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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 9 (1979), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. Constraints upon the vertical distribution of a population of Ceratium hirundinella, in a productive English lake during the summer stratification of 1976, are considered. They are interpreted in relation to vertical gradients of temperature, dissolved oxygen and irradiance, and to rates of photosynthesis and respiration measured as oxygen exchange in long- and short-term exposures. The motile cells tended to aggregate at an intermediate depth in the epilimnion, associated with a relative irradiance level of c. 10% or c. 140 μ einsteins m−2s−1 as measured with a horizontal PAR sensor. Higher irradiances, and conditions below the oxycline, were apparently unfavourable, but the intervening layer was severely compressed at the height of summer stratification, when concentrations of inorganic nitrogen were also minimal. Thus the population apparently passed through a critical period, at which the cellular content of chlorophyll-α was much reduced. The preferred irradiance level in the lake corresponded to that at which measured rates of net photosynthesis were maximal. Increased rates of oxygen evolution were measured at higher irradiances in very short exposures; this behaviour may be of importance to cells experiencing vertical movement in nature.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 48 (2003), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY 1. Unialgal cultures of three species common in the freshwater phytoplankton were used to test limitation of specific growth rate and final yield in defined media of low K+ concentration (range 〈0.3–6 μmol L−1 or mmol m−3).2. Growth rate of the diatom Asterionella formosa was independent of K+ concentration above 0.7 μmol L−1. Final yield was dependent on initial concentration when accompanied by K+ depletion below this concentration, but not by lesser depletion with more residual K+. Analyses of particulate K in the biomass indicated a mean final cell content of 2.8 μmol K 10−8 cells, approximately 1.0% of the organic dry weight.3. Less detailed work with the diatom Diatoma elongatum showed no dependence of growth rate or final yield upon the initial K+ concentration in the range 0.8–3.2 μmol L−1. The phytoflagellate Plagioselmis nannoplanctica suffered net mortality in the lowest concentration tested, 0.8 μmol L−1.4. Comparison with the range of K+ concentration in natural fresh waters, including a depletion induced by an aquatic macrophyte, suggests that K+ is unlikely to limit growth of phytoplankton. Nevertheless, there can be correlation of K+ with lake trophy.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 17 (1987), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. 1. An inexpensive pumping and reservoir system has been developed for circulating water over intact sediment cores. The system facilitates both measurement and manipulation of supernatant properties and flow velocities.2. The apparatus has been used to evaluate the effect of flow velocity and pH on nutrient exchange at the sediment-water interface.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 8 (1978), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. The variation in the ratio (R) between cellular fluorescence of chlorophyll-a and unit extractable chlorophyll-a was examined with natural populations of phytoplankton and unialgal cultures. Photo-inhibition of in vivo fluorescence was observed al high values of irradiance with natural populations and in algal cultures, except with blue-green algae. If samples were dark-adapted (〈 6 W m−2) before measurements were made, changes of fluorescence due to photo-inhibition could be minimized. Measurements of in vivo fluorescence with dark-adapted samples of phytoplankton, dominated by species showing large values of R, gave significant correlations (P〈 0.001) with determinations of chlorophyll-a concentration over periods of several weeks.The values for R for blue-green algae were appreciably lower than for other algal groups. This, and their lack of photo-inhibition effects at high irradiance values, are attributed to the association of most of chlorophyll-a with photosystem I which fluoresces weakly compared to chlorophyll-a in photosystem II. The significance of these findings for ecological studies is discussed.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 6 (1976), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The growth of Ceratium hirundinella in Esthwaite Water, a small productive lake, was investigated during 1975; the horizontal distribution of the alga was studied on four occasions over a 3-week period. Measurements of lake temperature, oxygen concentration, and vertical stratification of Ceratium at close intervals of depth, were also made. Lake population estimates from large samples at many stations were compared with small samples at the regular sampling station. On two occasions the means of these samples were significantly different (P〈0·01). On one date, the estimate of Ceratium abundance in the lake from the large sample at many stations was more than twice the value obtained from the sample collected at the regular sampling station. The population of Ceratium was contagiously distributed in all the large samples. On 3 days the horizontal distribution showed an increase in Ceratium numbers towards the windward shore of the lake. Very large accumulations of Ceratium were found in the metalimnion, just above the anaerobic hypolimnion, during late afternoon. Possible mechanisms of horizontal pattern development are considered, based on the measurements of the vertical distribution of Ceratium, and meteorological factors. The ecological consequences for Ceratium of vertical and horizontal movements, and its spatial distribution in the lake, are discussed.