Distribution of glycerol ether lipids in halophilic,methanogenic and hyperthermophilic archaea

Four representatives of methanogenic Euryarchaeota (Methanosarcina mazei strain Gö1, Methanosphaera stadtmanae, Methanobrevibacter smithii and Methanosaeta thermophila), the hyperthermophilic euryarchaeon Thermococcus kodakarensis and the halophilic euryarchaeon Haloferax volcanii were studied for their glycerol ether lipid composition. The predominant core membrane lipid in all of them was archaeol, which was accompanied by variable quantities of sn-2-hydroxyarchaeol in the methanogens M. mazei (Methanosarcinales) and M. stadtmanae (Methanobacteriales). All methanogenic and hyperthermophilic Euryarchaeota also contained comparatively high abundances of the glycerol dialkyl glycerol tetraether without a cyclopentane moiety (GDGT-0). The methanoarchaeon M. stadtmanae, in addition to GDGT-0, contained GDGT core lipid structures with 1–4 cyclopentane moieties (GDGTs 1–4). We also found minor amounts of a glycerol trialkyl glycerol tetraether (GTGT) and a glycerol dialkanol diether (GDD), both of which did not contain cyclopentane moieties, as well as methylated and dimethylated GDGT-0 in all the archaea with the exception of H. volcanii. Like its GDGT distribution, M. stadtmanae showed an extended range of GDD structures with up to two cyclopentane ring systems. Our results thus indicate that both methanogenic and hyperthermophilic Euryarchaeota may represent source organisms of GTGT-0, GDDs and methylated-GDGTs in natural environments. All the latter components have recently been reported to be ubiquitously distributed in marine sediments but their biological origin is largely unknown. Moreover, a suite of unsaturated GDGTs without a cyclopentane moiety and up to four double bonds in the hyperthermophile T. kodakarensis was tentatively assigned.     

不同pH值条件下石英溶解的分子机理

对于石英-水反应体系,石英表面的Si-O-Si键的水解断裂是溶解反应过程的关键步骤。采用高级分子轨道从头计算法,研究了不同pH值下石英表面Q1（Si）位置的溶解反应动力学过程。对反应过程的势能面、过渡态、反应路径进行了量子化学计算（包括使用从头计算的分子动力学方法）,结果表明：（1）酸性条件下,H^＋连接的是石英表面末端Si-0H上的非桥氧,而非Si-O-Si键上的桥氧,这一链接反而增强了Si—O—Si键;（2）在中性和酸性条件下,石英溶解反应的速度控制步是Q1（Si）—Obr的断裂过程,而碱性条件下反应速率却由水分子靠近Q1（Si）的过程控制,它比Q1（Si）-Obr的断裂过程更慢;（3）活化能计算数据表明,碱性条件下石英溶解速率会随着pH值的增大而迅速增大;相对照的是,在酸性条件下,溶解速率与中性条件时相比变化不大,甚至还略有降低。本文纠正了一些关于石英溶解机理的长期的错误认识,比如前人错误地认为在酸性条件下首先形成Si-O（H^＋）-Si形式的复合物,然后Si-O-Si发生断裂。本研究结果表明,实际上是形成Si—O—Si-OH2^＋…H2O形式的过渡态复合物。然后Si-O-Si发生断裂。前人模型的结果与实验结果分歧,是一个长期遗留的困惑,而本文发现的断键机理模型及其计算结果,可以很好地与不同pH值下石英溶解的实验数据吻合。     

Radiocarbon analysis of halophilic microbial lipids from an Australian salt lake

Assigning accurate dates to hypersaline sediments opens important terrestrial records of local and regional paleoecologies and paleoclimatology. However, as of yet no conventional method of dating hypersaline systems has been widely adopted. Biomarker, mineralogical, and radiocarbon analyses of sediments and organic extracts from a shallow (13 cm) core from a hypersaline playa, Lake Tyrrell, southeastern Australia, produce a coherent age-depth curve beginning with modern microbial mats and extending to ~ 7500 cal yr BP. These analyses are furthermore used to identify and constrain the timing of the most recent change in hydrological regime at Lake Tyrrell, a shift from a clay deposit to the precipitation of evaporitic sands occurring at some time between ~ 4500 and 7000 yr. These analyses show the potential for widespread dating of hypersaline systems integrating the biomarker approach, reinforce the value of the radiocarbon content of biomarkers in understanding the flow of carbon in modern ecologies, and validate the temporal dimension of data provided by biomarkers when dating late Quaternary sediments.     

