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Christian Bigler Evastina Grahn Isabelle Larocque Adam Jeziorski Roland Hall 《Journal of Paleolimnology》2003,29(4):509-510
Volume Contents
Volume contents 相似文献2.
Jennifer L. Barrow Adam Jeziorski Kathleen M. Rühland Kristopher R. Hadley John P. Smol 《Journal of Paleolimnology》2014,52(1-2):61-75
In recent decades, softwater lakes across Canada have experienced a wide array of anthropogenic influences, with acidification and climate warming of particular concern. Here, we compare modern and pre-industrial sedimentary diatom assemblages from 36 softwater lakes located on the Canadian Shield in south-central Ontario to determine whether lake acidification or reduced calcium availability was the main stressor responsible for recent declines in Ca-sensitive cladoceran taxa. Regional surveys of south-central Ontario water chemistry have identified the pH recovery of many formerly acidified lakes, and our fossil diatom-inferred pH analyses indicate that modern lakewater pH in the 36 study lakes is similar to (or higher than) pre-industrial levels, with diatom assemblages from both time periods dominated by taxa with similar pH preferences. In addition, modern diatom assemblages compared to pre-industrial assemblages contained higher relative abundances of planktonic diatom taxa (e.g. Asterionella formosa and the Discostella stelligera complex) and lower relative abundances of heavily silicified diatoms (e.g. Aulacoseira taxa) and benthic fragilarioid taxa. These taxonomic shifts are consistent with warming-induced changes in lake properties including a longer ice-free period, decreased wind speed and/or increased thermal stability. We conclude that recent changes observed within the cladoceran assemblages of these lakes are not a response to acidification, but are likely a consequence of Ca declines. In addition, our data suggest that regional climate warming is now responsible for the diatom changes observed in this region. 相似文献
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Adam Jeziorski Andrew M. Paterson Norman D. Yan John P. Smol 《Journal of Paleolimnology》2008,39(3):421-425
Despite reductions in atmospheric sulphur emissions and the resulting decline in acidic deposition, many lakes on the Canadian
Shield that have experienced acidification are either recovering at a rate slower than expected or not recovering at all.
This lack of recovery is believed to be partly the consequence of the depletion of exchangeable base cations (principally
calcium, Ca) from watershed soils. Although the implications of reduced Ca availability for biological communities remain
poorly understood, the effects on crustacean zooplankton populations may be severe, as Ca is the primary structural component
of the crustacean zooplankton exoskeleton. Because the daphniid resting egg is protected by a modified portion of the exoskeleton
(ephippia) and because these ephippia are well preserved in lake sediments, we investigated whether inter-specific differences
in Ca content are recoverable from Daphnia ephippia. However, using two methods, we did not find a recoverable Ca signal in the ephippia, indicating that future efforts
should be focused upon sedimentary taxonomic assemblage differences, not differences in ephippial Ca levels. 相似文献
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Christian Bigler Evastina Grahn Isabelle Larocque Adam Jeziorski Roland Hall 《Journal of Paleolimnology》2003,29(1):13-29
We assess Holocene environmental change at alpine Lake Njulla(68°22N, 18°42E, 999 m a.s.l.) innorthernmost Sweden using sedimentary remains of chironomid head capsules anddiatoms. We apply regional calibration sets to quantitatively reconstruct meanJuly air temperature (using chironomids and diatoms) and lake-water pH(using diatoms). Both chironomids and diatoms infer highest temperatures(1.7–2.3°C above present-day estimates, includinga correction for glacio-isostatic land up-lift by0.6°C) during the early Holocene (c.9,500–8,500 cal. yrs BP). Diatoms suggest a decreasing lake-waterpH trend (c. 0.6 pH units) since the early Holocene. Usingdetrended canonical correspondence analysis (DCCA), we compare the Holocenedevelopment of diatom communities in Lake Njulla with four other nearby lakes(Lake 850, Lake Tibetanus, Vuoskkujávri, Vuolep Njakajaure) locatedalong an altitudinal gradient. All five lakes show similar initial DCCA scoresafter deglaciation, suggesting that similar environmental processes such ashigh erosion rates and low light availability associated with high summertemperature appear to have regulated the diatom community, favouring highabundances of Fragilaria species. Subsequently, the diatomassemblages develop in a directional manner, but timing and scale ofdevelopment differ substantially between lakes. This is attributed primarily todifferences in the local geology, which is controlling the lake-waterpH. Imposed on the basic geological setting, site-specific processessuch as vegetation development, climate, hydrological setting andin-lake processes appear to control lake development in northernSweden. 相似文献
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Jeziorski Adam Nelligan Clare Corrigan Dara Meyer-Jacob Carsten Paterson Andrew M. Smol John P. 《Journal of Paleolimnology》2021,66(4):371-387
Journal of Paleolimnology - Peninsula Lake, Ontario, Canada, is a Precambrian Shield lake that has experienced many environmental stressors since European settlement of the watershed in the... 相似文献
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Joshua Kurek Jennifer B. Korosi Adam Jeziorski John P. Smol 《Journal of Paleolimnology》2010,44(2):603-612
The effects of low counts on assemblage inferences in paleolimnological investigations have been examined for many biological
proxies, but not yet for Cladocera. Established guidelines leading to the determination of an adequate, minimum count are
absent with respect to sampling cladoceran remains from lake sediments. Using simulated subsamples derived from observed assemblages
of considerably higher counts, we investigated the effect of counting effort on three principal characteristics of an assemblage:
richness, number of new taxa encountered, and the absolute differences in relative abundances of dominant taxa. Results from
six lakes located within diverse ecological regions (i.e. Subarctic, Canadian Shield, Acadian Forest) suggest that a minimum
of between 70 and 100 individuals is satisfactory to characterize most assemblages. Doubling counting effort from 100 to 200
individuals leads to only modest gains in subsample relatedness to the observed assemblage. Greater counting effort may be
necessary when the primary interest is in presence-absence or distributional data, or when abundances of ecologically relevant
taxa are exceptionally low. 相似文献
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Aqueous calcium (Ca) concentrations are currently decreasing in many softwater lakes on the Boreal Shield. As the onset of these declines often pre-date direct monitoring programs, indirect techniques are required to examine the impacts of reduced Ca availability on aquatic communities with relatively high Ca demands such as the Cladocera (Class: Branchiopoda). Among the Cladocera, the family Daphniidae has been identified as a taxonomic group potentially useful for inferring past Ca concentrations due to their high Ca demands and preservation in lake sediments. Here, we use a ??top/bottom?? paleolimnological analysis to compare present-day cladoceran communities preserved in the surface sediments of 36 softwater lakes in south-central Ontario, Canada, which are potentially vulnerable to Ca decline (i.e. small headwater systems with present-day lakewater [Ca]?<?3?mg?L?1), with the communities present in lake sediments deposited prior to the onset of regional acid deposition. To distinguish the potential impacts of lake acidification from those of Ca availability (as Ca and pH trends are strongly correlated in this region), the study lakes were chosen to be evenly distributed about a present-day lakewater pH of 6 and Ca concentration of 1.5?mg?L?1 (threshold values). Despite the importance of pH as an explanatory variable for the present-day assemblages, a comparison of the sedimentary remains from the two time periods indicate there have been large declines since pre-industrial times in the relative abundances of Ca-rich Daphnia spp. (particularly of the Daphnia longispina species complex), regardless of present-day pH, accompanied by increases in the Ca-poor species Holopedium glacialis. These observations suggest that recent declines in Ca concentration may have already fallen below baseline conditions, with marked implications for ecosystem function due to the differential responses among cladoceran taxa. 相似文献
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