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 18 (1987), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY 1. The influence of solar heating on the formation of temperature and density profiles of ice-covered lakes is considered.2. Mathematical models are derived to quantify the effect of solar heating on vertical stability and its dependence on critical parameters,3. Solar heating is shown to be able to account for the thermal structure and mixing patterns of certain ice-covered lakes.4. The importance of convective mixing is discussed in relation to the distribution of phytoplankton and nutrients.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 10 (1980), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. Diel vertical migrations of a dinoflagellate, Ceratium hirundinella, were induced in a laboratory tube (1.63 × 0.15 m) under a light-dark cycle. The timing of vertical migrations differed between cultures in the exponential and stationary phases of growth; the latter showed a greater coincidence with the light regime.Migration of cells into the surface layers occurred at low values of surface irradiance (〈550 μeinsteins m−2 s−1). At irradiances more closely approaching summer sunshine (〉 1300 μE m−2 s−1) there was a marked avoidance of surface waters, and population maxima were found at depths associated with a relative irradiance level of 10% or c. 150 μE m−2 s−1). Thermal stratification restricted downward movement of cells into the cooler layers. The combination of high surface irradiance and thermal stratification resulted in large, stable, sub-surface maxima of Ceratium, similar to those observed in natural waters under comparable environmental conditions.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 50 (2005), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Growth rates of seven species of planktonic algae were determined in culture over a range of temperature from 2 to 35 °C. Additional observations on growth and viability were made for 13 species in the temperature range 20–35 °C.2. There was a wide range of growth rates between species at their optimal temperatures, from 1.7 divisions day−1 (Asterionella formosa) to 0.3 divisions day−1 (Ceratium furcoides).3. There were considerable differences between species for growth at low and high temperature. Certain algae, including the diatom A. formosa and the flagellates Cryptomonas marssonii, Dinobryon divergens and Eudorina unicocca var. unicocca, had growth rates of 0.4 divisions day−1 or more at 5 °C. The cyanophyte Tychonema (formerly Oscillatoria) bourrellyi, the xanthophyte Tribonema sp., the desmid Staurastrum cingulum and the large dinoflagellate C. furcoides grew poorly or not at all at this temperature. All 21 species tested could grow at 25 °C, but many – including most of the diatoms, some cyanophytes, and all the flagellates – failed to grow persistently at 30 °C. Only Aphanizomenon flos-aquae survived with moderate increase at 35 °C, a lethal temperature for the other species.4. The applicability was considered of proposed quantitative formulations of the rate-temperature relationship. Simple exponential relationships applied only to very limited lower ranges of temperature. The relationship proposed by Bĕlehrádek was a better fit over a wider temperature range, but still excluded rate-decline at high temperature.5. The interspecific differences found are of potential significance for restrictions in natural distributions associated with season, altitude (especially above 500 m) and latitude.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Freshwater biology 4 (1974), S. 0 
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A pneumatically-operated sampler for collecting water samples at close intervals of depth in lakes is described. The sampler uses plastic disposable syringes and may be operated at various depths and at the mud-water interface. Examples of results obtained with the sampler are given.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 37 (1990), S. 0 
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: All English populations of Arctic charr, Salvelinus alpinus (L.), are found in the Lake District (northwest England). There are at least four races of charr in Windermere, the largest lake in England; the North and South basins of the lake each contain two distinct races that spawn in autumn and spring respectively. The spring spawners in both basins probably represent less than 15% of the total population in the lake.Changes in the population density of charr in the lake are described briefly and examined in relation to the trophic status of the lake. Other factors that could possibly affect the charr population are reviewed, especially the influence of climate change.
    Type of Medium: Electronic Resource
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