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25321. 题目: Promoting revegetation and soil carbon sequestration on decommissioned forest roads in Colorado, USA: A comparative assessment of organic soil amendments
文章编号: N18062608
期刊: Forest Ecology and Management
作者: M. Ramlow, C.C. Rhoades, M.F. Cotrufo
更新时间: 2018-06-26
摘要: Forest roads are commonly decommissioned and revegetated to decrease erosion, prevent weed encroachment, manage recreation and improve overall watershed condition on federal lands, but may also provide a complementary opportunity to sequester carbon (C) in soils. Soils on decommissioned roads are typically compacted with limited capacity for water retention, decreased mineral nitrogen (N) availability and low organic matter content, impairing revegetation and soil C sequestration efforts. We evaluated the effects of an organic fertilizer, wood strand mulch and a woody biochar on soil physical, chemical and biological processes to improve revegetation and C sequestration on decompacted forest roads. We monitored plant and soil responses to the treatments and their combinations over three growing seasons on four decommissioned road segments in northern Colorado. The organic fertilizer increased plant available mineral N for the first year of the study and resulted in a 21% increase in total plant cover and 67% increase in root biomass. The wood strand mulch increased total plant cover and root biomass to a similar extent, but had no effect on soil water content or mineral N availability. Instead, mulch stimulated soil microbial respiration and increased soil C content, two of the best predictors of plant cover and biomass. The woody biochar increased soil water content by 26% and elevated mineral N availability throughout the study, but did not improve plant cover, above- or belowground biomass. Mulch, biochar and their combined treatments sequestered C, but through distinct pathways. Microbial processing of wood strand mulch added C to the mineral soil fraction, whereas biochar added C directly to the coarse particulate fraction with no effect on mineral soil C or soil respiration. Restoration practitioners can utilize these results to inform management decisions and guide further research on different rates and combinations of organic amendments to revegetate and sequester C on decommissioned forest roads.

25322. 题目: How do logging residues of different tree species affect soil N cycling after final felling?
文章编号: N18062607
期刊: Forest Ecology and Management
作者: Tiina T?rm?nen, Veikko Kitunen, Antti-Jussi Lindroos, Juha Heikkinen, Aino Smolander
更新时间: 2018-06-26
摘要: The aim of this study was to compare how logging residues of Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth.) affect the dynamics of N and C cycling processes in forest soil after final felling. The study site was located in southeastern Finland. After clear-cutting, piles consisting of 40 kg m 2 of fresh logging residues of each tree species were established, together with a control plot as an additional treatment. Samples were taken from the organic layer and uppermost mineral soil at the beginning of the experiment and each spring and autumn in the two following years. Logging residues stimulated net N mineralization and net nitrification and increased both NH4- and NO3-N concentrations in the organic layer. Logging residues increased the soil pH, organic matter content (%) and C mineralization, whereas microbial biomass C and N decreased. No major, consistent differences were observed between the effects of the separate tree species, although there were tree-species-specific differences on the dynamics of soil processes. Logging residues of spruce, pine and birch all strongly accelerated the processes of soil N cycling soon after clear-cutting. This study provides new information for the discussion on the sustainability of logging residue distribution and harvesting in boreal forests.

25323. 题目: Effects of tree species and soil properties on the composition and diversity of the soil bacterial community following afforestation
文章编号: N18062606
期刊: Forest Ecology and Management
作者: Jinliang Liu, Peng Dang, Yang Gao, Hailan Zhu, Huinan Zhu, Fei Zhao, Zhong Zhao
更新时间: 2018-06-26
摘要: Afforestation with single and mixed tree species on cropland alters soil properties and the composition and diversity of soil bacterial community. We investigated changes in soil properties and the soil bacterial community composition in the topsoil (0–20 cm) following afforestation on cropland on the Loess Plateau. Forests of six types ranging from 23 to 25 years in age were chosen in this study: Robinia pseudoacacia (RP), Platycladus orientalis (PO), Pinus tabuliformis (PT), Robinia pseudoacacia + Platycladus orientalis (RPPO), Robinia pseudoacacia + Pinus tabuliformis (RPPT), and Platycladus orientalis + Pinus tabuliformis (POPT). Afforestation with different tree species altered the soil nutrient contents, with total nitrogen (TN) and ammonium nitrogen (NH4 +) contents increased by 18.28–87.10% and 13.97–141.34%, respectively, and available phosphorus (AP) content decreased by 56.09–82.13% compared to cropland sites. Cropland afforestation reduced the soil bacterial richness and core bacterial genera abundance (relative abundance ≥ 0.1%), and significantly altered the bacterial diversity. Soil properties explained 73.41% of the total variation in the core soil bacterial community composition at the genus level, and soil organic carbon (SOC), TN, nitrate nitrogen (NO3 ), NH4 +, AP, pH and the carbon:phosphorus (C:P) ratio were significantly correlated with first two RDA (redundancy analysis) axes. The results of hierarchical clustering indicated that the soil bacterial community composition in the RPPO, RPPT and POPT sites was largely affected by Platycladus, Pinus tabuliformis and Platycladus, respectively. Our observations suggest that soil bacterial community composition and diversity following afforestation were mainly affected by tree species, followed by soil parameters. The effect of afforestation on the soil bacterial diversity was larger than its effect on bacterial richness.

