Ecologia do fitoplâncton em áreas de cultivo de Tilápia do Nilo, Oreochromis niloticus, em tanques-rede no açude Ministro João Alves, Parelhas, Rio Grande do Norte
The dams are limnic ecosystems of great importance for its multiple uses, among them, water supply for the public and to culture of artisanal fish are most relevant. The aim of the present study is to evaluate the physical-chemical characteristics and the phytoplankton community in two chosen sit...
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Formato: | Dissertação |
Idioma: | por |
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Universidade Federal do Rio Grande do Norte
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Endereço do item: | https://repositorio.ufrn.br/jspui/handle/123456789/13058 |
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Resumo: | The dams are limnic ecosystems of great importance for its multiple uses, among them,
water supply for the public and to culture of artisanal fish are most relevant. The aim of the
present study is to evaluate the physical-chemical characteristics and the phytoplankton
community in two chosen sites (Point 1 littoral zone of point source; Point 2 pelagic zone of
non-point source) of the Minister João Alves dam, which is also known as Boqueirão de
Parelhas/RN. This represents the spatial distribution of the phytoplankton species in order to
understand any possible alterations of the water quality and the phytoplankton composition in
relation to the water quality originating from the impact of the tilapia, Oreochromis niloticus,
culture. The study period also encompasses temporal variations exhibited in two seasons of an
annual cycle, one during the dry season (Oct, Nov and Dec of 2008 and Jan of 2009), and the
other rainy season (Mar, Apr, May and June of 2008) to extend the observation. The physicalchemical
parameters, such as pH, temperature, electrical conductivity, concentration of dissolved
oxygen were measured in situ and the values of the inorganic nutrients (nitrate, ammonium and
orto-phosfato) and chlorophyll in the laboratory. The quali-quantitative analyses of the
phytoplankton had been carried through sedimentation technique and the enumeration of the
random of 400 cells, colonies and filaments counted using Sedgwick-Rafter counting chamber.
The results of pH varied widely from the acidic to alkaline range with the minimum of 5.8 (± 0.8)
and the maximum of 9.2 (± 0.7-0.8), at point 1 and 2. The dissolved oxygen content was higher in
the rainy period than that in the dry period. The maximum electrical conductivity was of 1409
μScm-1 in point 1 and 431 minim of μScm-1, in point 2. There was a considerable alteration in the
levels of inorganic nutrients such as nitrate-nitrogen, ammoniacal nitrogen and orthophosphate
during the two cycles of study period. Phytoplankton assemblages presented a picture of alternate
dominance among species Cyanobacteria, Bacillariophyceae and Chlorophyceae. The trophic
state index diagnosed to the category of mesotrophic, which is based on the values of chlorophyll,
total phosphorus and Secchi-disc measurements. The wind driven turbulence of the water column
and the fresh inflow of water (flushing and dilution) during rainy season acted as constraint and
did-not allow an exaggerated growth of the species of cyanobacteria. On the basis of the present
we conclude that the culture of tilapias in cage-culture fails to produce pollution load that could
compromise the quality of the water of the dam, probably be due to small dimension of the culture
in relation to the size, volume of the water and the reservoir capacity support its own environment |
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