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2001 | Buch

Using Biology to Study Long-Term Environmental Change Kapitel lesen Erstes Kapitel lesen

Tracking Environmental Change Using Lake Sediments

Terrestrial, Algal, and Siliceous Indicators

herausgegeben von: John P. Smol, H. John B. Birks, William M. Last, Raymond S. Bradley, Keith Alverson

Verlag: Springer Netherlands

Buchreihe : Developments in Paleoenvironmental Research

Enthalten in: Professional Book Archive

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Inhaltsverzeichnis

Frontmatter
1. Using Biology to Study Long-Term Environmental Change
John P. Smol, H. John B. Birks, William M. Last
2. Pollen
Summary
Pollen grains are produced and dispersed as part of the plant reproductive process. They are usually spherical or elliptical and in the size range 0.01 mm to 0.1 mm. The outer walls are extremely resistant to chemical and physical attack and are ornamented and perforated in various ways. Pollen grains are found abundantly in a variety of sediment types, from which they can be concentrated and identified, using combinations of shape, size, ornamentation, and perforations. Identification is typically at the level of genus or family, but within some groups may be possible to species level.
Analysis of the pollen content of sediments, especially from peats and freshwater lakes, was introduced about a century ago, and has developed into the most widely used and applicable technique for determining past vegetation dynamics through time. Results of pollen analyses have also been used to estimate past climate and human impact on vegetation. Numerical models of pollen dispersal are becoming increasingly sophisticated and are being used, for example, to help determine the relative proportions of woodland and open vegetation in past landscapes, solely from fossil pollen data. Numerical analyses are also helping to interpret fossil pollen by identifying major directions of variation in datasets. Problems exist with taxonomy and taphonomy, but pollen analysis remains a leading technique in past environmental reconstruction.
K. D. Bennett, K. J. Willis
3. Conifer Stomata
Glen M. Macdonald
4. Plant Macrofossils
Hilary H. Birks
5. Charcoal as a Fire Proxy
Cathy Whitlock, Chris Larsen
6. Non-Pollen Palynomorphs
Bas Van Geel
7. Protozoa: Testate Amoebae
Louis Beyens, Ralf Meisterfeld
8. Diatoms
Summary
The basic requirements for diatom analysis have changed little over the last few decades in terms of sampling, slide preparation, microscopy and taxonomy but, on the other hand, there have been major improvements in our knowledge of diatom distribution and ecology and a revolution in our ability to analyse diatom data. These changes have been driven by the increasing recognition of the practical uses of diatoms as indicators of environmental change and by the development of novel numerical and computing techniques that allow diatom-environment relationships to be quantified. However, in the future and despite the application of new techniques (e.g., Vasko et al., 2000), it is unlikely that there will be significant improvements in transfer function statistics or in the range of environmental variables for which diatoms can be confidently used. Nevertheless, there is real scope for making transfer functions much more widely applicable around the world principally through web-based information systems such as EDDI (Battarbee et al., 2000), and in using the databases generated through merged training sets to explore unresolved and vastly under-researched questions of diatom biogeography. In addition, as multi-proxy approaches in palaeolimnology become common, diatomists should be able to focus more on questions of ecological response to environmental change rather than on reconstructing environmental change per se. Such a move would be especially welcome as it would herald a change from purely empirical mechanistic approaches inherent in the transfer function method to approaches that require a deeper understanding of diatom habitats, life-cycles and competitive strategies and a wider consideration of the role of diatoms in the overall functioning of aquatic ecosystems
Richard W. Battarbee, Vivienne J. Jones, Roger J. Flower, Nigel G. Cameron, Helen Bennion, Laurence Carvalho, Stephen Juggins
9. Chrysophyte Scales and Cysts
Barbara A. Zeeb, John P. Smol
10. Ebridians
Summary
Ebridians are a group of microscopic, heterotrophic marine plankters. Their siliceous endoskeletons are preserved in sedimentary deposits, and so they can be studied using the same techniques developed for other siliceous indicators, such as diatoms. They are primarily marine, and so are not frequently encountered by palaeolimnologists, but they may be common in brackish waters, such as the Baltic Sea, estuaries, and some lacustrine environments that may have had an influx of marine material. Only a few species are known to exist today. Relatively little is known about the ecological optima and tolerances of taxa, which currently hampers palaeoecological interpretations. However, ongoing research suggests they have some potential in palaeoenvironmental studies.
Atte Korhola, John P. Smol
11. Phytoliths
Summary
