: Purpose: Soil organic carbon (SOC) in mountainous regions is characterized by strong topography-induced heterogeneity, which may contribute to large uncertainties in regional SOC stock estimation. However, the quantitative effects of topography on SOC stocks in semiarid alpine grasslands are currently not well understood. Therefore, the purpose of this research study is to determine the role of topography in shaping the spatial patterns of SOC stocks. Materials and methods: Soils from the summit, shoulder, backslope, footslope, and toeslope positions along nine toposequences within three elevation-dependent grassland types (i.e., montane desert steppe at ~ 2450 m, montane steppe at ~ 2900 m, and subalpine meadow at ~ 3350 m) are sampled at four depths (0–10, 10–20, 20–40, and 40–60 cm). SOC content, bulk density, soil texture, soil water content, and grassland biomass are determined. The general linear model (GLM) is employed to quantify the effects of topography on the SOC stocks. Ordinary least squares regressions are performed to explore the underlying relationships between SOC stocks and the other edaphic factors. Results and discussion: In accordance with the present results, the SOC stocks at 0–60 cm show an increasing trend in respect to the elevation zone, with the highest stock being approximately 37.70 g m⁻² in the subalpine meadow, about 2.07 and 3.41 times larger than that in the montane steppe and montane desert steppe, respectively. Along the toposequences, it is revealed the SOC stocks are maximal at toeslope, reaching to 14.98, 31.76, and 49.52 kg m⁻², which are also significantly larger than those at the shoulder by a factor of 1.38, 2.31, and 1.44, in montane desert steppe, montane steppe, and subalpine meadow, respectively. Topography totally is seen to explain about 84% of the overall variation in SOC stocks, of which 70.61 and 9.74% are attributed to elevation zone and slope position, while the slope aspect and slope gradient are seen to plausibly explain only about 1.84 and 0.01%, respectively. Conclusions: The elevation zone and the slope position are seen to markedly shape the spatial patterns of the SOC stocks, and thus, they may be considered as key indicating factors in constructing the optimal SOC estimation model in such semiarid alpine grasslands.

30096. 题目: Biodegradation of humic substances by microscopic filamentous fungi: chromatographic and spectroscopic proxies
文章编号: N18120611
期刊: Journal of Soils and Sediments
作者: Elena Fedoseeva, Andrey Stepanov, Olga Yakimenko, Svetlana Patsaeva, Mikhail Freidkin, Daria Khundzhua, Vera Terekhova
更新时间: 2018-12-06
摘要: Purpose: The study of interactions between humic substances (HSs) and soil filamentous fungi is the key to understanding the sustainable soil functioning. The present work aims to examine the decomposition of HSs by filamentous dark-pigmented fungus Alternaria alternatа under the laboratory conditions and to determine the effect of easily assimilable organic carbon on this process. Analyzing such polydisperse substances like HSs by a complex integrated methodology makes it possible to explore the data on their decomposition by microorganisms. Materials and methods: To achieve the aforementioned goals, we used chromatographic and spectroscopic approaches: low-pressure size-exclusion and hydrophobic interaction chromatography accompanied by absorption and fluorescence spectroscopy. To determine the effect cometabolism conditions produced on HS decomposition, two types of carbon substrates were added to the nutrient media: easily assimilable organic carbon (standard 0.3% or reduced 0.03% sucrose content) and hardly assimilable organic carbon (HSs), as well as their combinations. Five HS samples of different organic matter origin have been inspected: potassium humates (HPs) and humic acids (HAs) from coal, peat, and lignosulfonate. Correlation matrix and principal component analysis (PCA) were calculated for comprehensive data analysis. Results and discussion: Transformations of the investigated HSs under fungal cultivation lead to the increase in the low molecular weight fraction, rise of hydrophilic fraction, enlargement of absorbance ratio A₂₅₀/A₃₆₅, shortening of the emission wavelength of the humic-type fluorescence, and growth in the fluorescence quantum yield measured with excitation at 355 nm. A positive correlation was observed between the accumulation of fungal biomass and the degree of HS decomposition. PCA analysis confirms that the difference in the results of HS decomposition largely depends on the sucrose content and the nature of HSs. We divided all the HS samples into four groups according to the degree of HS decomposition: original HS solutions, HPs altered using fungal cultivation at 0.03% sucrose, HAs after fungal cultivation at 0.03% sucrose, and finally, HSs (both HPs and HAs) after fungal cultivation at 0.3% sucrose. Conclusions: In the laboratory experiments, we showed that (1) the isolated HAs were more effectively degraded than the parent HPs, and this process was more pronounced at a reduced sucrose content, and (2) the decomposition of stable organic compounds (HSs) was activated by the easily assimilable carbon sources (especially 0.3% sucrose) being present. We assume that it is the easily assimilable organic carbon that most likely triggers the HS degradation working as the priming effect in natural environments.

