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71.
Ziel dieser Untersuchung war die Beantwortung der Frage, in wieweit mit Hilfe der Messung der Radioaktivit?t von Umweltisotopen
eine Aussage zum Alter von Einzelproben des Gew?ssersediments m?glich ist. Voraussetzung ist, da? die Sedimente n?herungsweisegleichf?rmig abgelagerte Schwebstoffe sind, und sei es auch nur in gewissen Zeitabschnitten (Zeitfenstern). Proben chaotisch wechselnder Sedimentation und Erosion
sind z.Zt. nicht beurteilbar im Hinblick auf ihr Alter.
Folgerung aus den Messungen von Umweltisotopen: Die Einzelproben werden mitReferenzschwebstoffen der 0 bis 38 μm Feinkornfraktion hinsichtlich ihrer Radioaktivit?tskonzentration verglichen. Dann werden sie grob in vier Altersklassen
eingeteilt:
相似文献
– | -überwiegend aktuelle Sedimente (seit etwa dem letzten Hochwasser) |
– | -überwiegende Anteile um das Jahr 1986 |
– | -überwiegende Anteile um die 60er Jahre |
– | -überwiegende Anteile vor 1955 (und Gew?sserboden) |
72.
Pathway of CH4 formation in anoxic rice field soil and rice roots determined by 13C-stable isotope fractionation 总被引:1,自引:0,他引:1
In anoxic rice fields methane is produced by either reduction of CO2 or cleavage of acetate. We measured the delta 13C-values of CH4 and CO2, acetate and organic carbon during time course experiments with anoxic methanogenic soil and root samples and used these values to calculate the fractions of CH4 (and acetate) produced from CO2 reduction. Comparison with radiotracer and/or inhibitor studies constrained the kinetic fractionation factors used for calculation. The fractionation factors for the conversion of CO2 to CH4 and of acetate to CH4 were on the order of alpha = 1.07 (epsilon = -70%) and epsilon > or = - 20%, respectively. The pathway of CH4 production changed with time of anoxic incubation. Anoxic slurries of rice field soil first produced CH4 predominantly (>50%) from CO2, then predominantly (>80%) from acetate and finally (after about one month) according to the theoretically expected ratio (33% CO2 and 67% acetate). Anoxic rice roots, on the other hand, initially produced CH4 exclusively from CO2, followed by contribution of acetate of about 40-60%. Rice roots also produced acetate that partially originated (< or = 1 30%) from reduction of CO2 as determined by calculation of isotopic fractionation using fractionation factors from the literature. The results demonstrate that there is quite some variability in pathways of CH4 production, and also indicate that isotopic fractionation factors may be different in different habitats and change with time. 相似文献
73.
Combined effects of lead, salinity and temperature on the embryonic development of the mussel Mytilus galloprovincialis Lmk. were studied under laboratory conditions. The basic experimental design was a 4x6 factorial experiment using 4 lead concentrations (100, 250, 500 and 1000 ppb Pb2+) and 6 salinity levels (from 25 to 37.5 with 2.5 intervals). These factorial designs were carried out at three constant temperatures (150, 17.50 and 20°C). The statistical analysis indicated that salinity changes have more effect on the embryonic development than temperature. Optimal development was observed at 34.8 and 15.6°C, which is in accordance with observations in the field. The effect of lead was mininal in optimal salinity and temperature conditions. The deleterious effect of lead on the embryonic development was especially conspicuous at 20°C. Since in nature spawning occurs at temperatures inferior to 20°C, lead will probably not drastically decrease the potential recruitment of mussel spat in the littoral populations of the northern Adriatic Sea, where the salinity of the water is relatively stable. Under experimental conditions, lead caused a delay or inhibition of the embryonic development with the occurrence of a large number of abnormal larvae. 相似文献
74.
Monoterpenes are structurally diverse natural compounds that play an essential role in the chemical ecology of a wide array
of organisms. A key enzyme in monoterpene biosynthesis is geranyl diphosphate synthase (GPPS). GPPS is an isoprenyl diphosphate
synthase that catalyzes a single electrophilic condensation reaction between dimethylallyl diphosphate (C5) and isopentenyl diphosphate (C5) to produce geranyl diphosphate (GDP; C10). GDP is the universal precursor to all monoterpenes. Subsequently, monoterpene synthases are responsible for the transformation
of GDP to a variety of acyclic, monocyclic, and bicyclic monoterpene products. In pheromone-producing male Ips pini bark beetles (Coleoptera: Scolytidae), the acyclic monoterpene myrcene is required for the production of the major aggregation
pheromone component, ipsdienol. Here, we report monoterpene synthase activity associated with GPPS of I. pini. Enzyme assays were performed on recombinant GPPS to determine the presence of monoterpene synthase activity, and the reaction
products were analyzed by coupled gas chromatography–mass spectrometry. The functionally expressed recombinant enzyme produced
both GDP and myrcene, making GPPS of I. pini a bifunctional enzyme. This unique insect isoprenyl diphosphate synthase possesses the functional plasticity that is characteristic
of terpene biosynthetic enzymes of plants, contributing toward the current understanding of product specificity of the isoprenoid
pathway. 相似文献
75.
