喜马拉雅山中段北坡地表水体主要离子特征及其控制因素——以叶如藏布流域为例

为调查喜马拉雅山中段北坡地表水环境特征,2015年9月在叶如藏布流域采集24个地表水体水样并对其水化学特征分析测定,研究结果表明:(1)叶如藏布流域水化学特征存在显著空间差异.随着海拔升高,地表水体p H值、TDS值呈微弱的减小趋势.24个水样中23个水样属于淡水,1个为微咸水.(2)叶如藏布流域内地表水阳离子主要为Ca~(2+),阴离子以SO_4~(2-)为主,其次为HCO_3~-,即地表水为Ca~(2+)-SO_4~(2-)型.(3)叶如藏布流域地表水中各离子之间具有不同程度的相关性.其中Cl~-、HCO_3~-、Na~+和K~+4种离子共源性好;阳离子的来源不同,Na~+和K~+主要来源于碳酸氢盐,Ca~(2+)主要来源于硫酸盐,而Mg~(2+)的来源比较广泛.(4)叶如藏布流域大部分离子主要来源于陆地,受陆源影响从小到大排列顺序为:Na~+Mg~(2+)SO_4~(2-)Ca~(2+)K~+HCO_3~-.流域水文化学过程主要受岩石风化作用控制,特别是受到碳酸盐风化影响.以强木村为界,流域下游地区地表水化学特征受人类活动影响逐渐变大,特别是畜牧活动及人类施肥的影响.     

应用于矿山修复的高效菌株鉴定与溶岩机制:基于增强回归树分析

岩石矿区废弃地水土流失问题极度严峻,微生物对修复该问题造成的退化生境具有重要意义,为探究微生物对岩石矿区生境修复的有效性与作用机制,采用两次定向筛选,获得1株高效产铁载体及吲哚乙酸(IAA)的硅酸盐矿物分解细菌,利用16S rRNA基因序列分析鉴定该细菌为Pseudomonas protegens.通过该细菌对硅酸盐岩的岩石分解实验,测定培养液pH值,K、Al、Si这3种元素的释放量,检测岩石溶蚀的粒径变化,并分析培养液中不同有机酸,氨基酸及多糖的浓度变化,研究Pseudomonas protegens NLX-4对硅酸盐的溶蚀效果,同时引入增强回归树(boosted regression tree analysis,BRT)分析,探究其促溶机制.分析表明,该细菌通过代谢积累一定浓度的酒石酸(777 mg·L~(-1))以及多糖(8.21 g·L~(-1)),对硅酸盐岩产生释钾、释铝、脱硅的作用,从而有效促进岩石的分解.菌株Pseudomonas protegens NLX-4可作为修复废弃矿地被破坏生境的良好菌种资源.     

Petrographic carbon in ancient sediments constrains Proterozoic Era atmospheric oxygen levels

Oxygen concentration defines the chemical structure of Earth''s ecosystems while it also fuels the metabolism of aerobic organisms. As different aerobes have different oxygen requirements, the evolution of oxygen levels through time has likely impacted both environmental chemistry and the history of life. Understanding the relationship between atmospheric oxygen levels, the chemical environment, and life, however, is hampered by uncertainties in the history of oxygen levels. We report over 5,700 Raman analyses of organic matter from nine geological formations spanning in time from 742 to 1,729 Ma. We find that organic matter was effectively oxidized during weathering and little was recycled into marine sediments. Indeed, during this time interval, organic matter was as efficiently oxidized during weathering as it is now. From these observations, we constrain minimum atmospheric oxygen levels to between 2 to 24% of present levels from the late Paleoproterozoic Era into the Neoproterozoic Era. Indeed, our results reveal that eukaryote evolution, including early animal evolution, was not likely hindered by oxygen through this time interval. Our results also show that due to efficient organic recycling during weathering, carbon cycle dynamics can be assessed directly from the sediment carbon record.

