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  • 1
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    Nitrogen deficiency, phosphorus sufficiency, and the invasion of Lake Kinneret, Israel, by the N (1999)
    Springer
    Details
    Publication Date: 1999-01-01
    Print ISSN: 1015-1621
    Electronic ISSN: 1420-9055
    Topics: Biology
    Published by Springer
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  • 2
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    Nitrogen deficiency, phosphorus sufficiency, and the invasion of Lake Kinneret, Israel, by the N2-fixing cyanobacterium Aphanizomenon ovalisporum (1999)
    Springer
    Details
    Publication Date: 1999-12-01
    Print ISSN: 1015-1621
    Electronic ISSN: 1420-9055
    Topics: Biology
    Published by Springer
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  • 3
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    Some aspects of perturbation in the structure and biodiversity of the ecosystem of Lake Victoria (East Africa) (1995)
    EDP Sciences
    Details
    Publication Date: 1995-01-01
    Print ISSN: 0990-7440
    Electronic ISSN: 1765-2952
    Topics: Biology
    Published by EDP Sciences
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  • 4
    Electronic Resource
    Electronic Resource
    Factors which affect the abundance of an invasive cladoceran, Daphnia lumholtzi, in U.S. reservoirs (1999)
    Oxford, UK : Blackwell Science Ltd
    Freshwater biology 42 (1999), S. 0 
    Details
    ISSN: 1365-2427
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: 1. Daphnia lumholtzi is a subtropical, Old World species which is rapidly spreading throughout reservoirs in the southern U.S.A. It was first recorded in Lake Texoma (Oklahoma–Texas) in September 1991.2. Southern U.S. reservoirs typically have strong spatial and temporal gradients in temperature, conductivity, turbidity and in the distribution of organisms. Therefore, the present experiments examined the reproductive and moulting rates, and survival of D. lumholtzi in relation to extremes of food concentration, temperature, conductivity and turbidity.3. Increases in temperature (range = 15–29 °C) and decreases in turbidity (range = 0.6–470 NTU) increased reproductive and moulting rates, whereas food concentration only affected the rate of reproduction, while conductivity had no effects. Survival was affected only by temperature.4. Daphnia lumholtzi tolerates high temperatures (27–30 °C) at which other cladocerans in Lake Texoma disappear. Therefore, D. lumholtzi may exploit resources in midsummer, when there are few potential competitors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2427.1999.00449.x
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  • 5
    Electronic Resource
    Electronic Resource
    Nitrogen deficiency, phosphorus sufficiency, and the invasion of Lake Kinneret, Israel, by the N2-fixing cyanobacterium Aphanizomenon ovalisporum (1999)
    Springer
    Aquatic sciences 61 (1999), S. 293-306 
    Details
    ISSN: 1420-9055
    Keywords: Key words: Aphanizomenon, cyanobacteria, N-deficiency, P-sufficiency, N : P ratios, Lake Kinneret.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract: Historically, the phytoplankton community of Lake Kinneret, Israel, has been dominated by the dinoflagellate Peridinium gatunense and other edible species that are important in the lake's food web. However, major changes have occurred both in external nutrient loading and in the water column chemistry of the lake since the mid-1980's. Epilimnetic particulate nitrogen: particulate phosphorous (PN : PP) ratios have declined, and measurements of seston chemistry suggest that the intensity of seasonal nitrogen limitation has increased. The phytoplankton community also was altered in 1994 and 1995 by a lake-wide summer invasion of the nitrogen-fixing cyanobacterium Aphanizomenon ovalisporum. This abrupt change in phytoplankton community structure is consistent with the development of conditions increasingly N-deficiency and P-sufficiency in the water column, which should favor cyanobacterial dominance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00001326
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  • 6
    Electronic Resource
    Electronic Resource
    Lake Kinneret dissolved oxygen regime reflects long term changes in ecosystem functioning (1998)
    Springer
    Biogeochemistry 42 (1998), S. 253-283 
    Details
    ISSN: 1573-515X
