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  • 1
    Electronic Resource
    Electronic Resource
    Late and post-glacial history of meromictic Längsee (Austria), in respect to climate change and anthropogenic impact (1998)
    Springer
    Aquatic sciences 60 (1998), S. 56-88 
    Details
    ISSN: 1420-9055
    Keywords: Key words: Längsee, palaeolimnology, meromixis, climate change, anthropogenic impact.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract: Multidisciplinary palaeolimnological approaches were applied to long sediment cores from Längsee, Carinthia. Climate amelioration after deglaciation allowed the expansion of shrubs and timber-line trees and the onset of plankton and probably lake summer stratification. This phase called Pre-Bölling has an upper boundary of approx. 16 kyrs BP. The change from a steppe to a tundra-like vegetation culminated during the following less temperate, humid phase, with lower in-lake productivity (Oldest Dryas, Ia; 16-13.6 kyrs BP). At about 13.6 kyrs BP when reforestation took place, summer surface water temperature increased towards recent temperatures and hypolimnetic anoxia developed. Different anoxic levels in respect to climate change underline the dynamic type of meromixis. Levels varied, being highest during the Preboreal/Boreal, and lowered during the Atlantic towards recent levels. The contrast between low trophic status and sediments enriched in organic matter characterizes "pseudeutrophic lake stratification" before the onset of human impact. Changes in the pelagic cladoceran communities during this time seem to be related to changes in predation. Aside long-term climatic change during the Atlantic, short-term fluctuations of precipitation within climate oscillations are suggested as possible causes of erosion processes, changes in lake level and water temperature. These are indicated for the Oldest and Younger Dryas, the Boreal/Atlantic and the Subboreal/Subatlantic transitions. They most likely act as the trigger mechanism for temporary mixing and changes in redox conditions. Extensive forest clearance in the catchment during Bronze-Age settlement caused a change in sediment type and temporary nutrient enrichment. The perturbations are comparable with erosion processes during the late-glacial when climate oscillations were the only driving forces. Anthropogenic influences on the lake environment vary according to land-use type.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00001313
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  • 2
    Electronic Resource
    Electronic Resource
    Chemistry and critical loads of Alpine lakes in Canton Ticino (Southern Central Alps) (1998)
    Springer
    Aquatic sciences 60 (1998), S. 300-315 
    Details
    ISSN: 1420-9055
    Keywords: Key words: Alpine lakes, hydrochemistry, acidification, trends, critical loads.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract: We studied the chemistry of atmospheric deposition and of 55 Alpine lakes in Canton Ticino (Switzerland). The chemistry of the precipitation and the deposition of ions from the atmosphere were characterized by a marked gradient, with higher values for sulphate, nitrate, ammonium and acidity in the southernmost part of the Canton, and a halving of the values in the northern area. Results showed that most of the 55 lakes, mainly located in the north, are sensitive to acidification, 87 % and 33 % of them having alkalinity values of below 200 and 20 μeq l-1, respectively. The main processes determining water chemistry were carbonate and silicate weathering depending on the geo-lithology of the watershed, while the input of atmospheric deposition was a source of variability for nitrogen and chloride.¶A comparison between the critical and present loads of acidity to the lakes showed that a reduction of more than 50 % of the acidifying compounds would be required to keep a safe level of alkalinity in all the lakes. Ammonium plays an important role in acidification processes and must be considered in the reduction of emissions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s000270050043
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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Evidence for short-lived oscillations in the biological records from the sediments of Lago Albano (Central Italy) spanning the period ca. 28 to 17 k yr BP (2000)
    Springer
    Journal of paleolimnology 23 (2000), S. 117-127 
    Details
    ISSN: 1573-0417
