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24721. 题目: A novel calcium-based magnetic biochar reduces the accumulation of As in grains of rice (Oryza sativa L.) in As-contaminated paddy soils
文章编号: N20032006
期刊: Journal of Hazardous Materials
作者: Jizi Wu, Zhangtao Li, Lu Wang, Xingmei Liu, Caixian Tang, Jianming Xu
更新时间: 2020-03-20
摘要: The present study used calcium-based magnetic biochar (Ca-MBC), a novel material made through pyrolyzing rice straw impregnated with iron oxide (Fe3O4) and calcium carbonate (CaCO3) under oxygen-limited conditions, to reduce arsenic (As) accumulation in rice plants (Oryza sativa L.) through a 130-day pot experiment. The BCR (European Community Bureau of Reference) sequential extraction confirmed that Ca-MBC decreased the unstable fraction of As through transforming to the stable fraction at both tillering stage and maturity. The addition of Ca-MBC decreased while the pristine biochar increased the concentrations of NH4H2PO4- and BCR-extracted As. The μ-XRF test revealed that iron oxide on the Ca-MBC played an important role in decreasing As bioavailability. The addition of Ca-MBC greatly decreased As concentration in rice grains, mainly due to (1) the decreases in bioavailability of As in soil and (2) adsorption of As in pore water by Ca-MBC; and (3) the enhanced formation of iron plaque that acted as a barrier for plant As uptake. Furthermore, the addition of Ca-MBC at 1% but not 2% promoted plant growth. The results suggest that Ca-MBC can be used as an efficient material to lower As accumulation in grains and promote plant growth in rice paddy fields.

24722. 题目: Evaluating soil and nutrients (C, N, and P) loss in Chinese Torreya plantations
文章编号: N20032005
期刊: Environmental Pollution
作者: Xiongwen Chen, Pengfei Xiao, Jianzhi Niu, Xi Chen
更新时间: 2020-03-20
摘要: Improper land-use changes may lead to a loss of soil resources and cause environmental pollution. Chinese Torreya plantation (hereafter CTP) is an important cash tree plantation for nuts production in the mountainous areas of subtropical China. The increasing development of CTPs, to increase seed production, can result in the complete erasure of local natural vegetation. In this study, the vulnerability to soil erosion, loss of soil organic carbon (SOC) and nutrients in CTPs due to land-use change were evaluated. The results indicated that the rates of diffusive soil erosion in the young CTPs with extreme precipitation were about six-fold higher than with the natural vegetation. At sites with a similar slope, there was no significant difference in soil erosion levels between the young and old CTPs. The old CTPs did not hold significantly higher levels of SOC and soil total nitrogen (STN) in their topsoil when compared with the young CTPs. The natural mixed broadleaved subtropical forests lost about 35% of their SOC and 25% of their STN after they were converted into CTPs, but the CTPs had higher soil total phosphorus. The C: N ratios at the different sites were close to 11:1, but the N: P ratios were diverse. There were high levels of organic carbon, nitrogen and phosphorus in stream water. Adequate coverage of natural vegetation within or around the CTPs should be maintained to decrease soil erosion and nutrient loss. Suggestions to develop CTPs while protecting the environment are discussed. Overall, it was determined that aspects of the current management practices and strategies for developing CTPs should be changed to decrease soil erosion and nutrient loss.

24723. 题目: Frequency but not amount of stover mulching orchestrates the decomposition pathways of soil micro-foodwebs in a no-tillage system
文章编号: N20032004
期刊: Soil Biology and Biochemistry
作者: Xinchang Kou, Ningning Ma, Xiaoke Zhang, Hongtu Xie, Xudong Zhang, Zhengfang Wu, Wenju Liang, Qi Li, Howard Ferris
更新时间: 2020-03-20
摘要: In the decomposition pathways of the soil micro-foodweb, resource-transfer links between bacteria, fungi and microbivorous nematodes are extremely important for the transformation and cycling of soil organic carbon and for the quality, productivity and sustainability of soil ecosystems. However, the changes in organic decomposition pathways in response to different amounts and frequencies of stover mulching are less clear. Here, we investigate the responses of the soil micro-foodweb to maize stover mulching amounts (33% and 67% amounts of all harvest stover) and frequencies (high frequency with continuous mulching per year and low frequency with interval mulching every three years) in a 10-year no-tillage mulching experiment. The frequency but not the amount of stover mulching had significant effects on soil microorganism and nematode communities. Greater bacterial PLFAs and their higher correlation with bacterivores were observed in high mulch-frequency treatments while in low frequency treatments fungal PLFAs and their correlations with fungivores were higher. The increased nematode enrichment footprint in high frequency treatments indicated more carbon flow into soil micro-foodweb, while a higher structure footprint in low frequency treatments suggested the development of a relatively stable soil micro-foodweb. We conclude that trophic interactions regulate decomposition pathways in a binary coupling between bacteria and nematodes at high input frequencies and between fungi and nematodes at low input frequencies. The structure and activity of the pathways are determined by the bottom-up effects of different stover mulching frequencies.

