scholarly journals Varying degradation of subfossil Daphnia longispina during the past 250 years and the discovery of fossil helmet-type head shields: preliminary results

2016 ◽  
Vol 1 (1S) ◽  
Author(s):  
Jaakko Johannes Leppänen ◽  
Jan Weckström
Keyword(s):  
Environmental History ◽  
Zooplankton Community ◽  
Sediment Geochemistry ◽  
Daphnia Longispina ◽  
Explanatory Variables ◽  
Directional Change ◽  
Water Ph ◽  
Subfossil Remains ◽  
Most Significant Change ◽  
Helmet Type

<p>Zooplankton are regarded as a good indicator of environmental change, but comprehensive monitoring programs including  zooplankton are uncommon and only rarely extend over longer periods of time. A part of the zooplankton community can be reconstructed using palaeolimnological methods, yet challenges remain. For example, cladoceran subfossil remains preserve selectively in sediments. In particular, the remains of <em>Daphnia</em> spp. are known to usually exhibit poor level of preservation; the reasons for this are still unclear. In the rural Lake Kivijärvi, located in central Finland, <em>Daphnia</em> subfossil remains preserve extraordinary well and multiple fossil components are found. However, the preservation level is not uniform and exhibits directional change throughout the sediment record. To investigate the changes in <em>Daphnia</em> preservation in lake sediments, we graded caudal spines from 20 fossil sediment samples into three taphonomic groups. A dataset of sediment geochemistry, diatom-inferred lake water pH, predation indices, and the catchment land use history was used to assess the environmental history of our study lake. In Lake Kivijärvi, the most significant change in <em>Daphnia</em> preservation seems to correspond best with the historical fishing activities. Additional explanatory variables include forestry in the catchment area, and pH, which, however, had contradicting effects on the preservation of <em>Daphnia</em> remains in this study. Finally, a fossil <em>Daphnia longispina</em> helmet type head shield derived from the lake sediment is presented for the first time.</p>

scholarly journals Interactions between climate and landscape drive Holocene ecological change in a High Arctic lake on Somerset Island, Nunavut, Canada

2017 ◽  
Vol 3 (1) ◽  
pp. 17-38 ◽  
Author(s):  
Tara M. Paull ◽  
Sarah A. Finkelstein ◽  
Konrad Gajewski
Keyword(s):  
Environmental History ◽  
Lake Water ◽  
Sediment Accumulation ◽  
Base Cations ◽  
High Arctic ◽  
Ecological Change ◽  
Diatom Assemblages ◽  
Time Period ◽  
Water Ph ◽  
Somerset Island

This study presents a diatom-based analysis of the post-glacial Holocene environmental history at Lake RS29 on Somerset Island in the Canadian High Arctic. Earliest post-glacial diatom assemblages (10 200–10 000 cal yr BP) consisted mainly of small, benthic fragilarioid taxa. Poor diatom preservation in the early Holocene (~10 000–6200 cal yr BP) is associated with warm conditions, as determined by pollen data from the same core and other paleoclimate estimates from the region. Analysis of this and other sites from across the Canadian Arctic suggest that zones of poor diatom preservation or diatom absence in lake sediment records may be associated with warm conditions. After 6200 cal yr BP, acidophilic assemblages consisting of Aulacoseira spp. and a suite of periphytic taxa indicate acidification since the mid-Holocene. During this time period, cooling causing changes in lake ice phenology was likely a major driver of the reconstructed mid-Holocene pH decline. Watershed processes, including reduced fluxes of base cations as the rate of sediment accumulation slowed, may also be contributors to long-term shifts in lake water pH and associated changes in diatom assemblages. The uppermost sediments in the Lake RS29 record were characterized by abrupt declines in Aulacoseira alpigena and increases in benthic diatom taxa Cyclotella sensu lato, suggesting an increase in lake water pH and longer ice-free seasons.

Zooplankton community response to experimental acidification in boreal shield lakes with different ecological histories

2007 ◽  
Vol 64 (6) ◽  
pp. 887-898 ◽  
Author(s):  
Alison M Derry ◽  
Shelley E Arnott
Keyword(s):  
Lake Water ◽  
Biotic Interactions ◽  
Zooplankton Community ◽  
Acid Tolerance ◽  
Dispersal Limitation ◽  
Community Response ◽  
Boreal Lakes ◽  
Local Conditions ◽  
Water Ph ◽  
Zooplankton Communities

Community responses to acidification and recovery of boreal lakes are poorly understood, particularly after several years of recovered lake-water pH (pH ≥ 6.0). We tested if zooplankton communities in two circumneutral lakes with different acidification histories were adapted to historical lake-water pH with a reciprocal transplant field enclosure experiment. A second objective was to assess the influence of local environments on zooplankton survival and abundance. Differences in acid tolerance could be detected in some zooplankton among the two lakes with different acidification histories — zooplankton from acid-recovering Carlyle Lake, recovered to pH ≥ 6.0 for 6 years were more speciose and maintained higher total abundance at pH 4.8 than the community from a buffered lake. The zooplankton community in this historically acidified lake was comprised of two dominant species with acid-adaptable tolerances, Holopedium gibberum and Leptodiaptomus minutus. High establishment of transplanted zooplankton in our experiment has important implications for the recovery of zooplankton communities because it suggests that local conditions are suitable for most species in acid-recovering lakes with pH ≥ 6.0 and that other factors such as dispersal limitation and biotic interactions may be impeding recovery.

