17421. 题目: Temporal variation in riverine organic carbon concentrations and fluxes in two contrasting estuary systems: Geum and Seomjin, South Korea
期刊: Environment International
作者: Sujin Kang, Jung-Hyun Kim, Daun Kim, Hyeongseok Song, Jong-Sik Ryu, Giyoung Ock, Kyung-Hoon Shin
摘要: In this study, surface water samples were collected at sites located in the lowest reaches of closed (Geum) (i.e. with an estuary dam at the river mouth) and open (Seomjin) estuary systems between May 2016 and May 2018. We analyzed concentrations and stable isotopes of particulate organic carbon (POC) and dissolved organic carbon (DOC) to assess OC sources, to estimate fluxes of riverine OC, and to assess some of the factors driving OC exports in these two contrasting Korean estuary systems. Our geochemical results suggest that the contribution of the phytoplankton-derived POC to the total POC pool was larger in the Geum River than in the Seomjin River. Notably, a heavy riverine algae bloom occurred in the Geum River in August 2016, resulting in a high carbon isotopic composition (−19.4‰) together with low POC/PN ratio (<10) and POC/Chl-a ratio (<100). In contrast, potential DOC sources in both the Geum River and the Seomjin River were a mixture of C3-derived forest soils and cropland organic matter. During the study period, the catchment area-normalized fluxes of POC and DOC were 0.40 × 10−3 tC/km2/yr and 6.5 × 10−2 tC/km2/yr in the Geum River and 5.2 × 10−4 tC/km2/yr and 8.6 × 10−4 tC/km2/yr in the Seomjin River, respectively. It appears that the POC flux was more weakly associated with the water discharge in the Geum River than in the Seomjin River, but the DOC fluxes were in general controlled by the water discharges in both rivers. Accordingly, the estuary dam of the Geum River might be one of the most strongly influencing factors on seasonal patterns in POC fluxes into the adjacent coastal seas, strongly modifying water residence times and thus biogeochemical processes.
17422. 题目: Natural and anthropogenic signatures on sedimentary organic matters across varying intertidal habitats in the Korean waters
期刊: Environment International
作者: Jongmin Lee, Bong-Oh Kwon, Beomgi Kim, Junsung Noh, Kyuwon Hwang, Jongseong Ryu, Jinsoon Park, Seongjin Hong, Jong Seong Khim
摘要: Sedimentary organic matters in the typical intertidal areas were investigated to address year-round monthly distributions and site-specific sources. Target areas included four natural tidal flats (Ganghwa, Garolim, Sinan, and Suncheon) and one artificially closed estuary (Nakdong River), South Korea (in 2018). Among the parameters monitored, mud content was a key factor controlling organic matter contents, across varying habitats, with significant positive correlations to total organic carbon (TOC, r = 0.66, p < 0.001) and total nitrogen (TN, r = 0.44, p < 0.001). The elevated TOC and TN contents and heavier carbon stable isotope ratios (δ13C) in sediments of Garolim and Suncheon from February to April reflected the winter microphytobenthos blooms, receiving prevailed marine sources. Whilst, the depleted δ13C and δ15N values in sediments of Nakdong River estuary were observed during flood season (September–October), indicating direct influence of terrestrial organic input through freshwater discharge. Overall, distributions and sources of sedimentary organic matters in the Korean coastal waters suggested variabilities in season and space, with anthropogenic alteration. The data accumulated in this study would provide baseline information for sediment organic carbon stocks in the Korean coastal waters and elsewhere.