30097. 题目: Humic acid removal by gas–liquid interface discharge plasma: performance, mechanism and comparison to ozonation
文章编号: N18120610
期刊: Environmental Science: Water Research & Technology
作者: Yanyan Cui, Jianwei Yu, Ming Su, Zeyu Jia, Tingting Liu, Gaku Oinuma, Tokiko Yamauchi
更新时间: 2018-12-06
摘要: The removal of natural organic matter (NOM) is a major objective for drinking water treatment. In this study, a novel advanced oxidation process (AOP) based on plasma in gas–liquid interface discharge was investigated for removing humic acid (HA), and ozonation treatment effect was evaluated as a comparison. Several indexes including UV₂₅₄, dissolved organic carbon (DOC), specific UV absorbance (SUVA), and excitation-emission matrix (EEM) fluorescence spectra were employed to characterize HA transformation. The results showed that typical species including ozone, hydrogen peroxide and HO˙ were produced in the plasma process, which made better removal efficiency than ozonation. Especially, UV₂₅₄ was removed effectively by 96.5% and 90.3% within 15 min by plasma and ozonation, while DOC was 49.2% and 41.1%, respectively. HO˙ radicals were majorly responsible for the degradation of HA in the plasma process, which were mainly generated via reaction of in situ produced ozone and H₂O₂ during the discharge process. UV/vis absorbance and EEM results further showed that HA with the large molecular weight fraction was decomposed to small molecular weight fraction. This study indicates that plasma technology has a significant application prospect as a replacement for ozone in drinking water industry.
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30098. 题目: Effect of organic matter on phosphorus adsorption and desorption in a black soil from Northeast China
文章编号: N18120609
期刊: Soil and Tillage Research
作者: Xiaoyan Yang, Xiangwei Chen, Xitian Yang
更新时间: 2018-12-06
摘要: Phosphorus (P) adsorption–desorption in soil is an important internal cycle related to soil fertility problems, as well as for determining the environmental fate of P. Soil organic matter (SOM) has been identified as an important factor affecting the adsorption–desorption of soil P through different mechanisms. In this study, humic acids were added to change the SOM content in black soil. Following an incubation period of 30 days, the changes in soil P adsorption–desorption capacity were studied. The results indicated that increased SOM led to increases in the soil available P and the P activation coefficient. All soil treatments fitted well with both Langmuir and Freundlich equations. The P adsorption and desorption characteristics were analyzed using the Langmuir equation as a local isotherm. The maximum adsorption capacity of P increased with the increase in SOM, but the P bonding energy and maximum buffering capacity first decreased, and then increased, with the lowest values obtained with a SOM content of 75.3 mg kg⁻¹. Both the maximum desorption capacity of P and the ratio of soil P desorption showed a fluctuating trend, which were the greatest when the SOM content reached 75.3 g kg⁻¹ in black soil, showing an improved ability to release P. Thus, the addition of organic matter could efficiently enhance P availability by reducing the strength of P adsorption and the maximum phosphate buffering capacity and increasing the desorption of P to some extent, with the greatest P availability obtained at a SOM content of 75.3 g kg⁻¹.

30099. 题目: Effects of carbon on moisture storage in soils of the Wisconsin Central Sands, USA
文章编号: N18120608
期刊: European Journal of Soil Science
作者: J. L. Yost, A. E. Hartemink
更新时间: 2018-12-06
摘要: Quantifying soil water storage is important for plant growth and agricultural production. This is particularly important in sandy soils since they are widely cultivated and prone to drought. We investigated the effect of soil organic carbon (SOC), soil texture, and gravel content on soil moisture characteristics in sandy soils. Soil moisture characteristics were analyzed using standard soil physical characterization as well as visible–near infrared (vis–NIR) spectroscopy and pedotransfer functions (PTFs). Volumetric water content (–10, –33, –1500 kPa) and available water capacity (AWC) increased by 0.01 to 0.02 m³ m^–3 with a 2% increase in silt plus clay content. Available water capacity increased by about 0.05 m³ m^–3 with a 1% increase in SOC. A 5% increase in gravel in the subsoil decreased the volumetric water content of the soil by 0.01 m³ m^–3. Predictions of volumetric water contents and AWC by vis–NIR were the best when using a random forest model. Pedotransfer functions for AWC predictions performed best when sand, silt, clay, bulk density, and SOC were included. Soil moisture storage ranged from 44 to 65 mm in the top 50 cm. At mean evapotranspiration (4.2 mm day^–1), irrigation requirements were reduced by 6 days in the sandy soils that have larger SOC and silt contents in the topsoil. These soils are sandy throughout but have subtle differences in particle–size distribution, SOC concentrations and gravel content. These differences affect soil moisture storage considerably. Soil management practices that increase the SOC contents in these sandy soils favor moisture storage and tend to reduce irrigation requirements.

30100. 题目: Contrasting responses of soil fungal communities and soil respiration to the above‐ and below‐ground plant C inputs in a subtropical forest
文章编号: N18120607
期刊: European Journal of Soil Science
作者: L. L. Shi, W. T. Feng, X. Jing, H. D. Zang, P. Mortimer, X. M. Zou
更新时间: 2018-12-06
摘要: The roles of soil fungal diversity and community composition in regulating soil respiration when above‐ and below‐ground plant carbon (C) inputs are excluded remain unclear. In the present study, we aimed to examine: (i) how does the exclusion of above‐ and below‐ground plant C inputs affect soil respiration and soil fungi singly and in combination and (ii) are changes in soil fungal diversity aligned with changes in soil respiration A field experiment with manipulation of plant C inputs was established in a subtropical forest in southwest China in 2004 with litter removal and tree stem‐girdling to exclude inputs of the above‐ and below‐ground plant C, respectively. In 2009, we measured the rates of soil respiration with an infrared gas analyser and soil fungal community structure using Illumina sequencing. We found that the rates of soil respiration were reduced significantly by litter removal and girdling, by similar magnitudes. However, they were not decreased further by the combination of these two treatments compared to either treatment alone. In contrast, litter removal increased the diversity of soil fungal communities, whereas girdling decreased the abundance of symbiotrophic fungi but increased the abundance of saptrotrophic and pathotrophic fungi. These changes in soil fungal community might initiate CO₂ emission from soil C decomposition, offsetting further decline in soil respiration when plant C inputs are excluded. These results revealed that the exclusion of the above‐ and below‐ground plant C inputs led to contrasting soil fungal communities but similar soil function. Our findings suggest that both above‐ and below‐ground plant C are important in regulating soil respiration in subtropical forests, by limiting substrates for soil fungal growth and altering the diversity and composition of soil fungal community.