Oxygen isotopes in calcite grown under cave-analogue conditions

Speleothem oxygen isotopes and growth rates are valuable proxies for reconstructing climate history. There is debate, however, about the conditions that allow speleothems to grow in oxygen isotope equilibrium, and about the correct equilibrium fractionation factors. We report results from a series of carbonate growth experiments in karst-analogue conditions in the laboratory. The setup closely mimics natural processes (e.g. precipitation driven by CO₂-degassing, low ionic strength solution, thin solution film) but with a tight control on growth conditions (temperature, pCO₂, drip rate, calcite saturation index and the composition of the initial solution). Calcite is dissolved in water in a 20,000 ppmV pCO₂ environment. This solution is dripped onto glass plates (coated with seed-carbonate) in a lower pCO₂ environment (<2500 ppmV), where degassing leads to calcite growth. Experiments were performed at 7, 15, 25 and 35 °C. At each temperature, calcite was grown at three drip rates (2, 6 and 10 drips per minute) on separate plates. The mass of calcite grown in these experiments varies with temperature (T in K) and drip rate (d_r in drips min⁻¹) according to the relationship daily growth mass = 1.254 + 1.478 ∗ 10⁻⁹ ∗ e^0.0679T + (e^0.00248T − 2) ∗ (−0.779d_r² + 10.05d_r + 11.69). This relationship indicates a substantial increase of growth mass with temperature, a smaller influence of drip rate on growth mass at low temperature and a non-linear relationship between drip rate and growth mass at higher temperatures. Low temperature, fast dripping conditions are found to be the most favourable for reducing effects associated with evaporation and rapid depletion of the dissolved inorganic carbon reservoir (rapid DIC-depletion). The impact of evaporation can be large so caves with high relative humidity are also preferable for palaeoclimate reconstruction. Even allowing for the maximum offsets that may have been induced by evaporation and rapid DIC-depletion, δ¹⁸O measured in some of our experiments remain higher than those predicted by Kim and O’Neil (1997). Our new results are well explained by equilibrium at a significantly higher α_{calcite-water}, with a kinetic-isotope effect that favours ¹⁶O incorporation as growth rate increases. This scenario agrees with recent studies by [Coplen, 2007] and [Dietzel et al., 2009]. Overall, our results suggest that three separate processes cause δ¹⁸O to deviate from true isotope equilibrium in the cave environment. Two of these drive δ¹⁸O to higher values (evaporation and rapid DIC-depletion) while one drives δ¹⁸O to lower values (preferential incorporation of ¹⁶O in the solid carbonate at faster growth rates). While evaporation and DIC-depletion can be avoided in some settings, the third may be inescapable in the cave environment and means that any temperature to δ¹⁸O relationship is an approximation. The controlled conditions of the present experiments also display limitations in the use of the Hendy test to identifying equilibrium growth.     

The growth of submersed macrophytes under experimental salinity and light conditions