Development of apical pits in chloride cells of the gills of Pimephales promelas after chronic exposure to acid water

1983 ◽  
Vol 41 ◽  
pp. 462-463
Author(s):  
Richard L. Leino ◽  
Jon G. Anderson ◽  
J. Howard McCormick
Keyword(s):  
Confidence Interval ◽  
Chronic Exposure ◽  
Lake Superior ◽  
Pimephales Promelas ◽  
Chloride Cells ◽  
Fathead Minnows ◽  
Secondary Lamellae ◽  
Untreated Water ◽  
Water Ph ◽  
Flow Through

Groups of 12 fathead minnows were exposed for 129 days to Lake Superior water acidified (pH 5.0, 5.5, 6.0 or 6.5) with reagent grade H2SO4 by means of a multichannel toxicant system for flow-through bioassays. Untreated water (pH 7.5) had the following properties: hardness 45.3 ± 0.3 (95% confidence interval) mg/1 as CaCO3; alkalinity 42.6 ± 0.2 mg/1; Cl- 0.03 meq/1; Na+ 0.05 meq/1; K+ 0.01 meq/1; Ca2+ 0.68 meq/1; Mg2+ 0.26 meq/1; dissolved O2 5.8 ± 0.3 mg/1; free CO2 3.2 ± 0.4 mg/1; T= 24.3 ± 0.1°C. The 1st, 2nd and 3rd gills were subsequently processed for LM (methacrylate), TEM and SEM respectively.Three changes involving chloride cells were correlated with increasing acidity: 1) the appearance of apical pits (figs. 2,5 as compared to figs. 1, 3,4) in chloride cells (about 22% of the chloride cells had pits at pH 5.0); 2) increases in their numbers and 3) increases in the % of these cells in the epithelium of the secondary lamellae.

Language in mental retardation: Individual and syndromic differences, and neurogenetic variation 1Based on a keynote presentation at the Third European Conference on Psychological Theory and Research in Mental Retardation, Geneva, September 1st, 2000.

2001 ◽  
Vol 60 (3) ◽  
pp. 161-178 ◽  
Author(s):  
Jean A. Rondal
Keyword(s):  
Mental Retardation ◽  
Language Development ◽  
Oral Language ◽  
Psychological Theory ◽  
Genetic Syndromes ◽  
Explanatory Variables ◽  
Keynote Presentation ◽  
Genetic Origins ◽  
The Sixties ◽  
The Individual

Predominantly non-etiological conceptions have dominated the field of mental retardation (MR) since the discovery of the genetic etiology of Down syndrome (DS) in the sixties. However, contemporary approaches are becoming more etiologically oriented. Important differences across MR syndromes of genetic origin are being documented, particularly in the cognition and language domains, differences not explicable in terms of psychometric level, motivation, or other dimensions. This paper highlights the major difficulties observed in the oral language development of individuals with genetic syndromes of mental retardation. The extent of inter- and within-syndrome variability are evaluated. Possible brain underpinnings of the behavioural differences are envisaged. Cases of atypically favourable language development in MR individuals are also summarized and explanatory variables discussed. It is suggested that differences in brain architectures, originating in neurological development and having genetic origins, may largely explain the syndromic as well as the individual within-syndrome variability documented. Lastly, the major implications of the above points for current debates about modularity and developmental connectionism are spelt out.

A Strategy for Analysing Multiple Risk Factors with Application to Cervical Pain Syndrome

1989 ◽  
Vol 28 (01) ◽  
pp. 14-19 ◽  
Author(s):  
J. F. Dartigues ◽  
Ph. Peytour ◽  
E. Puymirat ◽  
P. Henry ◽  
M. Gagnon ◽  
...  
Keyword(s):  
Risk Factors ◽  
Low Power ◽  
Head Trauma ◽  
Pain Syndrome ◽  
Psychological Status ◽  
Confounding Factors ◽  
Cervical Pain ◽  
Extreme Form ◽  
Explanatory Variables ◽  
Multiple Risk Factors

Abstract:When studying the possible effects of several factors in a given disease, two major problems arise: (1) confounding, and (2) multiplicity of tests. Frequently, in order to cope with the problem of confounding factors, models with multiple explanatory variables are used. However, the correlation structure of the variables may be such that the corresponding tests have low power: in its extreme form this situation is coined by the term “multicollinearity”. As the problem of multiplicity is still relevant in these models, the interpretation of results is, in most cases, very hazardous. We propose a strategy - based on a tree structure of the variables - which provides a guide to the interpretation and controls the risk of erroneously rejecting null hypotheses. The strategy was applied to a study of cervical pain syndrome involving 990 subjects and 17 variables. Age, sex, head trauma, posture at work and psychological status were all found to be important risk factors.

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