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  • Articles  (9)
  • paleolimnology  (9)
  • 2000-2004  (9)
  • Geosciences  (9)
  • Technology
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  • Articles  (9)
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  • Geosciences  (9)
  • Technology
  • Biology  (10)
  • 1
    Electronic Resource
    Electronic Resource
    Changes in fossil midge (Chironomidae) assemblages in response to cultural activities in a shallow, polymictic lake (2000)
    Springer
    Journal of paleolimnology 23 (2000), S. 207-212 
    Details
    ISSN: 1573-0417
    Keywords: chironomids ; nutrient enrichment ; macrophytes ; paleolimnology ; shallow lakes ; Rideau Canal ; alternative lake equilibria ; Ontario
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Chironomid (Diptera: Chironomidae) head capsules were studied from a core of recent sediments from shallow, macrophyte-dominated Lake Opinicon, Ontario, Canada, to determine if assemblages have changed in response to lake-level changes and other watershed disturbances, including deforestation and agriculture. Our results indicate that the construction of the Rideau Canal in the early 1830s and subsequent flooding of Lake Opinicon has had the greatest impact on this system, but that even this disturbance did not greatly affect chironomid assemblages. Despite other significant cultural disturbances in the watershed, the lake sediments have recorded only minor changes in its recent history, providing support for the hypothesis of alternative lake equilibria. These results correspond well with diatom inferences of only minor changes in past lake trophic status.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008005604602
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  • 2
    Electronic Resource
    Electronic Resource
    A 6000 year water level history of Europe Lake, Wisconsin, USA (2000)
    Springer
    Journal of paleolimnology 23 (2000), S. 175-183 
    Details
    ISSN: 1573-0417
    Keywords: Late Holocene ; paleolimnology ; oxygen isotopes ; molluscs ; ostracodes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Europe Lake occupies a small, closed, basin that would have been an embayment in Lake Michigan during the high water level events in the larger lake. Cores recovered from the lake reveal late Holocene water level fluctuations in the basin that are inferred from changes in taxa and abundance of molluscs, ostracodes, magnetic susceptibility, organic carbon, and oxygen isotopes. Non-glacial, Holocene lacustrine/paludal sedimentation in this portion of the Europe Lake basin started after 6600 RCYBP and was probably initiated by a rise in the water table of the deep bedrock aquifer, during the Nipissing transgression in Lake Michigan. Isotopically light ground water from this source was probably a major contributor during this phase to the negative δ18O spikes in Valvata tricarinata and Amnicola limosa. The start of stable lacustrine conditions is marked by maximum diversity of ostracode and mollusc taxa and a shift toward much more positive δ18O values. The Europe Lake basin at this time became an embayment of Lake Michigan. This event was probably coeval with the peak of the Nipissing transgression, when the water plane reached an altitude of about 183 m. The isolation of Europe Lake from Lake Michigan started at about 2390 RCYBP and is probably due to a drop in water level in Lake Michigan and/or to isostatic uplift of the Door Peninsula. Since isolation from Lake Michigan, water levels in Europe lake have been controlled primarily by fluctuations in local precipitation, evaporation and ground water discharge.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008009805511
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  • 3
    Electronic Resource
    Electronic Resource
    Holocene environmental history of thermokarst lakes on Richards Island, Northwest Territories, Canada: Theocamoebians as paleolimnological indicators (2000)
    Springer
    Journal of paleolimnology 23 (2000), S. 261-283 
    Details
    ISSN: 1573-0417
    Keywords: thecamoebians ; paleolimnology ; Holocene ; thermokarst lakes ; Arctic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Richards Island, Northwest Territories, Canada, is characterized by thermokarst lakes which record Holocene limnological change. This study is the first report of thecamoebian assemblages and continuous annual lake water temperatures from these Arctic lakes. Ecological environments on Richards Island are influenced by a climatic gradient resulting from the contrasting influences of the cold Beaufort Sea to the north and the warm waters of the Mackenzie Delta to the east and west. This climatic gradient in turn influences modern thecamoebian assemblages, and is an indication of the complexity involved in interpreting past conditions from core material in this area. Population abundance and species diversity of thecamoebian assemblages on Richards Island are not significantly different from those reported from temperate and semi-tropical latitudes. However, certain assemblage characteristics, such as large and coarse agglutinated tests, dominance of assemblages by one or two species and low morphological variation are interpreted to be diagnostic of Arctic conditions. Thecamoebian assemblages in core material from the area indicate that the local paleolimnological conditions may have changed within the last 3 ka, and this is unrecorded in previously reported pollen data. Paleoenvironmental interpretations in a permafrost landscape have to take into account morphological instability of thermokarst lakes, which can be the cause of paleolimnological and consequently faunal change. In this area ecosystem development is clearly related to geomorphology and local climatic effects and is not exclusively controlled by regional climate change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008184522637
