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32121. 题目: Shifts in priming partly explain impacts of long‐term nitrogen input in different chemical forms on soil organic carbon storage
文章编号: N18052503
期刊: Global Change Biology
作者: Minghua Song, Yu Guo, Feihai Yu, Xianzhou Zhang, Guangmin Cao, Johannes H. C. Cornelissen
更新时间: 2018-05-25
摘要: Input of labile organic carbon can enhance decomposition of extant soil organic carbon (SOC) through priming. We hypothesized that long‐term nitrogen (N) input in different chemical forms alters SOC pools by altering priming effects associated with N‐mediated changes in plants and soil microbes. The hypothesis was tested by integrating field experimental data of plants, soil microbes and two incubation experiments with soils that had experienced 10 years of N enrichment with three chemical forms (ammonium, nitrate and both ammonium and nitrate) in an alpine meadow on the Tibetan Plateau. Incubations with glucose–13C addition at three rates were used to quantify effects of exogenous organic carbon input on the priming of SOC. Incubations with microbial inocula extracted from soils that had experienced different long‐term N treatments were conducted to detect effects of N‐mediated changes in soil microbes on priming effects. We found strong evidence and a mechanistic explanation for alteration of SOC pools following 10 years of N enrichment with different chemical forms. We detected significant negative priming effects both in soils collected from ammonium‐addition plots and in sterilized soils inoculated with soil microbes extracted from ammonium‐addition plots. In contrast, significant positive priming effects were found both in soils collected from nitrate‐addition plots and in sterilized soils inoculated with soil microbes extracted from nitrate‐addition plots. Meanwhile, the abundance and richness of graminoids were higher and the abundance of soil microbes was lower in ammonium‐addition than in nitrate‐addition plots. Our findings provide evidence that shifts toward higher graminoid abundance and changes in soil microbial abundance mediated by N chemical forms are key drivers for priming effects and SOC pool changes, thereby linking human interference with the N cycle to climate change.

32122. 题目: Lead Speciation and Association with Organic Matter in Various Particle-Size Fractions of Contaminated Soils
文章编号: N18052502
期刊: Environmental Science & Technology
作者: Gautier Landrot, Saengdao Khaokaew
更新时间: 2018-05-25
摘要: Lead (Pb) stabilization in polluted soils treated by a Pb immobilization technique may be dependent on the speciation of Pb present in specific particle-size fractions of the soil. However, the scale-dependency of Pb speciation in contaminated soils is still not clearly understood. In this study, the natures and amounts of Pb chemical forms were determined in five Pb-polluted soil samples from Klity Village, Thailand, and their particle-size fractions. This was achieved using multiple analytical tools, including bulk extended X-ray absorption fine structure (EXAFS) spectroscopy at the Pb LIII edge. Results suggested that cerussite, Pb sorbed to goethite, and Pb-humate were present in specific amounts in all bulk samples and their particle-size fractions. The highest amounts of Pb-humate were found in the smallest particles of the soil samples. This Pb form was present in the fine particles of a soil sample, but remained undetected when analyzing the bulk sample. Since Pb-SOM association may impede the formation of pyromorphite in soils, the results implied that the extent of Pb immobilization in a polluted soil treated by P may be less than predicted if Pb speciation is only characterized at the macroscopic scale from the bulk soil sample prior remediation.
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32123. 题目: Spatial Associations and Chemical Composition of Organic Carbon Sequestered in Fe, Ca, and Organic Carbon Ternary Systems
文章编号: N18052501
期刊: Environmental Science & Technology
作者: Tyler D. Sowers, Dinesh Adhikari, Jian Wang, Yu Yang, Donald L. Sparks
更新时间: 2018-05-25
摘要: Organo-mineral associations of organic carbon (OC) with iron (Fe) oxides play a major role in environmental OC sequestration, a process crucial to mitigating climate change. Calcium has been found to have high coassociation with OC in soils containing high Fe content, increase OC sorption extent to poorly crystalline Fe oxides, and has long been suspected to form bridging complexes with Fe and OC. Due to the growing realization that Ca may be an important component of C cycling, we launched a scanning transmission X-ray microscopy (STXM) investigation, paired with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, in order to spatially resolve Fe, Ca, and OC relationships and probe the effect of Ca on sorbed OC speciation. We performed STXM-NEXAFS analysis on 2-line ferrihydrite reacted with leaf litter-extractable dissolved OC and citric acid in the absence and presence of Ca. Organic carbon was found to highly associate with Ca (R2 = 0.91). Carboxylic acid moieties were dominantly sequestered; however, Ca facilitated the additional sequestration of aromatic and phenolic moieties. Also, C NEXAFS revealed polyvalent metal ion complexation. Our results provide evidence for the presence of Fe–Ca–OC ternary complexation, which has the potential to significantly impact how organo-mineral associations are modeled.