17423. 题目: Characteristics of airborne water-soluble organic carbon (WSOC) at a background site of the North China Plain
期刊: Atmospheric Research
作者: Yuanyuan Luo, Xuehua Zhou, Jingzhu Zhang, Likun Xue, Tianshu Chen, Penggang Zheng, Jingjing Sun, Xiaolong Yan, Guangxuan Han, Wenxing Wang
摘要: Water-soluble organic carbon (WSOC), a significant part of organic carbon (OC) in fine particles, can alter the hygroscopic properties of aerosols and affect global climate change. In this study, PM2.5 filter samples were collected in 2017 winter and summer to investigate the secondary formation, sources and light absorption properties of WSOC. The average WSOC/OC was 66% with the higher value in summer (74%). There are strong correlations between WSOC and secondary components like secondary organic carbon (SOC) and inorganic ions while the correlation between WSOC and EC was weak, indicating secondary formation contributed a dominant portion to WSOC at this site. Moreover, high aerosol liquid water (ALW) and particle acidity were found to enhance the secondary formation of WSOC. The sources of WSOC investigated with Positive Matrix Factorization model (PMF) demonstrated that secondary formation was dominated with 59.9% in winter and 77.9% in summer. The absorption Ångstrom exponents (AAE) were 6.88 in winter and 9.15 in summer. The MAE365 in winter (1.32 m2 g−1) was higher than that in summer (0.38 m2 g−1), indicating the stronger light absorption ability of WSOC in winter. The radiative forcing of WSOC by light absorption corresponded to only 1–10% of that caused by EC. The potential source contribution function (PSCF) identified inland cities in Shandong province, eastern Henan and Jiangsu province as major source regions of WSOC. The findings from this study imply a critical role of secondary formation characteristics of WSOC at the regional background site of the North China Plain.
17424. 题目: Biochar alleviates Cd phytotoxicity by minimizing bioavailability and oxidative stress in pak choi (Brassica chinensis L.) cultivated in Cd-polluted soil
期刊: Journal of Environmental Management
作者: Muhammad Kamran, Zaffar Malik, Aasma Parveen, Yutong Zong, Ghulam Hassan Abbasi, Muhammad Tariq Rafiq, Muhammad Shaaban, Adnan Mustafa, Saqib Bashir, Muhammad Rafay, Sajid Mehmood, Muhammad Ali
摘要: The production of leafy vegetables such as Brassica chinensis L. in cadmium (Cd)-polluted soil causes serious threats to human health and food safety around the globe. A pot culture was established to examine the efficacy of rice-straw induced biochar (applied to soil at the rate of 0%, 2.5% and 5%, w/w) on growth, gaseous exchange attributes, antioxidative capacities and Cd uptake in pak choi (Brassica chinensis L.), when soil was spiked with Cd (CdCl2) at 0, 5, 10 and 20 mg kg−1 soil. The results revealed that Cd stress significantly (P < 0.05) reduced plant biomass and physiological attributes, and accumulated higher Cd concentrations in plant tissues with the increasing rate of Cd concentration in the soil. However, incorporation of biochar at 5% application rate prominently increased the shoot (98.27%) and root (85.96%) dry biomass, net photosynthesis (45.52%), transpiration rate (161.34%), stomatal activity (111.76%) and intracellular CO2 concentration (32.25%) when Cd was added at 20 mg kg−1 soil, relative to the respective treatment without biochar. Whereas, incorporation of biochar at 5% significantly reduced the bioavailable Cd by 16.64% under 20 mg kg-1 soil, compared to respective Cd treatment without biochar.Similarly, Cd accumulation in shoots and roots was decreased by 42.49% and 29.23%, and thereby reduced leaf MDA and H2O2 contents by 21.45% and 31.28%, respectively, at 20 mg Cd kg−1 spiked soil relative to without biochar amended soil. An increment was noticed in the activities of guaiacol peroxidase (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT) and glutathione (GSH) by 37.31%, 66.35%, 115.94%, 122.72% and 59.96%, respectively, with 5% biochar addition in 20 mg kg−1 Cd spiked soil. Moreover, biochar induced a synergistic impact on plants by increasing soil alkalinization and thereby reducing Cd phytotoxicity throughimmobilization. Overall, results proposed that rice-straw biochar has an ability to restore Cd polluted soil and increased pak choi production and thereby reduced food security risks in polluted soil.
17425. 题目: Terrestrial organic carbon storage modes based on relationship between soil and lake carbon, China
期刊: Journal of Environmental Management
作者: Lingmei Xu, Yu Li, Wangting Ye, Xinzhong Zhang
摘要: Terrestrial ecosystems have received considerable attention as a significant sink for organic carbon at regional to global scales. Previous studies were focused on assessment and quantification of carbon sinks for one ecotype, and few have worked on the interconnection of terrestrial sinks. In this paper, we synthesized the data from China's second national soil survey and direct measurements from 54 lakes. Meanwhile, we investigated the controlling factors of carbon accumulation dynamics in soils and lakes. Results showed varied spatial distribution of soil and lake organic carbon in different regions, and three storage modes were found. The storage mode of watershed collection was observed in the region of the Qinghai-Tibetan Plateau, while the northeast China and Yunnan-Guizhou Plateau revealed another storage mode of autochthonous deposition, and the mode of human activities affection was represented by the East Plain and Mongolia-Xinjiang Plateau. The spatial difference throughout China was regulated by various climate patterns, geological conditions and anthropogenic interference. Our results provide insights into carbon storage modes in various regions, and also inform strategies for enhancing global carbon sequestration and future mitigation policies towards global climate change.
