12441. 题目: Dissolved Organic Matter Controls Seasonal and Spatial Selenium Concentration Variability in Thaw Lakes across a Permafrost Gradient
期刊: Environmental Science & Technology
作者: Oleg S. Pokrovsky, Maite Bueno, Rinat M. Manasypov, Liudmila S. Shirokova, Jan Karlsson, David Amouroux
摘要: Little is known about the sources and processing of selenium, an important toxicant and essential micronutrient, within boreal and sub-arctic environments. Upon climate warming and permafrost thaw, the behavior of Se in northern peatlands becomes an issue of major concern, because a sizable amount of Se can be emitted to the atmosphere from thawing soils and inland water surfaces and exported to downstream waters, thus impacting the Arctic biota. Working toward providing a first-order assessment of spatial and temporal variation of Se concentration in thermokarst waters of the largest frozen peatland in the world, we sampled thaw lakes and rivers across a 750-km latitudinal profile. This profile covered sporadic, discontinuous, and continuous permafrost regions of western Siberia Lowland (WSL), where we measured dissolved (<0.45 μm) Se concentration during spring (June), summer (August), and autumn (September). We found maximum Se concentration in the discontinuous permafrost zone. Considering all sampled lakes, Se exhibited linear relationship (R2 = 0.7 to 0.9, p < 0.05, n ≈ 70) with dissolved organic carbon (DOC) concentration during summer and autumn. Across the permafrost gradient, the lakes in discontinuous permafrost regions demonstrated stronger relationship with DOC and UV-absorbance compared to lakes in sporadic/isolated and continuous permafrost zones. Both seasonal and spatial features of Se distribution in thermokarst lakes and ponds suggest that Se is mainly released during thawing of frozen peat. Mobilization and immobilization of Se within peat–lake–river watersheds likely occurs as organic and organo-Fe, Al colloids, probably associated with reduced and elemental Se forms. The increase of active layer thickness may enhance leaching of Se in the form of organic complexes with aromatic carbon from the deep horizons of the peat profile. Further, the northward shift of permafrost boundaries in WSL may sizably increase Se concentration in lakes of continuous permafrost zone.
12442. 题目: Biochar enhances soil hydraulic function but not soil aggregation in a sandy loam
期刊: European Journal of Soil Science
作者: H. Zhou, H. Fang, Q. Zhang, Q. Wang, C. Chen, S. J. Mooney, X. Peng, Z. Du
摘要: Biochar has the potential to modify soil structure and soil hydraulic properties because of its small particle density, highly porous structure, grain size distribution and surface chemistry. However, knowledge of the long‐term effects of biochar on soil physical properties under field conditions is limited. Using an 8‐year field trial, we investigated the effect of successive additions of high‐dose maize cob‐derived biochar (9.0 t ha‐1 year‐1, HB), low‐dose maize cob‐derived biochar (4.5 t ha‐1 year‐1, LB), straw return (SR) and control (no biochar or straw, CK) on soil aggregate distribution, three‐dimensional (3‐D) pore structure, hydraulic conductivity and water retention in the upper 10 cm of a sandy loam soil from the North China Plain. Results showed that LB and HB treatments increased soil organic C content by 61.0–116.3% relative to CK. Interestingly, biochar amendment did not enhance the proportion of macroaggregates (>2 and 0.25–2 mm) or aggregate stability, indicating limited positive effects on soil aggregation. The HB treatment decreased soil bulk density, increased total porosity and macroporosity (>30 μm). The retention of soil water, including gravitational water (0–33 kPa), capillary water (33–3100 kPa) and hygroscopic water (> 3100 kPa), were all improved under HB soil. The HB and LB treatments increased plant available water content by 17.8 and 10.1%, respectively, more than that of CK. In contrast, SR showed no significant increase in soil porosity and water retention capacity but improved the water stability of macroaggregates. We concluded that biochar used in the coarse‐textured soil enhanced saturated hydraulic conductivity and water‐holding capacity, but did not improve soil aggregation.
