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28701. 题目: Longitudinal trends in concentration and composition of dissolved organic nitrogen (DON) in a largely unregulated river system
文章编号: N18070110
期刊: Biogeochemistry
作者: Clayton W. Harris, Gavin N. Rees, Rick J. Stoffels, John Pengelly, Kirsten Barlow, Ewen Silvester
更新时间: 2018-07-01
摘要: Dissolved organic nitrogen (DON) can comprise up to 80% of the dissolved N pool in riverine ecosystems, but concentration and compositional responses to catchment conditions has received limited attention. We examined the suite of nitrogenous nutrients along the length of the Ovens River, Victoria, Australia, a river with identifiable regions of native vegetation, agricultural activity and floodplain forest connection, carrying out longitudinal surveys in winter during a period of high flow and in summer during a period of stable base flow. We examined: the concentrations of DON, the proportion of DON that occurs as dissolved combined amino acids (DCAAs), whether concentration and DCAA composition varied between flow and whether land-use and tributaries have an impact upon nutrient concentration and DON composition. DON concentrations were greater than dissolved inorganic nitrogen under both base flow and high flow conditions. Under base flow DON exhibited a continuous increase in concentration downstream (ranging from 50 to 300 μg/L), compared to a much larger increase under high flow (150–600 μg/L) coupled with a major discrete increase of ~ 350 μg/L at a tributary input (King River). Concentrations of NOx (oxides of nitrogen) species were much higher under high flow conditions (range 50–250 μg/L) compared to 0–50 g/L at base flow, and showed a significant increase in concentration with distance downstream. A discrete change in NOx concentrations was also observed at the King River confluence under high flow, although in this case causing a decrease in concentration of ~100 g/L. DCAA concentrations varied little along the length of the river at base flow but increased with distance downstream at high flow. The DCAA concentrations were of the same order of magnitude as ammonium at both base and high flows and nitrate concentrations at base flow. The proportion of DON that was in the form of DCAA was reasonably uniform during high flow (3–6%), but highly variable at base flow (5–44%). The amino acid (AA) composition of the DCAA varied along the river and differed between flow regimes (except below the confluence with the King River where AA composition under the two flow conditions converged) suggesting a strong influence of land use. We show that DON is potentially a large component (4–81%) of the total N budget and given that 5–23% is in the form of peptide/protein, represents an important source of N. DON and more specifically DCAAs should therefore be considered both when constructing N budgets and monitoring levels of in-stream nitrogen.

28702. 题目: Minerals in the rhizosphere: overlooked mediators of soil nitrogen availability to plants and microbes
文章编号: N18070109
期刊: Biogeochemistry
作者: Andrea Jilling, Marco Keiluweit, Alexandra R. Contosta,Serita Frey, Joshua Schimel, J?rg Schnecker, Richard G. Smith, Lisa Tiemann, A. Stuart Grandy
更新时间: 2018-07-01
摘要: Despite decades of research progress, ecologists are still debating which pools and fluxes provide nitrogen (N) to plants and soil microbes across different ecosystems. Depolymerization of soil organic N is recognized as the rate-limiting step in the production of bioavailable N, and it is generally assumed that detrital N is the main source. However, in many mineral soils, detrital polymers constitute a minor fraction of total soil organic N. The majority of organic N is associated with clay-sized particles where physicochemical interactions may limit the accessibility of N-containing compounds. Although mineral-associated organic matter (MAOM) has historically been considered a critical, but relatively passive, reservoir of soil N, a growing body of research now points to the dynamic nature of mineral-organic associations and their potential for destabilization. Here we synthesize evidence from biogeoscience and soil ecology to demonstrate how MAOM is an important, yet overlooked, mediator of bioavailable N, especially in the rhizosphere. We highlight several biochemical strategies that enable plants and microbes to disrupt mineral-organic interactions and access MAOM. In particular, root-deposited low-molecular-weight exudates may enhance the mobilization and solubilization of MAOM, increasing its bioavailability. However, the competitive balance between the possible fates of N moers—bound to mineral surfaces versus dissolved and available for assimilation—will depend on the specific interaction between mineral properties, soil solution, mineral-bound organic matter, and microbes. Building off our emerging understanding of MAOM as a source of bioavailable N, we propose a revision of the Schimel and Bennett (Ecology 85:591–602, 2004) model (which emphasizes N depolymerization), by incorporating MAOM as a potential proximal mediator of bioavailable N.

28703. 题目: A quantitative method for the high throughput screening for the soil adhesion properties of plant and microbial polysaccharides and exudates
文章编号: N18070108
期刊: Plant and Soil
作者: Jumana Akhtar,Andrew F. Galloway,Georgios Nikolopoulos,Katie J. Field,Paul Knox
更新时间: 2018-07-01
摘要: Background and aims: Understanding the structures and functions of carbon-based molecules in soils is an important goal in the context of soils as an ecosystem function of immense importance. Polysaccharides are implicated in maintaining soil aggregate status but have not been extensively dissected in terms of their structures and soil adhesion properties. This is largely because of the technical difficulties in identifying polysaccharide structures and quantifying any functional properties.Methods: Here, we describe the use of a novel nitrocellulose-based adhesion assay to determine the relative capacities for soil adhesion of over twenty plant and microbial polysaccharides that are likely to be present in soil and to contribute to organic matter content and properties. Weights of soil adhered to spots of known amounts of specific polysaccharides were quantified by scanning of the nitrocellulose sheets.Results: The most effective polysaccharides identified from this survey included chitosan, β-1,3-glucan, gum tragacanth, xanthan and xyloglucan. We also demonstrate that the soil adhesion assay is suitable to assess the soil-binding properties of plant exudates.Conclusions: The soil adhesion assay will be useful for the functional dissection of the organic matter components of soils and also of the factors involved in soil attachment to plant roots and in rhizosheath formation.