17426. 题目: Do corn-soybean rotations enhance decomposition of soil organic matter?
期刊: Plant and Soil
作者: Steven J. Hall, Ann E. Russell, A’lece R. Moore
摘要: Aims: Corn and soybean crops are often grown in rotation, requiring lower nitrogen (N) inputs than continuous corn. However, soil organic carbon (C) may be declining in corn-soybean systems despite sustained residue inputs. We asked whether corn-soybean rotations increase decomposition of litter and soil C as compared with continuous corn. Methods: We incubated soils from a long-term field experiment including continuous corn and both phases of the corn-soybean rotation. Soils were amended with corn litter, soybean litter, or no litter. We measured natural abundance C stable isotopes (δ13C values) in respiration and microbial biomass to partition C sources. Results: Addition of soybean litter increased microbial biomass while corn did not. However, corn litter addition consistently increased (i.e., primed) soil C decomposition while soybean litter did not. Soils most recently planted to corn following soybeans had the greatest soil C decomposition and N mineralization irrespective of litter addition, and they decomposed corn litter faster and had a faster priming response than the other treatments. Conclusions: Our data support the hypothesis that alternating inputs of N-rich soybean litter and relatively N-poor corn litter could enhance litter and SOC decomposition by driving microbial growth following the soybean phase and stimulating priming following the corn phase. Increased decomposition and N mineralization from litter and SOC in corn-soybean rotations may contribute to the soybean N credit but could also contribute to longer-term soil C and N declines, consistent with field data.
17427. 题目: Chloro-phosphate impregnated biochar prepared by co-precipitation for the lead, cadmium and copper synergic scavenging from aqueous solution
期刊: Bioresource Technology
作者: Rui Deng, Danlian Huang, Jia Wan, Wenjing Xue, Lei Lei, Xiaofeng Wen, Xigui Liu, Sha Chen, Yang Yang, Zhihao Li, Bo Li
摘要: This work evaluated the possibility of lead (Pb2+), cadmium (Cd2+) and copper (Cu2+) ions synergic scavenging by a chloro-phosphate impregnated biochar (CPBC) from aqueous solution. Adsorption experiments displayed that the adsorption capacity of heavy metals by CPBC can be improved better compared with the pristine biochar (BC). The X-ray diffraction (XRD) analysis further demonstrated that the precipitation of Pb5(PO4)3Cl, Cd5(PO4)3Cl and Cu3(PO4)3 might be responsible for Pb2+, Cd2+ and Cu2+ scavenging. The competitive adsorption exhibited that Pb2+, Cd2+ and Cu2+ would compete for the same adsorption sites of CPBC when they coexisted and the adsorption affinity of CPBC was observed in the following order: Pb2+ > Cd2+ > Cu2+. The available phosphorus results suggested that the combination of biochar with phosphate materials can both improve the adsorption performance and reduce the risk of eutrophication by using phosphate materials which can provide a promising application for multiple heavy metals scavenging.
17428. 题目: The practical utility of the synthesis FeNi3@SiO2@TiO2 magnetic nanoparticles as an efficient photocatalyst for the humic acid degradation
作者: Maryam Khodadadi, Tariq J. Al-Musawi, Hossein Kamani, Marcela Fernandes Silva, Ayat Hossein Panahi
摘要: Humic acid (HA) compounds in drinking water and wastewater disinfection processes are viewed as precursors of highly toxic, carcinogenic, and mutagenic disinfection by-product chemicals. In recent times, these compounds have gained considerable attention of scientists for their successful removal from aqueous solutions to permissible limits. To achieve this aim, the present study investigated, for the first time, the photocatalytical performance of the synthesis FeNi3@SiO2@TiO2 nanoparticles for the HA degradation under different environmental conditions. The photocatalytic reactions were performed using ultraviolet (UV) radiation, whose intensity was fixed at 2500 μW/cm2 throughout the experimental study. The characterization study performed, using specific diagnostic techniques, revealed the presence of several good morphological, magnetic, and catalytic specifications of the synthesized nanoparticles. The use of the simplified form of the Langmuir-Hinshelwood equation sufficiently describes the experimental data of the HA kinetic degradation, as it shows a high coefficient of regression values. Furthermore, the complete HA degradation was reached under conditions of pH = 3; initial HA concentration = 10 mg/L; FeNi3@SiO2@TiO2 nanoparticles dosage = 0.01 g/L; and reaction time >30 min. Thus, the results obtained from this research suggested that the catalyst of FeNi3@SiO2@TiO2 nanoparticles was an attractive, novel, and effective agent, which could be used for the degradation of HA in the photocatalytic processes.