12443. 题目: Decreased sedimentation efficiency of petro- and non-petro-carbon caused by a dispersant for Macondo surrogate oil in a mesocosm simulating a coastal microbial community
期刊: Marine Chemistry
作者: Chen Xu, Saijin Zhang, Morgan Beaver, Andrew Wozniak, Wassim Obeid, Youmin Lin, Terry L. Wade, Kathleen A. Schwehr, Peng Lin, Luni Sun, Patrick G. Hatcher, Wei-Chun Chin, Meng-Hsuen Chiu, Anthony H. Knap, Kendra Dean, Antonietta Quigg, Peter H. Santschi
摘要: Large amounts of mucous-rich oil-containing marine snow formed in surface waters adjacent to the Deepwater Horizon spill. This marine oil snow (MOS) was implicated in oil delivery to the seafloor. Whether the use of chemical dispersants increased or decreased MOS sedimentation remains controversial. We conducted mesocosm experiments testing the effects of oil and oil plus a dispersant on MOS formation and sedimentation, in coastal seawater. The four treatments used were a surrogate Macondo oil water accommodated fraction (“WAF”), two concentrations of chemically-enhanced WAF (“CEWAF” and diluted CEWAF, “DCEWAF”) containing a dispersant and oil, and Controls (no additions). Based on radiocarbon and 13C NMR results, the presence of dispersants enhanced the amounts of petro-carbon being incorporated into the sinking oil-carrying aggregates (aka MOS). However, most of chemically-dispersed oil preferentially partitioned into the colloidal and suspended particulate fractions rather than into the rapidly forming MOS. Thus the oil and non-petro-carbon sedimentation efficiency in treatments with a dispersant was much lower, compared to those in the Control and WAF treatments, during the four-day mesocosm experiment. Formation of MOS and its subsequent sinking sequestered the oil in two stages: first via terrestrial-derived detritus containing humic compounds, and subsequently via freshly produced material, such as exopolymeric substances produced by phytoplankton and bacteria.
12444. 题目: Tropical peatland carbon storage linked to global latitudinal trends in peat recalcitrance
期刊: Nature Communications
作者: Suzanne B. Hodgkins, Curtis J. Richardson, René Dommain, Hongjun Wang, Paul H. Glaser, Brittany Verbeke, B. Rose Winkler, Alexander R. Cobb, Virginia I. Rich, Malak Missilmani, Neal Flanagan, Mengchi Ho, Alison M. Hoyt, Charles F. Harvey, S. Rose Vining, Moira A. Hough, Tim R. Moore, Pierre J. H. Richard, Florentino B. De La Cruz, Joumana Toufaily, Rasha Hamdan, William T. Cooper, Jeffrey P. Chanton
摘要: Peatlands represent large terrestrial carbon banks. Given that most peat accumulates in boreal regions, where low temperatures and water saturation preserve organic matter, the existence of peat in (sub)tropical regions remains enigmatic. Here we examined peat and plant chemistry across a latitudinal transect from the Arctic to the tropics. Near-surface low-latitude peat has lower carbohydrate and greater aromatic content than near-surface high-latitude peat, creating a reduced oxidation state and resulting recalcitrance. This recalcitrance allows peat to persist in the (sub)tropics despite warm temperatures. Because we observed similar declines in carbohydrate content with depth in high-latitude peat, our data explain recent field-scale deep peat warming experiments in which catotelm (deeper) peat remained stable despite temperature increases up to 9 °C. We suggest that high-latitude deep peat reservoirs may be stabilized in the face of climate change by their ultimately lower carbohydrate and higher aromatic composition, similar to tropical peats.
12445. 题目: Effects of Different Land Types on Soil Enzyme Activity in the Qinghai Lake Region
作者: Yuguo Yang, Ying Yang, Yuqing Geng, Guilin Huang, Xueqing Cui, Meng Hou
摘要: This study sought to investigate the influence of different land types on soil enzyme activities and identify the driving factors behind it. Three prevalent land cover types and one land use type by Qinghai Lake were selected (original wetland, natural grassland, recovered shrubland, and farmland), and the surface soil at a depth of 0–10 cm was collected for analysis. The results indicated that soil organic carbon, active carbon, dissolved organic carbon, total nitrogen content, microbial biomass, and soil hydrolase activity decreased, whereas phenol oxidase activity increased after converting the wetland into other land types. However, the differences in microbial biomass and enzyme activities between farmland and recovered shrubland were not significant. Similar trends in β-glucosidase and cellobiohydrolase activities were detected and these were more sensitive to the changes in land types. Soil carbon and nitrogen contents were shown to be responsible for the variability in hydrolase activity, with active carbon showing the strongest influence. Wetland conversion induces the loss of soil carbon and nitrogen stock, which may further decrease the availability of organic matter for microbes. A decrease in hydrolase activity and an increase in phenol oxidase activity may indicate shifts in organic carbon bioavailability after wetland conversion.