28704. 题目: Effects of snow depth on acid-unhydrolyzable residue and acid-hydrolyzable carbohydrates degradation rates during foliar litter decomposition of Pinus koraiensis and Quercus mongolica
文章编号: N18070107
期刊: Plant and Soil
作者: Qiqian Wu
更新时间: 2018-07-01
摘要: Background and aims: Differences in snow depth induced by climate change alter the microenvironments under snowpack, which affect litter decomposition. The degradation of acid-unhydrolyzable residue (AUR) and acid-hydrolyzable carbohydrates (ACID) is a key factor controlling soil organic matter formation. However, how snow depth affects the degradation is poorly understood.Methods: A snow depth manipulation experiment with snow-addition, snow-removal, and control treatments was conducted in Northeast China. Foliar litter of Pinus koraiensis and Quercus mongolica was placed on top of the ground in each treatment and sampled for six times from November 2014 to October 2015.Results: AUR and ACID degradation rates decreased with the reduction of snow depth during the snow-covered season because of the insulating effect provided by snowpack; this relationship was reversed during the snow-free season due to more labile carbon remaining after the snowmelt. During the snow-covered season, AUR and ACID degradation rates were positively correlated to the sum of degree days above 0 °C. In contrast, AUR and ACID degradation rates were positively correlated with litter microbial biomass carbon during the snow-free season.Conclusions:Snow depth plays an important role in determining litter AUR and ACID degradation rates, but the effects on degradation rates differed between the snow-covered and snow-free seasons.

28705. 题目: Biochar application as a soil amendment for decreasing cadmium availability in soil and accumulation in Brassica chinensis
文章编号: N18070106
期刊: Journal of Soils and Sediments
作者: Yuxue Liu, Yuying Wang, Haohao Lu,Linson Lonappan, Satinder Kaur Brar,Lili He,Jinyuan Chen, Shengmao Yang
更新时间: 2018-07-01
摘要: Purpose: Biochar has emerged as a promising material for limiting the bioavailability of potentially toxic elements in contaminated soils. Despite the benefits associated with the agricultural use of biochar, there is minimal information available on biochar amendment of Cd accumulation in leafy vegetable cultivars.Materials and methods: A pot experiment was carried out to evaluate the feasibility of bamboo biochar (BB) and rice straw biochar (RSB) for decreasing cadmium (Cd) availability in artificially contaminated (Cd at 50 mg kg 1) soil, and its accumulation in Brassica chinensis. Biochar was applied at 0 (control), 0.5, 1, 2.5, and 5% (w/w).Results and discussion: RSB at 5% significantly reduced the availability of Cd in soil (by 19.3%) compared with BB (by 8.6%). Application of BB and RSB at 1–5% markedly enhanced soil pH by 1.17–5.48 and 2.47–7.46%, respectively. Moreover, soil organic carbon was improved by 40.3–155 and 22.2–111% with 1–5% BB and RSB amendment, respectively. Soil total N was significantly increased by 24.5 and 31.1% with 5% BB and RSB application, respectively. Soil available P was increased by 10.8–24.4 and 14.6–30.7% with 2.5–5% BB or RSB amendment, respectively. Application of 2.5–5% BB and RSB significantly increased soil available K by 76.8–291 and 203–627%, respectively. Biochar at 2.5–5% ratio significantly improved nutrient (P and K) uptake in B. chinensis. Furthermore, biochar was more effective at higher rates, and RSB performed better than BB as a soil nutrient supplement. Cd accumulation in B. chinensis was significantly reduced by 12.0–48.3 and 17.0–35.4% with 0.5–5% BB and 1–5% RSB amendment, respectively. Greater biochar application further decreased bioconcentration factor (BCF) in harvested B. chinensis (all values < 1). Incorporation of 5% BB and RSB significantly reduced BCF by 51.0 and 40.6%, respectively.Conclusions:Our results suggest that BB and RSB, especially at higher rates (> 2.5%), could be recommended as safe amendments for the immobilization of Cd in contaminated agricultural soils, thereby decreasing its threat to the food chain and human health.

