1,721,021 research outputs found
Phytoplankton assemblages in twenty-one Sicilian reservoirs: relationships between species composition and environmental factors
No full textData collected in a limnological survey, carried out between 1987 and 1988 on 21 Sicilian reservoirs of varying trophic state, were ordinated using CANOCO 3.1 to generalise the way in which the structure of phytoplankton assemblage is conditioned by both physical and chemical variables. The results showed that in these man-made lakes, characterised by conspicuouswater-level fluctuations, the annual and interannual variability in the abundance and composition of phytoplankton may be strongly influenced by their peculiar hydraulic regimes rather than by nutrient availability. In particular, it was highlighted that, from the early summer, water abstraction often leads to increased circulation and to the deepening of the mixed layer. In this way, an increase of the ratio of mixing depth to euphotic depth is forced, with the result that phytoplankton cells experience longer periods in darkness as they are carried through the mixed layer. Phytoplankton assemblages change in species composition in response to the environmental variation. Both the raising of the trophic state, with an increase in phytoplankton biomass and a decrease in transparency, and the intensified abstraction enhance the role of light availability in promoting the development of specific phytoplankton assemblages adapted to the modified physical environment. Light climate is an important influence on the species structure of the phytoplankton, especially in the higher part of the trophic gradient. In contrast, the influence of nutrients on the structure of the assemblages appears to be higher in the lower part of the trophic spectrum or in those environments characterised by a higher hydrological stability during the
year
Limnological aspects of sicilian reservoirs: A comparative, ecosystemic approach
No full textThis paper is a report on the state-of-the-art of reservoir limnology in Sicily, the largest island of the Mediterranean Sea. The territory is characterised by a semi-arid climate with a dry and a wet semester occurring in the year. Evaporative losses are strong during the summer and, on an annual basis, they often exceed precipitation. Thus, reservoirs constitute an important water resource for the island to supply drinking water and to provide for agricultural needs in the periods of drought. However, despite their importance, they receive poor attention from the scientific and political communities and in the absence of any environmental policy or suitable territorial planning, their water quality is undergoing a rapid decline, principally due to the inadequate treatment of urban waste waters and to the excessive and irrational spreading of fertilizer. The convinction that reservoirs may differ significantly from lakes and the necessity to better understand what rules drive the functioning of these environments, were the engine to carry out several limnological investigations on these artificial environments with special reference to their pelagic compartment. The principal characteristics of these water bodies lie in their peculiar hydrological cycle. The absence of precipitations during summer, when the reservoirs are intensively used, and their re-filling in winter without any outflow contribute to water-level fluctuations which interfere with their thermal structure, underwater light climate and nutrient dynamics'. The structure of phytoplankton assemblages is, in the absence of a severe nutrient limitation, modulated by hydrological forcing. In addition to these "bottom-up" effects some "top-down" ones, also mediated by the water-level fluctuations. These involved the strength of predation pressure exherted by fish on zooplankton assemblage. Ultimately, it has been demonstrated that these water movements influence the structure of these ecosystems profoundly and their effects have to be carefully considered when management procedures have to be developed
The effects of absolute and relative nutrient concentrations (N/P) on phytoplankton in a subtropical reservoir
Full text linkThe elemental composition of phytoplankton is a critical factor for primary production and nutrient recycling. The increase anthropogenic nutrient input into freshwater ecosystems is affecting phytoplankton assemblage structure and its stoichiometry. Reservoirs of South China generally show low level of phosphate and it is not clear how phytoplankton can grow and occasionally bloom in such conditions. Therefore, an indoor experiment was conducted to investigate the response of natural phytoplankton communities to 25 levels of supplied nitrogen to phosphorus ratios (N/P), arising from the combination of 5 levels of N and P. Our aim was to check the effects of absolute and relative N and P on phytoplankton growth and structure. We assumed that Alkaline Phosphatase (APA) provides a way to use alternative P resource. Our hypotheses include: (1) phytoplankton stoichiometry would be in homeostasis (sensu Sterner & Elser, 2002) under different N and P treatments; (2) absolute nutrient values rather than its ratio matters for phytoplankton assemblage; and (3) phytoplankton cell size declines to lower P requirements facing P limitation. Results showed that phytoplankton in this subtropical reservoir use alternative P sources via APA to support its growth. The absolute values of N and P instead and not their ratios were important for phytoplankton. The N/P ratio cannot be a reliable indicator for nutrient limitation or phytoplankton shift. During the fast-growing phase, their elemental contents were not sensitive to supplied nutrients, and their stoichiometry was more constrained compared to that in slow-growing phase. The plasticity of cellular stoichiometry was mainly due to the variations of cellular P. Phytoplankton stoichiometry was weakly homeostatic, and this mechanism provides a strategy to keep growth relatively stable in a variable nutrient environment
Towards a functional classification of the freshwater phytoplankton
No full textThis paper considers the structure of freshwater phytoplankton assemblages and promotes a scheme of ‘vegetation recognition’, based upon the functional associations of species represented in the plankton. These groups are often polyphyletic, recognizing commonly shared adaptive features, rather than common phylogeny, to be the key ecological driver. Thirty-one such associations are outlined and the basic pattern of their distinctive ecologies is outlined. An invitation to other plankton scientists to assist in the development of this scheme is issued
Limnology in Sicily: A history of fresh waters surrounded by the sea
Full text linkAlthough the practice of limnological sciences in an island located in themiddle of the Mediterranean Sea and characterised by a semi-arid climate couldappear, at a first sight, somewhat misplaced, limnology in Sicily is in some wayrelated to one of the finest scientists of this century who tightly linked his nameto limnology: G. E. Hutchinson. Actually, one of the excursions most requestedby those researchers involved in limnology who reach the island, and Palermoin particular, is to the sanctuary of Santa Rosalia and the nearby little pond (Fig.1) which was the scenario of one of the most famous papers by Hutchinson(1959). In addition, part of the second volume of his monumental work "ATreatise on Limnology" (Hutchinson 1967) was written while he was inPalermo as a guest at the Institute of Zoology of the University.The aim of this short article is to trace the history of limnology in Sicily,from the end of the last century up to the present, and pay a little homage to ascientist to whom limnology is deeply indebted
Mediterranean Climate and Eutrophication of Reservoirs: Limnological Skills to Improve Management
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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