12446. 题目: Submarine groundwater discharge-derived carbon fluxes in mangroves: An important component of blue carbon budgets?
期刊: Journal of Geophysical Research: Oceans
作者: Xiaogang Chen, Fenfen Zhang, Yanling Lao, Xilong Wang, Jinzhou Du, Isaac R. Santos
摘要: Mangroves are blue carbon systems characterized by high soil carbon storage and sequestration. Soil carbon losses via groundwater or pore water pathways are potentially important yet poorly understood components of mangrove carbon budgets. Here, we quantified submarine groundwater discharge (SGD) and associated dissolved inorganic carbon (DIC) and organic carbon (DOC) fluxes into a mangrove‐dominated tropical bay (Maowei Sea, hereafter MWS) using a radon (222Rn) mass balance model. The SGD fluxes in MWS were estimated to be 4.9 × 107 (0.36 ± 0.33 m d−1) and 2.6 × 107 m3 d−1 (0.20 ± 0.18 m d−1) for the wet and dry seasons, respectively, implying that SGD may respond to precipitation. The SGD‐derived DIC and DOC fluxes (mol m−2 d−1) in the wet season (DIC: 0.70 ± 0.82; DOC: 0.31 ± 0.30) were higher than those in the dry season (DIC: 0.25 ± 0.24; DOC: 0.25 ± 0.23). These SGD‐derived carbon fluxes exceed local river inputs and constituted > 70% of the total DIC and DOC input into the bay. If scaled up to the global weighted mangrove area in combination with data from other 32 study sites, carbon fluxes via SGD into mangroves may be equivalent to 29–48% of the global riverine input into the ocean. Therefore, we suggest that SGD is a major component of coastal carbon budgets and that accounting for SGD helps to reduce uncertainties in mangrove blue carbon budgets.
12447. 题目: Short-term carbon emissions: Effect of various tree harvesting, transport and tillage methods under a eucalyptus plantation
期刊: Land Degradation & Development
作者: Ricardo Cardoso Fialho, Rafael da Silva Teixeira, Ana Paula Mendes Teixeira, Ivo Ribeiro da Silva
摘要: Eucalyptus forests stand out for their potential to sequestrate atmospheric CO2 in soil organic matter (SOM) throughout its growth. Our study evaluated the harvesting and tillage effect in eucalyptus plantations to the soil CO2, 13C‐CO2 and CH4 fluxes. The study was carried out in a eucalyptus plantation, under Typic Haplustox. The study used stands cultivated with eucalyptus at the end of the first rotation (7‐years), established over degraded pastures. The effect of harvesting was assessed through comparisons of samples taken before and after harvesting with Feller + Skidder (F+S) and Harvester + Forwarder (H+F) methods and separate samples of plant rows (R) and plant inter‐rows (IR). The effect of tillage was assessed through comparisons of R and IR samples taken before and after subsoiling tillage in areas harvested with F+S and H+F methods. A nested experimental design was used with eight replicates. The harvest operation (F+S and H+F methods) in eucalyptus plantations increased soil CO2 fluxes, which were primarily derived from eucalyptus materials (“new C”). The F+S harvesting method resulted in the highest soil density (Ds) and soil moisture (SM) reduction in the IR. The tillage operation (subsoiling) resulted in higher soil CO2 fluxes in eucalyptus plantations harvest with F+S and H+F methods. However, the H+F method preserved the older SOC” (40.8% in R and 50.4% IR of C4‐CO2). The soil in the eucalyptus plantations showed soil CH4 influxes, and the harvest and tillage (subsoiling) operations did not negatively affect the net soil CH4 influx in the studied eucalyptus plantations.
