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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. The discovery of a third species of alderfly (Sialis nigripes) in Britain and Ireland necessitates a new larval key for the group in these islands. Characters are now provided to distinguish the larvae of the three species, and their habitat and distribution in the British Isles are outlined.
    Type of Medium: Electronic Resource
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  • 2
    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. Following the impoundment of the River Oshun to form Lake Asejire, Nigeria, in 1970, changes in the water chemistry were monitored. Chemical stratifications followed closely the pattern of thermal stratifications as the lake was chemically stratified from February to April and destratified from June to September and in January.
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  • 3
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. Asellus aquaticus was fed for 49 days at 15°C on aquatic actinomycetes in the laboratory. Specific growth rates (wet weight) of animals initially 2.5mm in length ranged from 0.85 to 2.33% day−1 on Micromonospora and Streptomyces S2 respectively. Asellus newly released from the brood-pouch (1.0 mm length) had a similar growth rate (2.74% day−1) on Streptomyces S2. The growth rates of animals fed on actinomycetes were lower than those of animals feeding on macroscopic foods such as Elodea and decaying oak leaves, regardless of the initial size of the animal. However, it was concluded that actinomycetes, and by inference bacteria also, could maintain a population, albeit a slow-growing one, in a situation where macroscopic foods are largely absent.The possible significance of hyphal diameter of micro-organisms in relation to assimilation from them is discussed. In this connection actinomycetes are considered as model filamentous bacteria.
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  • 4
    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. Asellus aquaticus and A. meridianus are freshwater isopods common more or less throughout Britain. It has been suggested that the former species is replacing the latter. To investigate this, the distributions of the species were determined in the English Lake District, near Merseyside, and elsewhere. Additionally, some field transference experiments were conducted in Anglesey and near Merseyside. Particular attention was given to changes in distribution with time; many of the observations reported relate to a time span of almost 20 years. Taken together, the results provide qualified support for the suggestion that A. aquaticus is replacing A. meridianus.
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  • 5
    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. The freshwater littoral meiofauna along a temperature gradient in Par Pond (a cooling reservoir receiving thermal effluents from a nuclear reactor) was sampled from September 1975 to October 1976. Monthly samples were taken at three stations; ‘hot-water’ (15–40°C), ‘warm-water’ (13–37°C) and ambient or ‘cold-water’ (8–37°C) sites. Total numbers of individuals at the ambient site ranged from 971 to 3674 per 10 cm2 (mean = 2263), approximating the density reported from productive estuarine environments. Nematodes, rotifers, ostracods, cladocerans and mites comprised 80% of overall density. When compared to the ambient site, thermally affected sites demonstrated reduced faunal density.Contrary to other environmental perturbation studies, the Shannon-Weaver diversity index (H') did not reflect alteration of structural complexity within the rotifer taxocene when hot-water, warm-water and cold-water sites were compared. Though there was a significant reduction in number of species at the thermally altered sites, high ‘equitability’ among the reduced species resulted in H’ values comparable to those in natural communities. Distinct winter-spring and summer-autumn assemblages were evident in the ambient community while no seasonal clustering was apparent at the thermally affected sites. It is hypothesized that the maintenance of temperatures above ambient normals masks environmental cues that normally would elicit seasonal changes in the rotifer fauna at those two sites.
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  • 6
    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. Organic detritus resulting from microbial attack on algal material contains lipids directly extractable by organic solvents and also contains bound lipids, obtained by solvent extraction following acid hydrolysis. Differences between the composition of bound and extractable n-alkanes, n- and branched/cyclic alkanoic acids from each source are attributed to a major bacterial input to these bound lipid classes. Similarities in composition between bound lipid classes of algal detritus and corresponding classes in a lake sediment support earlier suggestions of a considerable bacterially-derived contribution to sedimentary bound lipids.