24724. 题目: Adsorption of organic contaminants on biochar colloids: effects of pyrolysis temperature and particle size
文章编号: N20032003
期刊: Environmental Science and Pollution Research
作者: Rashida Hameed, Cheng Lei, Daohui Lin
更新时间: 2020-03-20
摘要: Biochar (BC) colloids attract increasing interest due to their unique environmental behavior and potential risks. However, the interaction between BC colloids and organic contaminants that may affect their fates in the environment has not been substantially studied. Herein, adsorption and desorption of phenanthrene (PHN), atrazine (ATZ), and oxytetracycline (OTC) by a series of BC colloids derived from bulk rice straw BC samples with 6 pyrolysis temperatures (200–700 °C), and 3 particle sizes (250 nm, 500 nm, and 1 μm) were investigated. Regardless of pyrolysis temperature, BC colloids from a given sized bulk BC had a comparable size, being 30 ± 6, 70 ± 18, and 140 ± 15 nm corresponding to the three sized bulk BCs, respectively. The adsorption kinetics curves were well explained by the pseudo-second-order model, and pore diffusion was the primary rate-determining step. Both Freundlich and Langmuir models well fitted the adsorption isotherms. With increasing pyrolysis temperature or decreasing particle size of bulk BC, the specific surface area and pore volumes of the derived BC colloids increased, the kinetics model fitted adsorption rates (k2) of the three organics by the BC colloids all largely decreased, and the Langmuir model fitted adsorption capacities (Qmax) increased. The highest Qmax was obtained by BC colloids from the smallest (250 nm) bulk BC with the highest pyrolysis temperature (700 °C), being 212 μmol g−1 for PHN, 815 μmol g−1 for ATZ, and 72.4 μmol g−1 for OTC. The adsorption was reversible for PHN and ATZ, while significant desorption hysteresis was observed for OTC on BC colloids with middle pyrolysis temperatures (300–500 °C). The underlying mechanisms including hydrophobic interaction, π–π electron donor-acceptor interaction, molecular size effect, and irreversible reactions were discussed to explain the difference in the adsorption and desorption behaviors. The findings increased our understanding of the environmental fate and risk of BC.

24725. 题目: Soil carbon dynamics in Indian Himalayan intensified organic rice-based cropping sequences
文章编号: N20032002
期刊: Ecological Indicators
作者: Subhash Babu, Raghavendra Singh, R.K. Avasthe, Gulab Singh Yadav, K.P. Mohapatra, Thiru Selvan, Anup Das, Vinod K. Singh, Donatella Valente, Irene Petrosillo
更新时间: 2020-03-20
摘要: The contribution of soil to supporting, regulating, provisioning and cultural functions as well as its role in the ecosystem services is well-known in the international literature. However, in the domain of organic agriculture, the impact of cropping systems shifts from cereal-cereal to high-frequency diversified cropping sequences with legume as a component crop on soil carbon dynamics is not widely known. In order to identify an alternative cropping system to widely prevalent rice-fallow production system in Himalayan region of India, seven cropping sequences viz., rice -fenugreek (green vegetable) - maize (R-F-M); rice -vegetable pea - maize (R-Vp-M); rice-coriander (leaves)-cowpea (R-C-Cp); rice - fenugreek (green vegetable) - baby corn (R-F-Bc); rice - broccoli - Sesbania (green manuring) (R-B-S); rice - buckwheat (R-Bw) and rice - maize (R-M) were assessed for five consecutive years from 2013 to 2018 for their productivity and resource conservation values. Results revealed that the inclusion of legumes in rice-based sequences increased the rice grain yield by 13.4 to 24.6% over R-M (3.13 Mg ha−1) sequence. The R-B-S sequence had the highest very labile carbon (VLC) (4.6 g kg−1 soil) followed by the R-Vp-M. Relative proportion of various organic carbon fractions in the top 10 cm soil followed the order of VLC (30.2%) > non labile carbon (NLC, 27.6%) > labile carbon (LC, 23.4%) > less labile carbon (LLC, 18.9%). The carbon management index (CMI) was the highest (100.9%) in the R-B-S sequence followed by R-C-Cp (98.0%). The addition of a third crop in the sequence increased the active carbon (AC) pool by 1.1 to 5.8%. The passive carbon (PC) pool was highest in soil under the R-C-Cp sequence (9.15 Mg ha−1) at 0–10 cm soil depth. The carbon retention efficiency under the R-C-Cp cropping sequence was the highest (15.1%) followed by the R-B-S (14.9%). R-B-S and R-C-Cp sequences had 12.5% and 10.6% higher soil microbial biomass carbon (SMBC) over the R-M sequence, respectively. Similarly, R-B-S and R-C-Cp increased the FDA by 49.6 and 41.8%, and DHA by 135.0% and 103.9%, respectively over R-M sequence. In conclusion, the management of crops from organic agriculture aimed at improving soil ecosystem services, in contrasting degradation of soil health and the decline of SOC, can also have positive effects on crop productivity in the eastern Himalayan region of India as well as all over the world.