    Keywords: dissolved oxygen concentration ; yearly oxygen budgets ; hypolimnetic respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Lake Kinneret (Israel) has undergone several prominent chemical and biological changes since 1970. Between 1970 and 1991 significant, long-term gradual increase were recorded in epilimnetic dissolved oxygen (DO) concentrations (about 20%), and in pH levels (0.2 units). Concomitantly there was a significant increase in hypolimnetic H2S concentrations (about 75%) and a long-term gradual drop in zooplankton biomass (50%). Since 1994 these trends were reversed and the levels of the three chemical parameters have returned to those found in the 1970's and that of zooplankton to mid 1980's levels. The present study is an attempt to relate some of these long term changes by means of yearly oxygen budgets, based on fluxes of oxygen producing and consuming processes. This analysis raises the possibility that part of the long-term increase in epilimnetic DO and pH between 1970 to 1990 may be attributed to reduced inputs of organic matter from alochthonous sources and possibly to enhanced burial of organic matter in the bed sediments. However, the major cause for the observed increase in epilimnetic DO and pH is increased sedimentation of organic matter to the hypolimnion during stratification. As indicated by the amount of H2S formed in the hypolimnion during stratification added to the amount of oxygen entrapped in this layer at the onset of thermal stratification, between 1970 to 1991 the sedimentation flux of organic matter increased by approximately 40%. It is estimated that during these two decades hypolimnetic respiration increased from ca. 8% of the annual amount of oxygen evolved due to photosynthesis during the early 1970's to ca. 12.5% during the 1980's. The shift in the layer of oxidative processes is suggested to be the result of a multi-annual decline in zooplankton grazing pressure, which led to increased sedimentation of organic matter. The reversed trends for DO, pH and H2S since 1994 may have partially been due to the increase in zooplankton activity and partially due to changes in phytoplankton community structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005921029867
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  • 7
    Electronic Resource
    Electronic Resource
    Environmental variability and the population dynamics of the exotic Daphnia lumholtzi and native zooplankton in Lake Texoma, U.S.A. (1999)
    Springer
    Hydrobiologia 405 (1999), S. 11-23 
    Details
    ISSN: 1573-5117
    Keywords: exotic species ; zooplankton ; Daphnia lumholtzi ; reservoirs ; Lake Texoma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Daphnia lumholtzi has invaded the U.S. from its original distribution of Africa, southern Asia and Australia. We examined the factors that affected the abundance and distribution of D. lumholtzi during 1994–1995 in Lake Texoma, a large southern plains reservoir. Daphnia lumholtzi was most abundant during summer months when temperatures were highest. The population exhibited a distributional shift in mid July from the upstream, more riverine portion of the reservoir to the cooler area near the dam when epilimnion temperatures upreservoir exceeded 30 °C. The pattern of variation in distribution and abundance did not correspond to the spatio-temporal patterns of most other resident zooplankton, nor did it correspond to changes in the phytoplankton assemblage. We conclude that the ability of D. lumholtzi to withstand the physiological effects of high temperature on reproduction and survival have a strong influence on the distribution and abundance of this organism in Lake Texoma. Furthermore, because D. lumholtzi became abundant only in the summer, after the decline of many of the native zooplankton, we suggest that it probably has little competitive impact on the other members of the zooplankton assemblage.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003742709605
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  • 8
    Electronic Resource
    Electronic Resource
    Food composition of the fish community in Lake Agmon (1998)
    Springer
    Hydrobiologia 380 (1998), S. 49-57 
    Details
    ISSN: 1573-5117
    Keywords: Fish community ; Lake Agmon ; freshwater ; feeding habits
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Lake Agmon was created in the Hula Valley in Israel, in the northern part of the dried-up Hula Lake site, in summer, 1994. Samples of fish at ten stations were taken by electroshocker once a month, from January to December, 1996. The fish species whose food composition in the gut was examined in this study were: Tilapia zillii, Gambusia affinis, Clarias gariepinus, Cyprinus carpio, Pseudophoxinus kervillei, Acanthobrama lissneri, Hemigrammocapoeta nana and Oreochromis aureus. Food components were determined qualitatively and quantitatively. Assessment of the organism biomass in the gut contents was based on available data of phytoplankton and zooplankton. The food of G. affinis changed during the year, consisting high level of algae in winter and spring, and insects and crustaceans in summer. In T. zillii, a high percentage of algae were found in winter, and a high percentage of plants in summer. The food of H. nana consisted mainly of phytoplankton, but included high plants during most months; P. kervillei ingested mainly insects and crustaceans, with a high percentage of Daphnia spp.; and the diet of C. gariepinus comprised fish and invertebrates species, which varied with the seasons. C. carpio ate mainly invertebrates; O. aureus are vegetarian, and A. lissneri fed on both animals and plants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003225210226
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