28706. 题目: Cadmium bioavailability well assessed by DGT and factors influencing cadmium accumulation in rice grains from paddy soils of three parent materials
文章编号: N18070105
期刊: Journal of Soils and Sediments
作者: Dongqin Li, Wenyan Li, Qin Lu, Yongtao Li, Ning Li, Huijuan Xu, Zongling Ren, Yulong Zhang, Jinjin Wang
更新时间: 2018-07-01
摘要: Purpose:High Cd resulted from natural background or agricultural activities in some of the paddy soils in South China is a concern. It is imperative to understand the relationship between Cd bioavailability in high Cd soils and Cd accumulation in rice grains. Therefore, our objectives are to explore the relationship between Cd accumulation in rice grains and Cd availability which was characterized with five different methods, and to investigate factors influencing Cd accumulation in rice.Materials and methods: One hundred and twenty-two paired soil and rice plant samples were collected from paddy fields of three parent materials (sandshale, limestone, and Quaternary red earth) in Guangxi Province. Soil Cd availability was assessed using three chemical extractants (0.43 M HNO3, 0.01 M CaCl2, and 0.005 M DTPA) and compared with Cd in soil solution and that sampled by the diffusive gradients in thin films (DGT) method. A five-step sequential fractionation of Cd was also carried out. Random forest (RF) was employed for assessing factor relative importance in Cd accumulation in rice plants and grains in high Cd soils.Results and discussion: All of the soil samples had a total Cd content exceeding the maximum permissible concentration (0.3 mg kg 1) for soils with the exchangeable fraction taking up 50, 56, and 39%, respectively. For the rice grains harvested from the soils derived from sandshale, limestone, and Quaternary red earth, 67, 95, and 28%, respectively, had a Cd content exceeding the maximum permissible concentration for grain (0.2 mg kg 1). The results demonstrated high Cd bioavailability in these areas and indicated potential health risk when people ingest the rice grains. Cd measured by DGT best reflected Cd bioavailability. The Cd in soil solution (Cdsoln), which is directly available, and CaCl2-extracted Cd were also significantly related to grain Cd content. Factor relative importance assessment based on random forest (RF) showed that soil pH was among the top two most important physicochemical factors of the three types of soils influencing Cd accumulation in rice grains. Besides, dissolved organic carbon (DOC), clay, and dithionite-citrate-bicarbonate-extracted Mn (MnDCB) was the other major influencing factor in the sandshale soils, limestone soils, and Quaternary red earths, respectively.Conclusions: The results indicated that DGT technique better predicted Cd bioavailability. Manipulating soil pH could be used to reduce Cd bioavailability and its accumulation in plants. However, manipulating soil DOC, clay and Fe/Mn content were soil-type-dependent.

28707. 题目: Early structural stability of fine dam sediment in soil construction
文章编号: N18070104
期刊: Journal of Soils and Sediments
作者: Gaetan Fourvel, Laure Vidal-Beaudet,Agathe Le Bocq,Violaine Brochier,Fran?ois Théry, David Landry, Thagshayini Kumarasamy,Patrice Cannavo
更新时间: 2018-07-01
摘要: Purpose: Fine sediments accumulate upstream of hydroelectric dams. To ensure that dams can operate properly, most sediments are returned downstream reaches, but a portion of them have to be dredged and land managed. In parallel, using topsoil from agricultural parcels for urban greening is currently controversial because arable surface areas are decreasing. An alternative idea for protecting these natural resources consists in reusing fine dredged sediment to construct functional soils. The agronomical use of fine dredged sediment raises the question of its ability to provide acceptable physical properties for plant growth. Materials and methods: Six dredged sediments with contrasted initial agronomical properties were mixed or not with green waste compost and submitted or not to drying-wetting cycles in a 105-day-long experiment under greenhouse conditions. The sediments were analyzed for their capacity to generate stable aggregates. We measured the proportion of macro aggregates > 2 mm with dry-sieved aggregate (DSA) fraction and the > 0.25 mm water-stable aggregate (WSA) fraction for each treatment over time. We also assessed the main sediment physicochemical properties, microbial biomass carbon, and carbon mineralization potential. Results and discussion: Compost addition (40% in volume) enhanced the WSA fraction of the low-organic-matter-content sediments (< 30 g kg 1), whereas it had a non-significant effect in the other sediments. Multiple linear regressions highlighted a determining role of organic matter in the WSA fraction. At this scale of aggregation, organic matter seemed to mainly interact with clay in an acidic context. Compost addition had either no significant effect or a negative effect on the DSA fraction. Multiple linear regressions suggested that organic matter was not clearly involved in DSA formation in the sediment, whereas macro-porosity was. The first drying-wetting cycles enhanced the DSA proportion of the sediments, but the following cycles had a negative effect. We suggest that disaggregating mechanisms gradually predominated over aggregating mechanisms over time. Conclusions: All sediments showed acceptable physicochemical properties for plant growth. WSA formation in low-organic-matter-content sediments was improved by adding compost. Drying-wetting cycles had a controversial effect on DSA formation, and only the very first cycles had a beneficial effect on macro-aggregation. The mechanisms involved in aggregation and aggregate stability in soil constructed from sediments seem to be similar to those involved in natural soils. That is why we propose that the soil hierarchical aggregation model initially developed for natural and cultivated soils could be adapted to sediments.