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  • 7
    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. A pigment ratio representing the ratio of carotenoid pigments to chlorophyll-a was calculated by dividing the optical density at 480 nm by that at 664 nm for a 90% acetone extract of phytoplankton. Its seasonal variation in three Norfolk broads was examined and, except for nitrogen-fixing species, it was found to vary independently of the algal species composition.A good inverse correlation with the particulate nitrogen to carbon ratio was found. The seasonal variation in the pigment ratio was considerably affected by measurable lake concentrations of inorganic nitrogen supplied from ttie catchment. Other sources of nitrogen such as nitrogen fixation and release from the sediment were also indicated by changes in the ratio.By comparison with the distinctions of extreme, moderate and no nitrogen deficiency drawn by Healey (1975) for the nitrogen/carbon ratio, values for the pigment ratio of 〈 1.4, 1.4–2.4 and 〉 2.4 were found to indicate no, moderate and extreme nitrogen deficiency respectively in the phytoplankton. The relation ship is attributed to the measurement of secondary carotenoids in response to nitrogen deficiency.
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  • 8
    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. Seasonal changes in photosynthetic rates of phytoplankton and underwater light in four Kenyan fresh waters (Lake Naivasha, Crescent Island Crater, Oloidien Lake and Winam Gulf) were measured in 1973 and 1974. Daily variations in water temperature were only slightly less than seasonal changes, and complete vertical mixing usually occurred each day. Well oxygenated water from top to bottom provided evidence for daily mixing.The vertical profiles of photosynthetic rates in the four lakes had the familiar feature of subsurface maxima. Of the photosynthetically available radiation (PAR), 1% coincided with the limit of detection of photosynthesis in Naivasha and Crescent Island Crater. The PAR at the depth of the maximal photosynthetic rate was higher for Naivasha (mean= 1.71 einsteins (E) m−2) than for the Oloidien and Crescent Island Crater (means = 1.23 and 1.20 E m−2 h−1, respectively).The maximal rates of photosynthesis (mg O2 m−3 h−1) were usually higher in Oloidien (260–750) and Winam Gulf (230–640) than in Naivasha (150–240) and were least in Crescent Island Crater (50–180). Chlorophyll-a concentrations were directly related to photosynthetic rates. Because of the inverse relation between euphotic zone depth and maximal photosynthetic rates, the areal rates varied less among the lakes than the volumetric rates (i.e. 3.0–12.1 g O2 m−2 day−1).The efficiency of utilization of PAR expressed on a molar basis ranged from 6.1 to 1.9 mmol O2 E−1, but was usually 2–4 mmol O2 E−1.The seasonal changes over a 12-month period in the areal photosynthetic rates ranged from a 3-fold variation in Oloidien and Crescent Island Crater to a 1.5-fold variation in Naivasha. In Winam Gulf over a 5-month period a 2.3-fold variation occurred.
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  • 9
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: SUMMARY. The gut contents of Nais pseudobtusa and Chaetogaster diastrophus, two co-existing littoral-dwelling Naididae (Oligochaeta), differed over a period of one and a half years due to strong selection by C. diastrophus for specific diatom genera, Cymbella spp. and Navicula spp. In contrast, N. pseudobtusa showed less selection and the gut contents consisted mainly of detritus, diatoms and mineral particles. These differences in the food niche are likely to contribute to the co-existence of the two species in this habitat.Seasonal changes in the relative abundance of diatom genera in the habitat greatly influenced the gut contents of N. pseudobtusa; however, these changes had less influence on those of C. diastrophus. This and the highly selective nature of the gut contents of C. diastrophus suggests that the two species have different feeding strategies. It is suggested that C. diastrophus actively seeks out certain diatom genera in preference to other food items, while the unseslective gut contents of N. pseudobtusa are more typical of an opportunist feeder.
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  • 10
    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. A 5-year study was made of the hydrology and water chemistry in the watershed of Lake Stugsjön, a small lake in the sub-arctic region of northern Sweden. Of the total yearly runoff, 80% occurs during the spring thaw in May and June and largely regulates the nutrient loading. The ice-free period of the lake is June—October. Atmospheric deposition of nitrogen and phosphorus was among the lowest recorded anywhere, in spite of which it accounts for approximately half of the total summer nutrient loading. Dry fall-out made up the major part of the total atmospheric deposition of nitrogen and phosphorus during the summer.Conductivity measurements showed that the major constituents were not influenced by processes within the lake.The nitrogen concentration in the lake during the summer was probably regulated by benthic algae which assimilated inorganic nitrogen from the sediments and released organic nitrogen to the lake water.Phosphorus loading and water temperature in combination showed a clear relationship with the mean concentration of chlorophyll-α during the ice-free period.
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