17429. 题目: Diversity evolution of functional bacteria and resistance genes (CzcA) in aerobic activated sludge under Cd(II) stress
期刊: Journal of Environmental Management
作者: Meixue Dai, Guangqing Zhou, How Yong Ng, Jinyong Zhang, Yan Wang, Ning Li, Xiaoyu Qi, Mingsheng Miao, Qi Liu, Qiang Kong
摘要: An activated sludge sequencing batch reactor (SBR) was used to treat divalent cadmium (Cd(II)) wastewater for 60 d to investigate the overall treatment performance, evolution of the bacterial community, and abundance of the Cd(II) resistance gene CzcA and shifts in its potential host bacteria. During stable operation with a Cd(II) concentration of 20 mg/L, the average removal efficiencies of Cd(II) and chemical oxygen demand (COD) were more than 85% and that of total phosphorus was greater than 70%, while the total nitrogen (TN) was only about 45%. The protein (PN) content in the extracellular polymeric substances (EPS) increased significantly after Cd(II) addition, while polysaccharides displayed a decreasing trend (p < 0.05), indicating that EPS prefer to release PN to adsorb Cd(II) and protect bacteria from damage. Three-dimensional fluorescence spectral analysis showed that fulvic acid-like substances were the most abundant chemical components of EPS. The addition of Cd(II) adversely affected most denitrifying bacteria (p < 0.05), which is consistent with the low TN removal. In addition, quantitative polymerase chain reaction analysis revealed that CzcA gene abundance decreased as the Cd(II) concentration increased, possibly because expression of the CzcA gene was inhibited by Cd(II) stress. The majority of CzcA gene sequences were carried by Pseudomonas, making it the dominant genus among Cd(II)-resistant bacteria.
17430. 题目: Effects of intercropping mulch on the content and composition of soil dissolved organic matter in apple orchard on the loess plateau
期刊: Journal of Environmental Management
作者: Rongqin Zhang, Qianqian Huang, Taoyu Yan, Jianfeng Yang, Yue Zheng, Huike Li, Ming Li
摘要: Dissolved organic matter (DOM) is an important parameter that reflects soil fertility and quality. In this study, the effects of intercropping perennial ryegrass and straw mulch on the content, composition and spectral characteristics of soil DOM in orchards in arid and semi-arid areas were investigated by three-dimensional fluorescence excitation-emission matrix (EEM) combined with parallel factor analysis (PARAFAC). Three treatments were applied in a 6-year-old apple orchard on the Loess Plateau: (1) clean tillage (CT); (2) intercropping perennial ryegrass mulch (RE); (3) intercropping straw mulch (CS). Soil samples (0–10, 10–20, 20–40, 40–60, 60–80, 80–100 cm) were collected from different treatments. The total soil organic carbon (SOC) and dissolved organic carbon (DOC) content were ranked as CS> RE> CT, and decreased with soil depth. In addition, the vertical distribution of DOC with different soil depth was caused by organic matter input but not leaching. Three humic-like components and two protein-like components were identified by EEM-PARAFAC. Fluorescence spectra showed that humic-like compounds were the dominant fractions in soil DOM in the CS treatment. Fluorescence Index (FI) indicated that the proportion of plant residues and soil organic matter derived DOM ranked as CT> RE> CS and gradually decreased with soil depth. Our results highlight the key role of orchard intercropping mulch in improving the content and compositions of soil DOM through different forms of organic inputs and provide new theoretical support for the evaluation of soil fertility in orchards.
