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28661. 题目: Redoximorphic Bt horizons of the Calhoun CZO soils exhibit depth-dependent iron-oxide crystallinity
文章编号: N18070604
期刊: Journal of Soils and Sediments
作者: Chunmei Chen, Diego Barcellos, Daniel D. Richter, Paul A. Schroeder, Aaron Thompson
更新时间: 2018-07-06
摘要: Purpose: Iron (Fe) oxyhydroxides and their degree of ordering or crystallinity strongly impact the role that Fe plays in ecosystem function. Lower crystallinity phases are generally found to be more reactive than higher crystallinity phases as sorbents for organic matter and chemical compounds, as electron acceptors for organic matter mineralization or as electron donors for dysoxic respiration. We investigated Fe solid phase speciation as a function of soil depth in a redoximorphic upland soil profile. Materials and methods: We examined a redoximorphic upland soil profile, which displayed alternating Fe-enriched and Fe-depleted zones of the Bt horizons with platy structure from 56 to 183 cm depth at the Calhoun Critical Zone Observatory in South Carolina, USA. Redoximorphic Fe depletion and enrichment zones were sampled to enable a detailed investigation of Fe mineralogy during redox transformations. All samples were characterized by total elemental analysis, X-ray diffraction, and 57Fe M ssbauer spectroscopy. Results and discussion: Total Fe in the Fe-enriched and Fe-depleted zones was 26.3 – 61.2 and 15.0 – 22.7 mg kg 1 soil, respectively, suggesting periodic redox cycling drives Fe redistribution within the upland soil profile. The M ssbauer data clearly indicated goethite (56 – 74% of total Fe) and hematite (7 – 31% of total Fe) in the Fe-enriched zones, with the proportion of hematite increasing with depth at the expense of goethite. In addition, the overall crystallinity of Fe phases increased with depth in the Fe-enriched zones. In contrast to Fe-enriched zones, Fe-depleted zones contained no hematite and substantially less goethite (and of a lower crystallinity) but more aluminosilicates-Fe(III) (e.g., hydroxy-interlayered vermiculite, biotite, kaolinite) with XRD and M ssbauer data suggesting a shift from oxidized biotite-Fe(III) at depth to hydroxy-interlayered vermiculite plus low-crystallinity goethite in the Fe-depleted zones in the upper Bt. Conclusions: Our data suggest the varied crystalline states of hematite and goethite may be important for Fe reduction over long-term time scales. The persistence of low-crystallinity Fe phases in Fe depletion zones suggests that both dissolution and re-precipitation events occur in the Fe-depleted layers. These variations in Fe phase abundance and crystallinity within similar redoximorphic features suggest that Fe likely shifts ecosystem roles as a function of soil depth and likely has more rapid Fe cycling in the upper Bt horizons in upland soils, while serving as a weathering engine at depth.

28662. 题目: Climate and plant controls on soil organic matter in coastal wetlands
文章编号: N18070602
期刊: Global Change Biology
作者: Michael J. Osland , Christopher A. Gabler , James B. Grace , Richard H. Day , Meagan L. McCoy , Jennie L. McLeod , Andrew S. From , Nicholas M. Enwright , Laura C. Feher , Camille L. Stagg , Stephen B. Hartley
更新时间: 2018-07-06
摘要: Coastal wetlands are among the most productive and carbon‐rich ecosystems on Earth. Long‐term carbon storage in coastal wetlands occurs primarily belowground as soil organic matter (SOM). In addition to serving as a carbon sink, SOM influences wetland ecosystem structure, function, and stability. To anticipate and mitigate the effects of climate change, there is a need to advance understanding of environmental controls on wetland SOM. Here, we investigated the influence of four soil formation factors: climate, biota, parent materials, and topography. Along the northern Gulf of Mexico, we collected wetland plant and soil data across elevation and zonation gradients within ten estuaries that span broad temperature and precipitation gradients. Our results highlight the importance of climate‐plant controls and indicate that the influence of elevation is scale and location dependent. Coastal wetland plants are sensitive to climate change; small changes in temperature or precipitation can transform coastal wetland plant communities. Across the region, SOM was greatest in mangrove forests and in salt marshes dominated by graminoid plants. SOM was lower in salt flats that lacked vascular plants and in salt marshes dominated by succulent plants. We quantified strong relationships between precipitation, salinity, plant productivity, and SOM. Low precipitation leads to high salinity, which limits plant productivity and appears to constrain SOM accumulation. Our analyses use data from the Gulf of Mexico, but our results can be related to coastal wetlands across the globe and provide a foundation for predicting the ecological effects of future reductions in precipitation and freshwater availability. Coastal wetlands provide many ecosystem services that are SOM dependent and highly vulnerable to climate change. Collectively, our results indicate that future changes in SOM and plant productivity, regulated by cascading effects of precipitation on freshwater availability and salinity, could impact wetland stability and affect the supply of some wetland ecosystem services.