25324. 题目: C and N cycle monitoring under Quercus castaneifolia plantation
文章编号: N18062605
期刊: Forest Ecology and Management
作者: Mohammad Kazem Parsapour, Yahya Kooch, Seyed Mohsen Hosseini, Seyed Jalil Alavi
更新时间: 2018-06-26
摘要: In temperate forests, oak (Quercus castaneifolia) is an important species that grows along an elevation gradient from the flood prone plains to high topographical positions of the landscape. This study was aimed to monitor the effect of oak plantation on the soil C and N cycles and dynamics in the north of Iran. We tested the following hypotheses: (i) reclamation of deforested areas, planting of oak can improve topsoil fertility via forest floor inputs in the long-term, (ii) soil C and N microbial indices can be enhanced under oak plantation, 25 years after planting. For this purpose, three afforested oak stands with 15, 20, and 25 years old, besides a site without plantation, were selected and thirty samples per each site were taken from forest floor and soil (20 × 20 × 10 cm) layers and their physicochemical, biological, and enzymatic properties were assessed. The acquired data demonstrated that forest floor quality, physicochemical and biological properties and enzymatic activities (i.e. urease, acid phosphatase, arylsulfatase and invertase) have been changed over time of oak plantation. Moreover, the microbial activity of soil C and N include basal respiration (BR), substrate inducted respiration (SIR), microbial biomass carbon (MBC), Metabolic quotient (qCO2), microbial entropy (MBC/C), carbon availability index (CAI), carbon management index (CMI), particle organic carbon (POC) and dissolved organic carbon (DOC) were significantly higher in the plantation areas than without plantation site. Oak plantation significantly improved the N microbial characteristics [NH4 +, NO3 , N mineralization, microbial biomass nitrogen (MBN), particle organic nitrogen (PON) and dissolved organic nitrogen (DON)]. Under different land covers, soil microbial activities were more affected by variations in forest floor and soil chemical properties with higher ratio of C, N and available nutrients. Taken together, plantation with suitable native broadleaved species could be considered to rehabilitate degraded natural forests through improving soil quality. Findings also highlighted the importance of understanding C and N cycles in the plantation areas which could involve in global warming phenomena.

25325. 题目: Preparation, characterizations and performance evaluations of alumina hollow fiber membrane incorporated with UiO-66 particles for humic acid removal
文章编号: N18062604
期刊: Journal of Membrane Science
作者: Norfazliana Abdullah, Mukhlis A. Rahman, Mohd Hafiz Dzarfan Othman, Juhana Jaafar, Azian Abd Aziz
更新时间: 2018-06-26
摘要: Humic acid removal requires ceramic membranes incorporated with metal organic framework (MOF) to display remarkable stability over water. Recent work has shown UiO-66, a Zr-based MOF, as an emerging material with the potential to fulfill this requirement. This work investigated the preparation, characterization and performance of UiO-66 particles deposited on alumina hollow fiber membranes. Concentrations of Zr precursors and synthesis period were varied in the preparation of UiO-66 using solvothermal synthesis. The presence of UiO-66 particles was characterized using the field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) mapping, x-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) analysis. Pure water flux and humic acid rejection tests were carried out on both pristine alumina hollow fiber membranes and alumina hollow fiber membranes deposited with UiO-66 particles. In the former, a high pure water flux value of 231.24 L m 2 h 1 was recorded, while in the latter the recorded value dropped to 9.36 L m 2 h 1. Pristine ceramic hollow fiber membranes used to separate humic acid (1 g L 1) from an aqueous solution showed a rejection rate of 98%. When UiO-66 particles were deposited on the ceramic membranes, the solute flux of the membranes increased to 68.36 L m 2 h 1. Surprisingly, it was found that 99% humic acid was rejected from a feed solution using the membranes incorporated with UiO-66 particles. Findings showed that the weight loading of the UiO-66 particles on the alumina hollow fiber membranes was very low, showing a reading of only approximately ~ 0.01 g. Based on the adsorption-desorption analysis, at high pH values (≥ 9), UiO-66 particles and humic acid displayed a similar surface charge, creating a repulsion effect during the filtration process. UiO-66 particles on alumina hollow fiber membranes showed excellent stability, making it viable for water purification applications.