The growth, morphology, and chemical composition ofHydrilla verticillata, Myriophyllum spicatum, Potamogeton perfoliatus, andVallisneria americana were compared among different salinity and light conditions. Plants were grown in microcosms (1.2 m⁵) under ambient photoperiod adjusted to 50% and 8% of solar radiation. The culture solution in five pairs of tanks was gradually adjusted to salinities of 0, 2, 4, 6, and 12‰. With the exception ofH. verticillata, the aquatic macrophytes examined may be considered eurysaline species that are able to adapt to salinities one-third the strength of sea water. With increasing salinity, the inflorescence production decreased inM. spicatum andP. perfoliatus, yet asexual reproduction in the latter species by underground buds remained constant. Stem elongation increased in response to shading inM. spicatum, while shadedP. perfoliatus had higher concentrations of chlorophylla. In association with high epiphytic mass, chlorophylla concentrations in all species were greatest at 12‰. The concentration of sodium increased in all four species of aquatic macrophytes examined here, indicating that these macrophytes did not possess mechanisms to exclude this ion. The nitrogen content (Y) of the aquatic macrophytes tested increased significantly with higher sodium concentration (X), suggesting that nitrogen may be utilized in osmoregulation (Y = X × 0.288 + 6.10, r² = 0.71). The tolerance ofV. americana andP. perfoliatus to salinity was greater in our study compared to other investigations. This may be associated with experimental methodology, whereby macrophytes were subjected to more gradual rather than abrupt changes in salinity. The two macrophytes best adapted to estuarine conditions in this study by exhibiting growth up to 12‰, includingM. spicatum andV. americana, also exhibited a greater degree of response in morphology, tissue chemistry (including chlorophyll content and total nitrogen), and reproductive output in response to varying salinity and light conditions.     

Properties of iron alloys under the Earth's core conditions

The Earth's core is constituted of iron and nickel alloyed with lighter elements. In view of their affinity with the metallic phase, their relative high abundance in the solar system and their moderate volatility, a list of potential light elements have been established, including sulfur, silicon and oxygen. We will review the effects of these elements on different aspects of Fe–X high pressure phase diagrams under Earth's core conditions, such as melting temperature depression, solid–liquid partitioning during crystallization, and crystalline structure of the solid phases. Once extrapolated to the inner–outer core boundary, these petrological properties can be used to constrain the Earth's core properties.     

An empirical approach simulating evapotranspiration from groundwater under different soil water conditions

Based on the approaches of FAO24 and FMP1, a new empirical approach simulating evapotranspiration from groundwater (ET_gw) under different soil water conditions was proposed in present study. Then, through the data from volumetric lysimeter, the new approach was compared with the two approaches of FMP1, C1 and C2. The new approach gave acceptable simulation results for the treatments under different water conditions, and especially gave better results for the treatments influenced markedly by precipitation or irrigation than the other approaches. The large errors in the late stage in 2009 might be due to the effect of the early maturity of winter wheat. It also indicated that the critical soil water storages in the equation in FAO24 were not suitable to describe the relationship between ET_gw and soil water storage in root zone when water table was at or above 150?cm depth, and could be replaced with the storage corresponding to the field capacity and the steady storage. The new approach was more suitable for estimating the ET_gw under different soil water conditions comparing with C1 and C2.     

Electrochemical characterization of pyrrhotite reactivity under simulated weathering conditions

A previously reported methodology applied to evaluate the factors affecting the reactivity pyrite and pyritic samples under simulated weathering conditions is now utilized to analyze pyrrhotite reactivity at different environmental alteration stages. The methodology is based on the comparison of the voltammetric responses of the mineral obtained through the alteration process; changes in the electrochemical behavior are associated with changes in the surface state of the mineral and finally are related with changes of the mineral reactivity. The results of an initial study of the electrochemical behavior of pyrrothite before alteration suggest that its alteration involves the formation of 3 surface layers (in agreement with previous reports): (1) in immediate contact with pyrrhotite corresponding to a metal-deficient sulfide; (2) an intermediate layer corresponding to elemental S, and; (3) the most external layer, consisting of precipitates of Fe oxy-hydroxides, like goethite. The pyrrhotite reactivity seems to be controlled by the formation of oxidation product layers that coat and passivate the pyrrhotite surface, where the elemental S layer has most significance. The results confirm the advantage of incorporating cyclic voltammetry as an auxiliary method for acid rock drainage prediction, due to its demonstrated capacity to describe the factors that influence sulfide mineral reactivity which are not evaluated by other predictive techniques.     