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  • 4
    Electronic Resource
    Electronic Resource
    Paleolimnological investigation of recent acidity changes in Sawanoike Pond, Kyoto, Japan (2000)
    Springer
    Journal of paleolimnology 23 (2000), S. 285-304 
    Details
    ISSN: 1573-0417
    Keywords: paleolimnology ; acidification ; sediment chemistry ; diatoms ; metals ; spheroidal carbonaceous particles ; pollen ; radionuclides ; Japan
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Sawanoike Pond, an artificial reservoir constructed ca. 150 yrs. ago, lies in an area geologically sensitive to acidification and contains water that is presently weakly acidic (pH 5.5; alkalinity 15 μeq 1-1). Sediments from a core obtained from the northern part and a core from the central part of the pond were analyzed for organic matter, total organic carbon, total nitrogen, natural and artificial radionuclides, pollen, diatoms, metals and spheroidal carbonaceous particles. A peaty silt layer at the bottom of the central core was replaced by a silt layer initially rich in humic substances, but became more mineral-rich near the surface. Although most of the dominant diatoms throughout the cores were acidophilous taxa, some acidobiontic species increased moderately in abundance after the middle 1960's. Diatom-inferred pH values for the northern core are relatively low before about 1930, then increase, reaching a maximum level between the 1930's and the late 1940's. They then decrease to the surface and reach minimum level during the middle 1980's. Diatom-inferred pH declined by 0.4-0.5 units in the northern core and 0.2-0.3 units in the central core since ca. 1910, when vegetation around the shore changed to a community similar to that of recent years. An increase in labile Pb, Zn, Cd and spheroidal carbonaceous particles, indicative of atmospheric deposition of fossil fuel combustion by-products, preceded the decline in inferred pH. The inferred pH decline of the pond could be an acidification due to acidic precipitation caused by fossil fuel combustion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008199830698
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  • 5
    Electronic Resource
    Electronic Resource
    Holocene lake sediment records of Arctic hydrology (2000)
    Springer
    Journal of paleolimnology 24 (2000), S. 1-13 
    Details
    ISSN: 1573-0417
    Keywords: Arctic ; Holocene ; paleohydrology ; paleolimnology ; climate change
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Although paleoclimatic research in the Arctic has most often focused on variations in temperature, the Arctic has also experienced changes in hydrologic balance. Changes in Arctic precipitation and evaporation rates affects soils, permafrost, lakes, wetlands, rivers, ice and vegetation. Changes in Arctic soils, permafrost, runoff, and vegetation can influence global climate by changing atmospheric methane and carbon dioxide concentrations, thermohaline circulation, and high latitude albedo. Documenting past variations in Arctic hydrological conditions is important for understanding Arctic climate and the potential response and role of the Arctic in regards to future climate change. Methods for reconstructing past changes in Arctic hydrology from the stratigraphic, isotopic, geochemical and fossil records of lake sediments are being developed, refined and applied in a number of regions. These records suggest that hydrological variations in the Arctic have been regionally asynchronous, reflecting the impacts of different forcing factors including orbitally controlled insolation changes, changes in geography related to coastal emergence, ocean currents, sea ice extent, and atmospheric circulation. Despite considerable progress, much work remains to be done on the development of paleohydrological proxies and their application to the Arctic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008100714795
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  • 6
    Electronic Resource
    Electronic Resource
    A paleoclimate record for the past 250,000 years from Summer Lake, Oregon, USA. 1. chronology and magnetic proxies for lake level (2000)
    Springer
    Journal of paleolimnology 24 (2000), S. 125-149 
    Details
    ISSN: 1573-0417
    Keywords: paleolimnology ; paleoclimate ; Great Basin ; environmental magnetism ; paleomagnetic secular variation ; pleistocene ; quaternary
