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  • Articles  (393)
  • Engineering  (351)
  • diatoms  (42)
  • Marine Geosciences and Applied Geophysics
  • 1990-1994  (393)
  • Geosciences  (393)
  • 1
    Electronic Resource
    Electronic Resource
    Diatom responses to late Quaternary vegetation and climate change, and to deposition of two tephras in an alpine and a sub-alpine lake in Yoho National Park, British Columbia (1994)
    Springer
    Journal of paleolimnology 11 (1994), S. 173-188 
    Details
    ISSN: 1573-0417
    Keywords: Late Quaternary ; diatoms ; pollen ; climate change ; tephra ; shallow alpine and sub-alpine Iakes ; British Columbia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The late Quaternary diatom records from alpine Opabin Lake (altitude 2285 m a.s.l.) and sub-alpine Mary Lake (altitude 2054 m a.s.l.), located in Yoho National Park, British Columbia (lat. 51 ° 21′N; long. 116 ° 20′), have been analyzed, and changes in these records have been used to reconstruct lake histories. The results have also been related to independently inferred vegetation and climate changes. Following deglaciation, when both lakes were receiving high inputs of clastic materials, benthic diatom taxa dominate the records of these two shallow lakes with small species ofFragilaria being particularly prominent. During the early to mid-Holocene period, when treeline was at a higher elevation than today, the diatom flora of both lakes became more diverse with previously minor species becoming more prominent.Cyclotella radiosa occurs in cores from both Mary Lake, and much deeper, neighbouring Lake O'Hara during the warm early Holocene, and may reflect this warmer climate, a longer ice-free season than presently, and perhaps less turbid water, or its presence may reflect a subtly higher nutrient status of the lake water during this period. The Neoglacial is marked by increased amounts of sediments originating from glacial sources in Opabin Lake, which undoubtedly led to very turbid water, and by the presence ofEllerbeckia arenaria f.teres andCampylodiscus noricus v.hibernica in Opabin Lake; however, these species are absent from Mary Lake which has not been influenced by either glacial activity since the recession of the glaciers prior toc. 10 000 years BP or water originating from Opabin Lake. The impact of the two tephras during the Holocene was dramatic in terms of increased diatom production, as exemplified by the increases in diatom numbers, but there was little effect upon species composition. The diatom records and changes in the diatom:cyst ratio suggest that the chemical status of these two small, shallow lakes has changed little during the Holocene, other than after deposition of the two tephras. These results provide evidence that shallow alpine and high sub-alpine lakes are sensitive recorders of past environmental changes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00686864
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  • 2
    Electronic Resource
    Electronic Resource
    Rescaling species optima estimated by weighted averaging (1994)
    Springer
    Journal of paleolimnology 12 (1994), S. 155-162 
    Details
    ISSN: 1573-0417
    Keywords: calibration ; weighted averaging ; diatoms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The common practice of linear deshrinking in weighted averaging is known to be equivalent to a linear rescaling of the estimated species optima. In published lists of species optima, the use of rescaling is recommended, as it allows values derived from different data sets to be compared and used for new inferences, assuming that taxonomic consistency is assured. Rescaling optima is also shown to influence WA estimates of species tolerances. Non-linear rescaling is also discussed, in the form of cubical rescaling and weighted averaging-partial least squares (WA-PLS). The use of a different deshrinking equation in a small data set did lead to similar prediction errors, probably because of the small size of the data set used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00678091
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  • 3
    Electronic Resource
    Electronic Resource
    A new method for the determination of absolute abundance of diatoms and other silt-sized sedimentary particles (1994)
    Springer
    Journal of paleolimnology 12 (1994), S. 171-179 
    Details
    ISSN: 1573-0417