Polar and neutral isopranyl glycerol ether lipids as biomarkers of archaea in near-surface sediments from the Nankai Trough

The molecular and carbon isotopic compositions of polar isopranyl glycerol ether lipids, which are direct indicators of viable archaea, and neutral isopranyl glycerol ether lipids, which are derived from polar lipids via hydrolysis, in near-surface sediments from a methane seep in the Nankai Trough (off central Japan) were investigated. Procedures for extracting, separating and derivatizing polar and neutral ether lipids for detection using gas chromatography were first examined with one sediment sample and a cultivated methanogen. For all sediment samples, archaeol and hydroxyarchaeol were detected in both the polar and neutral ether lipid fractions. Acyclic and cyclic biphytanes were also detected in both types of lipid fractions after treatment with HI/LiAlH₄ for ether cleavage and alkylation. The δ¹³C values of archaeol, sn-2-hydroxyarchaeol, and sn-3-hydroxyarchaeol in the sample from 0.82 m below the seafloor were lower than −100‰ relative to PDB, indicating that diverse living methanotrophic archaea are present in the seep sediments. Biphytanes released from polar ether lipids in the same sample were less depleted in δ¹³C (−71‰ to −36‰). The wide range of δ¹³C values suggests that the biphytanes were derived not only from methanotrophic but also from non-methanotrophic archaea, and that the relative contributions of the methanotrophic and non-methanotrophic archaea differed, depending on the biphytane compound. The vertical profiles and δ¹³C values of the neutral ether lipids were similar to those of the intact polar ether lipids, suggesting that neutral ether lipids derived from fossil archaea in the samples had mainly been lost by the time of sampling.     

Single-particle crushing strength under different relative humidity conditions

This paper presents a fundamental study on the effect of the relative humidity on the rockfill crushing strength. This aspect plays an important role in the mechanical behaviour of rockfill, and it is known that certain characteristics of the granular materials, such as compressibility and shear strength, depend on the confining stress, which is a function of the particles crushing. An increased interest has been observed regarding the effect of the relative humidity in the mechanical behaviour of rockfill. Unfortunately, limited research has been conducted until now regarding the study of individual particle crushing. Therefore, this paper thoroughly investigated particle crushing, by performing single-particle crushing tests on rockfill particles divided into four size ranges, under different relative humidity conditions. The experimental results reveal a considerable influence of the relative humidity in the studied rockfill particles, whose strength of the particles with the greatest dimensions in saturated conditions was reduced by half. Consistent macro-mechanical evidence demonstrates that particle’s size and relative humidity conditions depict the most important factors that influence particle crushing strength.

     

Thermo-mechanical behavior of energy pile under different climatic conditions

Acta Geotechnica - The thermal–mechanical behavior of the energy pile under three kinds of climatic conditions was investigated in this study. A small-scale floating energy pile and a...     

Spatial dynamics of soil salinity under arid and semi-arid conditions: geological and environmental implications

Salinity is a highly important problem in arid and semi-arid regions. Consequently, the analysis of soil salinity plays a crucial role in environmental sciences. Environmental variables show spatial variability and statistical tools able to analyze and describe the spatial dependence and quantify the scale and intensity of the spatial variation are needed. Moreover, the spatial prediction has special importance for agricultural transformation of the land or for environmental restoration (selection of the most appropriate species adapted to soil salinity). In this paper we propose a methodological framework based on geostatistics to model the spatial dynamics of soil salinity measurements to further analyze the case of a region in southeastern Spain.     

