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481.
成都市河道表层沉积物(淤泥)铅污染特征   总被引:5,自引:0,他引:5  
文章分析了成都市河道(沙河、府河、南河)表层沉积物淤泥铅含量特及铅同位素丰度比的测定数据,结果表明铅含量变化范围是21.1~279 mg/kg,平均值为65.3 mg/kg,中值55.2 mg/kg,统计标准差65.03,变异系数为0.996,说明河道表层沉积物含量变化大。端元物质的铅同位素组成特征是燃煤的放射成因铅高于燃油,可以示踪和鉴别成都市环境铅的污染来源。三河淤泥铅同位素组成均大多落在崔家店热电厂降尘和华能热电厂燃煤飞灰的范围,沙河、府河有少数几个样品点落在燃煤铅(崔家店热电厂燃煤降尘)和柴油铅之间,其铅的来源可能是两者的混合。  相似文献   
482.
伊乐藻和氮循环菌技术对太湖氮素吸收和反硝化的影响   总被引:1,自引:7,他引:1  
刘丹丹  李正魁  叶忠香  张万广 《环境科学》2014,35(10):3764-3768
从太湖梅梁湾采集无扰动泥芯样,分别添加固定化氮循环细菌、水生植物伊乐藻建立室内微宇宙,模拟生态修复,探讨不同修复处理下,硝氮的去除机制.采用15N标记结合同位素配对技术测定了各生态模拟柱中的反硝化速率和植物吸收速率.结果表明,不同处理的实验柱反硝化速率差异明显,同时添加了水生植物和固定化氮循环细菌的实验柱反硝化速率最高,为99.35μmol·(m2·h)-1,植物氮吸收速率为36.55μg·(m2·h)-1.沉水植物伊乐藻在自身吸收氮素的同时也提高了耦合硝化反硝化的作用.与植物吸收相比,反硝化过程是主要的氮去除途径.沉水植物与固定化氮循环菌组合生态修复技术促进了湖泊水体氮素的脱除,起到了净化作用.  相似文献   
483.
针对燃煤电厂锅炉烟气实现低排放的目标,阐述了燃煤电厂采用袋式除尘的有效性和趋势性;通过几个典型工程案例的对比分析,阐明了燃煤电厂袋式除尘的先进性、可靠性及其实现"恒稳低排"的可行性,并就采用袋式除尘实现燃煤锅炉烟尘"恒稳低排"的技术措施提出了一些思考和建议。  相似文献   
484.
Real world observations suggest that social norms of cooperation can be effective in overcoming social dilemmas such as the joint management of a common pool resource—but also that they can be subject to slow erosion and sudden collapse. We show that these patterns of erosion and collapse emerge endogenously in a model of a closed community harvesting a renewable natural resource in which individual agents face the temptation to overexploit the resource, while a cooperative harvesting norm spreads through the community via interpersonal relations. We analyze under what circumstances small changes in key parameters (including the size of the community, and the rate of technological progress) trigger catastrophic transitions from relatively high levels of cooperation to widespread norm violation—causing the social–ecological system to collapse.  相似文献   
485.
Chemical and isotopic investigations indicate that the recharge source for the groundwater in the Tahta district, adjacent to the Nile, is mainly from the Nile water seeping from irrigation channels. The water's chemical type is sodium bicarbonate, with values of oxygen-18 and deuterium close to that of Nile water. Another minor source of recharge to the far west of the Nile bank is palaeowater. This water's chemical type is sodium sulphate and sodium chloride. The change of water quality in some groundwater samples could be due to the extensive use of fertilizers to improve soil characteristics in new reclamation projects. In addition, these wells are slightly depleted in oxygen-18, deuterium and tritium. Recommendations for the periodic monitoring of groundwater quality for proper use are given.  相似文献   
486.
选择黔中清镇市王家寨小流域内不同石漠化植物群落,通过分析测定喀斯特小生境内5种常见木本植物,鼠李、火棘、烟管荚蒾、圆果化香和云贵鹅耳枥与其潜在水源稳定性氢氧同位素组成,研究植物水分来源特征,并通过线性混合模型确定水源贡献比,探讨喀斯特小生境植物水分利用对石漠化过程的适应与响应。结果表明:多数情况下,研究区不同小生境内各植物种在雨季同时利用土壤水和表层岩溶带水,对土壤水的利用比例大于表层岩溶带水。各植物种对表层岩溶带水的利用比例随着石漠化的进行而减小。常绿灌木火棘、鼠李和烟管荚蒾在轻度、无石漠化样地同时利用土壤水和表层岩溶带水,但在中、强度石漠化则多利用土壤水,落叶小乔木圆果化香和云贵鹅耳枥在无石漠化同时利用土壤水和表层岩溶带水,而在轻度石漠化样地仅利用土壤水,这跟不同样地植被类型、干扰方式、土壤情况及裂隙发育等不同有关。  相似文献   
487.