12448. 题目: Wetland Soil Properties and Resident Bacterial Communities Are Influenced by Changes in Elevation
作者: Philip O. Lee, Cory Shoemaker, Julie B. Olson
摘要: Soils from four sites distributed along an elevation gradient from marsh to coastal forest in a wetland bordering the Gulf of Mexico were sampled over a 16-months period. In addition to measuring a suite of environmental conditions, terminal restriction fragment length polymorphism analyses of the resident bacterial communities were performed. Wetland soil bacterial communities varied across both space and time, with all measured variables (temperature, pH, percentage of soil organic matter, salinity, and concentrations of sulfide, NH4+, NO3−, and soluble reactive phosphorus) showing significant site by time interactions. Analyses of bacterial communities showed both marsh zones (Spartina and Cladium) supported similar communities, as did the ecotone and coastal forest. Bacterial communities within coastal forest soils were significantly different than those within marsh soils, and the ecotone communities were significantly different from the Spartina marsh soil. Temperature and pH were the most influential environmental factors impacting bacterial community composition but no predictable patterns were identified, suggesting that community changes are likely the result of intrinsic factors that are affected by local-scale processes. The dynamic nature of the physiochemical variables within wetlands suggests that more work is needed to determine potential interactive effects on bacterial community structure.
12449. 题目: Removal and recovery of phosphate from water by Mg-laden biochar: batch and column studies
期刊: Colloids and Surfaces A: Physicochemical and Engineering Aspects
作者: Dan Jiang, Bei Chu, Yoshimasa Amano, Motoi Machida
摘要: The work investigated the potential application of Mg-laden biochar prepared from Mg-enriched bamboo to remove and recover phosphate from water. The Mg-laden biochar samples were synthesized at 400 °C, 500 °C and 600 °C. With the increasing synthesized temperature, the production rate of adsorbent decreased but the Mg content and specific surface area increased. Factors on phosphate adsorption including kinetic, isotherm, pH, dosage were examined through batch experiments. The maximum phosphate adsorption amount was 344, 357 and 370 mg/g for biochar-Mg-400, biochar-Mg-500 and biochar-Mg-600, respectively. The effect of phosphate adsorption on Mg-laden biochar samples was also investigated by fixed-bed column experiments, and the maximum adsorption amount calculated by Thomas model was 60.7, 61.2 and 62.2 mg/g, respectively. The adsorbed phosphate could be successfully desorbed by 3 M NaOH solution and the regenerated Mg-laden biochar samples could be reused at least 5 times for phosphate adsorption. The bioavailability of postsorption biochar was proved very well through the Mehlich 3 method. Phosphate adsorption characteristic and FTIR analysis indicated that the adsorption was mainly controlled by two mechanisms: ligand exchange and electrostatic attraction.
12450. 题目: Effect of functional groups of biochars and their ash content on gaseous methyl tert-butyl ether removal
期刊: Colloids and Surfaces A: Physicochemical and Engineering Aspects
作者: Waleeporn Pongkua, Rujira Dolphen, Paitip Thiravetyan
摘要: Air pollution is considered a major problem, especially the pollution from transportation. Methyl tert-butyl ether (MTBE) is commonly used as a gasoline additive. MTBE is obtained from incomplete combustion of gasoline and causes environmental problems. Biochars derived from agricultural waste, including rice husk, bone, corncob, bamboo, sawdust and bagasse, were used for methyl tert-butyl ether (MTBE) removal. It was found that bagasse biochar had the highest maximum adsorption capacity (Qmax) (8.26 mg g-1), while bone biochar had the lowest (3.51 mg g-1). It might be due to the fact that bone biochar had the highest ash content and functional groups of bone biochar surface was mainly phosphate and ether groups. These functional groups cannot react with MTBE. While bagasse biochar contained less ash content and had the highest functional groups of ester (CO) and carbonyl (CO) groups. These functional groups can bind with MTBE effectively. Therefore, functional groups on materials and their ash content can be used as a criteria for selecting the materials for MTBE removal.
12451. 题目: Significant HONO formation by the photolysis of nitrates in the presence of humic acids
期刊: Environmental Pollution
作者: Wangjin Yang, Chong Han, He Yang, Xiangxin Xue
摘要: The generation of HONO and NO2 by the photolysis of nitrates in the presence of humic acids (HA) was measured under various conditions. The photolysis experiments of HA, KNO3 and KNO3/HA under simulated sunlight was carried out by a flow tube reactor at ambient temperature and pressure. HONO and NO2 were major products by the photolysis of KNO3. By contrast, the photolysis of HA and KNO3/HA mainly generated HONO. HA significantly enhanced the formation of HONO during the photolysis process of KNO3. With increasing the KNO3 mass, the HONO formation rate (RHONO) on KNO3/HA increased while the photolysis rate normalized by the KNO3 mass exhibited an opposite trend. RHONO on KNO3/HA linearly increased with irradiation intensity (88–262 W/m2) and relative humidity (7–70%), whereas it linearly decreased with the pH (pH = 2–12). In addition, the reaction paths of the HONO formation by the photolysis of nitrates in the presence of HA were proposed according to experimental results. Finally, atmospheric implications of the enhanced HONO formation by the photolysis of nitrates in the presence of HA were discussed.