24726. 题目: Soil organic carbon increase in semi-arid regions of China from 1980s to 2010s
文章编号: N20032001
期刊: Applied Geochemistry
作者: Tao Yu, Yesi Fu, Qingye Hou, Xueqi Xia, Beizhan Yan, Zhongfang Yang
更新时间: 2020-03-20
摘要: Soil carbon plays a key role in agriculture and ecosystem. Semi-arid regions cover many parts of China, holding a carbon pool that should not be ignored. Thus, systematic studies of the carbon distribution and variation in semi-arid regions are necessary. In this study, we comprehensively analyzed the factors that influence the distribution and variation in soil carbon covering area over 0.92 × 106 km2. Results indicated that the average values of soil organic carbon density (at the soil sampling depth of 0–20 cm) in the study area were 0.58–4.50 kg/m2. Soil organic carbon density (SOCD) was clearly related with climate conditions (e.g., temperature and precipitation), soil properties (e.g., pH and soil texture) and human activities. The results revealed a significant negative relationship between SOCD and temperature. Meanwhile, SOCD showed positive relationship with precipitation. Correlation analysis also demonstrated a negative correlation between SOCD and soil pH, but positively associated with soil Al:Si ratio. Land utilization and fertilization would also affect SOCD in the regions. Upon comparing the current data with that of the 1980s, soil organic carbon storage presented a remarkable increasing trend with 2.55 Tg in these studied regions due to land use change. These findings would provide evidences and insights for the future land managements of semi-arid regions of China in the context of global climate change.

24727. 题目: Light absorption of brown carbon in PM2.5 in the Three Gorges Reservoir region, southwestern China: Implications of biomass burning and secondary formation
文章编号: N20031918
期刊: Atmospheric Environment
作者: Chao Peng, Mi Tian, Xiaoliang Wang, Fumo Yang, Guangming Shi, Ru-Jin Huang, Xiaojiang Yao, Qiyuan Wang, Chongzhi Zhai, Shumin Zhang, Ruozhi Qian, Junji Cao, Yang Chen
更新时间: 2020-03-19
摘要: Brown carbon (BrC) is known as a light-absorbing organic aerosol which affects the visibility and radiative forcing budget in the troposphere. The optical properties were studied for filter-based PM2.5 samples collected from the winter of 2015 to the summer of 2016 at one rural and three urban sites in the Three Gorges Reservoir (TGR) region, China. The average light absorption coefficient for BrC (βabs, 405,BrC) at 405 nm and its contributions to total aerosol light absorption during winter were 12.1 ± 7.0 Mm−1 and 23.8 ± 9.1% respectively, higher than those during summer (1.7 ± 0.8 Mm−1 and 11.2 ± 4.1%). Spatially, the average βabs,405,BrC was higher at the urban sites (13.4 ± 7.3 Mm−1) than that at the rural site (7.8 ± 3.2 Mm−1). The average mass absorption efficiency of BrC at 405 nm (MAE405,BrC) was 0.8 ± 0.4 m2 g−1 during winter which was 2.7 times higher than that during summer (0.3 ± 0.1 m2 g−1). Furthermore, the absorption Ångström exponents (AAE) at 405–980 nm (AAE405−980) were 1.1 ± 0.1 in summer and 1.3 ± 0.2 in winter respectively. Correlation analysis suggests that biomass burning (BB) played an important role in βabs,405,BrC during winter. Additionally, the relatively high AAE405−980 during winter was mainly due to the BrC from both BB and secondary organic aerosol. The fractional contribution of solar energy absorption by BrC relative to BC in the wavelengths of 405–445 nm was 23.9 ± 7.8% in summer and 63.7 ± 14.2% in winter, significantly higher than that in the range of 405–980 nm (11.9 ± 3.4% and 29.9 ± 6.1% respectively). Overall, this study contributes to the understanding of sources of BrC in the climate-sensitive TGR region of southwestern China.

24728. 题目: Agroforestry boosts soil health in the humid and sub-humid tropics: A meta-analysis
文章编号: N20031917
期刊: Agriculture, Ecosystems & Environment
作者: Mary N. Muchane, Gudeta W. Sileshi, Sofia Gripenberg, Mattias Jonsson, Lorena Pumariño, Edmundo Barrios
更新时间: 2020-03-19
摘要: Agroforestry has been increasingly recognized as a key example of agroecological praxis contributing to the sustainable intensification of food production while providing a number of additional benefits to society. However, a quantitative synthesis of the impact of agroforestry on soil health and associated ecosystem services in the humid and sub-humid tropics is still lacking. The objective of this study was to quantify the contribution of agroforestry practices to soil-mediated ecosystem services, specifically, regulation of soil erosion, storage of soil organic carbon (SOC) and nitrogen (N), availability of soil N and phosphorus (P) to crops, and alleviation of soil acidity across the humid and sub-humid tropics. The analysis demonstrated that agroforestry can reduce soil erosion rates by 50 % compared to crop monocultures. This finding is supported by higher infiltration rates, lower runoff, higher proportion of soil macroggregates, and greater stability of soil structure under agroforestry. SOC increased by 21 %, N storage increased by 13 %, available N by 46 % and available P by 11 % while soil pH increased by 2% under agroforestry compared to crop monocultures. We conclude that agroforestry can make significant contributions to provision of soil-mediated ecosystem services in the humid and sub-humid tropics.