25326. 题目: Rapid immobilisation of U(VI) by Eucalyptus bark: Adsorption without reduction
文章编号: N18062603
期刊: Applied Geochemistry
作者: Susan A. Cumberland, Siobhan A. Wilson, Barbara Etschmann, Peter Kappen, Daryl Howard, David Paterson, Jo?l Brugger
更新时间: 2018-06-26
摘要: Organic matter is increasingly shown to influence the mobility of uranium (U) in the environment. The mobility of U likely depends on whether the organic matter is in dissolved or solid form, with the latter able to retard U mobility. In this work, column experiments were used to reveal that solid organic matter, in the form of well characterized tree bark from Eucalyptus globulus, dramatically reduced the mobility of aqueous U(VI) which was introduced as uranyl nitrate [UO2(NO3)2]. Eucalyptus globulus bark contains high levels of carboxylic and phenolic acid groups which are known to bind to U. Admixtures containing 20 wt. % tree bark and sand were compared to columns containing sand only. We show that soluble U is adsorbed onto the tree bark, likely via a cation exchange with calcium, with no change in U oxidation state as confirmed by X-ray Absorption Near Edge Structure (XANES) analyses. Cation concentrations in column outflow solutions indicated that U was retained in the columns containing tree bark but was released from the sand-only columns. These results demonstrate that solid organic matter such as tree bark has potential applications in trapping U, possibly within permeable reactive barriers, without necessitating further engineering to reduce U(VI) to U(IV). Building on previous work on organic sedimentary U-deposits, this study also helps understand processes of U enrichment from groundwater as observed in environments high in organic matter including wetlands and sediment-hosted ore deposits.

25327. 题目: Iron reductive dissolution in vadose zone soils: Implication for groundwater pollution in landfill impacted sites
文章编号: N18062602
期刊: Applied Geochemistry
作者: Akua B. Oppong-Anane, Katherine Y. Deliz Qui?ones, Willie Harris, Timothy Townsend, Jean-Claude J. Bonzongo
更新时间: 2018-06-26
摘要: Iron (Fe) contamination of groundwater has become a problem of concern at a number of landfill impacted locations, and long-term monitoring studies suggest that the reductive dissolution of iron (hydr)oxide minerals present in soils and aquifer sediments could be one the sources of dissolved Fe measured in impacted aquifers. In this study, vadose zone soil samples were collected along a gradient emphasizing differences in both soil water saturation levels and degrees of crystallization of Fe-minerals. Collected soil samples were analyzed for pH, organic matter content, particle size distribution, and Fe speciation into amorphous and crystalline fractions. Batch experiments were conducted under anaerobic conditions using soil slurries with (treatments) or without (controls) landfill leachate addition to the liquid phase. Under the experimental conditions used in this study, tested soils released Fe primarily via reductive dissolution pathways, with rates ranging from 0.3 to 12 mg Fe/kg.day. However, no clear trend was evident between the amount of Fe released and the crystallinity degrees of the iron minerals present in the tested soils. The addition of organic carbon sources to prepared vadose soils slurries fueled the microbial driven Fe-reductive dissolution, suggesting that organic-rich landfill leachate would play a significant role in the dissolution of iron (hydr)oxide minerals, and potentially in the mobilization of toxic metals co-precipitated with or adsorbed onto iron (hydr)oxide minerals.

25328. 题目: Influence of colloids on metal concentrations and radiogenic strontium isotopes in groundwater and oil and gas-produced waters
文章编号: N18062601
期刊: Applied Geochemistry
作者: Thai T. Phan, J. Alexandra Hakala, Daniel J. Bain
更新时间: 2018-06-26
摘要: Concentrations and isotopic compositions of Li and Sr can be used to identify water-rock interactions and fluid mixing in petroleum reservoirs, such as mixing between hydraulic fracturing fluid and in-situ formation water in hydraulically fractured shales. However, the physical changes during mixing in the subsurface environment and during collection of produced water are not clear. We hypothesize that the colloidal particles potentially affect measured constituents in produced waters and degrade the utility of Li and Sr isotopes as geochemical tracers of fluid sources and water-rock interactions. Therefore, this study investigated the influence of colloids on the metal concentrations and isotopes (δ7Li and 87Sr/86Sr) by analyzing water that was filtered through successively smaller membranes (0.45 μm, 0.2 μm, and 3 kDa). We found that the differences in the concentrations of major and most minor elements (B, Ca, Ga, K, Li, Mg, Na, Ga, Rb, and Sr) in the <0.45 μm, the <0.2 μm, and the <3 kDa fractions of groundwater and oil produced water are not statistically different (p > 0.05; Student's t-test). Likewise, similar results were observed for the <0.45 μm, the <0.2 μm-centrifuged, and the <3 kDa fractions of gas produced water. In the <0.45 μm fraction of groundwater, U is up to 8% greater than U in the 3 kDa fraction, possibly due to complexation of U with natural organic matter. The formation of Fe oxyhydroxides during sample collection was observed in all three types of waters, however does not significantly affect the measured 87Sr/86Sr between three fractions of the study waters. On the other hand, Al, Si, and Ti are enriched in the <0.45 μm fraction relative to the <3 kDa fraction of gas produced water, likely due to aluminosilicate minerals (e.g., clays and quartz). However, interactions of Sr and Li with these minerals do not result in statistically significant differences (p > 0.05) in 87Sr/86Sr among three fractions of groundwater and both oil and gas produced waters. Similarly, no difference in δ7Li in <0.45 μm and <0.2 μm-centrifuged fractions of gas produced water was observed. Ultimately, overestimated concentration data of Al, Si, and Ti in water filtered through a 0.45 μm membrane due to the presence of colloidal clays can create misinterpretations of chemical water-rock interactions in hydraulically fractured shale in the subsurface.