12452. 题目: Dynamics of pyrite formation and organic matter sulfurization in organic-rich carbonate sediments
期刊: Geochimica et Cosmochimica Acta
作者: Lubna Shawar, Itay Halevy, Ward Said-Ahmad, Shimon Feinstein, Valeria Boyko, Alexey Kamyshny, Alon Amrani
摘要: Organic-rich carbonate sediments are deposited in a range of environments today and in the geologic past. A significant part of organic matter (OM) degradation in such sediments often occurs by microbial reduction of seawater sulfate, and the sulfide product may be preserved in pyrite and in organic sulfur (S) compounds. The isotopic composition (δ34S) of these phases can provide valuable information about S cycling in the ocean and in sediment porewaters, but only insofar as the processes governing these δ34S values are understood. To this end, we investigated the pathways, timing and interactions between pyrite and organic S formation during the deposition of organic-rich chalks. As a test case, we studied cores representing the thickest (∼350 m) and most complete Late Cretaceous organic-rich sequence along the southern Paleotethyan margin. The organic S and OM contents show an inverse relation with the pyritic S content, which together with the uniform FePy/FeHR ratio (∼40%), suggest competition between organic S and pyrite formation. Both kerogen and pyritic S are 34S-depleted relative to Late Cretaceous marine sulfate (δ34S∼17-20‰), but the kerogen S is consistently and unusually 34S-enriched relative to coexisting pyrite by up to ∼38‰. Large S isotope fractionation (∼60‰) during microbial sulfate reduction is necessary to reproduce the lowest pyrite δ34S values in the core, and relatively invariant δ34S values in organic S suggests that this large fractionation was approximately constant during deposition of the chalks in the core. Higher pyrite δ34S values observed in the most organic-rich parts of the core may be explained by Fe-limited pyrite formation, perhaps due to the reaction of Fe (e.g., complexation, sorption) with organic compounds. Lesser Fe availability, relative to the OM available for sulfate reduction, limits the ultimate abundance of pyrite, but importantly, it delays the formation of pyrite to deeper below the sediment-water interface, from 34S-enriched sulfide produced by Rayleigh distillation of a dwindling sulfate reservoir. Thus, it appears that competing Fe-OM, S-OM and Fe-S reactions can significantly affect the δ34S values recorded in pyrite in organic-rich carbonate sediments despite large and relatively constant microbial S isotope fractionation.
12453. 题目: Eutrophication assessment in the transit area German Bight (North Sea) 2006–2014 – Stagnation and limitations
期刊: Marine Pollution Bulletin
作者: U. Brockmann, D. Topcu, M. Schütt, W. Leujak
摘要: The eutrophication status of the German Bight (North Sea) has been assessed the third time since 1998 according to the OSPAR-Comprehensive Procedure between 2006 and 2014. Since the 1980s nutrient discharges and atmospheric nitrogen deposition had declined significantly but chlorophyll a and nutrient concentrations remained above assessment levels inshore and in inner coastal waters, reflecting continuing eutrophication. Recently local river discharges stagnated or increased again and total nitrogen remained above a reduction target of 200 μM. Most nutrients and conversion products were imported by a coastal current, passing the German Bight. Organic matter was trapped in offshore bottom waters in the ancient Elbe valley, causing repeated annual oxygen minima (<6 mg/L) and a classification as Problem Area. Effects of national reduction measures are limited in the transit area German Bight because improvements in open coastal waters require international efforts, based on comprehensive analyses.