17431. 题目: Enhanced phosphorus availability and heavy metal removal by chlorination during sewage sludge pyrolysis
期刊: Journal of Hazardous Materials
作者: Yunxue Xia, Yuanyuan Tang, Kaimin Shih, Bang Li
摘要: Increasing attention has been paid on the application of sewage sludge-derived biochar as soil amendments, but is always limited by heavy metals. This study conducted experiments on heavy metal removal by adding chlorinating agents (PVC, NaCl, MgCl2, CaCl2) during sludge pyrolysis. The chlorides addition can largely remove heavy metals by achieving the highest removal efficiency with dosage of 80 g(Cl)/kg(dry sludge) at 700 °C. The most effective removal effect was observed for Zn, Mn, Cu and Pb, with removal efficiency from 37.44% to 99.45%, 5.24% to 93.64%, 9.11% to 86.15% and 16.57% to 90.75%, respectively for the sludge before and after chlorination. Furthermore, the P-solubility in neutral ammonium citrate (Pnac) was enhanced after chlorination and the maximum P-solubility can be obtained at 700 °C for each series. After 700 °C pyrolysis, the P-solubility was significantly increased from 40.08% of the sludge biochar to 72.07%, 74.05%, 74.00% and 76.57% of the biochar obtained after adding PVC, NaCl, CaCl2, and MgCl2, respectively. The highest P-solubility was observed in samples with MgCl2 due to the formation of Mg3(PO4)2. This study proposed a novel method to use the sludge biochar as potential P-fertilizer with effective heavy metal removal, finally achieving a “waste-to-resource” strategy for integrated management of sewage sludge.
17432. 题目: Acidic surface functional groups control chemisorption of ammonium onto carbon materials in aqueous media
期刊: Science of The Total Environment
作者: Sumaraj, Zixi Xiong, Ajit K. Sarmah, Lokesh P. Padhye
摘要: Elucidation of mechanistic insight into the interaction of carbon materials' physicochemical surface properties and ammonium (NH4+) adsorption in aqueous media was made by conducting a systematic study using a wide range of carbon materials. Three types of biochars (rice husk, poultry litter, and enhanced poultry litter) and activated carbons (fresh and aged coconut shell-based and charcoal-based) were used for investigating the NH4+ adsorption mechanism. Poultry litter biochar, with lowest surface area (3 m2 g−1) and largest pore diameter (29 nm), showed the highest NH4+ adsorption capacity (0.34 mg NH4+g−1), while charcoal-based activated carbon, with the highest surface area (1133 m2 g−1) and small pore diameter (6 nm), had the least NH4+ adsorption capacity (0.09 mg NH4+g−1). The value of Freundlich isotherm constant ‘n’ was >1 for all tested carbon materials indicating chemisorption as the dominant sorption mechanism. Aging of the carbon surface resulted in 30% increase in NH4+ retention. Surface chemical properties that most influenced NH4+ chemisorption on to carbon materials were found to be acidic surface functional groups (ASFGs), elemental composition, ash content, and pH. The optimal conditions for NH4+ adsorption, regardless of type and source of carbon materials, were solution pH of 8, a high amount of ash content, and carboxyl, carbonyl, and phenolic functional groups. Evaluation of CEC and ASFGs indicated that CEC and ASFGs are not equivalent terms. Through this study, conducted on carbon adsorbents derived from different sources, with different surface physical and chemical properties, we established that ASFGs, and not CEC, play a critical role in ammonium chemisorption on carbon materials. The study showed that low cost and eco-friendly biochars, with optimal surface chemistry, can replace expensive activated carbons for NH4+ remediation in aqueous media.
17433. 题目: Unraveling long-term changes in lake color based on optical properties of lake sediment
期刊: Science of The Total Environment
作者: Yihua Xiao, Thomas Rohrlack, Gunnhild Riise
摘要: A number of boreal surface waters have become browner over the last two decades. Recovery from acid rain is regarded as an important driver for this lake color increase, indicating a general browner lake color in preindustrial times. However, the lack of long-term monitoring data makes it challenging to unravel historical changes in lake color. In this study, we estimated long-term development in lake color (1800 to 2015) based on the optical properties of alkaline extractable dissolved organic matter (DOM) from sediment using UV–Vis and fluorescence spectroscopy. We found that the present lake color (2015) was significantly browner (four times higher in absorption coefficient) than for the period from 1800 to 1915 when lake color was at a lower and more stable level. Fluorescence excitation–emission matrices combined with parallel factor analysis (EEM-PARAFAC) indicate that terrestrially derived DOM was the main source of sediment DOM. However, the importance of in-lake source of DOM has significantly increased with time. The long-term trend in DOM burial was not consistent with the anthropogenic sulfur (S) deposition pattern. However, along with the increased sediment DOM, there has been increased precipitation, temperature and forest growth with time, which affect the production and degradation of DOM. Even though S deposition might have delayed the runoff of terrestrial DOM for a certain period, it comes in addition to other color-regulating factors. Thus, there is no single driver for the observed lake browning, but rather an interplay between different drivers varying in strength over time, such as afforestation, changes in areal use, declined S deposition, and increased temperature and precipitation.
