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  • 1
    Electronic Resource
    Electronic Resource
    Lake diatom response to recent Arctic warming in Finnish Lapland (2002)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 8 (2002), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: High-resolution palaeolimnological data from a number of remote and nonpolluted lakes in Finnish Lapland reveal a distinct change in diatom assemblages. This parallels the post-19th century Arctic warming detected by examination of long-term instrumental series, historical records of ice cover and tree-ring measurements. The change was predominantly from benthos to plankton and affected the overall diatom species richness. A particularly strong relationship was found between spring temperatures and compositional structure of diatoms. The change is irrespective of the lake type and catchment characteristics, and is reflected by several other biological indicators, such as chrysophytes and zooplankton, suggesting that entire lake ecosystems have been affected. No corresponding change in the diatom-inferred lake-water pH was observed; hence, atmospheric fallout of acid substances cannot have been the driving force for the observed biological change. The mechanism behind the diatom response is unclear, but it may be related to decreased ice-cover duration, prolonged growing season and increased thermal stability. We postulate that 19th century Arctic warming, rather than acidic or other anthropogenic deposition, is responsible for the recent ecological changes in these high latitude lakes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2002.00463.x
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  • 2
    Electronic Resource
    Electronic Resource
    Surface sediment Chironomidae (Insecta: Diptera) distributions along an ecotonal transect in subarctic Fennoscandia: developing a tool for palaeotemperature reconstructions (1997)
    Springer
    Journal of paleolimnology 18 (1997), S. 45-59 
    Details
    ISSN: 1573-0417
    Keywords: Chironomidae ; Chaoborus ; treeline ; lakewater temperature ; CCA ; weighted averaging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract We used multivariate statistical techniques to analyse the distributions of surface sediment chironomid assemblages with respect to surface-water temperature, and an additional set of 27 environmental variables, in 30 freshwater lakes of northern Fennoscandia. Our study transect spans boreal coniferous forest to subarctic tundra and includes a steep temperature gradient. Canonical correspondence analysis (CCA) with forward selection and associated Monte Carlo permutation tests revealed that there were statistically significant (P〈0.05) relationships between chironomid distributions and two environmental variables, namely lakewater temperature and maximum lake depth. A constrained CCA with temperature as the only predictor variable suggested that the relationship between lakewater temperature and chironomid composition was sufficiently robust for developing a weighted-averaging (WA) based quantitative inference model that will allow palaeotemperature reconstructions using subfossil chironomid remains preserved in lake sediments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007906609155
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  • 3
    Electronic Resource
    Electronic Resource
    Reply to Janna Turkia's comment of Virkanen et al. (1997) (1998)
    Springer
    Journal of paleolimnology 20 (1998), S. 104-104 
    Details
    ISSN: 1573-0417
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007965012080
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  • 4
    Electronic Resource
    Electronic Resource
    Recent diatom assemblage changes in subarctic Lake Saanajärvi, NW Finnish Lapland, and their paleoenvironmental implications (1998)
    Springer
    Journal of paleolimnology 20 (1998), S. 205-215 
    Details
    ISSN: 1573-0417
    Keywords: subarctic lakes ; diatoms ; paleolimnology ; climate change ; Cyclotella ; Finnish Lapland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Diatoms were analysed from a 30-cm long sediment core obtained from remote subarctic Lake Saanaärvi (69°03′N, 20°52′E) in order to trace possible changes in the lake. Diatom assemblages were relatively constant throughout the core, except in the top 4–5 cm (approx 1850 A.D.) where relative frequencies of Aulacoseira italica subsp. subarctica, A. lirata var. biseriata, Cyclotella comensis and C. glomerata increased markedly. No significant trends were observed in the weighted averaging (WA) reconstructed pH values. Several hypotheses, including (i) airborne pollution, (ii) climatic change, and (iii) catchment disturbances have been put forth to explain the recent changes in diatom assemblages. The diatom change coincides with a marked increase in mean annual temperature that has been documented in the area since the termination of the Little Ice Age. Our evidence favours climate change as the main causative mechanism for the observed diatom compositional changes, although other explanations cannot be ruled out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007953515620