The history of life has been interwoven with levels of atmospheric oxygen through much of Earth’s history. For example, aerobic life could only prosper after the evolution of cyanobacteria, which introduced oxygen into the environment (1). Furthermore, the oxygen requirements of aerobic eukaryotes, representing most eukaryotes by far, scale positively with their size (2). For example, mammals could not have evolved into a low-oxygen environment that was sufficient for eukaryotic microbes. In this way, the history of atmospheric oxygen has both constrained and permitted evolutionary developments requiring specific oxygen levels (3). However, fully understanding how oxygen has impacted the history of life requires reconstructing the history of atmospheric oxygen.Direct measurements of atmospheric oxygen concentration over time can be made from air trapped in glacial ice, with a record extending over the past 800,000 y (4), or in evaporitic salt, extending the record to potentially over 1 billion years (5–8). The oxygen record from ice is continuous and precise, but young, while the salt record is infrequent and requires careful screening to ensure samples are appropriate for analysis (9). Otherwise, the history of atmospheric oxygen is estimated from oxygen-sensitive proxies. Oxygen impacts the chemical nature, isotopic composition, and/or concentrations of redox-sensitive substances in the oceans (like molybdenum, e.g., refs. 10 and 11, or cerium, e.g., refs. 12 and 13) and the chemical weathering of redox-sensitive substances on land (like chromium and iron, e.g., refs. 14–16). Oxygen is also directly incorporated into sulfate during redox transformation (17). None of the proxies deriving from these processes represent a direct oxygen barometer, and each requires interpretation through modeling with a variety of assumptions regarding reaction kinetics, isotopic behavior during redox transformations, and the activity level of the ancient biosphere. These approaches are also generally hindered by a limited geologic record.Furthermore, these approaches do not provide a consensus view as to the history of atmospheric oxygen. For example, some approaches suggest maximum Mesoproterozoic Era (1,600 to 1,000 Ma) oxygen levels of 0.1 to 1% times present levels (PAL) (15, 18), whereas other approaches suggest minimum oxygen levels of 1 to 4% PAL (19–21). Also, different approaches using the same proxy can yield dramatically different results. For example, a kinetic approach to modeling cerium anomalies suggests atmospheric oxygen levels of ≤0.1% PAL from the Mesoproterozoic Era (1,600 to 1,000 Ma) through the latest Neoproterozoic Era (1,000 to 541 Ma) (13), while thermodynamic modeling of the cerium anomaly suggests oxygen levels of 1 to 2% PAL through the same time window (12). Resolving such divergent views is critical, as the Mesoproterozoic Era was a time of emerging eukaryotic ecosystems (22) whose evolution could have been influenced by oxygen availability.The carbon cycle is also impacted by oxygen in which the weatherability of ancient “geologic” organic matter is a function of oxygen concentration (23). Indeed, existing carbon cycle models suggest that considerable unweathered organic matter should be recycled into marine sediments when oxygen concentrations fall below 10% PAL (24). Thus, the extent of organic matter recycling in the geologic past yields a potential oxygen barometer. Therefore, we have explored with Raman spectroscopy nine geologic formations of relatively low thermal maturity spanning 1 billion years of the Proterozoic Eon (Table 1). We find that recycled organic matter is rare and that organic matter was oxidized during weathering as efficiently then as now, placing rather firm lower limits on levels of atmospheric oxygen through this time.Table 1.Number of sampling points and estimates of petrographic carbon concentrations

Sample temperatures during outdoor and laboratory weathering exposures

Effective exposure temperatures (T_eff) in Arizona were calculated from hourly or 10-min parsed irradiation data along with ambient, black panel, and sample temperatures. The T_eff represents a constant temperature that creates the same amount of photodegradation as the naturally varying temperature and provides a benchmark temperature for making lifetime predictions from accelerated laboratory exposures. The annual ambient and black panel T_eff at a Wittmann, Arizona site were 30 °C and 42 °C, respectively, assuming that the photodegradation has an activation energy (E_a) of 21 kJ/mol (5 kcal/mol). T_eff was only weakly dependent on E_a over the range of 10-40 kJ/mol (3-10 kcal/mol). Samples exposed as van sunroofs were found to have T_eff that were offset from the black panel temperatures by a constant amount for the entire year. Thus, measurements of sample and black panel need to be made for only a few weeks to determine the offset and give the annual sample T_eff if the annual black panel T_eff is known. Light-colored samples probably are better compared with the ambient temperatures. Sample temperatures in xenon arc exposures usually are higher than the outdoor T_eff, so Arrhenius temperature corrections need to be carried out to relate accelerated to outdoor exposures. Temperatures in xenon arc exposure tests often correspond more closely to maximum temperatures that samples might encounter for only a few hours per year.     

Evaluation of elemental depletion weathering rate estimation methods on acid-sensitive soils of north-eastern Alberta, Canada

Immobile element-based weathering estimation methods assume that Zr (or Ti) is an immobile element, and that weathering rates of other elements can be estimated according to the enrichment of Zr in weathered horizons relative to an unweathered parent material. This approach was used to estimate base cation weathering rates for 33 soil profiles on acid-sensitive terrain in north-eastern Alberta. Zirconium generally showed enrichment within the rooting zone, but the deepest (subsoil) samples were not always associated with the lowest Zr concentrations. Weathering rates estimated with the Zr depletion and Pedological Mass Balance (PMB) methods were generally low (ranges: 0-51 and 0-58 mmol_c m^− 2 yr^− 1, respectively); however, low base cation oxide concentrations and heterogeneity within soil profiles complicated weathering rate calculations and net base cation gains were calculated for several (six) sites. Evaluation of the Zr depletion and PMB weathering estimates against those calculated with the process-oriented PROFILE model at a subset (n = 9) of the sites indicated the estimates were poorly related, with PROFILE rates typically being higher. The effects-based emissions management strategy for acid precursors in this region requires spatial coverage of soil properties (including weathering rates) across a large area, but the apparent limitations associated with the immobile element based methods in this region: identifying representative parent soils and deriving weathering rate estimates comparable to more robust methods are arguments against their candidacy for future use.     