不同饱水条件下蚀变岩边坡稳定性分析

露天矿坑蓄水后,边坡岩体长期处于浸水状态,导致岩石抗剪强度产生弱化,对边坡的稳定性产生不利影响。为分析不同饱水条件对边坡蚀变岩抗剪强度参数的影响,对仓上金矿露天矿蚀变岩试件分别进行0、8、20、35、60、100d的饱水处理。由饱水岩样的常规三轴试验结果可得,在不同酸性环境、不同饱水时间条件下,蚀变岩的内摩擦角和粘聚力产生明显的损伤弱化,饱水时间弱化作用强于浸水溶液的酸性状态。饱水时间大于60d后,抗剪强度参数的降低幅度明显减小,饱水时间产生的弱化作用是一定的。根据不平衡推力法对划分露天边坡条块,求解边坡的安全系数,随着饱水时间的增加和浸水溶液酸性的增强,边坡的安全系数呈现显著降低趋势,边坡发生滑坡的概率逐渐增大。试验与理论研究结果可以更好的为露天矿边坡的支护设计提供重要依据。     

不同固结条件下尾矿动孔压演化规律

地震作用下尾矿坝有液化失稳的危险,尾矿动孔压的演化规律可以间接体现其液化过程。为研究尾矿动孔压的演化规律,开展了一系列的动三轴试验。结果表明：尾矿动孔压演化具有明显的阶段性,在等压固结时可用S形反正弦函数曲线描述,在偏压固结时可用J形指数函数曲线描述;尾矿材料在等压固结条件下临界孔压接近于围压,在偏压固结条件下临界孔压小于围压,且随围压及固结应力比的增大而减小,随尾矿平均粒径的增大而增大。基于极限平衡理论推导了等压固结和偏压固结条件下的临界孔隙水压力方程,从理论上阐释了试验结果所揭示的动孔压演化规律,可以为地震区上游式尾矿坝的抗震设计提供参考。     

Comparison of debris-flow volume and activity under different formation conditions

Debris flows frequently occurred in Wenchuan earthquake region from 2008 to 2010, resulting in great damage to localities and being a prolonged threat to reconstruction. Forty three events' data including debris-flow volume, sediment volume and watershed area are analyzed and compared with other debris-flow events in Eastern Italian Alps, burned areas in USA and in Taiwan. The analysis reveals that there is a strong empirical relationship between debris-flow volume and loose materials volume in the earthquake region. In addition, the relationship between debris-flow volume and watershed area in the earthquake region has a wider variation range than that in other three regions while the debris volume also appears to be larger than that in the other three regions, which implies the volume of debris flows with strong influence of earthquakes is larger than that with no such influence and it is hard to predict the post-quake volume only by the watershed area. The comparison of the maximal debris-flow erosion modulus in the Wenchuan region and in Taiwan indicates that debris flows will be very active in a short time after strong earthquake.     

Phosphorus removal efficiency from wastewater under different loading conditions using sand biofilters augmented with biochar

Treated wastewater is a valuable resource, particularly in countries facing water shortage such as Jordan. Nevertheless, excess nutrients, especially phosphorus, may have detrimental impacts on receiving waterbodies. Treated wastewater in Jordan often exceeds the recommended levels set by the Jordanian Standards for wastewater reuse and discharge. Therefore, it is important to reduce phosphorus loads to acceptable levels before discharge. Biofiltration is a low-cost technology that has shown good potential for wastewater treatment. The performance of biofilters largely depends on the media used. In this study, local sand and sand augmented with biochar prepared from the olive oil processing waste (SBC) were used as filter media for phosphorus removal from clarified secondary treated wastewater. The two media types were tested under different hydraulic and phosphorus loading conditions to simulate shock, flooding, and inundation conditions. The results showed that sand media was more effective in removing phosphorus (90.8 ± 2.6%) than sand amended with biochar (83.3 ± 3.2%). Both media showed resilience under extreme loading conditions. Although phosphorus removal efficiency was negatively affected following the extreme loading events, the observed effects were temporary. The simulated inundation event further showed that the media was able to retain the adsorbed phosphorus. Furthermore, the phosphorus concentration in the effluent remained within the prescribed discharge guidelines at all times.     