28708. 题目: Pentachlorophenol dissipation and ferrous iron accumulation in flooded paddy soils with contrasting organic matter contents and incorporation of legume green manures
文章编号: N18070103
期刊: Journal of Soils and Sediments
作者: Yong Liu, Sifan Wang, Lian Zhu, Yunsheng Xia, Huihua Zhang, Shan Wang,Xiongsheng Yu, Jun Lou, Fangbai Li, Jianming Xu
更新时间: 2018-07-01
摘要: Purpose: The effects of different amendment rates (1 and 3%) of Chinese milk vetch (Astragalus sinicus L.) and bird vetch (Vicia cracca L.) on the dissipation of extractable pentachlorophenol (PCP) residues were investigated in two flooded paddy soils with contrasting soil organic matter (SOM) contents. Following incorporation of the legume green manures, whether acetate-extractable ferrous iron [Fe(II)NaOAc] is useful for revealing the reductive dechlorination mechanism of PCP in flooded paddy soils was verified. Materials and methods: The kinetic parameters of PCP dissipation and Fe(II)NaOAc accumulation were estimated using logistic curve fitting. Correlation and regression analyses were performed on PCP, Fe(II)NaOAc, water-soluble organic carbon (WSOC), pH, and oxidation-reduction potential data. Results and discussion: The kinetic parameters of PCP dissipation and Fe(II)NaOAc accumulation varied significantly with the amendment rate of legume green manure. The changes in pH value and WSOC content varied significantly with the level of SOM and with the amendment rate of legume green manure. At a low amendment rate of green manure, the pH increase and WSOC consumption greatly enhanced Fe(II)NaOAc accumulation and contributed to PCP dissipation. The rate of PCP dissipation decreased with decreasing pH and WSOC accumulation, especially in the high-SOM soil amended with the higher rate of green manure. Legume green manure species had no effect on PCP dissipation. Conclusions: In terms of soil chemistry, Fe(II)NaOAc was found to be the key variable that could explain the mechanisms involved in the reductive dissipation of PCP in flooded paddy soils with contrasting SOM contents and incorporation of legume green manures.

28709. 题目: Retention of silver nanoparticles and silver ion to natural soils: effects of soil physicochemical properties
文章编号: N18070102
期刊: Journal of Soils and Sediments
作者: Rui Wang, Huan Du, Yujun Wang, Dengjun Wang, Qian Sun, Dongmei Zhou
更新时间: 2018-07-01
摘要: Purpose: The mass production and widespread use of silver nanoparticles (AgNPs) have led to their wide dissimilation in the subsurface environments (e.g., natural soils). The retention propensities of AgNPs in soils dictate their fate, transport, and transformation in the subsurface environments. The aim of this study was to explore the retention behaviors of AgNPs and Ag+ ion (as a comparison) in ten natural soils with different physicochemical properties, identifying which properties dominate their mobility in soils. Materials and methods: Ten surface (0–20 cm) soils sampled across five geographical regions of China and AgNPs coated by polyvinylpyrrolidone (PVP) with an average transmission electron microscopy (TEM) diameter of ~ 10 nm were used in this study. Batch retention experiments of AgNPs and AgNO3 in ten soils (pass through 60-mesh sieve) were conducted in triplicate at 25 °C for 24 h. Multiple regression analyses of maximum retention capacity (Qmax for AgNPs or Ag+ ion) simulated by Langmuir retention models were performed to identify which soil physicochemical properties dominate the retention behavior of AgNPs and Ag+ ion. TEM combined with energy dispersive X-ray spectroscopy (EDS) analyses was applied to visually unravel the distribution and retention behavior of AgNPs on natural soils. Results and discussion: The results of batch retention experiments showed that Langmuir model well-approximated the retention isotherms of AgNPs and Ag+ on ten soils and that the Qmax value of AgNPs was generally lower than that of Ag+ on soils. The results of multiple regression analyses showed that the retention capacity of AgNPs on soils was positively correlated with the iron oxide content, which is visually confirmed by TEM-EDS observations, whereas retention capacity of Ag+ ions was mainly related to soil organic matter (SOM) content. Conclusions: Maximum retention capacity of AgNPs and Ag+ ion in soils varied with soil physicochemical properties, and particularly, iron oxide and SOM contents are two pivotal parameters controlling Qmax. These findings advance our current understanding of the mechanisms controlling retention and transport of AgNPs in natural soils, which represents an important step toward predicting the fate, transport, and potential toxicity of AgNPs in the subsurface environment.