28663. 题目: Lateral carbon transfer from erosion in noncroplands matters
文章编号: N18070601
期刊: Global Change Biology
作者: Pasquale Borrelli , Panos Panagos , Emanuele Lugato , Christine Alewell , Cristiano Ballabio , Luca Montanarella , David A. Robinson
更新时间: 2018-07-06
摘要: This study combines two unprecedentedly high resolution (250 × 250 m) maps of soil erosion (inter‐rill and rill processes) and soil organic carbon to calculate a global estimate of erosion‐induced organic carbon (C) displacement. The results indicate a gross C displacement by soil erosion of Pg C/year. The greatest share of displaced C (64%) comes from seminatural lands and forests. This suggests that lateral C transfer from erosion in noncroplands may play a more important role than previously assumed.

28664. 题目: Isotope record of mineralogical changes in a spectrum of aqueously altered CM chondrites
文章编号: N18070506
期刊: Geochimica et Cosmochimica Acta
作者: Elishevah M.M.E. van Kooten, Larissa L. Cavalcante, Kazuhide Nagashima, Takeshi Kasama, Zoltan I. Balogh, Zan Peeters, Silver Sung-Yun Hsiao, Hsien Shang, Der-Chuen Lee, Typhoon Lee, Alexander N. Krot, Martin Bizzarro
更新时间: 2018-07-05
摘要: The recent fall of the relatively unaltered CM chondrite Maribo provides a unique opportunity to study the early stages of aqueous alteration on the CM chondrite parent body. We show using transmission electron microscopy of a matrix FIB-section from Maribo that this meteorite mainly appears to consist of tochilinite-cronstedtite intergrowths (TCIs), but also contains regions of amorphous or nanocrystalline silicates, anhydrous silicates and FeNi metal aggregates with thin iron oxide rims, suggesting that it experienced aqueous alteration to a relatively small degree. A comparison of Maribo with increasingly altered CM chondrites such as Jbilet Winselwan and Bells shows that during progressive aqueous alteration (1) the TCIs are replaced by coarser sulfides and increasingly Mg-rich serpentine, and (2) the abundance of 15 N -rich hotspots increases, whereas the magnitude of their 15 N enrichment decreases. We observe that the overall N isotope variability related to aqueous alteration is an order of magnitude lower than the variability observed between different chondrite groups. We suggest these high order differences are the result of heterogeneous accretion of insoluble or soluble organic carriers of 15 N to the different chondrite parent bodies. D/H ratios of matrices from Maribo, Jbilet Winselwan and Bells increase with progressive aqueous alteration, a trend that is opposite to expectations of mixing between D-poor water and D-rich organic matter. We argue that this behaviour cannot be related to Fe oxidation or serpentinization reactions and subsequent loss of D-poor H2 gas. We offer an alternative hypothesis and suggest that CM chondrites experienced two-stage aqueous alteration. During the first stage occurring at relatively low temperature, mixing of increasing amounts of D-poor water with D-rich organic matter results in a decrease of D/H ratio with increasing degree of alteration. During the second stage of alteration occurring at relatively high temperature (T < 300 °C), decomposition of TCIs in CMs of petrologic type <2.7 releases gaseous D-poor water that results in increase of the D/H ratio of the CM matrices. Finally, we report on changes in the organic structure of Maribo, Jbilet Winselwan and Bells using Carbon-K and Nitrogen-K edge electron energy loss spectroscopy. The organic matter initially has higher aromatic/aliphatic ratios (e.g., Maribo) and lower abundances of ketone and carboxyl functional groups, which we suggest are the result of chemical degradation of double bonded carbon from oxidation during hydrothermal alteration. Consequently, we propose that the organic matter of the CM chondrite Paris, for which lower aromatic/aliphatic ratios have been observed, may have been different from Maribo, perhaps reflecting the early accretion of Paris relative to Maribo.