25329. 题目: Coagulation of low temperature and low turbidity water: Adjusting basicity of polyaluminum chloride (PAC) and using chitosan as coagulant aid
文章编号: N180625G3
期刊: Separation and Purification Technology
作者: Zhen Zhang, Ran Jing, Shuran He, Jin Qian, Kun Zhang, Guilin Ma, Xing Chang, Mingkuan Zhang, Yongtao Li
更新时间: 2018-06-25
摘要: This study evaluated the feasibility of integrating high-basicity polyaluminum chloride (PAC) and high-viscosity chitosan for the coagulation of low-temperature and low-turbidity water. The effects of PAC basicity on coagulation performance and residual Al control were also investigated. It was found that higher-basicity PAC with a larger proportion of Alc (colloidal Al species in PAC) and smaller proportion of Ala (monomeric Al species in PAC) was beneficial for removing turbidity and natural organic matter (NOM), as well as controlling the residual Al content. Further, the integration of PAC with a high basicity (90.3%) and chitosan with a high viscosity (500 mPa·s) realized the efficient removal of turbidity and NOM, with removal efficiencies of approximately 87%, 63%, and 82% for turbidity, dissolved organic matter (DOC) and UV254, respectively. It was speculated that larger and more settleable flocs tended to form via the synergistic effect of charge neutralization by Alb (polymeric Al species in PAC) and interparticle bridging by both the Alc species and chitosan, consequently leading to excellent coagulation performance. This study may provide a useful option to drinking water treatment operators for dealing with low-temperature and low-turbidity water in practice.

25330. 题目: Study of solar photocatalytic degradation of Acesulfame K to limit the outpouring of artificial sweeteners
文章编号: N180625G2
期刊: Separation and Purification Technology
作者: Malini Ghosh, Pankaj Chowdhury, Ajay K. Ray
更新时间: 2018-06-25
摘要: In this study, the photocatalytic degradation of an artificial sweetener, Acesulfame K (ACK), has been investigated with TiO2 photocatalyst using a solar simulator. Adsorption of ACK on TiO2 surface follows Freundlich adsorption isotherm in the pH range of 6–8 and shows an adsorption coefficient of 0.002 L/mg. Parametric studies for solar photocatalytic degradation are performed varying initial concentrations of ACK, photocatalyst dosage, and solar light intensity. Photocatalytic degradation rate of ACK gradually decreases with increasing initial concentration of ACK, and the rate follows pseudo first-order kinetics. The degradation rate of ACK gradually increases as the TiO2 dosage is increased and reaches maximum at 0.8–1.0 g/L. The rate constant for ACK degradation has been found to be directly proportional to light intensity, obeying a power law model. Complete degradation of ACK for 10–20 mg/L initial concentration is observed within the first 30 min of solar light irradiation of 100 mW/cm2 at pH 6. Complete mineralization of ACK can be achieved in 6 h with dissolved organic carbon (DOC) less than 1 mg/L. Complete mineralization of ACK and its by-products is successfully achieved with an apparent quantum yield of 0.02% at 1 sun thus making the process sustainable. This study manifests the efficacy of the solar photocatalytic process on degrading emerging pollutants like ACK where the use of artificial UV lamp has successfully been substituted by solar light, the most abundantly found sustainable source of energy in nature. Moreover, the process followed in this study is devoid of the use of any hazardous chemicals.