Hunkeler D Abe Y Broholm MM Jeannottat S Westergaard C Jacobsen CS Aravena R Bjerg PL 《Journal of contaminant hydrology》2011,119(1-4):69-79
The fate of chlorinated ethenes in a large contaminant plume originating from a tetrachloroethene (PCE) source in a sandy aquifer in Denmark was investigated using novel methods including compound-specific carbon and chlorine isotope analysis and quantitative real-time polymerase chain reaction (qPCR) methods targeting Dehaloccocoides sp. and vcrA genes. Redox conditions were characterized as well based on concentrations of dissolved redox sensitive compounds and sulfur isotopes in SO(4)(2-). In the first 400 m downgradient of the source, the plume was confined to the upper 20 m of the aquifer. Further downgradient it widened in vertical direction due to diverging groundwater flow reaching a depth of up to 50 m. As the plume dipped downward and moved away from the source, O(2) and NO(3)(-) decreased to below detection levels, while dissolved Fe(2+) and SO(4)(2-) increased above detectable concentrations, likely due to pyrite oxidation as confirmed by the depleted sulfur isotope signature of SO(4)(2-). In the same zone, PCE and trichloroethene (TCE) disappeared and cis-1,2-dichloroethene (cDCE) became the dominant chlorinated ethene. PCE and TCE were likely transformed by reductive dechlorination rather than abiotic reduction by pyrite as indicated by the formation of cDCE and stable carbon isotope data. TCE and cDCE showed carbon isotope trends typical for reductive dechlorination with an initial depletion of (13)C in the daughter products followed by an enrichment of (13)C as degradation proceeded. At 1000 m downgradient of the source, cDCE was the dominant chlorinated ethene and had reached the source δ(13)C value confirming that cDCE was not affected by abiotic or biotic degradation. Further downgradient (up to 1900 m), cDCE became enriched in (13)C by up to 8 ‰ demonstrating its further transformation while vinylchloride (VC) concentrations remained low (<1 μg/L) and ethene was not observed. The correlated shift of carbon and chlorine isotope ratios of cDCE by 8 and 3.9 ‰, respectively, the detection of Dehaloccocides sp genes, and strongly reducing conditions in this zone provide strong evidence for reductive dechlorination of cDCE. The significant enrichment of (13)C in VC indicates that VC was transformed further, although the mechanism could not be determined. The transformation of cDCE was the rate limiting step as no accumulation of VC occurred. In summary, the study demonstrates that carbon-chlorine isotope analysis and qPCR combined with traditional approaches can be used to gain detailed insight into the processes that control the fate of chlorinated ethenes in large scale plumes. 相似文献
76.
Gallagher FJ Pechmann I Holzapfel C Grabosky J 《Environmental pollution (Barking, Essex : 1987)》2011,159(5):1159-1166
Recognizing the growing importance of both structure (maintenance of biodiversity) and function (fostering natural cycles) of urban ecologies, we examine coarse scale (herbaceous, shrub and forest) beta guild trajectory in an urban brownfield. The distribution of the pioneer forest assemblage dominated by Betula populifolia Marsh. and Populus spp. could be correlated positively with total soil metal load (arsenic, cadmium, chromium, copper, lead, zinc, lead and vanadium),whereas herbaceous and shrub guilds were negatively correlated. Distinct assemblage development trajectories above and below a critical soil metal threshold are demonstrated. In addition, we postulate that the translocation of metals into the plant tissue of several dominant species may provide a positive feedback loop, maintaining relatively high concentrations of metals in the litter and soil. Therefore assembly theory, which allows for the development of alternate stable states, may provide a better model for the establishment of restoration objectives on degraded urban sites. 相似文献
77.
Spurgeon DJ Lawlor A Hooper HL Wadsworth R Svendsen C Thomas LD Ellis JK Bundy JG Keun HC Jarup L 《Environmental pollution (Barking, Essex : 1987)》2011,159(12):3425-3432
The relationship of measured or modelled Cd concentrations in soil, house dust and available to plants with human urinary Cd concentrations were assessed in a population living around a Cd/Pb/Zn smelter in the UK. Modelled air concentrations explained 35% of soil Cd variation indicating the smelter contributed to soil Cd loads. Multi-variate analysis confirmed a significant role of biological and life-style factors in determining urinary Cd levels. Significant correlations of urinary Cd with soil, house dust and modelled plant available Cd concentrations were not, however, found. Potential reasons for the absence of clear relationships include limited environmental contact in urban populations; the role of undefined factors in determining exposure; and the limited spatial scope of the survey which did not sample from the full pollution gradient. Further, the absence of any significant relationship indicates that environmental measures provide limited advantage over atmospheric model outputs for first stage human exposure assessment. 相似文献
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