28665. 题目: Lipid compound classes display diverging hydrogen isotope responses in lakes along a nutrient gradient
文章编号: N18070505
期刊: Geochimica et Cosmochimica Acta
作者: S. Nemiah Ladd, Daniel B. Nelson, Carsten J. Schubert, Nathalie Dubois
更新时间: 2018-07-05
摘要: Compound specific hydrogen isotope ratios (2H/1H) of lipid biomarkers preserved in sediments are used as paleohydrologic proxies. However, several variables, including contributions from different source organisms and their growth rates, can influence 2H/1H fractionation between lipids and source water. Significant uncertainties remain about how these factors combine to produce the net 2H/1H signal exported to sediments. To assess the influence of phosphorus availability on 2H/1H ratios of lipids accumulating in lake sediments, we analyzed surface sediments and sediment traps from ten central Swiss lakes representing a wide range of trophic states. In agreement with results from laboratory cultures, 2H/1H fractionation for the diatom biomarker brassicasterol (24-methyl cholest-5,22-dien-3β-ol) increased in more productive lakes (0.6 ± 0.1‰ per μg/L total P in sediment traps and surface sediments). In contrast, 2H/1H fractionation for phytol, the isoprenoid side-chain moiety of chlorophyll, decreased with increasing total P ( 0.4 ± 0.1‰ per μg/L total P in sediment traps), suggesting that different biochemical mechanisms are responsible for changes in 2H/1H fractionation for each type of isoprenoidal lipid. Opposing changes in 2H-fractionation for sterols and phytol cause their 2H/1H ratios to converge as total P increases. This response may be a new tracer for phytoplankton growth conditions and is not influenced by the source water isotope value. Interpreting the 2H/1H ratios of short to long chain (C14–C30) n-alkanoic acids and n-alkanols is complicated by likely contributions from heterotrophs and/or vascular plants. These values generally did not correlate with lake water isotopes, nor did their fractionation factors correlate with total P. For most lipids there was no significant difference between sediment trap and surface sediment 2H/1H ratios. However, n-C14–n-C18 fatty acids were 2H-enriched in the surface sediments, most likely due to degradation in the water column. Our results indicate that interpretations of short-chain fatty acid 2H/1H ratios as a water isotope signal likely require supporting information about ecological conditions and community structure, but that paired H isotope measurements of phytoplankton-derived sterols and phytol may be developed as a proxy for phytoplankton growth.

28666. 题目: Benthic nutrient cycling at the sediment-water interface in a lagoon fish farming system (northern Adriatic Sea, Italy)
文章编号: N18070504
期刊: Science of The Total Environment
作者: Elisa Petranich, Stefano Covelli, Alessandro Acquavita, Cinzia De Vittor, Jadran Faganeli, Marco Contin
更新时间: 2018-07-05
摘要: Metabolism and carbon, oxygen, and nutrient fluxes (DIC, DOC, DO2, NO2 , NO3 , NH4 +, PO4 3 and SiO4 4 ) were studied during three surveys at two sites (VN1 and VN3) located at a fish farm at the Marano and Grado Lagoon (northern Adriatic Sea), using an in situ benthic chamber. Field experiments were conducted in July and October 2015 and March 2016 at a depth of approximately 2 m along the main channels of the fish farm. Water samples were collected by a scuba diver every 2 h in order to investigate daily fluxes of solutes across the sediment-water interface (SWI). Regarding the solid phase, Corg/Ntot and Corg/Porg molar ratios suggested an autochthonous marine origin of the organic matter and a minor preservation of P in the sediments, respectively; high values of sulphur (Stot) were also encountered (0.8–2%). The conditions at VN3 were mostly anoxic with high NH4 + levels (30–1027 μM) and the absence of NO3 . Substantial daily patterns of all solutes occurred especially in autumn and winter. On the contrary, fluxes at VN1 were less pronounced. Usually, inverse correlations appeared between dissolved O2 and DIC trends, but in our system this was observed only at VN3 in autumn and accomplished by a parallel increase in NH4 +, PO4 3 and SiO4 4 during intense nutrient regeneration. These results are significantly different than those reported for open lagoon environments, where nutrient regeneration at the SWI and in surface sediments is the primary source of nutrients available for assimilation processes, especially during the warmer period of the year when the natural nutrient input by fresh water inflows is limited. Due to the importance of this site for aquaculture, biodiversity and ecosystem services, useful suggestions have been provided from this study in order to improve the quality of this unique aquatic system.

28667. 题目: Characterisation of dissolved organic matter using Fourier-transform ion cyclotron resonance mass spectrometry: Type-specific unique signatures and implications for reactivity
文章编号: N18070503
期刊: Science of The Total Environment
作者: Xi-Zhi Niu, Mourad Harir, Philippe Schmitt-Kopplin, Jean-Philippe Croué
更新时间: 2018-07-05
摘要: This study investigated the chemodiversity and unique signatures for dissolved organic matter (DOM) from different types of water using high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Eight freshwater hydrophobic DOM (HPO) share 10–17% formulas that were mainly lignin-like compounds. Unique signatures were synthesized: unique to the high-humic HPO (Suwannee River and Blavet River) were condensed aromatic and some aliphatic compounds with H/C > 1.5 and O/C < 0.2, which is considered as decisive of these black river water. Medium-humic isolates (Loire River, Seine River, South Platte River, and Ribou Dam) did not show explicit unique signatures. Nonetheless, enhanced chemodiversity was observed for medium-humic isolates extracted from a variety of indigenous environmental conditions. As an example, South Platte River HPO isolated in winter showed signatures similar to low-humic HPO (Colorado River), i.e., predominantly aliphatic CHO (H/C > 1.0). Effluent HPO was mainly aliphatic molecules with 0.2 < O/C < 0.5 and enriched in S-bearing molecules, and molecules unique to glacial DOM (Pony Lake) incorporated N-bearing compounds that were inferiorly oxidized and were considered as microbial-derived. The weight-averaged double bond equivalent and elemental ratio derived from FTICR-MS were compared with SUVA254 and the results from elemental analysis. This acts as the first study to synthesize unique chemical compositions that distinguish different types of DOM and determine certain reactivity. It is also a significant reference for future studies using similar types of DOM.