25331. 题目: Characterization of bacterial community and iron corrosion in drinking water distribution systems with O3-biological activated carbon treatment
文章编号: N180625G1
期刊: Journal of Environmental Sciences
作者: Xueci Xing, Haibo Wang, Chun Hu, Lizhong Liu
更新时间: 2018-06-25
摘要: Bacterial community structure and iron corrosion were investigated for simulated drinking water distribution systems (DWDSs) composed of annular reactors incorporating three different treatments: ozone, biologically activated carbon and chlorination (O3-BAC-Cl2); ozone and chlorination (O3-Cl2); or chlorination alone (Cl2). The lowest corrosion rate and iron release, along with more Fe3O4 formation, occurred in DWDSs with O3-BAC-Cl2 compared to those without a BAC filter. It was verified that O3-BAC influenced the bacterial community greatly to promote the relative advantage of nitrate-reducing bacteria (NRB) in DWDSs. Moreover, the advantaged NRB induced active Fe(III) reduction coupled to Fe(II) oxidation, enhancing Fe3O4 formation and inhibiting corrosion. In addition, O3-BAC pretreatment could reduce high-molecular-weight fractions of dissolved organic carbon effectively to promote iron particle aggregation and inhibit further iron release. Our findings indicated that the O3-BAC treatment, besides removing organic pollutants in water, was also a good approach for controlling cast iron corrosion and iron release in DWDSs.

25332. 题目: Effects of turbulence on carbon emission in shallow lakes
文章编号: N180625G0
期刊: Journal of Environmental Sciences
作者: Lin Zhu, Boqiang Qin, Jian Zhou, Bryce Van Dam, Wenqing Shi
更新时间: 2018-06-25
摘要: Turbulent mixing is enhanced in shallow lakes. As a result, exchanges across the air–water and sediment–water interfaces are increased, causing these systems to be large sources of greenhouse gases. This study investigated the effects of turbulence on carbon dioxide (CO2) and methane (CH4) emissions in shallow lakes using simulated mesocosm experiments. Results demonstrated that turbulence increased CO2 emissions, while simultaneously decreasing CH4 emissions by altering microbial processes. Under turbulent conditions, a greater fraction of organic carbon was recycled as CO2 instead of CH4, potentially reducing the net global warming effect because of the lower global warming potential of CO2 relative to CH4. The CH4/CO2 flux ratio was approximately 0.006 under turbulent conditions, but reached 0.078 in the control. The real-time quantitative PCR analysis indicated that methanogen abundance decreased and methanotroph abundance increased under turbulent conditions, inhibiting CH4 production and favoring the oxidation of CH4 to CO2. These findings suggest that turbulence may play an important role in the global carbon cycle by limiting CH4 emissions, thereby reducing the net global warming effect of shallow lakes.

25333. 题目: Formation process and mechanism of humic acid-kaolin complex determined by carbamazepine sorption experiments and various characterization methods
文章编号: N180625F9
期刊: Journal of Environmental Sciences
作者: Fei Wang, Jiangtao He, Baonan He, Xiaojing Zhu, Xiaocui Qiao, Liuyue Peng
更新时间: 2018-06-25
摘要: To explore the formation process and mechanism of organic matter and organic-mineral complex under humification and mineralization conditions, a series of samples including humic acid, kaolin, and humic acid-kaolin complex were prepared using a subcritical water treatment method (SWT) under specific temperature, pressure and reaction time conditions. HA was used as a surrogate for natural organic matter because it has a similar abundant pore structure, variety of carbon types, and chemical components. These samples were used in carbamazepine (CBZ) sorption experiments and characterized by a variety of techniques. The polymerization of humic acid under the conditions of increased temperature and pressure resulted in an increase in specific surface area and molecular quantity. In addition, the degree of aromaticity rose from 59.52% to 70.90%. These changes were consistent with the transformation from ‘soft carbon’ to ‘hard carbon’ that occurs in nature. The results of sorption experiments confirmed the interaction between humic acid and kaolin from the difference between the predicted and actual Q e values. The conceptual model of humic acid-kaolin complex could be deduced and described as follows. Firstly, the aromatic components of humic acid preferentially combine with kaolin through the intercalation effect, which protects them from the treatment effects. Next, the free carboxyl groups and small aliphatic components of humic acid interact on the surface of kaolin, and these soft species transform into dense carbon through cyclization and polymerization. As a result, humic acid-kaolin complex with a mineral core and dense outer carbonaceous patches were formed.

25334. 题目: Insight into removal of dissolved organic matter in post pharmaceutical wastewater by coagulation-UV/H2O2
文章编号: N180625F8
期刊: Journal of Environmental Sciences
作者: Feng Qian, Mengchang He, Jieyun Wu, Huibing Yu, Liang Duan
更新时间: 2018-06-25
摘要: The removal of four dissolved organic matter (DOM) fractions, non-acid hydrophobics, hydrophobic acids, hydrophilics and transphilics, was achieved by coagulation-UV/H2O2 oxidation in post-pharmaceutical wastewater (PhWW). Coagulation with Polyferric chloride (PFC), Polymeric ferric sulfate (PFS) and Polymeric aluminum ferric chloride (PAFC) was studied separately to evaluate the effects of the initial pH and coagulant dosage. The coagulation-UV/H2O2 oxidation method resulted in much higher reduction rates for dissolved organic carbon (DOC) (by 75%) and UV254 (by 92%) than coagulation or UV/H2O2 oxidation alone. The proportion of non-acid hydrophobics, hydrophobic acids, transphilics and hydrophilics removed by coagulation was 54%, 49%, 27% and 12 %, while the combined treatment removed 92%, 87%, 70% and 39%, respectively. Parallel factor analysis (PARAFAC) of fluorescence measurements revealed that the humic-like fluorescent component C4 showed the highest removal (by 44%) during the coagulation stage. After coagulation-UV/H2O2 treatment, the humic-like fluorescent component C3 had the highest removal (by 72%), whereas xenobiotic organic fluorescent components C1 and C4 remained recalcitrant to decomposition. Significant correlations (R 2 > 0.8) between C1 and the hydrophobic acids and non-acid hydrophobics suggested the possibility of using fluorescence spectroscopy as an effective tool to assess variations in DOM fraction treatment efficacy in coagulation-UV/H2O2 systems. After the combined treatment, toxic inhibition of cellular activity by post PhWW decreased from 88% to 47% and biodegradability increased from 0.1 to 0.52.