12454. 题目: Changes in nitrogen related functional genes along soil pH, C and nutrient gradients in the charosphere
期刊: Science of The Total Environment
作者: Mengjie Yu, Jun Meng, Lu Yu, Weiqin Su, Muhammad Afzal, Yong Li, Philip C. Brookes, Marc Redmile-Gordon, Yu Luo, Jianming Xu
摘要: The interface between biochar and soil differs from both the bulk soil and the biochar itself, and has been termed the “charosphere”. However, a complete definition of the charosphere, including aspects of size, properties, functional reach and effects on soil processes, is still required. In this study, the distributions of functional genes related to the soil N cycle within the charosphere were investigated over a multi-sectional gradient. We found that concentrations of dissolved organic carbon (DOC), available phosphorus and exchangeable cations (Ca2+, Mg2+, K+) increased with proximity to the biochar surface (termed the ‘near charosphere’). Similarly, the abundance of bacterial amoA was greater in the near charosphere, while archaeal amoA abundance was relatively homogenous. This taxonomic asymmetry resulted in a shift in the predominant ammonia-oxidizers from ammonia-oxidizing bacteria (AOB) to ammonia-oxidizing archaea (AOA) in the far charosphere. This was associated with other factors such as decreasing pH and carbon availability with increasing distance from the biochar. Moreover, the ratio of nosZ/(nirS + nirK) genes also showed functionally asymmetry in the charosphere: increasing with increasing distance from the biochar. This is the first study to map spatial distributions of a set functional genes related to soil N cycling in the soil around biochar. This exploration into the underlying heterogeneity of biochar-affected mechanisms of N transformation provides new insight into the functional geometry of the charosphere.
12455. 题目: Determination of nanoparticle heteroaggregation attachment efficiencies and rates in presence of natural organic matter monomers. Monte Carlo modelling
期刊: Science of The Total Environment
作者: Arnaud Clavier, Antonia Praetorius, Serge Stoll
摘要: Understanding the transformation and transport of manufactured nanoparticles (NPs) in aquatic systems remains an important issue due to their potential hazard. Once released in aquatic systems, NPs will interact with natural compounds such as suspended inorganic particles and/or natural organic matter (NOM) and heteroaggregation will control their ultimate fate. Unfortunately, systematic experimental methods to study heteroaggregation are not straightforward and still scarce. In addition, the description of heteroaggregation rate constants and attachment efficiencies is still a matter of debate since no clear definition exists.In this work, an original cluster-cluster Monte Carlo model is developed to get an insight into heteroaggregation process descriptions. A two-component system composed of NPs and NOM fulvic acid monomers is investigated by considering several water models to cover a range of (relevant) conditions from fresh to marine waters. For that purpose, homo- and hetero- individual attachment efficiencies between NPs and NOM units are adjusted (NP-NP, NOM-NOM and NP-NOM). The influence of NP/NOM ratio, NOM-NOM homoaggregation versus heteroaggregation, and surface coating effects is studied systematically. From a quantitative point of view, aggregation rate constants as well as attachment efficiencies are calculated as a function of physical time so as to characterize the individual influence of each parameter and to allow future comparison with experimental data. Heteroaggregation processes and global attachment efficiencies corresponding to several mechanisms and depending on the evolution of heteroaggregate structures all along the simulations are defined. The calculation of attachment efficiency values is found dependent on NP/NOM concentration ratios via coating effects, by the initial set of elementary attachment efficiencies and influence of homoaggregation.Marine water represents a specific case of aggregation where all particle contacts are effective. On the other hand, in “ultrapure” and “fresh waters”, a competition between homo- and heteroaggregation occurs depending on the initial attachment efficiencies therefore indicating that a subtle change in the NP surface properties as well as in the water chemistry have a significant impact on heteroaggregation processes.
12456. 题目: The potential adsorption mechanism of the biochars with different modification processes to Cr(VI)
期刊: Environmental Science and Pollution Research
作者: Qiang An, Xue-Qin Li, Hong-Yan Nan, Yang Yu, Jun-Nan Jiang
摘要: Modified biochar has attracted wide attention due to its advantageous adsorption performance. However, the influence of modification process of biochar on adsorption capacity was seldom studied. In this study, biochar derived from corn stalks was modified through two kinds of modification processes: pre-pyrolysis (MBCpre) and post-pyrolysis (MBCpost) modification with citric acid, sodium hydroxide, ferric chloride, respectively. The results showed that the biochar modified by ferric chloride (MBC) provided better adsorption capacity for Cr(VI), and the pre-pyrolysis offered more favorable adsorption capacity for biochar than post-pyrolysis. By means of instrumental analysis, it was found that MBCpre owned highly dispersed Fe3O4 particles and larger surface area, which could be the critical role for enhancing the adsorption capacity of MBCpre. Meanwhile, MBCpost appeared more protonated oxygen-rich functional groups(C=O, –OH, etc.) and adsorbed Cr(VI) by electrostatic attraction and complexation. This study will offer a novel idea for the treatment of chromium-containing wastewater by selecting the modification processes of biochar.