    Keywords: crater lake ; late Pleistocene ; pigments ; diatoms ; ostracods ; Cladocera ; chironomids ; climatic oscillation ; Italy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract We report the results of analyses of pigments (derived from algae and photosynthetic bacteria), diatoms and invertebrate fossil remains (ostracods, cladocerans, chironomids) in two late Pleistocene sediment cores from Lago Albano, a crater lake in Central Italy. The record contains evidence for oscillations in lake biota throughout the period ca. 28 to 17 k yr BP. The earliest of these are contained in the basal 3.5 m of light olive-gray and yellowish-gray spotted muds sampled in core PALB 94-1E from 70 m water depth. The later oscillations are best represented in the more extended sediment sequence recovered from a second core site, PALB 94-6B, in 30 m water depth. The sediments at site 1E, containing the earlier oscillations (ca. 28-24 k yr BP), predate any sedimentation at the shallower site, from which we infer an initially low lake level rising to permit sediment accumulation at site 6B from ca. 24 k yr onwards. At site 6B, massive silts rich in moss remains are interbedded with laminated silts and carbonates. These sediments span the period ca. 24 to 17 k yr and are interpreted as representing, respectively, times of shallow water alternating with higher lake stands, when the lake was stratified and bottom water was stagnant. A range of mutually independent chronological constraints on the frequency and duration of the oscillations recorded in the lake biota indicate that they were aperiodic and occurred on millennial to century timescales. We interpret them as responses to climate forcing through its impact on lake levels and changing aquatic productivity. The time span they occupy, their frequency and their duration suggest that at least some of these changes may parallel both the Dansgaard-Oeschger events recorded in Greenland Ice Cores and the contemporary oscillations in North Atlantic circulation documented in marine sediment cores.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008098010283
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  • 5
    Electronic Resource
    Electronic Resource
    Modern diatom, cladocera, chironomid, and chrysophyte cyst assemblages as quantitative indicators for the reconstruction of past environmental conditions in the Alps. I. Climate (1997)
    Springer
    Journal of paleolimnology 18 (1997), S. 395-420 
    Details
    ISSN: 1573-0417
    Keywords: transfer functions ; weighted-averagingpartial-least-squares ; summer temperatures ; surfacesediments ; modern training-sets ; Switzerland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Diatom, chrysophyte cyst, benthic cladocera, planktonic cladocera, and chironomid assemblages were studied in the surface sediments of 68 small lakes along an altitudinal gradient from 300 to 2350 m in Switzerland. In addition, 43 environmental variables relating to the physical limnology, geography, catchment characteristics, climate, and water chemistry were recorded or measured for each lake. The explanatory power of each of these predictor variables for the different biological data-sets was estimated by a series of canonical correspondence analyses (CCA) and the statistical significance of each model was assessed by Monte Carlo permutation tests. A minimal set of environmental variables was found for each biological data-set by a forward-selection procedure within CCA. The unique, independent explanatory power of each set of environmental variables was estimated by a series of CCAs and partial CCAs. Inference models or transfer functions for mean summer (June, July, August) air temperature were developed for each biological data-set using weighted-averaging partial least squares or partial least squares. The final transfer functions, after data screening, have root mean squared errors of prediction, as assessed by leave-one-out cross-validation, of 1.37 °C (chironomids), 1.60 °C (benthic cladocera), 1.62 °C (diatoms), 1.77 °C (planktonic cladocera), and 2.23 °C (chrysophyte cysts).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007982008956
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  • 6
    Electronic Resource
    Electronic Resource
    Modern diatom, cladocera, chironomid, and chrysophyte cyst assemblages as quantitative indicators for the reconstruction of past environmental conditions in the Alps. II. Nutrients (1998)
    Springer
    Journal of paleolimnology 19 (1998), S. 443-463 
    Details
    ISSN: 1573-0417
    Keywords: transfer functions ; WA-PLS ; total phosphorus ; trophic state ; eutrophication ; surface sediments ; Switzerland ; diatoms ; cladocera ; chironomids ; chrysophytes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Surface sediments from 68 small lakes in the Alps and 9 well-dated sediment core samples that cover a gradient of total phosphorus (TP) concentrations of 6 to 520 μg TP l-1 were studied for diatom, chrysophyte cyst, cladocera, and chironomid assemblages. Inference models for mean circulation log10 TP were developed for diatoms, chironomids, and benthic cladocera using weighted-averaging partial least squares. After screening for outliers, the final transfer functions have coefficients of determination (r2, as assessed by cross-validation, of 0.79 (diatoms), 0.68 (chironomids), and 0.49 (benthic cladocera). Planktonic cladocera and chrysophytes show very weak relationships to TP and no TP inference models were developed for these biota. Diatoms showed the best relationship with TP, whereas the other biota all have large secondary gradients, suggesting that variables other than TP have a strong influence on their composition and abundance. Comparison with other diatom – TP inference models shows that our model has high predictive power and a low root mean squared error of prediction, as assessed by cross-validation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1007994206432