    Keywords: diatoms ; methods ; absolute abundance ; microfossils ; paleolimnology ; paleoceanography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The determination of absolute abundances of diatoms in paleolimnological and paleoceanographic studies is now becoming a routine step in diatom paleoecological investigations. Several distinct methods have been described for establishing absolute diatom abundance. Each of these methods has its own strengths and weaknesses. The most common weakness in diatom preparation methods is the use of aliquot subsampling from an assumed ‘well-mixed’ diatom suspension. Described here is a simple, efficient and inexpensive method that utilizes settling of diatoms through a 10 cm water column, which yields an effectively random distribution, and uses no aliquot subsampling. Only a few milligrams of sample are needed, permitting microstratigraphic analysis of, for example, individual varves. The method is shown to be both reproducible and accurate for sediments ranging in diatom concentration from less than 10 million to more than one billion diatoms per gram. Multiple slides or SEM stubs can be simultaneously prepared. The method works well for the analysis of most silt-sized microfossils or other sedimentary particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00678093
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  • 4
    Electronic Resource
    Electronic Resource
    The CASPIA project: diatoms, salt lakes, and environmental change (1994)
    Springer
    Journal of paleolimnology 12 (1994), S. 191-196 
    Details
    ISSN: 1573-0417
    Keywords: diatoms ; saline lakes ; palaeolimnology ; palaeoclimate ; transfer functions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The Climate and Salinity (CASPIA) Project is concerned with diatoms as environmental indicators in inland waters and their use in reconstructing salinity and major ion composition from fossil diatom assemblages in lake sediments. By comparing saline lake diatom floras from around the world the project aims to establish a common, harmonised approach to sample collection, diatom identification and nomenclature, and to develop techniques for numerical analysis and data storage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00678020
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  • 5
    Electronic Resource
    Electronic Resource
    Diatom-salinity relationships in 111 lakes from the Interior Plateau of British Columbia, Canada: the development of diatom-based models for paleosalinity reconstructions (1994)
    Springer
    Journal of paleolimnology 12 (1994), S. 197-221 
    Details
    ISSN: 1573-0417
    Keywords: diatoms ; paleolimnology ; paleoclimatology ; salinity ; athalassic ; British Columbia ; CCA ; transfer function
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Diatoms were identified and enumerated from the surface sediments of 111 lakes, 45 from the Kamloops region and 66 from the Cariboo/Chilcotin region, located on the southern Interior Plateau of British Columbia, Canada. This paper is an extension of another study which investigated the relationship of diatoms to salinity and ionic composition in 65 lakes from the Cariboo/Chilcotin region. The 111 lakes spanned a large gradient in salinity, ranging from fresh through hypersaline (late-summer salinity values ranged from 0.04 to 369 g l−1), and included both carbonate- and sulphate-dominated lakes with sodium and magnesium as the dominant cations. The Kamloops region had more sulphate-dominated, hypersaline lakes and fewer carbonate-rich lakes than the Cariboo/Chilcotin region. Most lakes had higher salinities in the late-summer compared to the spring. Both salinity and brine-type were important variables that could explain the different diatom assemblages present in the lakes. The majority of diatom taxa had salinity optima in the freshwater to subsaline range (〈3 g l−1), and the taxa displayed a range of both narrow and broad tolerances along the salinity gradient. Weighted-averaging regression and calibration, and maximum likelihood techniques were used to develop salinity inference models from the diatom assemblages based on their relationship to the spring, late-summer and average lakewater salinity measurements. Simple weighted-averaging (WA) models generally produced the same or lower bootstrapped RMSEs of prediction than weighted-averaging with tolerance downweighting (WA(tol)) in the two regional and the combined datasets. Weighted averaging partial least squares (WA-PLS) showed little or no improvement in the predictive abilities of the datasets, as judged by the jackknifed RMSE of prediction. In all cases, the combined dataset of 102 lakes performed better than either of the smaller regional datasets, with relatively little difference between spring, average and late-summer salinity models. The maximum likelihood models gave lower apparent RMSEs of prediction in comparison to other methods; however, independent validation of this technique using methods such as bootstrapping were not undertaken because of the computer intensive nature of such analyses. These diatom-based salinity models are now available for reconstructing salinity and climatic trends from appropriately chosen closed-basin lakes in the Interior region of British Columbia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00678021
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  • 6
    Electronic Resource