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32124. 题目: Tale of Two Storms: Impact of Extreme Rain Events on the Biogeochemistry of Lake Superior
文章编号: N18052403
期刊: Journal of Geophysical Research: Biogeosciences
作者: Ellen M.Cooney, PaulMcKinney, RobertSterner, Gaston E.Small, Elizabeth C.Minor
更新时间: 2018-05-24
摘要: Climate change is expected to profoundly affect the Great Lakes region of North America. An increase in intensity and frequency of rain events is anticipated to deliver more runoff and to increase riverine inputs to Lake Superior's ecosystem. The effects of these changes on key biogeochemical parameters were analyzed by coupling satellite data, water column sensor profiles, and discrete surface‐water sampling after two “500‐year” flood events in the Lake Superior basin. This study provides both a spatial and a temporal sense of how plumes interacted within the ecosystem. We also determined the significant differences in water quality parameters for plume versus nonplume waters. These two plumes were important for delivery of nutrients, with variable transport of sediments and colored dissolved organic matter (CDOM). Data from the 2012 storm event showed a significant input of total nitrogen, total phosphorus, and CDOM to the system. In the 2016 storm event, carbon cycling parameters (acidity, total inorganic carbon, and dissolved organic carbon) and ammonia levels were elevated within the plume. In neither storm event was there a significant difference in chlorophyll a between plume and nonplume waters during our sampling cruises. These two plume events were similar in amount of precipitation, but their effect on the biogeochemistry of Lake Superior varied due to differences in the watersheds where the rain fell. The studied plume events were dynamic, changing with currents, winds, and the settling of suspended sediments.

32125. 题目: Chlorate Formation Mechanism in the Presence of Sulfate Radical, Chloride, Bromide and Natural Organic Matter
文章编号: N18052402
期刊: Environmental Science & Technology
作者: Shaodong Hou, Li Ling, Dionysios D. Dionysiou , Yuru Wang, Jiajia Huang, Kaiheng Guo, Xuchun Li, Jingyun Fang
更新时间: 2018-05-24
摘要: Halides and natural organic matter (NOM) are inevitable in aquatic environment and influence the degradation of contaminants in sulfate radical (SO4 –)-based advanced oxidation processes. This study investigated the formation of chlorate in the coexposure of SO4 –, chloride (Cl–), bromide (Br–) and/or NOM in UV/persulfate (UV/PDS) and cobalt(II)/peroxymonosulfate (Co/PMS) systems. The formation of chlorate increased with increasing Cl– concentration in the UV/PDS system, however, in the Co/PMS system, it initially increased and then decreased. The chlorate formation involved the formation of hypochlorous acid/hypochlorite (HOCl/OCl–) as an intermediate in both systems. The formation was primarily attributable to SO4 – in the UV/PDS system, whereas Co(III) played a significant role in the oxidation of Cl– to HOCl/OCl– and SO4 – was important for the oxidation of HOCl/OCl– to chlorate in the Co/PMS system. The pseudo-first-order rate constants (k′) of the transformation from Cl– to HOCl/OCl– were 3.32 × 10–6 s–1 and 9.23 × 10–3 s–1 in UV/PDS and Co/PMS, respectively. Meanwhile, k′ of HOCl/OCl– to chlorate in UV/PDS and Co/PMS were 2.43 × 10–3 s–1 and 2.70 × 10–4 s–1, respectively. Br– completely inhibited the chlorate formation in UV/PDS, but inhibited it by 45.2% in Co/PMS. The k′ of SO4 – reacting with Br– to form hypobromous acid/hypobromite (HOBr/OBr–) was calculated to be 378 times higher than that of Cl– to HOCl/OCl–, but the k′ of Co(III) reacting with Br– to form HOBr/OBr– was comparable to that of Cl– to HOCl/OCl–. NOM also significantly inhibited the chlorate formation, due to the consumption of SO4 – and reactive chlorine species (RCS, such as Cl·, ClO· and HOCl/OCl–). This study demonstrated the formation of chlorate in SO4 –-based AOPs, which should to be considered in their application in water treatment.
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32126. 题目: Understanding the Role of Extracellular Polymeric Substances on Ciprofloxacin Adsorption in Aerobic Sludge, Anaerobic Sludge, and Sulfate-Reducing Bacteria Sludge Systems
文章编号: N18052401
期刊: Environmental Science & Technology
作者: Huiqun Zhang, Yanyan Jia, Samir Kumar Khanal, Hui Lu , Heting Fang, Qing Zhao
更新时间: 2018-05-24
摘要: Extracellular polymeric substances (EPS) of microbial sludge play a crucial role in removal of organic micropollutants during biological wastewater treatment. In this study, we examined ciprofloxacin (CIP) removal in three parallel bench-scale reactors using aerobic sludge (AS), anaerobic sludge (AnS), and sulfate-reducing bacteria (SRB) sludge. The results showed that the SRB sludge had the highest specific CIP removal rate via adsorption and biodegradation. CIP removal by EPS accounted up to 35. 6 ± 1.4%, 23.7 ± 0.6%, and 25.5 ± 0.4% of total removal in AS, AnS, and SRB sludge systems, respectively, at influent CIP concentration of 1000 μg/L, which implied that EPS played a critical role in CIP removal. The binding mechanism of EPS on CIP adsorption in three sludge systems were further investigated using a series of batch tests. The results suggested that EPS of SRB sludge possessed stronger hydrophobicity (proteins/polysaccharides (PN/PS) ratio), higher availability of adsorption sites (binding sites (n)), and higher binding strength (binding constant (Kb)) between EPS and CIP compared to those of AS and AnS. The findings of this study provide an insight into the role of EPS in biological process for treating CIP-laden wastewaters.