28668. 题目: Culture and horticulture: Protecting soil quality in urban gardening
文章编号: N18070502
期刊: Science of The Total Environment
作者: Francesca Bretzel, Claudia Caudai, Eliana Tassi, Irene Rosellini, Manuele Scatena, Roberto Pini
更新时间: 2018-07-05
摘要: Urban cultivation for food production is of growing importance. The quality of urban soil can be improved by tillage and the incorporation of organic matter, or can be degraded by chemical treatments. Urban gardeners have a role in this process, through the selection of various cultivation techniques. Our study focuses on an allotment area in the town of Pisa (Italy), which since 1995 has been run as a municipal vegetable garden by the residents. We analysed the soil and compared the data with those collected five years previously, to verify the possible changes in soil properties and fertility. We also interviewed the gardeners regarding their backgrounds, motivations and cultivation practices. We looked for possible changes in the soil quality attributable to the cultivation techniques. We found that the allotment holders influenced the soil quality through the cultivation techniques. Organic carbon, electrical conductivity and the content of copper increased unevenly in relation to the gardeners' cultivation practices. At the same time the study highlights that the urban gardeners were not completely aware of how to protect and enhance the fertility and the quality of urban soil. We believe that town councils should be responsible for providing correct information to the allotment holders and thus prevent the possible misuse of urban soil to grow food, as this can affect everyone's health.

28669. 题目: Exposure of Brazilian soil and groundwater to pollution by coccidiostats and antimicrobial agents used as growth promoters
文章编号: N18070501
期刊: Science of The Total Environment
作者: Alejandro Yopasá-Arenas, Anne Hélène Fostier
更新时间: 2018-07-05
摘要: The World Health Organization has identified antimicrobial resistance as one of the most important threats to global health. Brazil is one of the world's leading meat producers and the Brazilian use of veterinary antimicrobials as therapeutic agents and prophylactic or growth promoters in animal production remains problematic. Many antimicrobials are not completely metabolized and their excretion represents a significant source of environmental exposure. The aim of this work was to estimate the exposure risk of soil and groundwater to pollution by growth promoters (GPs) and anticoccidial additives (AAs) in Brazil by using a method based on a geographical information system (GIS). The principle adopted is that the greater the amount of animals, the greater the quantity of antimicrobials present, and the greater the soil vulnerability to pollution. Our research showed that GPs and AAs are extensively used in the Brazilian animal production system. An analysis of market data showed that zinc bacitracin, monensin, salinomycin, colistin and tylosin are representative GPs and AAs. This study presents a qualitative approach for risk assessment based on worst-case scenarios. First, the probable environmental concentration was estimated using a correlation between the number of heads of the herds of poultry and cattle, and the amounts of drug released. The leaching risk potential was characterized for each compound, as proposed in ISO 15175. The potential of soil pollution was evaluated for each antimicrobial as a function of its binding and dissipation rates. These rates were calculated using georeferenced data of organic carbon, average temperature, water balance and hydro-geological parameters. The consequences were modeled based on Brazilian soil usage. Finally, the risk was calculated by combining the different maps generated using spatial multi-criteria decision analysis. Higher risk was found for the midwest, southeast and south regions of Brazil. Groundwater was found to be more vulnerable than soil.

28670. 题目: Environmental assessment concerning trace metals and ecological risks at Guanabara Bay, RJ, Brazil
文章编号: N18070402
期刊: Environmental Monitoring and Assessment
作者: Valquiria Maria de Carvalho Aguiar, Paula Ferreira Falheiro Abuchacra, José Ant?nio Baptista Neto, Allan Sandes de Oliveira
更新时间: 2018-07-04
摘要: Three-stage sequential extraction BCR was applied to surface sediments from the west part of Guanabara Bay to assess the mobility of Zn, Cu, Pb, Ni, Cr, and Mn. Results were satisfactory for the analysis of certificate standard material (BCR 701), with recoveries between 71 (Cu) and 123% (Cr). Evaluation of organic matter composition classified the area as eutrophic (CHO:PRT > 1), with aged organic detritus at some stations. Zn exhibited by far the greatest bioavailability, with 43.49% of its concentrations associated with the exchangeable fraction. Cu and Cr showed stronger affinity for organic matter, with 51.18 and 48.73% of their concentrations, respectively, bounded to the oxidizable fraction. Pb presented higher concentrations in the reducible fraction (45.41%). The strongest lithogenic contribution was shown by Ni (31.91%) and Mn (35.44%). PCA clearly showed the determinant role of organic matter and fine sediments in the distribution of metals in the study area and also a common source for these elements, with the exception of Cu. Risk Assessment Code (RAC) established Zn as the most concerning element in the study area. The decreasing mobility order, based on the sum of the three extractable fractions of BCR, was Pb > Cu > Cr > Zn > Ni > Mn. The comparison of the results with sediments quality guidelines (SQG) proved fractionation to be mandatory in the evaluation of effective ecological risk concerning trace elements in sediments.