17434. 题目: Soil organic matter decomposition and carbon sequestration in temperate coniferous forest soils affected by soluble and insoluble spruce needle fractions
期刊: Soil Biology and Biochemistry
作者: Veronika Jílková, Kateřina Jandová, Allan Sim, Barry Thornton, Eric Paterson
摘要: Temperate forest soils are important carbon (C) sinks, where the C-stock is largely determined by the balance of leaf inputs and losses through respiration. However, studies dealing with leaf inputs to coniferous forest soils are limited although coniferous forests are widespread through the Northern temperate zone. In this study, we focused on the effects of soluble, insoluble and whole-tissue coniferous needle fractions on soil organic matter (SOM) decomposition and C storage in soil fractions. In addition, the effect of future increased C input was tested by applying a doubled amount of the soluble fraction (whole-tissue + soluble fraction). 13C-labelled needles were produced from spruce seedlings in growth chambers and needle fractions were added to the coniferous forest soil in laboratory microcosms. CO2 respired during incubation from the microcosms was partitioned into needle- and SOM-derived components. After seven months, soils were destructively harvested and analysed for C content in soil fractions and microbial community composition.The soluble, insoluble and whole-tissue fractions resulted in cumulative priming (increased SOM-derived CO2 relative to unamended controls) of 25 ± 8%, 40 ± 1%, and 39 ± 7%, respectively. The doubled soluble-C addition caused a slightly lower priming (38 ± 2%) than the whole-tissue fraction alone. The addition of needle fractions did not significantly affect the C content of soil fractions. However, the soluble fraction retained in soil was mainly found adsorbed onto mineral particles, whereas the insoluble and whole-tissue fractions occurred mainly as free particulate organic matter or adsorbed onto mineral particles. The insoluble and whole-tissue fraction led to increased fungal abundance and decreased abundance of G+ bacteria and actinobacteria. All the fractions were primarily incorporated into fungal biomass after seven months suggesting that fungi were the main consumers of all needle fractions after the labile C had been depleted. When considering all the C gains and losses, the addition of all needle fractions resulted in net soil C increase. This suggests that, although the input of the coniferous needles leads to some C losses through the priming of SOM decomposition, these C losses are compensated by new C storage either in SOM fractions or microbial biomass.
17435. 题目: Improved voltammetric methodology for chromium redox speciation in estuarine waters
期刊: Analytica Chimica Acta
作者: Jasmin Pađan, Saša Marcinek, Ana-Marija Cindrić, Nicolas Layglon, Veronique Lenoble, Pascal Salaün, Cedric Garnier, Dario Omanović
摘要: Chromium is a toxic element naturally present in natural waters whose chemical speciation regulates its cycling, mobility and bioavailability. We present here: 1- an improved analytical method for chromium speciation (Cr(VI) vs Cr(III)) in estuarine samples by catalytic adsorptive cathodic stripping voltammetric (cat-AdCSV) and 2- a study highlighting a significant change of redox speciation during summer and winter. Initial measurements first revealed that surface-active substances (SAS) present in estuarine samples strongly influenced the analytical determination of Cr by partially masking the Cr peak through an increase of the background current. We found that the application of a low negative accumulation potential (-1.65 V) resulted in much better voltammograms compared to those obtained using the usual accumulation potential of -1.0 V. Using humic acid (HA) as a model SAS of natural origin, we show that this negative potential clearly prevents adsorption of SAS on the Hg-electrode surface, which in turns benefits the adsorption of the in-situ formed Cr(III)-DTPA complex and the resulting signal. The optimised method was applied to determine chromium redox speciation and distribution along the 23 km long salinity gradient, well oxygenated, Krka River estuary (Croatia). Cr(VI) was found to be the dominant redox species in both summer and winter, with Cr(III) contribution being lower in summer (up to ∼30%, average of ∼5%) than in winter (up to ∼50%, average of ∼30%). In summer, lower concentrations of Cr(VI) were found in the freshwater end-member (2.5 nM) than in the seawater end-member (4-5 nM), while the opposite trend was found in winter. Hexavalent chromium exhibited a non-conservative behaviour along the salinity gradient for both seasons. Chromium predominantly exists in dissolved phase, and contribution of particles reactive Cr(III) was minor.