24729. 题目: Changes in soil micro- and macro-aggregate associated carbon storage following straw incorporation
文章编号: N20031916
期刊: CATENA
作者: Dangwei Pang, Jin Chen, Min Jin, Haoyu Li, Yongli Luo, Wenqian Li, Yonglan Chang, Yong Li, Zhenlin Wang
更新时间: 2020-03-19
摘要: Inadequate soil management strategies weaken soil quality. Soil aggregates and aggregate-associated soil organic carbon (SOC) are important attributes of the soil and can serve as indicators of changes in soil quality. The objective of this study was to optimize an improved soil management that slowed turnover of aggregates and increased SOC storage in Northern China. Four tillage methods were examined: (i) RT (rotary tillage without straw return), (ii) RS (rotary tillage with straw return), (iii) DS (deep tillage with straw return), and (iv) TS (RS applied annually and with DS applied at a two-year interval). The results indicated that straw return treatments increased macroaggregate formation and sequestrated greater SOC. The C inputs among RS, DS, and TS were similar in magnitude, ranging from 8.86 to 8.99 t ha−1 year−1. Compared to RS, DS enhanced the turnover of macroaggregates in the 0–20 cm layers, and led to more SOC loss in occluded microaggregates than in macroaggregates in the 0–30 cm layers, indicating a reduced protection of aggregates to SOC. Similar to DS, the mass of macroaggregates under TS was greater than RS in the 10–30 cm layers. However, TS increased the SOC storage in macroaggregates by 0.66 and 0.90 t ha−1 in the 0–30 cm layers, respectively, compared to RS and DS. Moreover, the SOC storage in occluded microaggregates under TS was 0.52 and 1.06 t ha−1 greater than RS and DS, respectively, in the 0–30 cm layers. SOC variations among treatments in this study were dominated by tillage methods; thus, appropriate soil disturbance in deep layers (TS) has great potential in activating more C sequestration in macroaggregates and occluded microaggregates. These findings are of great importance for formulating soil management strategy and probably beneficial for crop production.

24730. 题目: On-line recovery system coupled to a Rock-Eval® device: An analytical methodology to characterize liquid and solid samples
文章编号: N20031915
期刊: Organic Geochemistry
作者: Pierre Cadeau, Maria-Fernanda Romero-Sarmiento, Olivier Sissmann, Valérie Beaumont
更新时间: 2020-03-19
摘要: The Rock-Eval® device has been widely used to identify the type and the thermal maturity of sedimentary organic matter as well as quantifying the total organic carbon content. Traditionally, it is a screening tool to estimate the petroleum generation potential of source rocks using standardize parameters. More recently, a new Rock-Eval® method (Shale PlayTM) was proposed to investigate the hydrocarbon content in liquid-rich tight rock samples. In this study, we describe a dual vacuum and on-line system that was developed to recover most compounds that are thermally released during a Rock-Eval® Shale PlayTM analysis. Thermally vaporized products are divided so that half is analyzed by the Rock-Eval® flame ionization detector (FID) while the other portion is cryogenically trapped in the on-line recovery system. The trapped products can then be transferred via a vacuum line system into a sample vial for subsequent molecular and/or isotopic composition analyses. The recovery vacuum line volumes were calibrated using known quantities of gas (CH4 and CO2). Sample transfer from without isotopic fractionation was demonstrated for CO2 evolved from Rock-Eval® preparation of pure carbonate standards (siderite, magnesite and azurite). Recovery efficiencies were first measured on C8-C16 n-alkane standards and then on produced oil samples. Results indicate a high quantitative recovery and an accurate mass balance of most compounds released during the Shale PlayTM Sh0 thermovaporization step (100-200°C). Thermally vaporized compounds released at higher temperatures Sh1 (200-350°C) are recovered at lower efficiencies but are still suitable for subsequent characterization. The coupled Rock-Eval® and recovery system could have applications beyond petroleum geochemistry.