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract This study presents the age control and environmental magnetism components of a new, late Pleistocene paleoclimate record for the Great Basin of western North America. Two new cores from the Summer Lake sub-basin of pluvial Lake Chewaucan, Oregon, USA are correlated to basin margin outcrops on the basis of tephrochronology, lithostratigraphy, sediment magnetism and paleomagnetic secular variation. Eleven tephra layers were found in the cores that correlate to tephra identified previously in the outcrop. The Olema ash was also found in one of the cores; its stratigraphic position, relative to 3 dated tephra layers, indicates that its age is 50-55 ka, somewhat younger than has been previously reported. The Summer Lake sediments are divided into deep and shallow lake lithosomes based on sedimentary features. The stratigraphic position of these lithosomes support the tephra-based correlations between the outcrop and the cores. These sediments contain a well resolved record of the Mono Lake Excursion (MLE) and an earlier paleomagnetic excursion as well as a high quality replication of the paleosecular variation immediately above the MLE. Relative sedimentation rates increased dramatically toward the depocenter during intervals of low-lake level. In contrast, during intervals of high-lake level, relative sedimentation rates were comparable along the basin axis from the basin margin to the depocenter. The magnetic mineralogy of the Summer Lake sediments is dominated by pseudo-single domain (titano)magnetite and intervals of high/low magnetite concentration coincide with lithosomes that indicate high/low lake levels. Magnetic grain size also varies in accord with bulk sediment grain size as indicated by the silt/clay ratio. To a first order, variations in magnetic parameters, especially those attributable to the concentration of magnetic minerals, correlate well with global glacial/interglacial oscillations as indicated by marine oxygen isotope stages. This relationship can be explained by increased dissolution of (titano)magnetite minerals as lake level dropped and the lake became more productive biologically. This inference is supported by a correspondence between lower concentrations of magnetite with higher levels of total organic carbon and vice-versa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008144025492
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  • 7
    Electronic Resource
    Electronic Resource
    A paleoclimate record for the past 250,000 years from Summer Lake, Oregon, USA: II. Sedimentology, paleontology and geochemistry (2000)
    Springer
    Journal of paleolimnology 24 (2000), S. 151-182 
    Details
    ISSN: 1573-0417
    Keywords: paleolimnology ; paleoclimate ; Great Basin ; ostracodes ; palynology ; Pleistocene ; Quaternary ; trace elements ; oxygen and carbon isotopes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract We have obtained a detailed paleoenvironmental record in the Summer Lake Basin, Oregon (northwestern Great Basin, US) spanning from 250ka-5 ka. This record is derived from core and outcrop sites extending from a proximal deltaic setting to near the modern depocenter. Lithostratigraphic, paleontologic (ostracodes and pollen) and geochemical indicators all provide evidence for hydroclimate and climate change over the study interval.Lithostratigraphic analysis of the Summer Lake deposits allows subdivision into a series of unconformity - or paraconformity-bound lithosomes. The unconformity and facies histories indicate that the lake underwent several major lake-level excursions through the Middle and Late Pleistocene. High stands occurred between ~200 and ~165 ka, between ~89 and 50 ka and between ~25 and 13 ka. Uppermost Pleistocene and Holocene sediments have been removed by deflation of the basin, with the exception of a thin veneer of late Holocene sediment. These high stands correspond closely with Marine Oxygen Isotope Stages 6, 4 and 2, within the margin of error associated with the Summer Lake age model. A major unconformity from ~158 ka until ~102 ka (duration varies between sites) interrupts the record at both core and outcrop sites.Lake level fluctuations, in turn are closely linked with TOC and salinity fluctuations, such that periods of lake high stands correlate with periods of relatively low productivity, fresher water and increased water inflow/evaporation ratios. Paleotemperature estimates based on palynology and geochemistry (Mg/Ca ratios in ostracodes) indicate an overall decrease in temperature from ~236 ka-165 ka, with a brief interlude of warming and drying immediately after this (prior to the major unconformity). This temperature decrease was superimposed on higher frequency variations in temperature that are not evident in the sediments deposited during the past 100 ka. Indicators disagree about temperatures immediately following the unconformity (~102-95 ka), but most suggest warmer temperatures between ~100-89 ka, followed by a rapid and dramatic cooling event. Cooler conditions persisted throughout most of the remainder of the Pleistocene at Summer Lake, with the possible exception of brief warm intervals about 27-23 ka. Paleotemperature estimates for the proximal deltaic site are more erratic than for more distal sites, indicative of short term air temperature excursions that are buffered in deeper water.Estimates of paleotemperature from Mg/Ca ratios are generally in good agreement with evidence from upland palynology. However, there is a significant discordance between the upland pollen record and lake indicators with respect to paleoprecipitation for some parts of the record. Several possibilities may explain this discordance. We favor a direct link between lake level and salinity fluctuations and climate change, but we also recognize the possibility that some of these hydroclimate changes in the Summer Lake record may have resulted from episodic drainage captures of the Chewaucan River between the Summer Lake and Lake Abert basins.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008165326401