17436. 题目: An assessment of the tea bag index method as a proxy for organic matter decomposition in intertidal environments
期刊: Journal of Geophysical Research: Biogeosciences
作者: AnnaClaire R.G. Marley, Craig Smeaton, William E.N. Austin
摘要: Intertidal wetlands capture and store carbon (C) for long periods of time, helping to reduce the concentration of CO2 in the atmosphere. Yet the processes which govern the decomposition and subsequent long‐term storage of organic matter (OM) and C in these habitats remains poorly understood. The Tea Bag Index (TBI) uses a standardized OM (green and Rooibos tea) and has the potential to shed light on OM decomposition across habitats, including saltmarshes. Here, we apply the TBI method at two saltmarshes within the same estuary with the aim of (i) reducing the influence of climatic variables and (ii) determining the role of the environment, including the soil characteristics, in the decomposition of OM. We extended the standard (3 months) incubation period over a full year in order to investigate the longer‐term decomposition processes at each site. The initial results partially support previous studies that the early stages of decomposition (leaching of the water‐soluble fraction) is governed by climatic conditions, but may be further enhanced by tidal flushing in saltmarshes. By extending the incubation period, we observed the initiation of mid‐stage OM decomposition (Cellulose degradation) upon which the soil characteristics appear to be the dominant control. These results highlight the importance of long‐term TBI incubations to understand early‐stage OM decomposition. The relationship between tea mass (OM) loss and C loss in these intertidal environments is not straightforward and we would caution the use of the TBI as a direct universal proxy for soil C degradation in such intertidal wetlands.
17437. 题目: Effects of aquatic phototrophs on seasonal hydrochemical, inorganic, and organic carbon variations in a typical karst basin, Southwest China
期刊: Environmental Science and Pollution Research
作者: Ping’an Sun, Shiyi He, Yaqiong Yuan, Shi Yu, Cheng Zhang
摘要: Karst processes play an important role in the global carbon cycle. Aquatic phototrophs can transform bicarbonate, which is mainly derived from the weathering of carbonates, into organic carbon. Carbonate mineral weathering coupled with aquatic photosynthesis can be considered a stable and durable carbon sink process. In this study, we addressed seasonal variations in water chemistry in the Lijiang River Basin, which is a typical karst basin, through a comprehensive geochemical study of the river water in four seasons. The parameters were measured in situ, including major ions and isotopes of inorganic and organic carbon. The results showed that (1) DIC was mainly derived from the weathering of carbonates; (2) the transformation from bicarbonate to organic carbon by aquatic phototrophs was evident, and the water chemistry changed, especially in spring and autumn and in the mainstream from Guilin to Yangshuo, which benefited the growth of aquatic phototrophs; and (3) the organic carbon derived from bicarbonates by aquatic phototrophs was nearly half the total organic carbon and 8% of the dissolved inorganic carbon. These results imply that aquatic phototrophs in karst basins can significantly stabilize carbon originating from carbonate rock weathering processes in karst areas.
