锶同位素在沉积学中的应用新进展

随着分析测试技术的不断提高 ,锶同位素研究取得了重大进展。近年来 ,显生宙以来海水锶同位素的变化曲线不断得以补充和修正 ,已建立起具有全球一致性、可对比的海水锶同位素变化曲线背景值 ,为锶同位素的应用奠定了基础。现在 ,锶同位素不仅在示踪岩浆及成矿热液的来源和演化、计算晚期成岩改造作用的规模和程度及流体 /岩石比等方面已趋于成熟 ,并且越来越广泛运用于海平面变化、板块活动、海底扩张、成岩演化等方面的研究。此外 ,在一些热点研究上 ,如全球变化、生态环境等方面 ,也逐渐显现出重要性     

地幔流体的稳定同位素地球化学综述

总结了 2 0年来国内外学者对地幔流体研究的成果和认识。主要包括地幔流体的性质和组成 ;地幔流体中同位素的含量、组成和赋存形式 ;同位素分馏和地幔脱气等作用对地幔组分的影响等。在不同地区和不同构造环境条件的地幔流体中 ,各种组分含量和同位素组成变化可以很大 ,从一个侧面指示地幔组分的不均一性 ,反映了不同地幔物质的形成历程不同或来自不同的地幔源区。此外 ,还讨论了目前存在的几个疑点     

A carbon-13 method for evaluating degradation of starch-based polymers

A new method for evaluating biodegradability of starch-based and certain other polymer blends uses the pre- and postexposure stable carbon isotope composition of material coupled with weight loss data to determine which components have degraded. The naturally occurring stable isotope of carbon.¹³C, is enriched in corn starch (¹³C, approx. –11) compared to petroleum-derived synthetic polymers (¹³C, approx. –32). Results on starch-synthetic polymer blends indicate that the ¹³C signatures of these blends are near-linear mixtures of their component ¹³C. Values of a ¹³C for starch-synthetic polymer blends exposed to biologically active laboratory soil and artificial seawater conditions are depleted in¹³C compared to unexposed samples, suggesting loss of the starch component. Combined with weight loss data for the exposed samples, the ¹³C values are statistically consistent with models requiring loss of the soluble component glycerin, followed by loss of starch, then petrochemical polymer, or simultaneous loss of starch and petrochemical polymer. Replicate ¹³C analyses of starch-synthetic polymer blends increase the statistical power of this relatively inexpensive, accessible technique to discriminate between degrading components.     

台风“麦德姆”福州降水δ18O特征及水汽来源分析

大气降水的氢氧同位素不仅在长时间尺度和短时间尺度上对气候环境有一定的响应,而且在极端天气事件中也响应强烈。论文基于2014年7月23—24日10号台风麦德姆登陆前后福州降水的氢氧稳定同位素分析,发现台风麦德姆降水的δ¹⁸O变化范围为-7.2‰~-15.4‰,整个降雨过程分为3个阶段：阶段1（23日3：00至23日12：00）,雨水δ¹⁸O相对偏正（加权平均值为-7.8‰）,降水开始增加,主要受台风外围环流的影响;阶段2（23日12：00至24日8：00）,雨水δ¹⁸O显著偏负（加权平均值为-13.9‰）,采样点降水量达134.8 mm,约占观测时段降水量的78%,降雨量效应明显,主要受台风云雨区影响;阶段3（24日8：00至24日17：00）,雨水δ¹⁸O偏正（加权平均值为-9.2‰）,降水减少,台风远离福州。通过降水δ¹⁸O的阶段性特征以及过量氘,结合水汽输送通量与HYSPLIT-4模拟水汽轨迹分析,确定此次降水的水汽源主要来自西北太平洋水汽通道与孟加拉湾和南海水汽通道。     

氢同位素组成及光合特征对梵净山珙桐水源的解析

珙桐(Davidia involucrata)系我国特有的单科单属植物,为第三纪孑遗种,被列为我国一级珍稀濒危植物。贵州省梵净山地区气候常年温凉湿润,在梵净山国家级自然保护区内,选取人工种植及天然分布的珙桐为研究对象,通过测定珙桐的光合参数,比较阴天和晴天珙桐光合日变化,分析生长地大气降水、土壤水分、地下水以及珙桐树枝水分氢同位素组成,研究了梵净山珙桐的水分利用状况和不同水源利用份额。结果表明,珙桐幼树为阳生植物,蒸腾速率较低,适宜在阴凉的环境生长,且温度不宜超过30℃。人工林种植和天然生长的珙桐利用大气降水分别为76%和58%。低蒸腾速率导致根部对土壤水的拉力小,因此,利用土壤深层水分的份额小。阴凉、多雨、云雾缭绕的环境为梵净山的珙桐生存提供良好的水分条件。     

用环境同位素研究灰场灰水对周围地下水的影响

应用环境同位素理论,根据燃煤火电厂灰场灰水中的氢、氧、硫同位素与天然地下水中的氢、氧、硫同位素存在的差异,建立了鉴别天然地下水和灰水的方法,并研究了灰场灰水对周围地下水的影响程度、范围和主要途径,为今后开展灰场对周围地下水影响的研究,确定地下水是否受到污染,提供了一条新的研究途径.      