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  • 7
    Electronic Resource
    Electronic Resource
    Acidification and weathering processes in high mountain lakes in Southern Alps (1994)
    Springer
    Hydrobiologia 274 (1994), S. 75-81 
    Details
    ISSN: 1573-5117
    Keywords: acidification ; weathering ; mountain lakes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract About 200 lakes in Southern Alps (Italy and Switzerland) were studied in order to quantify their acidification. Although samplings were carried out in summer, long after the acid shock caused by snowmelt, some lakes were found to be acidic and 47% of them show alkalinity values of below 50 µeq 1-1. Losses in alkalinity (acidification levels) were evaluated using a titration model with variable F-factor. Factor analysis shows that the main factors influencing water chemistry are related to rock weathering and nitrate uptake by vegetation. In watersheds containing carbonatic rocks the weathering of calcite is responsible for the most of the alkalinity production. We therefore focused on a set of 19 low-alkalinity lakes in the Maggia Valley lying in watersheds containing mainly acidic rocks. Results show that the weathering of silicate and calcite (present in small quantities, but highly soluble) and nitrate uptake account for most of the alkalinity production. Other watershed and in-lake processes may be important in some cases, but they never account for more than 27 % of the alkalinity production in these lakes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00014629
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  • 8
    Electronic Resource
    Electronic Resource
    Reconstruction of pH by chrysophycean scales in some lakes of the Southern Alps (1994)
    Springer
    Hydrobiologia 274 (1994), S. 83-90 
    Details
    ISSN: 1573-5117
    Keywords: acidification ; Mallomonas ; paleolimnology ; scales ; sediment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Chrysophycean scales were examined in surface sediments collected from 22 high mountain lakes on the southern slope of the Central Alps, some in Italy and some in Switzerland. The study area receives slightly acidic precipitation and summer lake pH ranges between 5.2 and 8.0. In each lake chrysophycean scale assemblage was dominated by one or two species and its composition was related to lakewater pH. Five short cores were examined in low-alkalinity lakes and evidence of recent lake acidification was found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00014630
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  • 9
    Electronic Resource
    Electronic Resource
    Paleolirnnological records of carotenoids and carbonaceous particles in sediments of some lakes in Southern Alps (1994)
    Springer
    Hydrobiologia 274 (1994), S. 57-64 
    Details
    ISSN: 1573-5117
    Keywords: sediment ; core stratigraphy ; algal and bacterial development ; acidification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Stratigraphic analyses of organic carbon, organic nitrogen and algal and bacterial carotenoids in short cores of profundal sediments of four alpine lakes (Tovel, Leit, Paione superiore and Tom) were used to reconstruct their trophic history. In addition, depth distribution of carbonaceous particle concentrations provided information on lake contamination from atmospheric deposition. In three lakes (Tovel, Leit and Tom), sedimentary carotenoids unique to sulfur photosynthetic bacteria (okenone and isorenieratene) provide evidence of changes in the oxygen, light and sulfide conditions in the water column. All the lakes are oligotrophic or moderately productive, and the algal community is dominated by Chlorophyta, Pyrrhophyta and Cryptophyta. Cyanobacteria are rather poorly represented. The steep increase of carbonaceous particles in the uppermost sediment layers of all the lakes suggests that lake contamination by atmospheric transport of pollutants began in the 1940s to 1950s. These data, coupled with those from a parallel study on Chrysophycean scale-inferred pH, indicate recent acidification in those which are poorly buffered (Paione superiore and Leit).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00014627
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  • 10
    Electronic Resource
    Electronic Resource
    Interlaboratory exercises to compare analytical method performances (1996)
    Springer
    Microchimica acta 123 (1996), S. 95-102 
    Details
    ISSN: 1436-5073
    Keywords: intercomparison ; analytical methods ; rainwater
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Three intercomparison exercises on simulated rainwater were held in the period 1991–93 involving 72 to 99 laboratories in Europe and South America. The exercises required the analysis of pH, conductivity, main anions (Cl−, NO 3 − and SO 4 2− ) and main cations (Ca2+, K+, Mg2+, Na+ and NH 4 + ). The concentrations of the single ions ranged between 5 and 150 μmoll−1. Results were used to evaluate and compare the precision of the analytical methods. A general improvement in precision was observed in the course of the exercises.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01244382
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