Environmental Effects of Marine Fish Pond Culture in the Ria Formosa (Southern Portugal) |
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Authors: | François Noël Hubert Marc Pellaud Sofia Gamito |
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Institution: | (1) IMAR, presently in CCMAR, Faculdade de Ciências do Mar e do Ambiente, Universidade do Algarve, Portugal;(2) Faculté des Sciences, Université de Genève, Switzerland;(3) IMAR, Faculdade de Ciências do Mar e do Ambiente, Universidade do Algarve, Portugal |
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Abstract: | Macrobenthic organisms, sediment and water characteristics were analysed in two fish farms in the Ria Formosa at control sites,
near the outflows and inside the decantation ponds, in winter and summer 2001. Both farms operate under semi-intensive and
intensive regimes. Statistical analysis reveals a very localised effect of fish farms near the outflow of the semi-intensive
ponds, with an increase of density of small-sized organisms. The fish farms released high concentrations of nutrients and
relatively low quantities of suspended solids. The effects of the effluents on the sediment were significant in the immediate
vicinity of discharge point-source. The effects were localized mainly because all farms operate near the sea inlets, where
water renewal rates are higher to ensure good fish production, thus permitting a important flushing of waste water. The effects
of the effluents were more pronounced in summer because of the farms’ higher productivity at that time of the year. The decantation
ponds, obligatory for the intensive regime, were apparently efficient in removing part of the solid waste. However, semi-intensive
fish farms represent important sources of dissolved nutrients in the Ria Formosa and the joint effect of several fish farms
in a semi-enclosed coastal system may be considerable. |
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Keywords: | lagoon system semi-intensive fish farms environmental impact |
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