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32127. 题目: Thermodynamic Analysis of Nickel(II) and Zinc(II) Adsorption to Biochar
文章编号: N18052103
期刊: Environmental Science & Technology
作者: Md. Samrat Alam, Drew Gorman-Lewis, Ning Chen, Shannon L. Flynn, Yong Sik Ok, Kurt O. Konhauser, Daniel S. Alessi
更新时间: 2018-05-21
摘要: While numerous studies have investigated metal uptake from solution by biochar, few of these have developed a mechanistic understanding of the adsorption reactions that occur at the biochar surface. In this study, we explore a combined modeling and spectroscopic approach for the first time to describe the molecular level adsorption of Ni(II) and Zn(II) to five types of biochar. Following thorough characterization, potentiometric titrations were carried out to measure the proton (H+) reactivity of each biochar, and the data was used to develop protonation models. Surface complexation modeling (SCM) supported by synchrotron-based extended X-ray absorption fine structure (EXAFS) was then used to gain insights into the molecular scale metal–biochar surface reactions. The SCM approach was combined with isothermal titration calorimetry (ITC) data to determine the thermodynamic driving forces of metal adsorption. Our results show that the reactivity of biochar toward Ni(II) and Zn(II) directly relates to the site densities of biochar. EXAFS along with FT-IR analyses, suggest that Ni(II) and Zn(II) adsorption occurred primarily through proton-active carboxyl (-COOH) and hydroxyl (-OH) functional groups on the biochar surface. SCM-ITC analyses revealed that the enthalpies of protonation are exothermic and Ni(II) and Zn(II) complexes with biochar surface are slightly exothermic to slightly endothermic. The results obtained from these combined approaches contribute to the better understanding of molecular scale metal adsorption onto the biochar surface, and will facilitate the further development of thermodynamics-based, predictive approaches to biochar removal of metals from contaminated water.
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32128. 题目: Insights and Model for Understanding Natural Organic Matter Adsorption onto Mixed Adsorbents
文章编号: N18052102
期刊: Environmental Science & Technology
作者: Siamak Modarresi Mark M. Benjamin
更新时间: 2018-05-21
摘要: Adsorption-based processes are commonly used to remove natural organic matter (NOM) from drinking water sources and thereby mitigate its impacts on other water treatment processes and the quality of the finished water. These processes are complicated by the fact that NOM comprises multiple fractions that can exhibit disparate adsorption behaviors. Prior modeling of NOM adsorption has invariably focused on systems with a single adsorbent, but results presented here demonstrate surprising and counterintuitive behavior in systems containing two or more adsorbents. Specifically, if the sequence of affinities of the different NOM fractions are the same for two adsorbents, then overall adsorption changes monotonically as one adsorbent is gradually replaced by the other. However, if the sequence differs for the two adsorbents, overall adsorption can increase even when the nominally stronger adsorbent is gradually replaced by the weaker one. This work demonstrates and explains such behavior for a particular mixture of adsorbents and introduces a mathematical model that illustrates how other mixtures might behave.
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32129. 题目: Factors Affecting the Leaching of Dissolved Organic Carbon after Tree Dieback in an Unmanaged European Mountain Forest
文章编号: N18052101
期刊: Environmental Science & Technology
作者: Ji?í Kopá?ek, Christopher D. Evans, Josef Hejzlar, Ji?í Kaňa, Petr Porcal, and Hana ?antr??ková
更新时间: 2018-05-21
摘要: Forest disturbances affect ecosystem biogeochemistry, water quality, and carbon cycling. We analyzed water chemistry before, during, and after a dieback event at a headwater catchment in the Bohemian Forest (central Europe) together with an un-impacted reference catchment, focusing on drivers and responses of dissolved organic carbon (DOC) leaching. We analyzed data regarding carbon input to the forest floor via litter and throughfall, changes in soil moisture and composition, streamwater chemistry, discharge, and temperature. We observed three key points. (i) In the first 3 years following dieback, DOC production from dead biomass led to increased concentrations in soil, but DOC leaching did not increase due to chemical suppression of its solubility by elevated concentrations of protons and polyvalent cations and elevated microbial demand for DOC associated with high ammonium (NH4+) concentrations. (ii) DOC leaching remained low during the next 2 years because its availability in soils declined, which also left more NH4+ available for nitrifiers, increasing NO3– and proton production that further increased the chemical suppression of DOC mobility. (iii) After 5 years, DOC leaching started to increase as concentrations of NO3–, protons, and polyvalent cations started to decrease in soil water. Our data suggest that disturbance-induced changes in N cycling strongly influence DOC leaching via both chemical and biological mechanisms and that the magnitude of DOC leaching may vary over periods following disturbance. Our study adds insights as to why the impacts of forest disturbances are sometime observed at the local soil scale but not simultaneously on the larger catchment scale.
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