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  • 5
    Electronic Resource
    Electronic Resource
    Observations of Ebria tripartita (Schumann) Lemmermann in Baltic sediments (1999)
    Springer
    Journal of paleolimnology 21 (1999), S. 1-8 
    Details
    ISSN: 1573-0417
    Keywords: Ebria triparita ; Baltic Sea ; sediments ; reconstruction ; dissolution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Sediment finds of Ebria tripartita (Schumann) Lemmermann in the Baltic Sea are reported and light and electron micrographs of the remains of the taxon are presented. Stratigraphic ebriid analysis performed on two sediment cores (one from the deep Gotland Basin and the other from the shallow Töölö bay, central Helsinki) provided clear indications of frequency changes of E. tripartita. These changes are apparently related to the variations in trophic status and salinity, yet competition and degree of preservation may also have contributed to the distributions. Due to identification problems, the species may actually be more common in the sediment material of the Baltic Sea than has hitherto been recognized. E. tripartita may have a significant potential as an indicator species in paleolimnological research as more information is gathered about its present-day ecological requirements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008019504122
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  • 6
    Electronic Resource
    Electronic Resource
    Cladoceran and chironomid assemblages as qualitative indicators of water depth in subarctic Fennoscandian lakes (2000)
    Springer
    Journal of paleolimnology 24 (2000), S. 43-54 
    Details
    ISSN: 1573-0417
    Keywords: cladocerans ; chironomids ; palaeohydrological proxies ; lake levels ; calibration models ; subarctic lakes ; northern Fennoscandia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The relationship between surface-sediment cladoceran and chironomid communities to lake depth was analysed in 53 lakes distributed across timberline in northern Fennoscandia using multivariate statistical approaches. The study sites are small and bathymerically simple, with water depth ranging from 0.85-27.0 m (mean 6.36 m). Maximum lake depth was the most important factor in explaining the cladoceran distributions and the second most important factor in explaining the chironomid distributions in these subarctic lakes, as assessed on the basis of a series of constrained RDAs, Monte Carlo permutation tests, and variance partitioning. Quantitative inference models for maximum lake depth were created for both groups of animals. Well-performing calibration functions for predicting lake depth were obtained in each case using linear partial least squares (PLS) regression and calibration, weighted averaging (WA) with an 'inverse' deshrinking regression, and weighted averaging partial least squares (WA-PLS). Quantitative reconstructions of lake level fluctuations should be possible from cladoceran and chironomid core data with a root mean squared error of prediction (RMSEP), as estimated by jack-knifing, of about 1.6-3.0 m.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008165732542
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  • 7
    Electronic Resource
    Electronic Resource
    Recent environmental changes in a naturally acidic rocky lake in southern Finland, as reflected in its sediment geochemistry and biostratigraphy (1997)
    Springer
    Journal of paleolimnology 17 (1997), S. 191-213 
    Details
    ISSN: 1573-0417
    Keywords: acidification ; geochemistry ; atmospheric loading ; diatoms ; in situ alkalinity ; forest fires
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Paleolimnological methods are combined with statistical multivariate analyses (PCA and CCA) to study the effects of local environmental disturbances and changes in loading of atmospheric origin on water acidity and the physiochemical properties of the sediment in a small, naturally acidic rocky lake in southern Finland. The pH of the lake as calculated from the diatom flora increased by 0.9 pH units as a consequence of a forest fire in the catchment area at the turn of the last century, and the changes in the diatom assemblages point to an increase in dys(eu)trophy and turbulence. In terms of element influx (in µg cm-2 yr-1), the effects of the fire are seen in a slight increase in the accumulation of lithophilous elements. Diatom-inferred pH values decline upwards in the sediment, but do not regain the level recorded before the fire. This is attributed to reactions between Fe3+ and S, which has partly accumulated from the air as SO2-, producing internal alkalinity. Accumulation rates of many elements increase markedly after the 1960s, an effect for Al, Mg, Na, P and Zn may be connected mainly with the enhanced accumulation of dry matter, whereas the accumulation of K, Ni, Pb, Ti and V in surface sediment are obviously related to atmospheric loading. Measured accumulation rates of Cd and Cu are lower than the calculated values especially in the surface sediment, possibly because of diagenetic changes. Accumulation of Ca and Mn decreases towards the surface on account of acidification of anthropogenic origin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007919922330