12457. 题目: Microbial explanations for field-aged biochar mitigating greenhouse gas emissions during a rice-growing season
期刊: Environmental Science and Pollution Research
作者: Zhen Wu, Xi Zhang, Yubing Dong, Xin Xu, Zhengqin Xiong
摘要: Knowledge about the impacts of fresh and field-aged biochar amendments on greenhouse gas (CH4, N2O) emissions is limited. A field experiment was initiated in 2012 to study the effects of fresh and field-aged biochar additions on CH4 and N2O emissions and the associated microbial activity during the entire rice-growing season in typical rice-wheat rotation system in Southeast China. CH4 and N2O fluxes were monitored, and the abundance of methanogen (mcrA), methanotrophy (pmoA), ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), nitrite reductase (nirS, nirK), N2O reductase (nosZ), and potential soil enzyme activities related to CH4 and N2O were simultaneously measured throughout different rice developmental stages. There were three treatments: control (urea without biochar), fresh BC (urea with fresh biochar added in 2015), and aged BC (urea with 3-year field-aged biochar added in 2012). Results showed that field-aged biochar significantly decreased seasonal CH4 emissions by 16.8% in relation to the fresh biochar, though no significant differences were detected between biochars and control treatment. The structural equation model indicated that soil pH, microbial biomass carbon (MBC), pmoA, and mcrA were the main factors directly influenced by fresh and aged biochar amendments; aged biochar showed a negative effect while fresh biochar showed positive effects on CH4 fluxes. Both fresh and field-aged biochar obviously increased AOA and AOB abundances and reduced the (nirS+nirK)/nosZ ratio during the entire rice-growing season, although no significant effects were observed on seasonal N2O emissions. Therefore, biochar amendment produced long-term effects on total CH4 and N2O emissions through observed influences of soil pH and functional gene abundance. The figure shows how fresh and field-aged biochar differentially affected CH4 production and oxidation and N2O production and reduction through related functional gene abundances. Blue arrows indicate suppressing while pink arrows indicate promoting effect.
12458. 题目: Fluorescent DOC characteristics are related to streamflow and pasture cover in streams of a mixed landscape
作者: Baek Soo Lee, Kate Lajtha, Julia A. Jones, Angelicque E. White
摘要: A growing body of research suggests that different land use activities may alter both the quantity and quality of dissolved organic carbon (DOC) exported from terrestrial landscapes. However, little is known about DOC from mixed-use landscapes where hydrology varies seasonally. This study examined how DOC and chemical properties of stream water were related to land use, drainage area, and streamflow in mixed-use landscape in the Willamette River Basin, Oregon. Stream water samples were collected at roughly monthly intervals over three water years from 21 sites whose drainage areas ranged from 1 to > 11,000 km2 and included pasture, forest, and developed land uses. DOC properties were characterized using PARAFAC (parallel factor) analyses of 3-D excitation and emission matrices (EEMs). We used the Cory-McKnight (CM) model, and we also developed a model unique to our samples. Thirteen components were identified using the CM model, and these were highly correlated with, and similar with respect to excitation and emission to the three components identified in our site-specific model. Fluorescent components of DOC were related to discharge and land cover, but not to drainage area. In our model, one component (C1) appeared to be associated with terrestrial detritus and was greater in streamflow from sites with forest/developed cover than from sites with high pasture cover. A second component (C2) was greater in streamflow from high-pasture sites than from high-forest sites. C2 was strongly correlated with a protein component identified in the CM model, and therefore we attributed this second component to more microbially-processed DOC. C1 increased significantly with discharge for both land covers, suggesting that periods of high flow produce less microbially-processed DOC from more surficial flow. C2 decreased significantly with discharge for both land covers, suggesting that deeper hydrologic flow paths produce more soil-associated, microbially processed DOC. SUVA254, often used as an index of chemical quality and aromaticity of DOC, was related only to streamflow but not land use, suggesting that while the chemistry of DOC differed among land use types as detected by EEMs analysis, the aromaticity of the DOC did not differ. The CM model and our site-specific model provided consistent results: those components that were highest in high pasture sites were also highest at low flow and appeared to be more microbially processed; components that were highest in low pasture sites were also greatest at high flow and appeared to reflect less microbially processed DOC. Taken together, these findings are consistent with a conceptual model of how differences in DOC chemistry among landscape types reflect differences in plant litter input chemistry, hydrologic connectivity, and degree of microbial processing. Such changes in DOC quality with land-use change can affect foodweb dynamics in receiving waters and change the balance between carbon storage and carbon flux to the atmosphere, and they imply that even non-intensive agricultural land use can have significant effects on terrestrial-aquatic carbon processes.