28671. 题目: Soil quality of an Iranian forest ecosystem after conversion to various types of land use
文章编号: N18070401
期刊: Environmental Monitoring and Assessment
作者: M. H. Rasouli-Sadaghiani, M. Barin, S. Siavash Moghaddam, C. A. Damalas, K. Ghodrat
更新时间: 2018-07-04
摘要: The impact of land-use change on parameters of the soil was evaluated in soil samples from arable land, orchard land, and grassland in West Azerbaijan, Iran, compared with their adjacent natural forestland, using some biological indices. Microbial biomass carbon (MBC); microbial basal respiration (BR); metabolic quotient (qCO2); substrate induced respiration (SIR); carbon availability index (CAI); the microbial quotient, i.e., the ratio of microbial carbon to soil organic carbon (Cmic/Corg); and soil organic carbon (SOC) were calculated in collected soil samples. Deforestation and long-term land use showed adverse effects on soil biological properties. The spatial distribution of MBC, BR, SIR, and SOC, followed the order: forestland > grassland > orchard land > arable land. SOC showed the highest decline by 67.7% in arable land, 43.6% in orchard land, and 36.3% in grassland, with an average reduction of 49.2% compared with forestland. Similarly, BR and MBC decreased by an average reduction of 41.3 and 34.8%, respectively, compared with forestland. By contrast, the qCO2 index, the CAI index, and the Cmic/Corg ratio were not affected significantly by land use, except from a significant raise of the Cmic/Corg ratio in the arable land. Land-use change exerted a remarkable negative influence on soil quality with several soil attributes affected due to cropping compared with adjacent grassland and forestland. At the field level, proper management practices that increase SOC in the soil, e.g., effective recycling of crop residues and manures, should be considered, when land is continuously cultivated.

28672. 题目: Oceanic fronts control the distribution of dissolved barium in the Southern Ocean
文章编号: N18070319
期刊: Marine Chemistry
作者: Kimberley M. Pyle, Katharine R. Hendry, Robert M. Sherrell, Oliver Legge, Andrew J. Hind, Dorothee Bakker, Hugh Venables, Michael P. Meredith
更新时间: 2018-07-03
摘要: The globally-observed relationship between oceanic barium and the macronutrient silicic acid results from the shared influence of large-scale ocean circulation and mixing on the two elements, and the inherent link between barium and organic matter formation and dissolution. A detailed examination of deviations from barium-silicon correlations can reveal variations in non-conservative processes within the marine barium cycle. Here, we present a high-resolution dataset of dissolved barium and macronutrients from the Drake Passage and the Scotia and Weddell Seas. Our new results highlight the influence of Southern Ocean frontal zones on barium cycling and the deviations of barium and macronutrient distributions as a result of spatial variations in phytoplankton assemblages and in barite formation processes. These new data also reinforce findings that water mass mixing and ocean circulation, in particular the location of oxygen minima, play a key role in barium distribution. Our findings have implications for the use of sedimentary barium as a proxy for export production, which may be complicated by physical water circulation changes or shifts in plankton community structure.

28673. 题目: Branched GDGT variability in sediments and soils from catchments with marked temperature seasonality
文章编号: N18070318
期刊: Organic Geochemistry
作者: Min Cao, Gemma Rueda, Pedro Rivas-Ruiz, M? Carmen Trapote, Mona Henriksen, Teresa Vegas-Vilarrúbia, Antoni Rosell-Melé
更新时间: 2018-07-03
摘要: The distributions of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in sediments are used as a proxy measurement to infer changes in past mean annual air temperatures (MAT). When applied to high resolution sedimentary sequences, measurement of brGDGT distributions is employed to reconstruct MAT at subdecadal time scales. In addition, brGDGT proxy estimates are also sometimes purported to be seasonally biased in environments where annual brGDGT production may not be constant during a seasonal cycle. The main aim of this study was to assess the occurrence of seasonality in the production and distribution of brGDGTs and the seasonality bias of the derived temperature proxy. For this purpose, we examined brGDGT distributions and brGDGT-derived MAT estimates in surface soils and settling/suspended particulate matter over one year, from two sites located in the same latitude but at different altitudes, in the Catalan Pyrenees, as well as at one site in southern Norway. These locations have marked seasonal temperature cycles, which were expected to maximize the possibility of detecting any seasonal bias in the production and compositions of brGDGTs. The results show that brGDGT abundance is heterogeneous and increases with soil humidity. The brGDGT distributions and some of the brGDGT-derived proxy measurements in soils are relatively stable throughout the year and do not change significantly in the suspended particulate matter in the river or settling particulate matter in traps. Our study shows that the impact of the seasonality of temperature on brGDGT distribution was absent in the soils studied, regardless of altitude or latitude on a catchment/regional scale. As soils are likely to contain a brGDGT signature which is representative of average environmental conditions in the catchment at least over decades, brGDGT proxy reconstructions derived from soil sources are more suitable to infer variability in environmental parameters over the same timescales (i.e. decades or longer). On shorter timescales (i.e. annual), sediment downcore variability in brGDGTs is likely to be related to changes derived from in situ production and sediment sources.