28710. 题目: Sorption mechanism of zinc on reed, lignin, and reed- and lignin-derived biochars: kinetics, equilibrium, and spectroscopic studies
文章编号: N18070101
期刊: Journal of Soils and Sediments
作者: Ping Wu, Peixin Cui, Guodong Fang, Juan Gao, Dongmei Zhou, Yujun Wang
更新时间: 2018-07-01
摘要: Purpose: Biochar is considered as a substitute for stabilizing heavy metals, yet systematic studies regarding the stabilization mechanism of Zn on biochars from different biomass sources under different pyrolysis temperatures are still lacking. This study was endeavored to assess the sorption behavior and mechanism of Zn on pristine reed, lignin, and reed- and lignin-derived biochars at different pyrolysis temperatures (350, 450, and 550 °C). Materials and methods: Batch experiments were performed to investigate the Zn sorption on pristine reed, lignin, and their derived biochars. Major functional groups on the surface of samples were measured using Fourier transform infrared (FTIR) spectroscopy and Boehm titration method, while the speciation and binding mechanisms were elucidated using X-ray absorption near-edge structure (XANES). Results and discussion: The FTIR results showed an abrupt decline in the oxygen-containing functional groups with elevating pyrolysis temperature. The total amount of three acidic functional groups (carboxyl, lactone, phenol) was highest (2.39 mmol/g) in lignin, and it significantly decreased in reed- and lignin-derived biochars (0.05–0.94 mmol/g). Lignin exhibited the highest sorption capacity to Zn (qe = 3360 mg/kg) in the batch sorption experiments, while the sorption capacities for biochars were reduced with increasing pyrolysis temperature, irrespective of biomass sources. The XANES results indicated that soil organic matter (SOM), iron, and phosphate mineral components in the tested sorbents played an indispensable role in Zn immobilization. A large fraction of Zn-OM complex was observed in lignin due to its highest abundance of acidic functional group, leading to the highest sorption capacity for lignin toward Zn. The combination of XANES with FTIR, Boehm titration, batch sorption, and kinetic experiments altogether revealed that the decline in sorption capacity of Zn on reed- and lignin-derived biochars with elevating pyrolysis temperature was attributed to the loss in O-containing functional groups. Conclusions: The complexation of Zn with surface functional groups contributed to the Zn sorption on reed, lignin, and their derived biochars. The projected results will not only provide the detailed stabilization mechanism of Zn on lignin and reed- and lignin-derived biochars but also develop a novel and effective material (lignin) for heavy metal remediation.

28711. 题目: Efficient PFOA degradation by persulfate-assisted photocatalytic ozonation
文章编号: N18063022
期刊: Separation and Purification Technology
作者: Dan Wu, Xukai Li, Jingxian Zhang, Weirui Chen, Ping Lu, Yiming Tang, Laisheng Li
更新时间: 2018-06-30
摘要: ZnO-reduced graphene oxide (ZnO-rGO) was synthesized successfully at 423 K by a hydrothermal method. The presence of reduced graphene oxide significantly improved the photocatalytic performance of ZnO and its optimal loading ratio was 0.6 wt%. The XRD, SEM, UV–vis and FT-IR were applied to characterize the prepared catalyst. Comparative experiments were conducted to evaluate perfluorooctanoic acid (PFOA) degradation efficiency and the results showed that 99.2% PFOA was degraded in persulfate-assisted photocatalytic ozonation with low dosage of ozone and persulfate at room temperature. The impact factors on PFOA degradation efficiency including loading ratios of GO on ZnO, reaction temperatures and persulfate concentration were inspected and analyzed. The sodium persulfate and ammonium persulfate were compared as common oxidants in photocatalytic ozonation for PFOA degradation and sodium persulfate showed the better PFOA removal. Chloride and humic acid (HA) were common substances in natural water, and they showed inhibition effects on PFOA degradation. Conversion of persulfate to sulfate ion was studied and persulfate concentration during PFOA oxidation was monitored. PFHpA, PFHeA, PFPeA and PFBA were main intermediates during PFOA degradation.

28712. 题目: Distribution of dissolved organic carbon in the Bay of Bengal: Influence of sediment discharge, fresh water flux, and productivity
文章编号: N18063021
期刊: Marine Chemistry
作者: Chinmay Shah, A.K. Sudheer, Ravi Bhushan
更新时间: 2018-06-30
摘要: Dissolved organic carbon (DOC) plays an important role in the oceanic carbon cycle, with its distribution and variation primarily controlled by in situ productivity. The vertical and spatial distribution of DOC measured during two cruises has been investigated to decipher the processes controlling DOC in the Bay of Bengal (BoB). The terrestrial DOC flux to the BoB constitutes a significant fraction of the total DOC and has implications for the carbon budget of the northern Indian Ocean. High concentrations of DOC were observed in the northern BoB, which is primarily due to high flux of terrestrially derived fresh water from various rivers draining to the BoB. Compared to surface DOC concentration of the world oceans, BoB surface water generally has a higher DOC concentration (75–100 μM), which can be attributed to the high DOC content of the riverine flux. Stratification of surface water helps to maintain DOC content due to inhibited vertical mixing in the BoB as a result of the fresh water lens. High subsurface DOC concentration is due to the remineralisation of biogenic sinking particles brought along with the sediments. Subsurface DOC concentrations in the BoB exhibit a conspicuous decreasing trend southwards due to reduced influence of riverine biogenic flux. This study demonstrates that the average contribution of apparent oxygen utilization (AOU) to the DOC remineralisation in the BoB was ~18%.