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  • 8
    Electronic Resource
    Electronic Resource
    Short-code paleolimnological investigation of Lake Pihlajavesi in the Saimaa Lake complex, eastern Finalnd: assessment of habitat quality of an endemic and endangered seal population (2000)
    Springer
    Journal of paleolimnology 24 (2000), S. 317-329 
    Details
    ISSN: 1573-0417
    Keywords: Lake Saimaa ; paleolimnology ; diatoms ; chironomids ; Saimaa seals ; Finland
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract A short-core paleolimnological investigation was carried out to acquire knowledge of the recent history of Lake Pihlajavesi, Saimaa Lake complex, and define its natural state before cultural disturbances. In the natural state, with negligible human interference, the basin was oligotrophic and oxygen-rich. The bioproductivity in the littoral zone was low and the profundal benthic quality was good according to Wiederholm's Benthic Quality Index.Based on diatom analyses, no significant changes have taken place in the phytoplankton communities during the past decades. Sedimentary chironomid communities reveal, however, slight changes on profundal life in the Pihlajavedenselkä basin, near the main pollution sources, whereas there were no significant changes in the outer basin. Three stages could be distinguished in the pollution history of Pihlajavedenselkä: (1) 'The natural state' up until the 1960s, (2) 'the period of increasing loading' during the 1960s and 1970s, and (3) 'the recovery of the basin' during the past two decades.Untreated municipal waste water from the town of Savonlinna was partly responsible for the commencement of eutrophication in the Pihlajavedenselkä basin in the 1960s. The paper and pulp industry in Varkaus, some 40 kilometres upstream from Lake Pihlajanvesi, has also increased eutrophication, especially during the worst period of water quality in the 1960s and 1970s. More effective waste water purification has markedly reduced effluent loading and led to a general recovery of the area. Neverthless the effects of slight nutrient loading can still be seen, especially in littoral bioproductivity.Our paleolimnological data indicate that the present ecosystem will offer living conditions for the endemic Saimaa ringed seal population that are similar to those that existed prior to human disturbances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008131205100
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  • 9
    Electronic Resource
    Electronic Resource
    Use of paleolimnology to document the effect of lake shoreland development on water quality (2000)
    Springer
    Journal of paleolimnology 24 (2000), S. 369-393 
    Details
    ISSN: 1573-0417
    Keywords: paleolimnology ; shoreland development ; geochemistry ; diatoms ; eutrophication ; Wisconsin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Four Wisconsin, USA lakes were examined with paleolimnological techniques to determine the effects of shoreland development on water quality. Geochemical parameters such as aluminum, iron, manganese, phosphorus, nitrogen, and carbon were used to document watershed inputs while redox sensitive elements provided information on changes in hypolimnetic oxygen levels. Changes in the diatom community were used to assess the impacts of development upon the lakes' trophic status as well as changes in the littoral community. We assessed the relative sensitivity of high vs. low ANC lakes. The initial shoreland development, late in the 19th or early in the 20th century, involved seasonal cabins and minimal disturbance of the shoreland. This development phase had minimal impact upon the lakes compared to that during the mid- and late-twentieth century. Increased levels of iron and aluminum indicated the highest input of sediment occurred during the construction phase of converting shoreland homes from seasonal to year-round usage. Phosphorus deposition increased moderately in the high alkalinity lakes but more so in the low alkalinity lakes. In the low alkalinity stratified lake, increased levels of iron and manganese in the last decade indicated more anoxia in the hypolimnion. Phosphorus levels have also increased during this time period most likely as a result of elevated phosphorus release from the sediments. In the high alkalinity lakes, as the nutrient levels increased, diatom production initially shifted from benthic taxa of the family Fragilariaceae to metalimnetic taxa and as nutrients increased further, epilimnetic species. In the low alkalinity lakes, prior to settlement the major site of diatom prodution was the open water. Coincidental with the early shoreland development was an increase of macrophyte density as indicated by the epiphytic diatom Achnanthidium minutissimum ((Kützing) Czarnecki (= Achnanthes minutissima Kützing). The water quality in the high alkalinity lakes showed some improvement following completion of the home construction phase, especially in the lake with lower development density. The low alkalinity lakes did not show improved water quality and appear more sensitive to shoreland development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1008107706726
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