24731. 题目: Bio-reduction of ferrihydrite-montmorillonite-organic matter complexes: Effect of montmorillonite and fate of organic matter
文章编号: N20031914
期刊: Geochimica et Cosmochimica Acta
作者: Qiang Zeng, Liuqin Huang, Jinyu Ma, Zihua Zhu, Chen He, Quan Shi, Wen Liu, Xi Wang, Qingyin Xia, Hailiang Dong
更新时间: 2020-03-19
摘要: Organic matter (OM) is often associated with Fe (hydr)oxides such as ferrihydrite (Fh) in soils and sediments, forming binary Fh-OM complexes. Microbial reduction of Fh results in destabilization of the complexes and mineral/OM transformation. However, little is known about the role of clay minerals in such processes, despite their common co-existence with Fh and OM in natural environments. Here Fh-OM complexes were synthesized in the presence of montmorillonite (SWy-2), forming ternary Fh-(SWy-2)-OM complexes. A metal-reducing bacterium Geobacter sulfurreducens was used to reduce Fh in the complexes under circumneutral pH and anoxic conditions with or without H2 as extra electron donor. Various spectroscopy and mass spectrometry methods were used to monitor the progress of Fh bio-reduction and mineral/OM transformation. Results showed that G. sulfurreducens utilized mineral-bound OM as electron donor and/or carbon source to couple with Fh reduction. Relative to Fh-OM complex, Addition of SWy-2 to Fh-OM complex enhanced the bio-reduction extent of Fh by increasing the proportion of bioavailable OM that was weakly bound to SWy-2. However, its effect on the bio-reduction rate was variable. SWy-2 initially decreased the rate, because it spatially separated OM (electron donor) from Fh (electron acceptor). During later incubation, SWy-2 increased the reduction rate by sorbing biogenic Fe2+ that would otherwise passivate the Fh and cell surfaces. Bio-reduction transformed mineral-bound OM to microbial products (e.g. necromass, extracellular polymeric substances), but organic compounds with aromatic structures, carboxyl groups and large molecular weight were more resistant to desorption and oxidation. The persistence of these compounds against bio-reduction induced transformation is likely due to their stronger binding with minerals and/or lower nominal oxidation states of carbon relative to other compounds. Our results provide new insights into the role of clay minerals in regulating biogeochemical cycling of solid-phase Fe and transformation of mineral-associated OM in anoxic soil environments.

24732. 题目: Investigation of hydrolysis acidification process during anaerobic treatment of coal gasification wastewater (CGW): Evolution of dissolved organic matter and biotoxicity
文章编号: N20031913
期刊: Science of The Total Environment
作者: Zhiqiang Chen, Da Li, Qinxue Wen
更新时间: 2020-03-19
摘要: Coal gasification wastewater (CGW) contains several types of aromatic pollutants, which impart high biotoxicity and reduce the quality of anaerobic treatment. Two types of hydrolysis acidification processes, namely microaerobic hybrid reactor (HA-1) and upflow anaerobic sludge blanket reactor (HA-2), were developed for pre-treatment before the anaerobic treatment. The changes in the dissolved organic matter and biotoxicity were investigated to comprehensively understand the degradation process. The results showed that HA-2 coupled with an anaerobic reactor achieved a 12.3% and 13.4% higher removal efficiency for chemical oxygen demand and total phenols, respectively, compared with the coupled process with HA-1. Furthermore, HA-2 could transform macromolecules into small molecules more efficiently and produce fewer intermediates. The coupled process with HA-2 preferentially removed complex aromatic substances with absorption wavelengths of 285 and 254 nm, according to the sequential orders interpreted from two-dimensional correlation spectroscopy. In addition, the results of fluorescence excitation-emission-matrix with regional integration analysis revealed that the contents of typical cyclic compounds in CGW, such as phenolic, heterocyclic, and polycyclic aromatic compounds were remarkably reduced by HA-2. In addition, HA-2 reduced the toxic unit value of CGW by 67.5% and increased the resazurin dehydrogenase activity of the sludge by 37.5% during CGW treatment, thus improving the biotoxicity removal and biodegradability. However, the coupled process with HA-2 did not significantly affect the indirect estrogenic activity of CGW. A Pearson correlation analysis indicated that spectral indicators, such as UV254 and ΦT,n, presented a high positive correlation with the reduction of acute toxicity and organics.

24733. 题目: Apply biochar to ameliorate soda saline-alkali land, improve soil function and increase corn nutrient availability in the Songnen Plain
文章编号: N20031912
期刊: Science of The Total Environment
作者: Wei Zhao, Qin Zhou, Zongze Tian, Yutong Cui, Ying Liang, Hongyan Wang
更新时间: 2020-03-19
摘要: Soda saline-alkali soils are characterized by high concentration of sodium cations on the exchange complex or in soil-water resulting in soils which are physically as well as nutritionally challenging for crop production. Biochar application has received growing interest as a sustainable technology to improve physicochemical properties in non-saline and non-alkali soils. However, information is inadequate regarding potential of using corn straw derived biochar as an organic material to reduce soda saline-alkali stress. Based on the established model of corn straw biochar-soda saline alkali soil-corn system, soil and plant samples were collected from long-term field experiment in soda saline-alkali land with different addition rates of corn straw biochar (CK: control, T5: 5 ton ha−1, T10: 10 ton ha−1, T15: 15 ton ha−1, T20: 20 ton ha−1, T25: 25 ton ha−1, T30: 30 ton ha−1). In the seedling and harvest period, addition of corn straw biochar enhanced the contents of cation exchange capacity (CEC), organic matter, and nutrients of 0–20 cm and 20–40 cm saline-alkali soil layers and the above ground and underground parts of corn. However, the results were contrary as far as pH, salt, and Na+ were concerned, and the effect of T20 was the most significant. Principal component analysis showed that CEC, pH, salinity, and organic matter could be used as indicators to evaluate the improvement effect of biochar on soda saline-alkali soil. Irrespective of the application of biochar, pH, salt content, Na+, and nutrients concentrations at seedling stage were higher than those at harvest stage, indicating that planting corn could improve soda saline-alkali soil. It may be concluded that corn straw biochar can be used as an organic amendment for reducing adverse effects of salinity and alkalinity on soil functions governed by their rates of addition.