28713. 题目: Distribution of thiol, humic substances and colored dissolved organic matter during the 2015 Canadian Arctic GEOTRACES cruises
文章编号: N18063020
期刊: Marine Chemistry
作者: Zhiyuan Gao, Céline Guéguen
更新时间: 2018-06-30
摘要: Organic sulfur and humics play a key role in the biogeochemistry of metals in natural waters but their distribution is not well understood. In this study, we measured the concentrations of thiol-like, humic substance (HS) -like and fluorescent dissolved organic matter (FDOM) during the 2015 Canadian Arctic GEOTRACES cruises in the Canada Basin and Canadian Arctic Archipelago (CAA). Concentrations of thiol-like (7–85 nM, expressed as equivalent to glutathione concentration) and HS-like (19 to 190 μg C/L) determined by cathodic stripping voltammetry (CSV) were congruent with previous marine CSV-based studies. Three humic-like (C1-C3) and one protein-like (C4) components identified and validated using excitation-emission matrix (EEM) and parallel factor analysis (PARAFAC) have been reported in previous ocean studies. The distributions of HS-like and humic-like components (C1 and C2) in the CAA were similar, whereas thiol-like and protein-like component C4 were closely related in the study area. Maximum CSV-based thiol-like levels were associated with chlorophyll-a maximum, confirming the biogenic origin of thiols. The distribution and concentrations of CSV-based thiol- and HS-like, and FDOM varied between four distinct water masses (i.e. surface waters, Arctic outflow waters, Arctic intermediate waters and North Atlantic deep waters) with the lowest levels associated with the surface waters, likely due to photobleaching and sea ice melt dilution. The concentrations in CSV-based HS-like and FDOM in the Arctic outflow waters decreased from western to eastern CAA, reflecting the influence of DOM-rich Pacific derived waters.

28714. 题目: Measuring total dissolved Fe concentrations in phytoplankton cultures in the presence of synthetic and organic ligands using a modified ferrozine method
文章编号: N18063019
期刊: Marine Chemistry
作者: Hanieh Tohidi Farid, Kai G. Schulz, Andrew L. Rose
更新时间: 2018-06-30
摘要: Low concentrations and complex speciation can present major challenges for measuring Fe in natural waters easily and accurately. This study describes an optimized ferrozine method for measuring total dissolved Fe in the nanomolar range in seawater samples containing various concentrations of organic matter, as well as the commercially available Fe ligands ethylenediaminetetraacetic acid (EDTA) and desferrioxamine B (DFB), which are widely used in phytoplankton cultures. The method involves sample acidification to liberate Fe from strong complexes and/or colloids, followed by reduction of Fe(III) to Fe(II) using sulfite, and finally the measurement of Fe(II)-ferrozine complexes using long optical path spectrophotometry. The performance of each step was improved in such a way as to achieve the most efficient dissociation rate of Fe from the given ligands in the least possible time, regardless of their type or concentration. Storage of samples at pH 1 for 15 days enabled full recovery of Fe in the presence of 50 μmol/L DFB, while the duration required for full Fe recovery in the presence of the same concentration of EDTA was only about 1 h. Addition of ferrozine after a brief (about 15 min) reduction step with subsequent incubation for 24 h resulted in stable color development in the samples over time. The approach was successfully applied to determine total dissolved Fe in samples from coastal waters containing 10.5 μmol/L of particulate organic carbon (POC), and also in samples containing 2 μmol/L EDTA and 800 μmol/L of POC collected from laboratory cultures of the marine cyanobacterium, Trichodesmium erythraeum.

28715. 题目: Effect of photo-biodegradation and biodegradation on the biogeochemical cycling of dissolved organic matter across diverse surface water bodies
文章编号: N18063018
期刊: Journal of Environmental Sciences
作者: M.S. Sankar, Padmanava Dash, Shatrughan Singh, YueHan Lu, Andrew E. Mercer, Shuo Chen
更新时间: 2018-06-30
摘要: The objective of this research was to quantify the temporal variation of dissolved organic matter (DOM) in five distinct waterbodies in watersheds with diverse types of land use and land cover in the presence and absence of sunlight. The water bodies were an agricultural pond, a lake in a forested watershed, a man-made reservoir, an estuary, and a bay. Two sets of samples were prepared by dispensing unfiltered samples into filtered samples in 1:10 ratio (v/v). The first set was exposed to sunlight (10 hr per day for 30 days) for examining the combined effect of photo-biodegradation, while the second set was stored in dark for examining biodegradation alone. Spectroscopic measurements in tandem with multivariate statistics were used to interpret DOM lability and composition. The results suggest that the agricultural pond behaved differently compared to other study locations during degradation experiments due to the presence of higher amount of microbial humic-like and protein-like components derived from microbial/anthropogenic sources. For all samples, a larger decrease in dissolved organic carbon (DOC) concentration (10.12% ± 9.81% for photo-biodegradation and 6.65% ± 2.83% for biodegradation) and rapid transformation of DOM components (i.e., terrestrial humic-like components into microbial humic and protein-like components) were observed during photo-biodegradation experiments. Results suggest that sunlight facilitated DOM biodegradation, resulting in simpler recalcitrant molecules regardless of original composition. Overall, it was found that combined effects of light and bacteria are more efficient than bacterial effects alone in remineralizing and altering DOM, which highlights the crucial importance of sunlight in transforming aquatic DOM.