不同环境条件下堆石料变形特性的试验研究

探讨了对处于受压状态的堆石料进行干湿、冷热变化等环境因素作用下力学性质研究的试验方法。使用新研制的堆石料风化试验仪,对某种泥质粉砂岩堆石料进行了干湿循环、冷热循环以及湿冷-干热耦合变化三种环境条件下的长期变形特性试验研究,探讨了堆石料长期劣化变形的机制。试验结果表明,干湿循环试验和湿冷-干热耦合循环均可导致堆石体产生较大幅度的附加变形,其变形机制包括湿化变形、堆石体颗粒湿胀和干缩循环变形以及堆石料的劣化变形等。环境因素的循环变化可导致堆石体颗粒的劣化,堆石体劣化变形是高土石坝后期变形的重要组成部分。     

不同地应力条件下双孔爆破的数值模拟

考虑岩石介质的非均匀性,把爆破过程视为爆炸应力波和爆生气体压力共同作用的结果,基于损伤力学理论建立了岩石爆破的力学模型,并对不同地应力条件下岩石双孔爆破裂纹演化规律进行了数值模拟,分析了不同侧压力系数和埋 深对裂纹扩展规律的影响。数值模拟结果表明：①爆炸应力波导致裂纹的萌生,爆生气体压力则会使裂纹进一步扩展和贯通; ②裂纹演化过程与地应力密切相关,裂纹扩展的主方向趋于最大地应力方向;③随着埋深增加和初始地应力增大,裂纹扩展半径和裂纹区面积减小,地应力对爆破致裂的抑制作用明显。     

不同赋存环境下碳酸盐岩溶蚀过程试验模拟研究

目前,有关碳酸盐岩溶蚀过程的研究多集中在单一环境平衡状态下,不同赋存环境、微观尺度上的研究较少。鉴于此,为探讨不同赋存环境下碳酸盐岩溶蚀过程及微观变化特征,借助研制的岩溶水系统不同赋存环境下水岩相互作用模拟装置,选取典型岩溶水系统开放环境、半封闭环境与封闭环境的岩样,以CO2溶液为酸性流体介质,开展室内溶蚀模拟试验,研究岩溶水中特征组分的变化规律进行模拟实验,并从宏观和微观尺度,研究岩溶水系统不同赋存环境下的碳酸盐岩溶蚀变化特征。结果显示：不同赋存环境下Ca2+、${\rm{HCO}}_3^- $含量、饱和指数及pH值空间变化特征不同,各特征组分均呈现出随径流方向、溶蚀时间逐渐增大的趋势。不同赋存环境下,碳酸盐岩受水溶液中CO2含量的影响,在补给区的开放环境下溶蚀性最强,形成连通性较高的溶孔、溶隙。碳酸盐岩总溶蚀率均值是半开放环境的1.43倍,是封闭环境的2.70倍,半封闭与封闭环境下碳酸盐岩溶蚀后的微观结构介于孤立微孔与完全连通性溶隙之间。此外随深度的变化溶蚀量呈逐渐减弱的趋势,且浅部的变化更为明显。碳酸盐岩的溶蚀作用还受岩性控制,其随岩石中CaO/MgO比值的增大而增强。     

不同pH环境下黏土类岩崩解过程分形演化规律

红砂岩广泛分布于我国南方地区,因强度低、胶结程度差,且含有一定的膨胀性黏土矿物,此类岩石受水影响易发生崩解,从而易诱发多种地质灾害。选取湖南株洲地区的微膨胀红砂岩进行静态与扰动崩解试验,采用耐崩解性指数、标准基础熵、崩解比和分形维数等作为评价红砂岩崩解特性指标,探讨了烘干温度、试块质量、外界扰动和干湿循环作用等因素对红砂岩崩解特性的影响。研究结果表明,静态崩解方式下,相比于105 ℃和30 ℃,60 ℃的烘干温度更利于岩样崩解。而扰动崩解下,烘干温度对红砂岩崩解的影响几乎可以忽略不计。在烘干温度、试块质量等因素不变的情况下,外界扰动对红砂岩崩解特性存在显著影响。试块质量对红砂岩崩解特性存在一定的影响,试块质量越大,红砂岩崩解速率越快。干湿循环作用对红砂岩崩解的影响十分显著,随着循环次数增加,红砂岩的崩解破碎程度逐渐加大。