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  • 8
    Electronic Resource
    Electronic Resource
    A Bayesian multinomial Gaussian response model for organism-based environmental reconstruction (2000)
    Springer
    Journal of paleolimnology 24 (2000), S. 243-250 
    Details
    ISSN: 1573-0417
    Keywords: environmental reconstruction ; regression analysis ; Bayesian modeling ; chironomids ; Bum ; Bummer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract We present a Bayesian hierarchical multinomial regression model (Bummer) for organism-based quantitative paleoenvironmental reconstruction. The model is based on the classical (direct) approach to calibration and on careful statistical environmental modeling that takes account of statistical dependencies among species. We compare our Bayesian model Bummer to seven other methods, including the widely used weighted averaging (WA) techniques and our previous Bayesian model Bum. The methods are evaluated on a surface-sediment chironomid training set of 62 subarctic lakes in northern Fennoscandia by comparing the cross-validation prediction statistics of different models. Bummer outperformed other methods, yielding the smallest prediction error, the smallest bias, and the largest correlation coefficient. We conclude that the promising performance of our Bayesian multinomial Gaussian response model is due to the following reasons: (i) the uncertainty concerning site specific latent variables is taken into consideration; (ii) ecological background knowledge is embedded to the model description; (iii) the species compositions are considered as a whole; and (iv) reconstruction is based on the classical approach to calibration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008180500301
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  • 9
    Electronic Resource
    Electronic Resource
    Diatoms as quantitative indicators of pH and water temperature in subarctic Fennoscandian lakes (1997)
    Springer
    Hydrobiologia 347 (1997), S. 171-184 
    Details
    ISSN: 1573-5117
    Keywords: diatoms ; pH ; water temperature ; weightedaveraging ; inference model ; subarctic ; Fennoscandia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Weighted averaging (WA) regression and calibrationbased optima and tolerances of lakewater pH andtemperature are presented for diatoms in ecologicallysensitive, subarctic Fennoscandian lakes. The studysites are mostly small, simple, oligotrophic,low-conductivity lakes with a pH range from 5.0 to7.7 and a temperature range (after data screening)from 9.3 to 15.0 °C. Experiments with inverse andclassical deshrinking, with or without tolerancedownweighting, were used to identify the bestcalibration functions. The model estimates wereadjusted by jackknifing procedures. WA by inversedeshrinking and with tolerance downweighting performedbest for pH prediction, whereas simple WA wasmarginally superior for predicting water temperature.The established pH model is accurate to within± 0.39 H units, and the temperature model towithin ± 0.88 degrees Celcius. Fifteen diatom taxawere identified as potential indicator species for pHand three for temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003091923476
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  • 10
    Electronic Resource
    Electronic Resource
    Marked early 20th century pollution and the subsequent recovery of Töölö Bay, central Helsinki, as indicated by subfossil diatom assemblage changes (1996)
    Springer
    Hydrobiologia 341 (1996), S. 169-179 
    Details
    ISSN: 1573-5117
    Keywords: urban palaeolimnology ; diatoms ; pollution ; recovery ; restoration ; Helsinki
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Diatoms were used to infer the trophic status history of a Baltic Sea inlet, Töölö Bay, located in central Helsinki. The waterbody received partially treated sewage effluent from the local sewage works and from a sugar factory from ca. 1890 until ca. 1960 when primary sewage treatment and the diversion of the effluent began. The increased nutrient input is shown in the diatom stratigraphy in the form of a rapid increase in planktonic eutrophic forms particularly Cyclotella cf. meneghiniana, and a reciprocal destruction of the periphytic flora. The overall diversity decreased markedly at this time. There is a gradual recovery of the system to the predisturbance conditions from 1960 onwards, as indicated by the re-emergence of the mesotrophic periphytic diatoms. Detrended correspondence analysis (DCA) is used to summarize the responses of the diatom assemblages to changing nutrient concentrations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00018120
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