We present a comment about "Ozone risk assessment for plants: central role of metabolism-dependent changes in reducing power" by Dizengremel, Le Thiec, Bagard, and Jolivet. As tools for summarizing plant O(3) sensitivity in simple indices, Dizengremel et al. suggest: reducing power, as antioxidant regeneration through the Halliwell/Asada cycle requires NADPH from the photosynthetic light reaction; Rubisco/PEPc ratio, as an index of the energy balance between anabolic and catabolic reactions; and water-use efficiency as a time-integrated approximation of the carbon gain to stomatal O(3) uptake ratio. The scientific background is solid, and simple enough (although expensive) to be translated into modelling and routine use. In the last decade, several approaches have been developed, mostly by using photosynthesis as a metric of defence. All these approaches should be experimentally tested in different and realistic conditions, before the results are transferred to the field and used in effective O(3) flux modelling and assessment.  相似文献   
488.
In situ biodegradation of benzene, toluene, and xylenes in a petroleum hydrocarbon contaminated aquifer near Fairbanks, Alaska was assessed using carbon and hydrogen compound specific isotope analysis (CSIA) of benzene and toluene and analysis of signature metabolites for toluene (benzylsuccinate) and xylenes (methylbenzylsuccinates). Carbon and hydrogen isotope ratios of benzene were between -25.9 per thousand and -26.8 per thousand for delta13C and -119 per thousand and -136 per thousand for delta2H, suggesting that biodegradation of benzene is unlikely at this site. However, biodegradation of both xylenes and toluene were documented in this subarctic aquifer. Biodegradation of xylenes was indicated by the presence of methylbenzylsuccinates with concentrations of 17-50 microg/L in three wells. Anaerobic toluene biodegradation was also indicated by benzylsuccinate concentrations of 10-49 microg/L in the three wells with the highest toluene concentrations (1500-5000 microg/L toluene). Since benzylsuccinate typically accounts for a very small fraction of the toluene present in groundwater (generally <1 mol%), the signature metabolite approach works best at higher toluene concentrations when it is not constrained by detection limits. In wells with lower toluene concentrations (410-640 microg/L), carbon and hydrogen isotopic values were enriched by up to approximately 2 per thousand for delta13C and approximately 70 per thousand for delta2H. This evidence of isotopic fractionation verifies the effects of biodegradation in these low concentration wells where metabolites may already be below detection limits. The combined use of signature metabolite and CSIA data is particularly valuable given the challenge of verifying biodegradation in subarctic environments where degradation rates are typically much slower than in temperate environments.  相似文献   
489.
The assessment of biodegradation in contaminated aquifers has become an issue of increasing importance in the recent years. To some extent, this can be related to the acceptance of intrinsic bioremediation or monitored natural attenuation as a means to manage contaminated sites. Among the few existing methods to detect biodegradation in the subsurface, stable isotope fractionation analysis (SIFA) is one of the most promising approaches which is pronounced by the drastically increasing number of applications. This review covers the recent laboratory and field studies assessing biodegradation of contaminants via stable isotope analysis. Stable isotope enrichment factors have been found that vary from no fractionation for dioxygenase reactions converting aromatic hydrocarbons over moderate fractionation by monooxygenase reactions (epsilon=-3 per thousand) and some anaerobic studies on microbial degradation of aromatic hydrocarbons (epsilon=-1.7 per thousand) to larger fractionations by anaerobic dehalogenation reactions of chlorinated solvents (epsilon=between -5 per thousand and -30 per thousand). The different isotope enrichment factors can be related to the respective biochemical reactions. Based on that knowledge, we discuss under what circumstances SIFA can be used for a qualitative or even a quantitative assessment of biodegradation in the environment. In a steadily increasing number of cases, it was possible to explain biodegradation processes in the field based on isotope enrichment factors obtained from laboratory experiments with pure cultures and measured isotope values from the field. The review will focus on the aerobic and anaerobic degradation of aromatic hydrocarbons and chlorinated solvents as the major contaminants of groundwater. Advances in the instrumental development for stable isotope analysis are only mentioned if it is important for the understanding of the application.  相似文献   
490.
The purpose of our study was to test the hypothesis that dissolved gaseous mercury (DGM) production and evasion is directly proportional to the loading rate of inorganic mercury [Hg(II)] to aquatic ecosystems. We simulated different rates of atmospheric mercury deposition in 10-m diameter mesocosms in a boreal lake by adding multiple additions of Hg(II) enriched with a stable mercury isotope (202Hg). We measured DGM concentrations in surface waters and estimated evasion rates using the thin-film gas exchange model and mass transfer coefficients derived from sulfur hexafluoride (SF6) additions. The additions of Hg(II) stimulated DGM production, indicating that newly added Hg(II) was highly reactive. Concentrations of DGM derived from the experimental Hg(II) additions (“spike DGM”) were directly proportional to the rate of Hg(II) loading to the mesocosms. Spike DGM concentrations averaged 0.15, 0.48 and 0.94 ng l−1 in mesocosms loaded at 7.1, 14.2, and 35.5 μg Hg m−2 yr−1, respectively. The evasion rates of spike DGM from these mesocosms averaged 4.2, 17.2, and 22.3 ng m−2 h−1, respectively. The percentage of Hg(II) added to the mesocosms that was lost to the atmosphere was substantial (33–59% over 8 weeks) and was unrelated to the rate of Hg(II) loading. We conclude that changes in atmospheric mercury deposition to aquatic ecosystems will not change the relative proportion of mercury recycled to the atmosphere.  相似文献   
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