24734. 题目: Dissolved organic nutrient uptake by riverine phytoplankton varies along a gradient of nutrient enrichment
文章编号: N20031911
期刊: Science of The Total Environment
作者: E.B. Mackay, H. Feuchtmayr, M.M. De Ville, S.J. Thackeray, N. Callaghan, M. Marshall, G. Rhodes, C.A. Yates, P.J. Johnes, S.C. Maberly
更新时间: 2020-03-19
摘要: The concentration of dissolved organic matter (DOM) in freshwaters is increasing in large areas of the world. In addition to carbon, DOM contains nitrogen and phosphorus and there is growing concern that these organic nutrients may be bioavailable and contribute to eutrophication. However, relatively few studies have assessed the potential for dissolved organic nitrogen (DON) or dissolved organic phosphorus (DOP) compounds to be bioavailable to natural river phytoplankton communities at different locations or times. Temporal and spatial variations in uptake, relative to environmental characteristics were examined at six riverine sites in two contrasting catchments in the UK. This study also examined how the uptake by riverine phytoplankton of four DON and four DOP compounds commonly found in rivers, varied with concentration. Total nitrogen (TN) and phosphorus (TP) concentrations, the proportion of inorganic nutrient species, and nutrient limitation varied temporally and spatially, as did the potential for DON and DOP uptake. All eight of the DOM compounds tested were bioavailable, but to different extents. Organic nutrient use depended on the concentration of the organic compound supplied, with simple compounds (urea and glucose-6-phosphate) supporting algal growth even at very low concentrations. DON use was negatively correlated with the TN and ammonia concentration and DOP use was negatively correlated with soluble reactive phosphorus (SRP) and dissolved organic carbon (DOC) concentration. The evidence indicates that DOM in rivers has been overlooked as a potential source of nutrients to phytoplankton and therefore as an agent of eutrophication.

24735. 题目: Tracking the evolution of particulate organic matter sources during summer storm events via end-member mixing analysis based on spectroscopic proxies
文章编号: N20031910
期刊: Chemosphere
作者: Morgane Derrien, Mi-Hee Lee, Kwangsoon Choi, Kwang-Sik Lee, Jin Hur
更新时间: 2020-03-19
摘要: Despite the growing attention to the effects of hydrological precipitation on organic carbon export along the continuum land-river-ocean, limited effort has been made to understand the export and the reactivity of particulate organic carbon (POC) compared to those of dissolved organic carbon (DOC). Yet, further understanding of the controlling mechanisms on the export of particulate organic matter (POM) from terrestrial systems is fundamental. In this study, we assessed the temporal changes of the source contributions to riverine POM in two adjacent rivers of the same watershed during two summer storm events, which included the early and the late events, using end-member mixing analysis (EMMA) based on spectroscopic proxies. The EMMA showed relatively high contributions of terrestrial materials to the riverine POM for both rivers during the early summer storm event. However, this trend did not persist until the late summer storm event, which presented the decreased contributions of the terrestrial sources and less dynamic changes in the source distributions compared to those observed in the early summer rain event. These results demonstrate the combined impacts of the land use/surrounding area, the hydrology, and the intra-seasonal variations on the dominant riverine POM sources. This study provides an interesting insight into the importance of the intense hydrological events on the export of the terrestrial OM and further on the potential modification of the existing carbon mass balance along the continuum land-river-ocean.