28674. 题目: Sedimentary records of human activity and natural environmental evolution in sensitive ecosystems: A case study of a coral nature reserve in Dongshan Bay and a mangrove forest nature reserve in Zhangjiang River estuary, Southeast China
文章编号: N18070311
期刊: Organic Geochemistry
作者: Dongyi Li, Yonghang Xu, Yunhai Li, Jianjun Wang, Xijie Yin, Xiang Ye, Aijun Wang, Liang Wang
更新时间: 2018-07-03
摘要: Total organic carbon (TOC), total nitrogen (TN), δ13Corg, δ15N, and grain size were measured in two sediment cores from reserves adjacent to Dongshan Bay, China. The aims were to identify organic matter (OM) sources and to evaluate the combined impact of human activity and natural environmental processes over the last 100 yr. In a coral reserve far from the estuary of Zhangjiang River, the average sediment accumulation rate (SAR) was 0.51 cm/yr from ca. 1839–2015, and the values of δ13Corg and C/N (atomic ratio of TOC to total N) ranged from 21.9‰ to 23.7‰ and from 5.7 to 8.1, respectively. In a mangrove forest reserve near the estuary, SAR averaged 0.49 cm/yr from ca. 1891–1985 and 2.41 cm/yr from ca. 1985–2015, and the δ13Corg and C/N values ranged from 22.7‰ to 26.3‰ and from 9.3 to 21.7, respectively. By combining a comparison plot of C/N and δ13Corg and a binary mixing model (based on δ13Corg and Norg/Corg, respectively), the major OM sources were assigned and their sedimentary contributions estimated. The sedimentary OM in the coral reserve had mainly an offshore marine authigenic signature with an average terrigenous contribution of <27%. In the mangrove forest reserve, the sedimentary OM was a mixture of terrestrial and marine sources, with an average terrigenous contribution of >56%. While input from the Zhangjiang River declined from the 1980 s, urban development, deforestation and land reclamation contributed to an overall increase in the total mass accumulation rate (MAR). The coral was also severely damaged by the advent of poaching around the same time. These two factors collectively resulted in a rapid decrease in OM content and OC accumulation rate (CARorg ) of the sediments until the establishment of the coral reserve in 1997. Changes in terrain and climate and the construction of water conservancy facilities were traditionally the primary factors responsible for changes in the sedimentary environment of the mangrove forest reserve. Since the 1980s, however, the expansion of the mangrove forest along with human activity has led to rapid increases in MAR and CARorg ; while, protective measures and a favorable climate have also promoted the growth of the mangrove forest.

28675. 题目: The composition and radiolysis impact on aromatic hydrocarbons in sedimentary organic matter from the Mulga Rock (Australia) uranium deposit
文章编号: N18070310
期刊: Organic Geochemistry
作者: Paul F. Greenwood, Chao Shan, Alex I. Holman, Kliti Grice
更新时间: 2018-07-03
摘要: Our interest in the effect of ionizing radiation on sedimentary organic matter (OM) has extended to the molecular distributions and stable isotopic values of aromatic hydrocarbons. Thermally immature sediments (%Ro = 0.26; Tmax < 421 °C) spanning a 173–5280 ppm radiolytic gradient from the Mulga Rock Uranium Deposit (Western Australia) contained high abundances of vascular plant sourced aromatic (and aliphatic) terpenoids. Terpenoids with 2–5 rings and various levels of aromatisation were detected in the aromatic fractions of these sediments. The extent of aromatisation increased with sedimentary U/radiolytic levels, attributed to free-radical promoted reactions including dehydrogenation and oxidation of aliphatic precursors. The sediment with the highest U content (5280 ppm) showed only diterpenoids and low MW PAHs, reflecting complete radiolytic removal of higher MW terpenoids. A larger number and variety of terpenoid products were detected from the other sediments (U ≤ 1700 ppm) from which several radiolytically promoted reaction pathways were identified. Cadinene, for instance, was subject to competing hydrogenation and dehydrogenation reactions which gave cadinane and progressively aromatised diterpenoid analogues, respectively. Pentacyclic terpane precursors were also progressively aromatised and partially converted to des-A-triterpenoid or C-ring cleaved triterpenoid (tetracyclic) products. These reactions are typical of the natural diagenetic transformation of plant terpenoids, with the main effect of the high radiolytic levels an apparent hastening of diagenetic processes. The δ13C values of several aromatised products indicated a slight 13C enrichment with increasing aromatisation, likely due to preferential abstraction of H from 12C.