28716. 题目: Ground-truthing the planktic foraminifer-bound nitrogen isotope paleo-proxy in the Sargasso Sea
文章编号: N18063014
期刊: Geochimica et Cosmochimica Acta
作者: Sandi M. Smart, Haojia Ren, Sarah E. Fawcett, Ralf Schiebel, Maureen Conte, Patrick A. Rafter, Karen K. Ellis, Mira A. Weigand, Sergey Oleynik, Gerald H. Haug, Daniel M. Sigman
更新时间: 2018-06-30
摘要: We report the nitrogen (N) isotope ratios (δ15N) of planktic foraminifera collected from upper-ocean net tows (surface to 200 m), moored sediment traps, and core-top sediments at the Bermuda Time-series Site in the northern Sargasso Sea between 2009 and 2013. Consistent with previous measurements from low-latitude core-top sediments, the annually-averaged δ15N of organic matter bound within the shells of euphotic zone-dwelling, dinoflagellate symbiont-bearing foraminifera collected in net tows (2.3‰ on average) approximates that of shallow thermocline ( 200 m) nitrate (2.6‰), the dominant source of new N to Sargasso Sea surface waters. Deeper-dwelling foraminifer species without dinoflagellate symbionts tend to have a higher δ15N (3.6‰ on average). We observe no systematic difference between the bulk tissue and shell-bound δ15N in net tow-collected foraminifera. A decline in shell N content is observed from net tows (6.8 nmol/mg) to sediment traps (5.4 nmol/mg) and surface sediment (3.0 nmol/mg). On average, shell-bound δ15N rises from net tows (3.1‰) to sediment traps (3.7‰) but does not change further upon incorporation into the sediments (3.7‰). Together, these observations are consistent with preferential loss of shells or shell portions with lower δ15N and higher N content during sinking through the upper 500 m, followed by a non-isotope fractionating decrease in N content between sinking and burial. Time-series data from sediment traps (and to a lesser extent, surface net tows) exhibit seasonal δ15N variations, with a minimum in early spring, a maximum in late spring and a decline from summer to fall. These variations appear to arise from seasonal changes in the δ15N of total upper-ocean biomass, which are, in turn, driven by early springtime nitrate supply, subsequent nitrate drawdown, and an increase in the relative importance of ammonium recycling into the late summer and early fall. The δ15N connection between total upper ocean biomass and foraminifera indicates that foraminifer-bound δ15N records the δ15N of the annual nitrate supply in oligotrophic (e.g., subtropical) environments but will also be sensitive to the degree of nitrate consumption in high-nutrient regions and possibly to changes in upper-ocean ammonium recycling under some conditions.

28717. 题目: Controls of climate, catchment erosion and biological production on long-term community and functional changes of chironomids in High Arctic lakes (Svalbard)
文章编号: N18063013
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: Tomi P. Luoto, Antti E.K. Ojala
更新时间: 2018-06-30
摘要: Arctic freshwater basins are diversity hotspots and sentinels of climate change, but their long-term variability and the environmental variables controlling them are not well defined. We examined four available lake sediment sequences from High Arctic Svalbard for their subfossil Chironomidae communities, biodiversity and functional traits and assessed the influence of climatic and limnological variability on the long-term ecological dynamics. Our results indicated that collector-filterers had an important role in the oligotrophic sites, whereas collector-gatherers dominated the nutrient-enriched sites with significant bird guano inputs. In the oligotrophic sites, benthic production, taxon richness and taxonomic and functional diversity were highest during the early Holocene, when temperatures showed a rapid increase. An increase in subfossil abundance and diversity metrics was also found in recent samples of the oligotrophic sites, but not in the bird-impacted sites, where the trends were decreasing. When partitioning out the environmental forcing on chironomid communities, the influence of climate was significant in all the sites, whereas in-lake production (organic matter) was significant in two of the sites and catchment erosion (magnetic susceptibility) had only minor influence. The findings suggest that major changes in Arctic chironomid assemblages were driven by climate warming with increasing diversity in oligotrophic sites, but deteriorating ecological functions in environmentally stressed sites. We found that although taxonomic and functional diversity were always coupled, taxonomical and functional turnovers were coupled only in the oligotrophic sites suggesting that the ecological functions operated by chironomids in these low-productivity sites may not be as resilient to future environmental change.