南京大气气溶胶中多环芳烃源识别及污染评价

采用GC、GC-MS等方法,研究了南京市不同功能区夏、冬季大气气溶胶中多环芳烃(PAHs)的污染状况和污染来源,并对不同功能区的PAHs进行了污染评价.结果表明,南京市各功能区气溶胶中PAHs总量在19.73～497.40ng/m³之间,且冬季高于夏季,细颗粒中含量高于粗颗粒.通过一些特征标志PAHs的比值,可判断夏季各功能区的PAHs污染主要来自于汽车尾气(主要是柴油型)的排放,冬季则为汽车尾气和燃煤污染.采用苯并(a)芘(BaP)及苯并(a)芘等效致癌浓度(BaPE)来评价5个功能区气溶胶中PAHs的污染状况,夏季除交通干道超过国家标准(BaP,10ng/m³),居民区细颗粒中略超过居民区标准(BaP,5ng/m³)外,空气质量良好.而冬季各功能区PAHs基本上均严重超标.     

Protocol for using compound‐specific isotope analysis in environmental forensics

Forensic arguments must be demonstrably objective. A protocol is proposed to supply a framework to achieve this when using data from compound specific isotope analysis (CSIA) in developing forensic arguments about volatile organic carbon (VOC) contamination in groundwater. The protocol uses a “line of evidence” approach to reiteratively refine a hypothesis by testing it against each of three criteria, modifying the hypothesis if it fails or accumulating supporting evidence if it passes. The criteria are intended to organize data interpretation and to maximize use of both site data and supporting literature. Specifically, the criteria are: 1) degradation: enrichment factors and dual isotope plot (DIP) slopes; 2) hydrogeology: groundwater flow and plume shape; and 3) site history: VOC use and previous remediation work. Each of these criteria is described in detail and examples are provided for these criteria to show how each criterion can be used to identify the more plausible explanation when alternate hypotheses are presented. The protocol built upon these criteria is intended to maximize the use of supporting data and to document that support, as well as to ensure that interpretations are self consistent. The protocol is intended to be flexible and provides the framework to use exceptions as a line of evidence supporting an explanation.     

Scientific Gear as a Vector for Non-Native Species at Deep-Sea Hydrothermal Vents

The fauna of deep-sea hydrothermal vents are among the most isolated and inaccessible biological communities on Earth. Most vent sites can only be visited by subsea vehicles, which can and do move freely among these communities. Researchers assume individuals of the regionally homogeneous vent fauna are killed by the change in hydrostatic pressure the animals experience when the subsea vehicles, which collected them, rise to the surface. After an Alvin dive, we found 38 apparently healthy individuals of a vent limpet in a sample from a hydrothermally inactive area. Prompted by our identification of these specimens as Lepetodrilus gordensis, a species restricted to vents 635 km to the south of our dive site, we tested whether they were from a novel population or were contaminants from the dive made 36 h earlier. The 16S gene sequences, morphology, sex ratio, bacterial colonies, and stable isotopes uniformly indicated the specimens came from the previous dive. We cleaned the sampler, but assumed pressure changes would kill any organisms we did not remove and that the faunas of the 2 areas were nearly identical and disease-free. Our failure to completely clean the gear on the subsea vehicle meant we could have introduced the species and any diseases it carried to a novel location. Our findings suggest that the nearly inaccessible biological communities at deep-sea vents may be vulnerable to anthropogenic alteration, despite their extreme physical conditions.     

Direct measurement of denitrification activity in a Gulf coast freshwater marsh receiving diverted Mississippi River water

Wetland loss along the Louisiana Gulf coast and excessive nitrate loading into the Gulf of Mexico are interrelated environmental problems. Nitrate removal by soil denitrification activity was studied in a ponded freshwater marsh receiving diverted Mississippi River water for the purpose of reversing or slowing wetland loss. Labeled ¹⁵N-nitrate was applied at 3.8 g N m⁻² into four replicate study plots after removing above ground vegetation. Nitrogen gas (N₂) and nitrous oxide (N₂O) emissions from the plots were determined by isotope ratio mass spectrometry (IRMS). Nitrous oxide emissions were also compared with the results determined by gas chromatograph (GC). Results showed that it took 2 weeks to remove the added nitrate with N₂O emission occurring over a period of 4 d. The apparent denitrification dynamics were assumed to follow the Michaelis–Menten equation. The maximum denitrification rate and K_m value were determined as 12.6 mg N m ⁻² h⁻¹, and 6.5 mg N l⁻¹, respectively. Therefore the maximum capacity for nitrate removal by the marsh soil would be equivalent to 110 g N m⁻² yr⁻¹, with more than 30% of nitrogen gas evolved as N₂O. For typical nitrate concentrations in Mississippi River water of about 1 mg N l⁻¹, nitrate would be removed at a rate of 14.7 g N m⁻² yr⁻¹ with N₂O emission about 1.5%. A denitrification dynamic model showed that the efficiency of nitrate removal would largely depend on the water discharge rate into the ponded wetland. Higher discharge rate will result in less retention time for the water in the marsh where nitrate is denitrified.