28676. 题目: Archaeal and bacterial glycerol dialkyl glycerol tetraether (GDGT) lipids in environmental samples by high temperature-gas chromatography with flame ionisation and time-of-flight mass spectrometry detection
文章编号: N18070309
期刊: Organic Geochemistry
作者: Sabine K. Lengger, Paul A. Sutton, Steven J. Rowland, Sarah J. Hurley, Ann Pearson, B. David A. Naafs, Xinyue Dang, Gordon N. Inglis, Richard D. Pancost
更新时间: 2018-07-03
摘要: Archaeal isoprenoidal glycerol dibiphytanyl glycerol tetraether lipids (iGDGTs) and their non-isoprenoidal branched bacterial analogues (brGDGTs) have widespread applications in biogeochemistry and paleothermometry. Analysis of GDGTs usually involves separation using high performance liquid chromatography, typically coupled via atmospheric pressure chemical ionisation to mass spectrometric detection in selected ion-monitoring mode (HPLC–APCI-MS). However, reliable determination of ratios and, in particular, quantification by this technique, can be challenging due to differences in ionisation efficiencies of the various compounds. Quantification of GDGTs also relies on external calibration of the relative response to an internal standard with authenticated GDGTs, which are often not readily accessible. Here, we tested the suitability of high temperature gas chromatography with flame ionisation detection (HTGC-FID) for the determination of concentrations and tetraether lipid-based ratios in marine and terrestrial samples. For this, we identified GDGTs in environmental samples using HTGC coupled to time-of-flight mass spectrometry (HTGC–MS). Using a purified GDGT standard, we show we can quantify GDGT-0 in environmental samples by GC-FID. Some GDGT-based ratios measured by HTGC-FID exhibited a linear correlation (1:1) with ratios derived from HPLC–MS and weight-based ratios of mixtures of purified standards. However, ratios relying on minor isomers, such as TEX86 and MBT/CBT have many unresolved challenges for determination by HTGC. Detection limits were higher than for HPLC–MS. However, the advantages of employing HTGC-based methods include: (1) the independence from MS tuning-related differences in ionisation energies; (2) the potential for direct comparison with other, non-GDGT based biomarkers; and (3) a more complete insight into biomarker distributions in environmental samples by the extension of the temperature range. Quantitative elution of GDGTs from a HTGC column as demonstrated herein, will also enable their analysis by compound-specific isotope ratio mass spectrometry.

28677. 题目: Assessment of apolar lipids in subseafloor rocks and potential contaminants from the Atlantis Massif (IODP Expedition 357)
文章编号: N18070308
期刊: Organic Geochemistry
作者: Katherine A. Hickok, Tran B. Nguyen, Susan Q. Lang
更新时间: 2018-07-03
摘要: International Ocean Discovery Program Expedition 357 drilled 17 boreholes across the Atlantis Massif with the goals of investigating carbon cycling and the presence of life in a zone of active serpentinization. The expedition recovered multiple lithologies including gabbros, basalts, carbonate sands, and serpentinites. A subset of contrasting lithologies were analyzed for apolar lipid content to determine if non-volatile organic molecules can be detected in the oceanic subsurface. The definitive detection and identification of abiotic and biological lipids in the subsurface of an actively serpentinizing system would be a significant step towards understanding a variety of scientific processes, including the evolution of pre-biotic chemistry, microbial habitability, and the global carbon cycle. Given the high potential for contamination during drilling, a suite of materials used in sample collection and processing were also analyzed to characterize their signatures. An n-alkane series ranging from C18 to C30 with δ13C isotopic values of 30.9‰ to 28.8‰ was present in lithologically diverse samples. Multiple lines of evidence point to the rock saw used to remove core exteriors during sample processing as the source of these compounds. Many of the other sample-handling procedures designed to reduce surface contamination were determined to be effective and could be implemented in future projects. This result highlights the value of careful prevention and characterization of contamination to allow for more accurate interpretations of complex and dynamic subsurface processes, and the importance that future reports of these compounds occurs in conjunction with thorough contamination assessments.

