Flux de matière en étangs piscicoles extensifs : Rétention, sédimentation, exportation

Abstract : In the first part of this thesis, we assessed the input and output of suspended matter, nitrogen and phosporus in extensively managed fishponds (North-Eastern France). Special attention was given to emptying period which was studied in six ponds with surface areas between 2 and 620 ha. The ponds are used for the production of various Cyprinidae. During the emptying operation, between 430 and 3880 kg ha-¹ of suspended matter, 9 and 74 kg ha-¹ of Kjeldahl-nitrogen and 1.2 and 14.4 kg ha-¹ of total-phosphorus were discharged from the pond. For the whole exploitation period 3615 ? 6220 kg ha-¹ of suspended matter, 66-106 kg ha-¹ of nitrogen and 1.6 ? 8.5 kg ha-¹ of phosphorus accumulated in the pond. In a second part, we assessed sedimentation fluxes in these shallow freshwater systems are rare and have often performed with unsuitable methods. In most cases, sedimentation traps mentioned in the literature are at least 25 cm high, thereby neglecting a large proportion of the water column in shallow systems. We have overcome this problem by designing a trap with a receptacle buried in the sediment. Next, 19 new traps wich made it possible to sample almost the whole water column in shallow systems were exposed on a monthly basis during 19 months in two ponds. Quantitative and qualitative temporal and spatial variation of settled particles was shown. Sedimentation rates fluctuated on a seasonal basis. They were minimum in spring and maximum in summer. These fluctuations were linked to the high primary production, to decaying of submersed macrophytes and of blue-green algae. Interference by fish farmer at various times of the year also caused sudden high sedimentation rates (> 200 g.m-².j-¹). Sedimentation in the fish ponds was controled by natural mechanisms partly similar to those that occur in lakes, and by mechanisms specific to shallow systems and to aquatic systems managed by man
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Damien Banas. Flux de matière en étangs piscicoles extensifs : Rétention, sédimentation, exportation. Sciences agricoles. Université Paul Verlaine - Metz, 2001. Français. ⟨NNT : 2001METZ030S⟩. ⟨tel-01775444⟩

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