    Electronic Resource
    A Holocene paleoenvironmental history of Lake Alexandria, South Australia (1994)
    Springer
    Journal of paleolimnology 12 (1994), S. 259-268 
    Details
    ISSN: 1573-0417
    Keywords: sediments ; 14C ; 210Pb ; diatoms ; geochemical analyses ; coastal paleoenvironments ; paleolimnology ; Nodularia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract An investigation of Holocene sediments within Lake Alexandrina, a shallow coastal lake at the mouth of the Murray River, South Australia, is presented based on a multidisciplinary approach.14C and210Pb radiometric dating methods are used to establish a geochronological framework for the last 7000 yr BP, and diatoms, sand-siltclay ratios, organic carbon, phosphorus and copper concentrations are used to infer paleoenvironmental changes. The diatom assemblages indicate a change from marine-brackish to oligosaline-freshwater conditions between 7000 and 6000 yr BP, with sea-level stabilisation and continuous barrier formation across the Murray mouth. Sand pulses after 2300 yr BP document sand spit formation in the lake and the commencement of extensive lacustrine sedimentation. In the past 100 years which include the advent of European settlement in the region, the short-term210Pb-based mass accumulation rate of 0.063 g cm−2 yr−1 is greater than that of the longer-term mean14C-based rate (0.023 g cm−2 yr−1), and high concentrations of phosphorus and copper correspond to historical records of blue-green algal blooms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00678024
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  • 7
    Electronic Resource
    Electronic Resource
    Acidity of twelve northern New England (U.S.A.) lakes in recent centuries (1994)
    Springer
    Journal of paleolimnology 12 (1994), S. 103-154 
    Details
    ISSN: 1573-0417
    Keywords: acidification ; alkalization ; pH ; alkalinity ; diatoms ; sediment chemistry ; New England ; catchment effects ; land use ; logging ; acidic deposition ; air pollutants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Studies of sediment cores from 12 acidic lakes in granitic, forested and uninhabited catchments in northern New England, U.S.A. produced diatom-inferred pH (IpH) 5.2 to 5.8 and alkalinity (Ialk) −12 to 31 µeq l−1, with slowly declining values at some lakes, for one to four centuries prior to logging. Increases of IpH (Δ0.05 to 0.60) and Ialk (Δ5 to 40 µeq l−1) correlate with logging in the catchments in the early-1800s to early-1900s. Recovery to pre-logging IpH and Ialk correlates with forest succession toward conifers, and is completed in the late-1800s to mid-1900s. Beginning at 1915–1920 (4 lakes), 1930–1950 (4 lakes) and 1965–1970 (4 lakes), IpH and Ialk start decreasing below pre-logging values due to atmospheric acidic deposition, leading to respective total decreases of 0.10 to 0.45 (X=0.25) and 5 to 25 µeq l−1 (X=15). Inputs of anthropogenic Pb, Zn, V, polycyclic aromatic hydrocarbons, and soot from the atmosphere are first detectable in early- to late-1800s sediment, and Cu in late-1800s sediment, increase rapidly in the late-1800s to mid-1900s, and level off or decrease since the 1960s — partly due to emission controls. Decreasing Ca, Mn, and possibly Zn relative to other metals and normalized to organic content, and increasing flux of Fe to the lakes, indicate soil and water acidification after 1900.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00678090
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  • 8
    Electronic Resource
    Electronic Resource
    The Holocene history of West Basin Lake, Victoria, Australia; chemical changes based on fossil biota and sediment mineralogy (1994)
    Springer
    Journal of paleolimnology 12 (1994), S. 235-258 
    Details
    ISSN: 1573-0417
    Keywords: West Basin ; crater lake ; salinity ; diatoms ; ostracods ; pollen ; carbonate geochemistry ; Cyclotella caspia ; dissolution ; Australia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Analyses of diatoms, ostracods, pollen and sediment mineralogy from a 524 cm core from a stratified, hypersaline crater lake, West Basin, Victoria, has revealed clear shifts in the lake's water balance and chemistry and the region's climate over the last 10 000 years. Diatom and ostracod analyses reveal lake water salinity changes which are consistent with the conditions suitable for the precipitation of the carbonate and other minerals identified using x-ray diffraction analysis. The fluctuations in lake water balance deduced from diatom and ostracod inferred lake salinity suggest that the lake began to fill at the beginning of the Holocene and was saline and shallow. Toward the mid-Holocene the water levels rose and yet the lake remained largely saline. The late Holocene is marked by a return to more shallow but fluctuating, water conditions. Through the whole period, the regional dryland vegetation was dominated by open sclerophyll woodland. Both the lacustrine and regional environments interpreted here are consistent with those from Holocene records elsewhere in the region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00678023