12459. 题目: Investigation of the Fate and Dynamics of Extracellular Polymeric Substances (EPS) during Sludge-Based Photogranulation under Hydrostatic Conditions
期刊: Environmental Science & Technology
Camilla Kuo-Dahab, Kristie Stauch-White, Caitlyn S. Butler, Gitau J. Gikonyo, Blanca Carbajal-González, Anastasia Ivanova, Sona Dolan, Chul Park
摘要: Oxygenic photogranules have received increasing interest due to their ability to treat wastewater without aeration and recover wastewater’s chemical energy and solar energy. It has been reported that these photogranules can be produced under both hydrostatic and hydrodynamic conditions, and enrichment of filamentous cyanobacteria is required for this photogranulation to occur. Despite the critical role extracellular polymeric substances (EPS) play in granulation, EPS in photogranulation is yet virtually unknown. Here, we present the fate and dynamics of different fractions of EPS in sludge-based photogranulation under hydrostatic conditions. The study shows that during the transformation of activated sludge into a photogranular biomass, sludge’s base-extractable proteins selectively degrade. Strong correlations between base-extracted proteins and the growth of chlorophyll a and chlorophyll a/b ratio suggest that the bioavailability of this organic nitrogen is linked with selection and enrichment of filamentous cyanobacteria under hydrostatic conditions. The results of soluble and sonication-extractable EPS and microscopy also show that the growth of filamentous cyanobacteria required large amounts of polysaccharide-based EPS for their motility and maintenance. With findings on the progression of photogranulation, the fate and dynamics of EPS, and microscopy on microstructures associated with EPS, we discuss potential mechanisms of photogranulation occurring under hydrostatic conditions.
12460. 题目: Nitrogen addition reduces dissolved organic carbon leaching in a montane forest
期刊: Soil Biology and Biochemistry
作者: Ruiying Chang, Na Li, Xiangyang Sun, Zhaoyong Hu, Xuesong Bai, Genxu Wang
摘要: Dissolved organic carbon (DOC) plays a significant role in the forest soil carbon cycle and can be regulated by nitrogen (N) addition. However, the regulatory direction, mechanism and seasonal pattern of DOC under N addition are less clear. Here, in a montane evergreen forest located at the eastern edge of the Tibetan Plateau, 2 levels of N were applied over 2 years to determine the effects of N addition on DOC release from organic (O layer) and mineral soil. Frequent sampling revealed that high levels of N addition could decrease the concentration of DOC and the flux from the O layer but not from mineral soil and that moderate N addition had no effect on DOC leaching from either the O or mineral layer. The effect of N addition on DOC leaching from the O layer was seasonally dependent, showing a significant reduction in DOC leaching during autumn/winter but no changes during summer and spring. This seasonally different response of DOC to N addition affected the seasonal pattern of DOC leaching. Soil and leachate pH were not influenced by N addition in the short term, indicating that there was not enough difference in DOC retention by mineral soil to significantly affect DOC leaching under N addition. In contrast, N addition-derived reduction in DOC leaching was likely to be due to suppressed fresh litterfall–derived DOC production during autumn/winter; this speculation was supported by lower values of O layer water-extractable organic carbon and microbial biomass carbon as well as lower saccharase and cellulose activities found with high N addition. These results suggested that the processes in control of DOC leaching and their responses to N addition were different for O and mineral soil and that short-term N addition could decrease O-layer DOC leaching, which is likely associated with decreased DOC production rather than greater DOC retention.