28718. 题目: Maastrichtian oil shale deposition on the southern Tethys margin, Egypt: Insights into greenhouse climate and paleoceanography
文章编号: N18063012
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: Douaa Fathy, Michael Wagreich, Susanne Gier, Ramadan S.A. Mohamed, Rafat Zaki, Mohamed M. El Nady
更新时间: 2018-06-30
摘要: A comprehensive set of organic and inorganic geochemical proxies, clay mineralogy, and molecular fossils are presented from two biostratigraphically well-dated oil shale horizons of Egypt, within the Upper Cretaceous Duwi and Dakhla formations. The studied oil shales were deposited within intracratonic sedimentary basins in a broad northern African epeiric sea. Calcareous nannofossil biostratigraphy indicates that the oil shales range from early to late Maastrichtian in age, covering nannofossil zones UC18, UC19, and UC20. The oil shales contain smectite and kaolinite as the main clay minerals that formed by weathering of precursor basement rocks. The relative abundances of clay minerals and several geochemical proxies (e.g. C-value, CIA, Ga/Rb, Rb/Sr and Sr/Cu), along with the occurrence of warm-water nannofossil taxa, demonstrate that the Maastrichtian oil shales accumulated under a warm, arid to humid greenhouse climate during a general Maastrichtian cooling trend. This episode of oil shale deposition in Egypt coincided with the first potential imprint of the global warming, that has been recorded during early-to-late Maastrichtian times (~70.6–67.7 Ma). Elevated eolian terrigenous input was recorded within the Duwi Formation oil shales, shown by high Ti/Al, Si/Al, Zr/Al and low La/Lu ratios. The Duwi Formation environment was characterized by enhanced salinity and a stratified water column, compared to that of the Dakhla Formation, shown by elevated values of the gammacerane index, tetracyclic terpane, β carotene and Sr/Ba ratio. The CaCO3 content and carbonate/siliciclastic ratio indicate that the Dakhla Formation oil shales were deposited during a relative sea-level rise in a deeper marine setting than the Duwi Formation oil shales. The data further imply a wind-driven upwelling scenario of nutrient inputs that simulated primary production and increased organic matter fluxes. Thus, paleoclimate and paleoceanography had a considerable impact on organic matter enrichment.

28719. 题目: Mercury anomalies, volcanic pulses, and drowning episodes along the northern Tethyan margin during the latest Hauterivian-earliest Aptian
文章编号: N18063011
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: Guillaume Charbonnier, Alexis Godet, Stéphane Bodin, Thierry Adatte, Karl B. F?llmi
更新时间: 2018-06-30
摘要: The latest Hauterivian-earliest Aptian time interval includes three episodes of significant environmental change (Faraoni, late early-Barremian, and Taxy Episodes). This time interval appears to partially overlap with large-scale volcanic activity related to the Tristan da Cunha plume along the Rio Grande Rise, High Arctic large igneous province volcanism, and the early phase in the formation of the greater Ontong Java LIP in the Pacific. The establishment of exact temporal relationships between volcanic activity and environmental change remains, however, a major challenge, due to the scarcity of numerical ages for the Early Cretaceous. We report mercury (Hg) contents in uppermost Hauterivian-lowermost Aptian marl/limestone alternations from seven sections along a NS transect in the Western Tethys. The Hg contents in marl samples display rather scattered records, which are generally well correlated with the total organic carbon (TOC) records. In associated limestone beds, five distinct spikes in Hg concentrations occur in three intervals (latest Hauterivian, early Barremian, and latest Barremian). The small amounts of organic matter (<0.2 wt%) in the limestones suggest that organic matter only played a limited role in Hg sequestration. Three Hg peaks in the middle of the Balearites balearis Zone, in the Faraoni level, and in the early Barremian occur only in one of the seven studied sections, which indicate a regionally variable distribution of Hg during these episodes. However, two distinct enrichments in Hg concentrations at the top of the B. balearis Zone (below the Faraoni level) and the M. sarasini Zone (below the Taxy level) appear comparable and correlatable between the sections. These data indicate that important volcanic activity antedating the Faraoni and the Taxy episodes may have contributed to the onset of associated environmental and ecological perturbations during the latest Hauterivian and latest Barremian, such as carbonate platform drowning phases.

28720. 题目: Volcanic and hydrothermal activities recorded in phosphate nodules from the Lower Cambrian Niutitang Formation black shales in South China
文章编号: N18063010
期刊: Palaeogeography, Palaeoclimatology, Palaeoecology
作者: Ping Gao, Zhiliang He, Shuangjian Li, Gary G. Lash, Boyuan Li, Boyu Huang, Detian Yan
更新时间: 2018-06-30
摘要: Deposition of black shale of the Lower Cambrian Niutitang Formation (NTT) of the Yangtze Block, South China, in association with the Ediacaran-Cambrian (E-C) transition was accompanied by widespread formation of phosphate nodules. Petrological and geochemical studies of the nodules and host sedimentary rocks were carried out to elucidate hydrographic conditions of the Early Cambrian ocean. Our results reveal that NTT phosphate nodules are composed principally of concentrically banded carbonate fluorapatite (CFA) that likely reflects changing Eh and pH conditions contemporaneous with diagenetic nodule growth. Accumulation of organic-rich sediment and nodule growth may have been induced and sustained by contemporaneous volcanic and hydrothermal activities on the Yangtze Block. The introduction of voluminous nutrients with volcanic ash, including phosphate and aqueous Fe and Si, promoted the bloom of plankton, including sponges and lower algae leading to organic matter enrichment. Productivity may have been further enhanced by upwelling of phosphate-rich bottom water that resulted in widespread phosphogenesis and formation of phosphate nodules. The hyalophane-quartz association documented from phosphate nodules suggests the possible interaction of K-feldspar-rich volcanic ash and Ba-rich hydrothermal fluids at lower pH levels in association with nodule growth. The formation of phosphate nodules of the Niutitang Formation, then, reflects the complex interaction among primary productivity, volcanic and hydrothermal activity, and the accumulation of organic matter at a critical period of Earth history.