28678. 题目: Glacial-interglacial vegetation changes in northeast China inferred from isotopic composition of pyrogenic carbon from Lake Xingkai sediments
文章编号: N18070307
期刊: Organic Geochemistry
作者: Weiwei Sun, Enlou Zhang, Enfeng Liu, Jie Chang, Rong Chen, Ji Shen
更新时间: 2018-07-03
摘要: Understanding the changes in monsoon intensity and ecosystem response at different timescales is crucial for the well-being of humans, yet the paleoclimatic interpretation of stable carbon isotope (δ13C) values from northeast China records is debatable. In this study, reported δ13C data from 76 surface soils in northeast China are compiled, and a δ13C record of pyrogenic carbon (δ13CPyC) from Lake Xingkai in northeast China since the last interglacial period is presented. The aim was to investigate the orbital timescale environmental implication of geological δ13CPyC data for northeast China. The results showed a distinct increase in δ13C values of surface soils, which correlated with increasing temperature of the warmest month. Higher temperature favored the expansion of C4 plants, while precipitation had only a weak correlation with δ13C values of surface soils in the region. On an orbital timescale, the δ13CPyC record from Lake Xingkai generally reflected paleovegetation change, suggesting that the abundance of C4 plants was relatively high during the warm periods, changing to almost purely C3 plants during the cold periods. Both modern and geological analysis suggest that the climatic factor determining the δ13C in northeast China was temperature of the warmest month. This is similar to the situation for mid-latitudes such as the Chinese Loess Plateau, in contrast to low latitudes such as southern China.

28679. 题目: Sediment records of long chain alkyl diols in an upwelling area of the coastal northern South China Sea
文章编号: N18070306
期刊: Organic Geochemistry
作者: Xiaowei Zhu, Guodong Jia, Shengyi Mao, Wen Yan
更新时间: 2018-07-03
摘要: Long chain alkyl diols in sediment cores were studied in the Yuedong Upwelling (YDU) area in the coastal northern South China Sea to investigate whether sea surface temperature (SST) and upwelling intensity over the last few decades can be traced by the diol-derived indices, i.e., the LDI (long chain diol index) as a proxy for SST and the DI-1 and DI-2 (diol index 1 and 2) as proxies for upwelling intensity. The influence of riverine long chain alkyl diols (e.g., 1,13- and 1,15-diols), which may affect LDI-reconstructed SSTs, was largely ruled out based on the comparison between diol distributions in suspended particulate materials in the Pearl River estuary and the core sediments. LDI-derived SSTs in downcore sediments matched well with local annual mean SSTs. The records of DI-2 changed in parallel with the local wind stress and inversely with SST at times of upwelling, suggesting that DI-2 is an effective proxy for upwelling intensity of YDU. The DI-1 showed a generally inverse variation pattern with DI-2, implying a major influence by SST, and it is thus not an applicable upwelling indicator for YDU. A negative relationship of DI-1 and a positive relationship of DI-2 with LDI-derived SST were observed. This occurrence might be attributed to El Ni o–Southern Oscillation (ENSO), because the SST and upwelling intensity were largely modulated by ENSO, showing a warm annual mean SST during the years of enhanced El Ni o and intensified summer upwelling.

28680. 题目: Variations in abundance and distribution of methyltrimethyltridecylchromans (MTTCs) in sediments from saline lacustrine settings in Cenozoic lacustrine basins, China
文章编号: N18070305
期刊: Organic Geochemistry
作者: Kaixi Jiang, Chunming Lin, Xia Zhang, Chunfang Cai, Fei Xiao, Wenxiang He, Li Peng
更新时间: 2018-07-03
摘要: This study examines the abundance and distribution of MTTCs and biomarker compositions in samples of MTTC-rich sediments obtained from Paleogene strata in the Bohai Bay, Jianghan and Western Qaidam Basins in China. Biomarker signatures, including high C35/C34 hopane ratios, high gammacerane index values, low pristane/phytane (Pr/Ph) ratios and the presence of aryl isoprenoids, indicate saline lacustrine settings and photic zone euxinia (PZE). The distributions of MTTCs indicate significant palaeosalinity differences in the depositional environments of the three sets of samples obtained from the Bohai Bay, Jianghan and Western Qaidam Basins. These sets of samples were deposited under normal to mesosaline, meso- to hypersaline and hypersaline environments, respectively. The δ-MTTC% values are positively correlated with the values of the gammacerane index, but are negatively correlated with the Pr/Ph ratios. This result demonstrates that MTTCs do not form in the upper or lower parts of stratified water columns, but may form in the euxinic portions of photic zones. Therefore, MTTC parameters can only be used to reconstruct palaeosalinity in the euxinic portions of photic zones and are not applicable to the upper or lower parts of stratified water columns. This paper infers that variations in palaeosalinity in the euxinic portions of photic zones likely play a key role in controlling the distribution and abundance of MTTCs.