17438. 题目: Effects of extraction conditions on the redox properties of soil organic matter (SOM) and its ability to stimulate microbial iron(III) mineral reduction by electron shuttling
作者: Yuge Bai, Edisson Subdiaga, Stefan B. Haderlein, Heike Knicker, and Andreas Kappler
摘要: Soil organic matter (SOM), including humic substances (HS), is redox-active, can be microbially reduced, and transfers electrons in an abiotic reaction to Fe(III) minerals thus serving as electron shuttle. The standard procedure to extract HS from soil and separate them into humic acids (HA) and fulvic acids (FA) involves alkaline and acidic solutions potentially leading to unwanted changes in SOM chemical and redox properties. To determine the effects of extraction conditions on the redox and electron shuttling properties of SOM extracts, we prepared HS and SOM extracts from a forest soil applying either a combination of 0.1 M NaOH and 6 M HCl, or water (pH 7). Both chemical extractions (NaOH / HCl) and water extractions were done in separate setups under either oxic or anoxic conditions. Furthermore, we applied the NaOH / HCl treatment to a subsample of the water-extracted-SOM. We found that soil extraction with NaOH lead to ca. 100 times more extracted C and the extracted HS had 2–3 times higher electron exchange capacities (EEC) than SOM extracted by water. For water-extracted SOM, anoxic extraction conditions lead to about 7 times more extracted C and 1.5 times higher EEC than under oxic extraction conditions. This difference was probably due to the occurrence of microbial reduction and dissolution of Fe(III) minerals in the soil during the water extraction at neutral pH and the concomitant release of Fe(III) mineral-bound organic matter. NaOH / HCl treatment of the water-extracted SOM lead to 2 times higher EEC values in the HA isolated from the SOM compared to the water-extracted SOM itself, suggesting the chemical treatment with NaOH and HCl caused changes of redox-active functional groups of the extracted organic compounds. Higher EEC of extracts in turn resulted in a higher stimulation of microbial Fe(III) mineral reduction by electron shuttling, i.e. faster initial Fe(III) reduction rates, and in most cases also in higher reduction extents. Our findings suggest that SOM extracted with water at neutral pH should be used to better reflect environmental SOM redox processes in lab experiments and that potential artefacts of the chemical extraction method and anoxic extraction condition need to be considered when evaluating and comparing abiotic and microbial SOM redox processes.
17439. 题目: Transformation of silver ions to silver nanoparticles mediated by humic acid in darkness at ambient temperature
期刊: Journal of Hazardous Materials
作者: Bin Dong, Guangfei Liu, Jiti Zhou, Jing Wang, Ruofei Jin
摘要: The conversion of silver materials in environments would impact their toxicity and risk. Previous studies have reported that silver ions (Ag+) could be reduced to silver nanoparticles (AgNPs) by natural organic matters (NOM) under sunlight or heating conditions. However, whether such reaction could occur in darkness at ambient temperature and the transformation mechanism were unclear. This study found that Ag+ at environmentally relevant concentrations (as low as 1 μg/L) could be reduced to AgNPs by Suwannee River humic acid (SRHA) in darkness at 30 °C. The reaction mechanism probed by X-ray absorption fine structure spectroscopy revealed that Ag+ was first bound to the carboxylic groups of SRHA to form Ag+-SRHA ligands, which were then reduced to metallic Ag. The increase of pH (6–9) and the coexistence of formate, acetate, carbonate, and sulfate promoted the formation of AgNPs. Besides, the formed AgNPs would coalesce to large aggregates under acidic conditions or in the presence of sulfate. These results suggest that the dark transformation of Ag+ to AgNPs mediated by NOM could occur in environments and are important for the better understanding of the natural origin of AgNPs.
17440. 题目: Hierarchical porous biochar from shrimp shell for persulfate activation: A two-electron transfer path and key impact factors
期刊: Applied Catalysis B: Environmental
作者: Jiangfang Yu, Lin Tang, Ya Pang, Guangming Zeng, Haopeng Feng, Jiajing Zou, Jingjing Wang, Chengyang Feng, Xu Zhu, Xilian Ouyang, Jisui Tan
摘要: Herein, hierarchical porous biochar from shrimp shell (PSS-bio) was prepared and applied for persulfate activation for 2,4-dichlorophenol removal. The pyrolysis temperature was found to play an important role in carbon structure and property modulation, where PSS-bio obtained at 800 °C (PSS-800) exhibited the fastest adsorption capacity and the best catalytic activity with the degradation rates 29 times higher than that of PSS-bio obtained at 400 °C (PSS-400). Further analysis demonstrated that hierarchical pores and carbon configuration were two key impact factors of biochar in AOP. Interestingly, the original free-radical dominated pathway in PSS-400 also changed into a non-radical one (direct two-electron transfer path) in PSS-800, whose efficiency could be somewhat disturbed by pH values, humic acid and anions regardless of their concentrations as low as 5 mM or as high as 500 mM, demonstrating its application potential for the treatment of both highly saline water and organic-rich water.