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  • 9
    Electronic Resource
    Electronic Resource
    Diatom succession related to land use during the last 6000 years: a study of a small eutrophic lake in southern Sweden (1993)
    Springer
    Journal of paleolimnology 8 (1993), S. 49-69 
    Details
    ISSN: 1573-0417
    Keywords: South Sweden ; Holocene ; diatoms ; pollen ; eutrophication ; catchment history
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Diatoms, pollen, physical and magnetic analyses of the sediments have been used to reconstruct the development over the last 6000 years of Lake Bussjösjön, a small lake in southern Sweden. Stratigraphic variations in a core of more than 15 m reveal changes in diatom assemblages, which correspond closely to changes in pollen, loss-on-ignition, and magnetic measurements that are related to land use and vegetation changes in the catchment. From ca 6000 BP to 2700 BP, a forest surrounded what was then a slightly eutrophic lake. The sudden appearance of Cyclostephanos dubius (Fricke) Round and several epiphytic/epipsammic diatoms at 2700 BP coincides with deforestation of the catchment (2700 BP to 2500 BP). A change in land use from predominantly pasture to arable land from 1300 BP to 1100 BP caused a high level of soil erosion with a decrease of C. dubius and the increase of Stephanodiscus species. An increase of epiphytic/epipsammic species coincides with increased arable farming and the change from a field-rotation to a crop-rotation system, and shows not only an increase in eutrophication but also changes in water depth. The influence of the catchment through time resulted in a smaller, shallower and eutrophic to hypertrophic lake.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00210057
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  • 10
    Electronic Resource
    Electronic Resource
    The history and impact of air pollution at Čertovo Lake, southwestern Czech Republic (1993)
    Springer
    Journal of paleolimnology 8 (1993), S. 211-231 
    Details
    ISSN: 1573-0417
    Keywords: Long-term air pollution ; trace metals ; pollen ; diatoms ; Chrysophyceae ; land-use ; lake acidification ; radionuclides ; Czech Republic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract This multi-disciplinary investigation documents the longterm effects of atmospheric pollution of metals and acids on a geologically sensitive catchment in the Šumava Mountains, southwestern Czech Republic, a region with a long history of human disturbance. A 30 cm long sediment core (I) from Čertovo Lake was analyzed for natural and artifical radionuclides, metals, diatoms, chrysophytes, and pollen in sediments accumulated during the last 200 years. A second core (II), extending to 95 cm, included sediment judged to be free of atmospheric deposition of pollutants associated with the Industrial Revolution. Chronostratigraphic markers include several changes in the pollen assemblages corresponding to well-documented changes in land-use, and distinct distributions of 137Cs, 134Cs and 241Am from weapons testing and the 1986 nuclear accident at Chernobyl, Russia. These markers corroborate the 210Pb dating and, together, produce a reliable chronology extending back nearly to 1800 A.D. Stratigraphic profiles of Cu, Pb, and Zn in Core I are unlike any previously reported in the literature. Concentrations of Cu, Pb, and Zn remain generally above 100, 400, and 200 μg g-1, respectively, for the 200 years represented by Core I. These values are unusually high for sediments from a watershed with no known heavy-metal ore bodies. Accumulation rates for Cu, Pb, and Zn, which include both atmospheric and watershed contributions, are also high (ca 1, 〉 1 and 〉 1 μg cm-2 yr-1, respectively) for the same period, although the anthropogenic contribution of Zn rose from nearly zero at 1800 A.D. The Cu and Pb accumulation rates rose dramatically about 1640 A.D. Accumulation rates of anthropogenically-derived Be, a relatively abundant element in the soft coals of the region, are also elevated by about 0.01 μg cm-2 yr-1 in sediments of this period. Vanadium accumulation rates increased only since 1980 A.D., presumably along with increased consumption of oil. Diatom assemblages illustrate that the lake was acidic (pH between 4.5 and 5) through at least the past 200 years. The pH declined significantly (from ca 5 to 4) between 1960 and 1985 with a slight increase to 4.5 in the last few years. Recent diatom and chrysophyte assemblages suggest high trace metal concentrations, consistent with the present lake-water chemistry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00177857
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