Many studies have evaluated the efficiency of constructed wetlands (CWs) for the treatment of fishpond effluents, but only a few have compared between CWs with emergent and free-floating macrophytes and assessed the amount of nutrients removed only by the macrophytes. For this purpose, we performed an experiment during 113 days in which we treated a fishpond effluent using four different CWs:(i) with the free-floating macrophyte Eichhornia crassipes (Ec); (ii) without E. crassipes (WEc); (iii) with a substrate and the emergent macrophyte Typha domingensis (Td); (iv) with a substrate and without T. domingensis (WTd). To verify the efficiency of CWs, the removal rates of total suspended solids (TSS), dissolved (DKN) and total (TKN) Kjeldahl nitrogen, total inorganic nitrogen (TIN), total phosphorus (TP) and Porthophosphate (P-ORT) were analysed using ANOVA-rm. The removal of TP and TKN was higher in CWs with substrate than without substrate. The removal of P-ORT, TIN and DKN was higher in Ec compared to others CWs. The average removal of TSS in Ec (78.9%), WTd (77.4%) and Td (75.0%) was higher than in WEc (68.3%).The contribution of E. crassipes towards the removal of all forms of N and P was higher than of T. domingensis. This greater contribution of E. crassipes can be due to the higher biomass that this species gained in comparison with T. domingensis.

We aimed in this study utilize environmental indicators as a quantitative method to evaluate and discuss the nitrogen (TN) and phosphorus (TP) flux by a production stage grow-out (termination) of Nile tilapia (Oreochromis niloticus) in fishpond. The TN and TP load, the mass balance, the input of TN and TP via feed and the converted nutrients in fish biomass are the environmental indicators applied in this study. During the production cycle (128 days), the system exported 15,931 g TN and 4,189 g TP that were related to the amount of feed supplied (r Pearson = 0.8825 and r = 0.8523, respectively), corroborated by the feed conversion ratio (1.61:1). The indicators showed that 26% TN and 45% TP were reversed into fish biomass, 62% TN and 40% TP were retained in the fishpond, and 12% TN and 15% TP were exported via effluent. The largest contribution of nutrients generated by the system and exported via effluent was observed in phase III and IV. This result is supported by the feed conversion ratio 2.14 and 2.21:1 obtained at this phase, a fact explained by the amount of feed offered and the fish metabolism. Application of environmental indicators showed to be an efficient tool to quantify flux of TN and TP produced during the grow-out period of Nile tilapia and therefore, guide management practices more sustainable. Concerning the environmental sustainability of the activity the implementation of best management practices such as the better control of the feed amount offered would lead to a smaller loss of TN and TP to the water. Furthermore, the use of better quality feeds would allow greater nutrient assimilation efficiency.Keywords: environmentally sustainable management, nutrients load, mass balance, fish-farming, Oreochromis niloticus. Fluxo de nitrogênio e fósforo na produção de tilápia-do-nilo (Oreochromis niloticus) a partir da aplicação de indicadores ambientais ResumoNós objetivamos neste estudo, utilizar indicadores ambientais como método quantitativo para avaliar e discutir sobre o fluxo de nitrogênio (TN) e fósforo (TP) na etapa final de crescimento (terminação) de tilápia-do-nilo (Oreochromis niloticus) em viveiro escavado. A carga de TN e TP, o balanço de massa, a entrada de nutrientes via ração e o TN e TP convertido em biomassa de peixe foram os indicadores ambientais utilizados neste estudo. Durante o ciclo produtivo (128 dias), o sistema exportou 15.931 g NT e 4.189 g PT os quais foram relacionadas às quantidades de alimento fornecido (r Pearson = 0,8825 e r = 0,8523, respectivamente), corroborada pela conversão alimentar (1,61:1). Os indicadores evidenciaram que 26% NT e 45% PT foram revertidos em biomassa de peixe, 62% NT e 40% PT ficaram retidos no viveiro e 12% NT e 15% PT foram exportados via efluente. O maior aporte de nutrientes gerado pelo sistema e exportado via efluente foi verificado nas fases III e IV. Este resultado é corroborado pelas taxas de conversão alimentar de 2,14 e 2,21:1 obtida nestas fases, fato explicado pela quantidade de ração ofertada e pelo metabolismo dos peixe...

The concern in mitigating the negative impact generated by the discharge of nutrients in the receiving water body is a challenge for the sustainable development of Brazilian fish farms. Thus, the purpose of this study was to evaluate the water quality and environmental impact caused by trout farming system effluent with focus on discharge of phosphorus. Sampling was performed on a weekly basis in triplicate from September to November 2010. Sample sites were distributed according to the water flow: upstream from trout farming system, water supply, effluent, artificial wetland, mixing zone and downstream (60 m from effluent). In the field, pH, conductivity, dissolved oxygen, water temperature and turbidity were measured. In laboratory, nitrogen and phosphorus series, chlorophyll a, total solids suspended and their organic and inorganic fractions were analyzed. For the good growth of trout in production system, the abiotic factors described in the water quality monitoring demonstrated acceptable values. Environmentally, after passing through the production system and artificial wetland, there was an increase in concentrations of total phosphorus, total nitrogen, orthophosphate, ammonium, chlorophyll a, total solids suspended and their organic and inorganic fractions (P < 0.05). These results are related with the quality of feed, feeding management and the inefficiency of the artificial wetland. Therefore, it is necessary to use best quality feed to meet the nutritional requirements of trout, maintaining an optimal feed conversion and reducing pollution generated by effluent.

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