花岗岩风化产物中高岭石和埃洛石的粒径分布及其对土壤发生的意义

The kaolins collected from a profile of weathered granite at Yichun County, Jiangxi Province have been subjected to particle size fractionation by the conventional sedimentation method and examined by XRD, SEM and TEM. All of them exhibit a mixture phase of poorly crystallized kaolinites and halloysites (0.7 nm) occurring as the main clay minerals. Electron micrographs reveal that plate kaolinites are the principal constitution in the coarse fraction, and more tubular and curled halloysite (0.7 nm) in the fine fraction. Both of them show normal probability curves in particle size distributions. The ratios of kaolinite and halloysite (0.7 nm) in different size fractions are examined by X-ray diffraction with a series of X-ray patterns characterized by three main peaks at d(001), d(002) and d(020),varying in intensity. Therefore, an index Q_hm expressed as (I_d(001) + I_d(002))/(2×I_d(002)), is designed to indicate relative ratios of the two clay minerals in a number of mixture phases. Because kaolinite and halloysite (0.7 nm) commonly occurred, respectively, in low and medium leaching microenvironment, the index Q_hm, can be used to indicate weathering and pedogenic conditions of a weathering crust.     

红土坡地崩岗侵蚀过程与机理

崩岗是广泛发育于华南红色风化壳坡地上的各种崩陷地形，其危害性很大。按其形态特征可分为：条形崩网，叉（分支）形崩岗、瓢形崩岗、箕形崩岗和劣地崩岗等几种类型，其形态演变过程经历了前期的水蚀为主阶段，以及后期的重力侵蚀为主阶段，崩网的发生与下述几种情况有关：红土的机械组成特征，以及与水作用发生的变化；风化壳内的各种软弱结构面的存在；大暴雨触发作用以及各种地形要素的影响等。     

Contribution of Parker and Product indexes to evaluate weathering condition of Yellow Brown Forest soils in Japan

Soil weathering is recognizable through study on physico-chemical characteristics of soil. In this study, Parker, ([(Na)_a / 0.35] + [(Mg)_a / 0.9] + [(K)_a / 0.25] + [(Ca)_a / 0.7]) × 100, and Product, [SiO₂ / (TiO₂ + Fe₂O₃ + SiO₂ + Al₂O₃)] × 100, weathering indexes, originally developed for study on rocks, were tested on Yellow Brown Forest soils from two different regions in Japan. The results showed that the contribution of the mentioned indexes can be used for study on soils weathering. In other word, in a two-dimensional coordination system where the axes are Parker and Product indexes, regarding to the chemical bases of the indexes, initial and lateral products of weathering can be tracked at the same time.

Additionally, the indexes relations with soil color were studied after exposing the samples at a high temperature. Remarkable relationships between a* / b* ratio–parameters of psychometric chromaticness of color in CIE color standard system–and these two weathering indexes demonstrated that a* / b* ratio can be applied reliably to estimate the quantities of Parker and Product indexes in Yellow Brown Forest soils.     

亚热带花岗岩地区土壤矿物风化过程中盐基离子的释放特征

矿物风化过程中盐基离子释放遵从一定的化学计量关系,这种化学计量关系一般只能通过模拟实验来获取。本研究采用pH 7.0的EDTA-乙酸铵溶液将土壤中的交换性盐基离子完全洗脱出来,然后用Batch方法模拟不同pH溶液淋溶洗脱盐基和未洗脱盐基土壤,旨在消除土壤中交换性盐基离子的影响后更为准确地判断土壤矿物风化的盐基离子释放特征。结果表明:未洗脱盐基土壤的淋出液pH由3.73±0.14逐渐上升到4.23±0.06,主要原因是淋溶液中有高浓度的NH_4~+;洗脱盐基土壤矿物风化后淋出液pH从7.39±0.02逐渐下降到5.39±0.17,主要是由于土壤中可风化矿物减少。土壤交换性盐基离子会改变盐基离子释放特征、释放总量:未洗脱盐基土壤经酸雨淋溶后,各盐基离子释放均呈现急速下降后逐渐平缓的趋势,洗脱盐基土壤矿物风化后,K~+及盐基离子释放总量呈波动上升趋势,且盐基离子释放总量比未洗脱盐基土壤低。土壤交换性盐基离子的存在还会改变淋出液中的盐基离子化学计量关系:未洗脱盐基土壤的K~+︰Ca~(2+)︰Mg~(2+)︰Na+化学计量关系为11︰13︰4︰1(当量比),而洗脱盐基土壤为7︰2︰2︰1。K~+是盐基离子中风化释放量最多的,大部分K~+来自于土壤中云母的风化。因此,只有利用洗脱盐基土壤的盐基离子释放量才能准确计算矿物风化速率并获得准确的化学计量关系。土壤矿物风化作用随着淋溶液酸度增大而增强,但模拟一年降雨量的情况下,p H 3.5、4.5和5.5三种不同p H溶液对矿物风化后盐基离子的释放在实验期间没有显著性影响,较长时间后的差异性有待观察。本研究表明,可以通过预洗脱盐基土壤然后模拟酸雨淋溶的方法,观察矿物风化特征,特别是盐基离子释放的化学计量特征。