24736. 题目: Nitrogen addition increased CO 2 uptake more than non-CO 2 greenhouse gases emissions in a Moso bamboo forest
文章编号: N20031909
期刊: Science Advances
作者: Xinzhang Song, Changhui Peng, Philippe Ciais, Quan Li, Wenhua Xiang, Wenfa Xiao, Guomo Zhou, Lei Deng
更新时间: 2020-03-19
摘要: Atmospheric nitrogen (N) deposition affects the greenhouse gas (GHG) balance of ecosystems through the net atmospheric CO 2 exchange and the emission of non-CO 2 GHGs (CH 4 and N 2 O). We quantified the effects of N deposition on biomass increment, soil organic carbon (SOC), and N 2 O and CH 4 fluxes and, ultimately, the net GHG budget at ecosystem level of a Moso bamboo forest in China. Nitrogen addition significantly increased woody biomass increment and SOC decomposition, increased N 2 O emission, and reduced soil CH 4 uptake. Despite higher N 2 O and CH 4 fluxes, the ecosystem remained a net GHG sink of 26.8 to 29.4 megagrams of CO 2 equivalent hectare −1 year −1 after 4 years of N addition against 22.7 hectare −1 year −1 without N addition. The total net carbon benefits induced by atmospheric N deposition at current rates of 30 kilograms of N hectare −1 year −1 over Moso bamboo forests across China were estimated to be of 23.8 teragrams of CO 2 equivalent year −1 .

24737. 题目: Community dynamics of As(V)-reducing and As(III)-oxidizing genes during a wet–dry cycle in paddy soil amended with organic matter, gypsum, or iron oxide
文章编号: N20031908
期刊: Journal of Hazardous Materials
作者: Chaolei Yuan, Jiangtao Qiao, Fangbai Li, Xiaofeng Zhang, Yanhong Du, Min Hu, Weimin Sun
更新时间: 2020-03-19
摘要: Microbe-mediated redox transformations regulate arsenic mobility in paddy soil. However, the community dynamics of the related genes, which might be affected by soil ameliorants, have not been systematically investigated during a wet–dry cycle. This study incubated arsenic-contaminated paddy soil amended with organic matter (OM), gypsum, or hematite in microcosms under alternate watering conditions. Added gypsum and hematite reduced arsenic mobility in the soil by 8–60% during the wet and dry periods. However, added OM increased arsenic mobility by 70–130% during the first 4 weeks (not the last 4 weeks) of submergence and the dry period. The results of quantitative real-time polymerase chain reaction (qPCR) depended heavily on the primers used, so the contribution of relevant genes to arsenic transformation cannot be compared using only the gene abundance assessed by qPCR. However, correlation analyses showed that the abundance and community members of the arrA gene, which mediates dissimilatory As(V) reduction [i.e., As(V) respiration], were related to soil arsenic concentrations. This was not the case for the arsC gene, which mediates cytoplasmic As(V) reduction, or the aioA gene, which mediates As(III) oxidation. These suggest that the dissimilatory pathway was mainly responsible for arsenic reduction and release in the soil studied.

24738. 题目: Influence characteristics and mechanism of organic carbon on denitrification, N2O emission and NO2− accumulation in the iron [Fe(0)]-oxidizing supported autotrophic denitrification process
文章编号: N20031907
期刊: Chemical Engineering Journal
作者: Shihai Deng, Shuai Peng, Binghan Xie, Xue Yang, Shaobin Sun, Hong Yao, Desheng Li
更新时间: 2020-03-19
摘要: Iron [Fe(0)]-oxidizing supported autotrophic denitrification [Fe(0)-AD] is a promising process for low-carbon water treatment. Organic-carbon (OC) has been a common pollutant associated with nitrogen pollution. However, its interaction with Fe(0)-AD remains unclear. In this study, influence characteristics and mechanism of OC on Fe(0)-AD were investigated. Fe(0)-AD was established based on iron-scraps (ISs) and iron-carbon micro-electrolysis (ME) (ME-ISs-AD). The results showed that the OC-free ME-ISs-AD obtained denitrification load of 0.191 ± 0.028 kgN/(m3·d), which shifted to 0.445 ± 0.011 kgN/(m3·d) at OC-dosage of 1.0 mgCOD/mgTN. N2O (1.52 ± 0.16 mgN/L) and NO2− (6.86 ± 1.11 mgN/L) accumulated markedly in Fe(0)-AD and were reduced to 0.03 ± 0.01 mgN/L and 0.31 ± 0.20 mgN/L at OC-dosage of 1.0 mgCOD/mgTN, respectively. XRD analysis demonstrated that OC could reduce the Fe(0)-passivation, accelerating biological transformation and storage of iron-compounds, enhancing H2 (from 0.06 ± 0.01 to 0.22 ± 0.04 mg/L) and Fe2+ (from 7.4 ± 1.0 to 13.9 ± 1.5 mg/L) production. High-throughput sequencing revealed the enrichment of iron-oxidizing bacteria (e.g. Sphaerotilus and Ferriphaselus) and autotrophic denitrifiers (e.g. Hydrogenophaga and Hyphomicrobium). Real-time qPCR and enzyme activity analysis indicated that the nosZ-encoded NosZ and nirK-encoded NIR controlled N2O and NO2− accumulation in OC-dosed Fe(0)-AD, respectively. Overdose of OC (≥1.5 mgCOD/mgTN) accelerated the bio-organics-Fe complexes (BioFe) production and blocked the H2/Fe2+ transfer. NaAC was more efficient and cost-effective than Glucose and EtOH for Fe(0)-AD enhancement. The utilization of ISs under the enhancement of ME reduced the cost of Fe(0)-AD by 3.87-times comparing to the in-situ ZVI-AD process, and the dose of OC further improved the denitrification load by 1.33-times. This study provided an in-depth understanding of the influence of OC on Fe(0)-AD and could contribute to the application, optimization and secondary pollutants control of Fe(0)-AD process in low-carbon water treatment.

