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Results from AMS dating applied to insect chitin from a variety of contexts and different preservation conditions and retrieval methods are presented. Secure contexts, which include other dated organic material from different geographic locations ranging from Egypt to Greenland and different chronological periods, from Lateglacial to Medieval, have been used. In addition, insect species with different dietary requirements have been selected for dating purposes in order to provide an understanding as to whether diet plays a role in the chitin dating results. Dates from each context/site are discussed separately in the context of their stratigraphy and/or archaeology. Our research concentrates on the results from pre-treatment methods which require small quantities of chitin as these could be applied in a variety of Quaternary and archaeological contexts. The dates from carbonised and desiccated remains where no chemicals had been involved in storage fell within the range of dates from other organics or the archaeology. Although some of the dates from waterlogged contexts were successful, problems were encountered and these have been linked with long term storage in various alcohols of uncertain provenance. Whilst short term immersion in paraffin (kerosene) and alcohols during processing probably has no impact, it is recommended that chitinous material for dating be stored in acidified distilled water. Our results demonstrate the potential of chitin as a dating medium and provide a basis for its wider application. 相似文献
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T. A. Davidson C. D. Sayer M. R. Perrow M. Bramm E. Jeppesen 《Journal of Paleolimnology》2007,38(1):117-134
To assess the similarity, not only in community structure, but also in the factors that shape cladoceran assemblages, we analysed
the contemporary zooplankton populations and their sub-fossil remains in 39 shallow UK and Danish lakes. Contemporary zooplankton
populations sampled from both the lake edge and the open water in August were compared with surficial sediment assemblages.
The sedimentary assemblage data combined counts of both ephippial and chitinous remains in order to provide some representation
of Daphnia and Ceriodaphnia. A relatively large volume of sediment (>5 cm3) was analysed for ephippial remains so as to include those species best represented by the larger ephippia. Ephippia were
identified to species level in the case of Daphnia magna, and to species aggregates for other groups such as Daphnia hyalina agg., Daphnia pulex agg. and Ceriodaphnia spp. In accordance with previous work several species found in contemporary samples (copepods and the cladocerans Polyphemus pediculus, Scapholeberis mucronata and Diaphanosoma brachyurum) were absent from the surface sediments. There were extensive supporting environmental data sets for the 39 sites. It was
therefore possible to determine the factors which influenced assemblage composition for the two datasets by a combination
of constrained ordination, in this case redundancy analysis (RDA), partial RDA and Procrustes rotation. The same two factors,
zooplanktivorous fish density and submerged macrophyte abundance, were not only the main structuring forces for both data
sets, but also explained very similar amounts of the variation in the different assemblages. Thus, we conclude that the living
communities and their sedimentary remains reflect the environment they are shaped by in broadly similar ways. Calibration
of sub-fossil cladoceran assemblages against modern environmental data to reconstruct environmental change can, therefore,
validly employ principles elucidated by contemporary studies to determine the most appropriate modelling technique. 相似文献
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Use of slow-release fertilizer and biopolymers for stimulating hydrocarbon biodegradation in oil-contaminated beach sediments 总被引：4，自引：0，他引：4
Nutrient concentration and hydrocarbon bioavailability are key factors affecting biodegradation rates of oil in contaminated beach sediments. The effect of a slow-release fertilizer, Osmocote, as well as two biopolymers, chitin and chitosan, on the bioremediation of oil-spiked beach sediments was investigated using an open irrigation system over a 56-day period under laboratory conditions. Osmocote was effective in sustaining a high level of nutrients in leached sediments, as well as elevated levels of microbial activity and rates of hydrocarbon biodegradation. Chitin was more biodegradable than chitosan and gradually released nitrogen into the sediment. The addition of chitin or chitosan to the Osmocote amended sediments enhanced biodegradation rates of the alkanes relative to the presence of Osmocote alone, where chitosan was more effective than chitin due to its greater oil sorption capacity. Furthermore, chitosan significantly enhanced the biodegradation rates of all target polycyclic aromatic hydrocarbons. 相似文献
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Although environmental factors such as grain size and organic carbon content may influence the distribution of microbes in marine sediments, there has been little experimental study of the topic to date. To investigate how those sediment variables affect microbial colonisation under in situ conditions, deep‐sea sediments and artificial sediments (glass beads, sands) were incubated in the Arctic deep sea at 2500 m water depth with or without chitin, one of the most important carbon polymers in marine environments. Microbial abundance, biomass, chitobiase activity and changes in community structure were monitored after 7 days and 1 year. In control sediments without chitin addition, no significant changes in microbial abundance, biomass and activity were observed after 1 year. In the presence of chitin, however, considerable increases in these parameters were recorded in all three sediment types tested. Regardless of chitin addition, natural deep‐sea sediments were always associated with higher values of microbial abundance, biomass and activity compared with artificial sediments. Sediment type was always found to be the most significant factor explaining variation in enzymatic activity and bacterial community structure as compared to the effects of chitin amount, incubation time, and changes in cell number or biomass. Overall, this is the first in situ study that has addressed the effects of multiple factors and their interactions on abundance, biomass, activity and community structure of microbial communities in the deep Arctic Ocean. 相似文献
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Several techniques are available to examine the isotopic composition of historic lake waters, providing data that can subsequently
be used to examine environmental changes. A recently-developed technique is the stable oxygen isotope analysis of subfossil
chironomid (Diptera: Chironomidae) head capsules (mostly chitin) preserved in lake sediments. This technique involves a high
Temperature Conversion Elemental Analyzer (TC/EA), which has been a relatively recent addition to the suite of online peripherals
for analyzing the stable isotopic composition of organic samples. The highly precise and accurate 18O/16O and D/H measurements obtainable using the TC/EA with samples in the microgram range make this instrumentation suitable for
studying geochemical and biological processes. Preparation of organic samples for isotopic analysis typically requires first
weighing each sample into silver/tin capsules. These capsules can introduce oxygen and hydrogen contamination (a “blank effect”),
which is especially problematic for analysis of small organic samples (e.g. less than 100 μg). Here we tested tin and silver
capsules from two manufacturers and a range of sizes to assess contamination to small organic samples on the TC/EA. We also
assessed how a method for cleaning silver capsules affected our analysis of commercial chitin. In general, capsules made of
silver have less detectible oxygen than those made of tin, and capsules from the two manufacturers varied in their detectible
oxygen. There was no detectable H contamination from silver capsules. In addition to our empirical findings, we present a
model demonstrating the influence that contaminant oxygen can have on the δ18O of small organic samples. Sample mass becomes an important issue for such analyses. In light of our findings, we recommend
a minimum sample mass ≥50 μg (approximately 120 whole chironomid head capsules) on a TC/EA-IRMS (Deltaplus XP system). Finally, we present a detailed protocol for preparing and transferring chironomid head capsules into silver capsules
that minimizes the influence of contaminant oxygen. This protocol provides the paleo-community with another potential method
for reconstructing paleoenvironments. 相似文献
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