Phytolith analysis of lake records is an important and currently underutilized tool of paleoenvironmental reconstruction. If investigators choose to undertake the time-consuming task of constructing modern phytolith reference collections for their study regions, their efforts are likely to be rewarded because phytoliths can be useful in the identification of specific taxa. Identifications of some key indicator families and genera should be possible utilizing existing published keys and photographs.
The potential advantages of carrying out phytolith and pollen studies of a single lake record as part of a multi-proxy analysis seem to be considerable. For example, where pollen analysis is weak, as in the recognition of herbaceous and arboreal taxa of mature tropical rain forest, phytolith analysis provides significant information (Piperno, 1993). Conversely, in the recognition of woody, secondary tropical forest growth where phytolith analysis may be “silent”, pollen data come to the rescue. Phytolith studies have also significantly increased the number of taxa represented in lake profiles from the American tropical forest (e.g., Piperno, 1993), an important improvement in our attempts to decipher the history of species-rich tropical formations. Phytoliths and pollen grains are complementary avenues of paleoenvironmental reconstruction and they should be studied in tandem whenever possible.
Dolores R. Piperno
12. Freshwater Sponges
Thomas M. Frost
13. Siliceous Protozoan Plates and Scales
Summary
Siliceous protozoan plates and scales are commonly observed on diatom and chrysophyte microscopic slide preparations, however they are rarely included in paleolimnological interpretations. A major deterrent to their full exploitation is that plates can rarely be identified to the species level, and at times even generic-level identifications are tentative. This relatively coarse taxonomic resolution discourages detailed paleoeoenvironmental interpretations. Hopefully, further research on disassociated plates, as well as continued ecological studies, may fine-tune these interpretations. However, even at these relative coarse levels of data presentation and analysis, valuable paleolimnological information can still be inferred (e.g., the succession and development of bog formation in and around the lake). In samples where preservation of siliceous microfossils is poor, the use of protozoan plates becomes more important as they are often more resistant to dissolution than other siliceous proxies. A major advantage of using siliceous protozoan plates and scales is that no additional preparation procedures are needed if, for example, diatoms are already being considered in the study.
Marianne S. V. Douglas, John P. Smol
14. Biogenic Silica
Summary
The measurement of the biogenic silica (BSi) content of sediments is a chemical estimate of the siliceous microfossil abundance. Briefly, sediments are leached with a weak base, usually Na2CO3, for a period of time (2–5 hours), and aliquots withdrawn over time. The aliquots are then measured for the amount of Si extracted and a least-squares regression is made on the increase in concentration with time to separate the Si extracted from amorphous Si compounds, e.g. diatoms, sponges, etc., from that of mineral silicates. Comparison of chemical estimates of BSi with diatom microfossil point counts demonstrate that the extraction techniques provide a valid proxy for the abundance of diatom microfossils in sediments. However, the exact choice of methodology will depend upon the type of siliceous components in the sediments and the ability of the digestion solution to dissolve those components. Therefore, both the strength of the digestion solution used and the time over which subsamples are taken should be adjusted for depending upon the type of sediment used. Application of these techniques as a proxy for siliceous microfossil abundance have been instrumental in unraveling the response of aquatic systems to nutrient enrichment and has provided important information on paleoproductivity in particular in studies of paleoclimate.
Daniel J. Conley, Claire L. Schelske
15. Sedimentary Pigments
Summary
Fossil pigments often preserve in lake sediments long after the morphological remains of most algae and bacteria are lost. In principle, analyses of sedimentary carotenoids, chlorophylls, their derivatives and other lipid-soluble pigments can be used to reconstruct historical changes in primary-producer community abundance and composition, so long as biomarkers are accurately isolated, identified and quantified. This chapter summarizes a series of practical techniques in order to familarize investigators with the potential and pitfalls inherent in fossil pigment analyses. First we describe the common uses of sedimentary pigments in paleolimnology and summarize knowledge of pigment biogeochemistry and taphonomy, especially as concerns water-column processes. Second we review a series of practical procedures to collect, isolate and quantify pigments, particularly by high performance liquid chromatography. We conclude with a summary of recent advances in pigment identification using various mass spectrometric techniques.
Peter R. Leavitt, Dominic A. Hodgson
Backmatter
Metadaten
Titel
Tracking Environmental Change Using Lake Sediments
herausgegeben von
John P. Smol
H. John B. Birks
William M. Last
Raymond S. Bradley
Keith Alverson
Copyright-Jahr
2001
Verlag
Springer Netherlands
Electronic ISBN
978-0-306-47668-6
Print ISBN
978-1-4020-0681-4
DOI
https://doi.org/10.1007/0-306-47668-1