24739. 题目: Post-glacial lake development and paleoclimate in the central Hudson Bay Lowlands inferred from sediment records
文章编号: N20031906
期刊: Journal of Paleolimnology
作者: Kathryn E. Hargan, Sarah A. Finkelstein, Kathleen M. Rühland, Maara S. Packalen, April S. Dalton, Andrew M. Paterson, Wendel Keller, John P. Smol
更新时间: 2020-03-19
摘要: We compile a multi-proxy Holocene record from North Raft Lake located in the sub-Arctic Hudson Bay Lowlands, Canada. Specifically, we use subfossil chironomid, diatom, and pollen assemblages, non-pollen palynomorphs, sedimentary chlorophyll a, magnetic susceptibility, and organic matter content to characterize terrestrial and lake processes and to track paleoclimate following land emergence from the postglacial Tyrrell Sea. Following recession of the Tyrrell Sea (~ 6600 cal yr BP), pollen assemblages are indicative of a salt marsh environment with the establishment of an opportunistic chironomid assemblage. By ~ 6200 cal yr BP, isostatic uplift reduced the marine influence and pollen and palynomorph assemblage changes indicate that North Raft Lake became a closed-basin freshwater system. At this time, pollen assemblages signify the establishment of a forested peatland dominated by Picea, and chironomid taxa indicate warming water temperatures. The North Raft Lake pollen/palynomorph record captures a warm and moist mid-Holocene (Holocene Thermal Maximum) period starting ~ 6200 cal yr BP. During this period, an increase in pollen concentration and a shift to higher abundances of Larix indicate watershed-scale succession and enhanced local ecosystem productivity. Shifts in chironomid taxa at ~ 5000 cal yr BP are indicative of abrupt limnological changes suggesting wet conditions that caused an expansion of littoral habitat. The gradual transition into Neoglacial cooling is signaled by an increase in the abundances of cold-stenothermal chironomid taxa and a small decline in pollen-reconstructed temperatures. Marked changes occur in the mid-twentieth century with the appearance of diatoms in notable abundances for the first time in the lake's sedimentary record, the arrival of new chironomid littoral taxa, and unprecedented increases in sedimentary chlorophyll a and organic matter content. Throughout the North Raft Lake Holocene sediment record, the pollen trends suggest slow centennial-scale changes in temperature and precipitation, whereas chironomid assemblages indicate abrupt mid-Holocene and twentieth century limnological changes, stressing that biota in lakes of the Hudson Bay Lowlands may change substantially under future scenarios of global climate warming.

24740. 题目: Elucidating the role of earthworms for the formation of organo-mineral associations in soil
文章编号: N20031905
期刊: Soil Biology and Biochemistry
作者: T. Guhra, K. Stolze, S. Schweizer, K.U. Totsche
更新时间: 2020-03-19
摘要: Earthworms are considered as ecosystem engineers impacting soil properties as well as nutrient and element cycles. To facilitate their movement through the soil, earthworms excrete extracellular polymeric substances, commonly referred to as earthworm cutaneous mucus. This type of biogenic organic matter may serve as nutrient source for plants and microorganisms. While the impact of earthworms burrowing through and ingesting the soil as well as earthworm-formed aggregate properties are rather well studied, still little is known about the interaction of mucus with soil constituents. The objective of this study was to investigate the small-scale interactions between earthworm mucus and secondary soil minerals, e.g. goethite and illite, and the resulting formation of organo-mineral associations. For this, we characterized the chemical composition of earthworm mucus by FTIR and 13C-NMR and compared the findings with those of microbial EPS as abundant and well investigated type of organic matter in soil. Mucus from anecic (Lumbricus terrestris L.) and endogeic (Aporrectodea caliginosa Sav.) earthworm species was dominated by proteins and carbohydrates. Adsorption to illite and goethite was pronounced and accompanied by a distinct compositional fractionation of mucus between the solid and liquid phase especially for goethite as shown by the investigation of mineral-freed supernatants after conducting completely mixed batch reactor experiments. Furthermore, we identified the formation of organo-mineral associations and determined the surface charge by measuring the isoelectric point (IEP). The IEP of mucus-goethite associations was lower while the IEP of mucus-illite associations was higher than the corresponding pure mineral phase. Our results show that the specific adsorption of earthworm mucus constituents to soil minerals results in the formation of mucus-mineral associations. These associations contribute to the enrichment of nutrient elements in the drilosphere and earthworm-formed aggregates. Furthermore, they explain the altered properties of earthworm-formed aggregates in comparison to the earthworm unaffected bulk soil material.