25335. 题目: Role of the floodplain lakes in the methylmercury distribution and exchanges with the Amazon River, Brazil
文章编号: N180625F7
期刊: Journal of Environmental Sciences
作者: Poliana Dutra Maia, Laurence Maurice, Emmanuel Tessier, David Amouroux, Daniel Cossa, Patricia Moreira-Turcq, Henri Etcheber
更新时间: 2018-06-25
摘要: Seasonal variability of dissolved and particulate methylmercury (F-MeHg, P-MeHg) concentrations was studied in the waters of the Amazon River and its associated Curuai floodplain during hydrological year 2005–2006, to understand the MeHg exchanges between these aquatic systems. In the oxic white water lakes, with neutral pH, high F-MeHg and P-MeHg concentrations were measured during the rising water stage (0.70±0.37pmol/L, n =26) and flood peak (14.19±9.32pmol/g, n =7) respectively, when the Amazon River water discharge into the lakes was at its maximum. The lowest mean values were reported during the dry season (0.18±0.07pmol/L F-MeHg, n =10 and 1.35±1.24pmol/g P-MeHg, n =8), when water and suspended sediments were outflowing from the lakes into the River. In these lakes, the MeHg concentrations were associated to the aluminium and organic carbon/nitrogen changes. In the black water lakes, with acidic pH and reducing conditions, elevated MeHg concentrations were recorded (0.58±0.32pmol/L F-MeHg, n =16 and 19.82±15.13pmol/g P-MeHg, n =6), and correlated with the organic carbon and manganese concentrations. Elevated values of MeHg partition coefficient (4.87< K d <5.08log (L/kg) indicate that MeHg is mainly transported associated with the particulate phase. The P-MeHg enrichment detected in all lakes suggests autochthonous MeHg inputs from the sediments into the water column. The MeHg mass balance showed that the Curuai floodplain is not the source of P-MeHg for the Amazon River.

25336. 题目: 234Th as a tracer of particulate export and remineralization in the southeastern tropical Pacific
文章编号: N180625F6
期刊: Marine Chemistry
作者: Erin E. Black, Ken O. Buesseler, Steven M. Pike, Phoebe J. Lam
更新时间: 2018-06-25
摘要: Oxygen minimum zones (OMZs) are thought to be regions of decreased carbon attenuation in the upper ocean with a biological pump that could deliver a greater percentage of exported carbon to the mesopelagic relative to surrounding waters. However, much is still unknown about carbon cycling through these zones and the areas of extreme oxygen minima (nM O2) or oxygen deficient zones (ODZs) within the OMZs. Paired sampling for 234Th (t ~24.1days) and particulate organic carbon (POC) was performed along a zonal transect between 77 and 152°W during the U.S. GEOTRACES Southeastern Tropical Pacific campaign in 2013 in order to constrain the magnitude of carbon export and remineralization through the Peruvian OMZ. POC export varied by an order of magnitude from the coast to 152°W, reflecting a decrease in POC:234Th ratios (>51μm) with distance offshore and the influence of upwelling at the coast. Modeling indicated that 234Th fluxes could be underestimated at coastal stations by up to 4-fold without adjustment for the impact of upwelling, which in turn would produce much lower carbon export estimates. Low carbon Export:NPP ratios (<0.15) at the base of the euphotic zone (Ez) in the gyre support previous findings of inefficient surface export via the biological pump in the southeastern tropical Pacific. A broad remineralization feature beginning at the Ez was observed across >7500km that resulted in, on average, 3% of the POC exported from the euphotic zone reaching 100m below the Ez. Although the highest percentages (>10%) of total exported POC at 100m below the Ez were observed in the coastal ODZ region, the observed remineralization was also most pronounced these stations. While an average of 75% of the carbon export from the euphotic zone remained at Ez+100m in the gyre, a range of 10 to 50% was observed at ODZ stations, reflecting increased attenuation. Local subsurface minima in light transmission and maxima in fluorescence were observed in the regions of greatest remineralization at the upper ODZ boundary, suggesting that complex bacterial community dynamics play a role in increased attenuation through these zones. With ODZs and OMZs predicted to grow worldwide with climate change, these areas require further large-scale and seasonal studies to assess the permanency of these attenuation features and the impact of high Gyre and lower ODZ transfer of POC on the overall efficiency of carbon export in the Pacific.

25337. 题目: A potential formation route for CHOS compounds in dissolved organic matter
文章编号: N180625F5
期刊: Marine Chemistry
作者: Jose J. Melendez-Perez, Mónica J. Martínez-Mejía, Roberto L. Barcellos, Ant?nio F.H. Fetter-Filho, Marcos Nogueira Eberlin
更新时间: 2018-06-25
摘要: Sulfur polyoxygenated organic compounds (CHOS compounds) had been detected in dissolved organic matter (DOM) from several aquatic systems around the world but the knowledge of its origin and geochemical behavior is still scarce. Previous studies have reported correlations between the content of CHOS compounds in DOM and the sulfide concentration in aquatic systems. We therefore performed a set of laboratorial experiments aiming to better understand the role of DOM in the sulfur cycle and we found that CHOS compounds can be formed in aquatic systems by the addition of sulfide/bisulfide ions to lignin-like CHO compounds. We also show that sediments act as heterogeneous catalysts that facilitate the formation of CHOS compounds.

25338. 题目: Copper-binding ligands in the NE Pacific
文章编号: N180625F4
期刊: Marine Chemistry
作者: Hannah Whitby, Anna M. Posacka, Maria T. Maldonado, Constant M.G. van den Berg
更新时间: 2018-06-25
摘要: Copper distribution and speciation were determined at stations P4 and P26 along Line P as part of a GEOTRACES Process Study in the Northeast Pacific, at depths between 10 and 1400 m. Two ligand classes (L1 and L2) were detected at both stations: the stronger L1 ligand pool with log K'Cu2+L1 15.0–16.5 and the weaker L2 ligand pool with log K'Cu2+L2 11.6–13.6. The L1 class bound on average 94% of dCu, with the ratio between L1 and dCu constant and close to unity (1.15 = [L1]:[dCu]). The concentrations of total ligands exceeded those of dCu at all depths, buffering Cu2+ concentrations ([Cu2+]) to femtomolar levels (i.e. pCu 14.1–15.7). Measurements using cathodic stripping voltammetry also identified natural copper-responsive peaks, which were attributed to thiourea- and glutathione-like thiols (TU and GSH, respectively), and Cu-binding humic substances (HSCu). Concentrations of TU, GSH and HSCu were determined by standard addition of model compounds in an attempt to identify Cu-binding ligands. HSCu concentrations were generally higher at P26 than at P4, consistent with a marine origin of the humic material. Overall, HSCu contributed to 1–27% of the total L concentration (LT) and when combined with the two thiols contributed to up to 32% of LT. This suggests other ligand types are responsible for the majority of dCu complexation in these waters, such as other thiols. Some potential candidates for detected, but unidentified, thiols are cysteine, 3-mercaptopropionic acid and 2-mercaptoethanol, all of which bind Cu. Significant correlation between the concentrations of TU-like thiols and L1, along with the high log K'Cu2+L1 values, tentatively suggest that the electrochemical TU-type peak could be part of a larger, unidentified, high-affinity Cu compound, such as a methanobactin or porphyrin, with a stronger binding capability than typical thiols. This could imply that chalkophores may play a greater role in oceanic dCu complexation than previously considered.

25339. 题目: DDT and related compounds in pore water of shallow sediments on the Palos Verdes Shelf, California, USA
文章编号: N180625F3
期刊: Marine Chemistry
作者: Robert P. Eganhouse, Erica DiFilippo, James Pontolillo, William Orem, Paul Hackley, Brian D. Edwards
更新时间: 2018-06-25
摘要: For nearly two and a half decades following World War II, production wastes from the world's largest manufacturer of technical DDT (1-chloro-4-[2,2,2-trichloro-1-(4-chlorophenyl)ethyl]benzene) were discharged into sewers of Los Angeles County. Following treatment, the wastes were released via a submarine outfall system to nearshore coastal waters where a portion accumulated in shallow sediments of the Palos Verdes Shelf (PVS). An investigation of the pore-water geochemistry of DDT-related compounds (DDX) was undertaken in an effort to understand factors controlling the rate of reductive dechlorination (RDC) of the major DDT degradate, 4,4′-DDE (1-chloro-4-[2,2-dichloro-1-(4-chlorophenyl)ethenyl]benzene). Equilibrium matrix-solid phase microextraction (matrix-SPMEeq) combined with automated thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) was used to determine freely dissolved concentrations of ten DDX analytes in sediment cores collected from three locations on the PVS (stations 3C, 6C, 8C, which are 7 km, 2 km, and 0 km, respectively, downcurrent from the outfall system). Pore-water concentrations (pM) of the principal DDX compounds involved in RDC were: 3C-DDE: 6.0–24, DDMU (1-chloro-4-[2-chloro-1-(4-chlorophenyl)ethenyl]benzene): 11–160, DDNU (1-chloro-4-[1-(4-chlorophenyl)ethenyl]benzene): 1.8–68; 6C-DDE: 5.6–170, DDMU: 5.6–177, DDNU: 1.7–87; 8C-DDE: 27–212, DDMU: 31–403, DDNU: 5.5–89. Variations in the spatial distribution of DDX analytes in pore water reflect several factors including proximity to the outfalls, RDC reaction rates, and natural variability in sedimentation and post-depositional transport processes. A comparison of pore-water data produced using matrix-SPMEeq/TD-GC/MS and whole-core squeezing/solvent extraction/liquid injection-GC/MS indicates that the majority of the DDE in the upper sediment column (≤about 10 cm) is associated with dissolved/colloidal organic matter. Below that depth, freely-dissolved DDE predominates. The principal organic geochemical phase controlling sorption of DDE in PVS sediments are residual hydrocarbons, the vast majority of which originated from petroleum refinery wastes. Organic carbon-normalized sediment-water distribution coefficients (K OC) were calculated from solid-phase and pore-water concentrations of DDX and organic carbon. Log K OC values (L/kg) were relatively invariant across the shelf and with depth in the sediment column. Shelf-wide compound-specific coefficients (log K OC) were: DDE: 7.5 ± 0.11, DDMU: 6.92 ± 0.13, DDNU: 6.37 ± 0.19. The spatial uniformity of K OC means that biological exposure and availability of the DDX compounds can, in principle, be estimated from solid-phase chemical measurements.

25340. 题目: Dissolved organic matter dynamics in Mediterranean lagoons: The relationship between DOC and CDOM
文章编号: N180625F2
期刊: Marine Chemistry
作者: A. Specchiulli, L. Cilenti, R. D'Adamo, A. Fabbrocini, W. Guo, L. Huang, A. Lugliè, B.M. Padedda, T. Scirocco, P. Magni
更新时间: 2018-06-25
摘要: Coastal lagoons are highly vulnerable to climate change-related pressures, such as floods and increasing temperatures, which lead to higher oxygen consumption, anaerobic metabolism and dystrophic events. Although these factors have a significant impact on the carbon cycle, the dynamics of dissolved organic matter (DOM) in these systems have not been extensively investigated. DOM can be analytically determined from the concentration of dissolved organic carbon (DOC) and/or from the spectral properties of chromophoric dissolved organic matter (CDOM), which is the light-absorbing fraction of DOM. In the present study, we investigated the spatio-temporal distribution of surface water trophic variables (Chl a and DOC) and CDOM in two Mediterranean lagoon systems, the Oristano Lagoon-Gulf system (OLG) and the Varano Lagoon (VL), in order to provide quantitative information on the dynamics of DOM in these systems. Furthermore, we assessed the value of CDOM-related indices (i.e. absorption coefficients, spectral slopes and Specific UV Absorbance at 254 nm [SUVA254]) as tools for describing the dynamics of DOM in coastal lagoons, irrespective of geographical settings, environmental conditions and anthropogenic pressures. In OLG, spatial heterogeneity and compartmentalization, with salinity varying from <1 (riverine sites) to >50 (Mistras Lagoon), affected the distribution of DOC and CDOM, with the lowest values on the south side and at sites far from riverine input. In OLG, the highest DOC and CDOM values were found in the sediment pore-water of the organic-rich Cabras Lagoon, where they were nearly double those of the water column. In VL, salinity was homogeneously distributed throughout the lagoon, which indicated a mixing of freshwater with marine waters. DOC and CDOM values were on average lower in VL than in OLG. However, in VL, DOC and CDOM showed strong peaks following a flood (September 2014) and a dystrophic event (July 2015), demonstrating the quick response of the system to environmental perturbation. In OLG, absorption coefficients at 280 nm and 350 nm were slightly negatively correlated with salinity, which indicated the influence of terrigenous inputs at riverine sites. In contrast, in VL, CDOM varied linearly and positively with salinity as a result of the in situ input of organic matter from phytoplankton during the dry season. Segment analysis showed that besides the differences between the two investigated systems, the trophic variables and optical parameters analyzed in the present study shared a common relationship. These results suggest that CDOM indices can be good predictors for the estimation of DOM. Overall, the present study provides insight into the dynamics of DOC and CDOM in little-studied Mediterranean lagoons and demonstrates that the CDOM indices can be a valuable, cost-effective and simple tool for describing the trophic conditions of these systems.