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The objective of the study was to evaluate the effect of different concentrations of nitrogen and phosphorus on the growth of the free-floating aquatic macrophytes Eichhornia crassipes, Pistia stratiotes, and Salvinia molesta. The plants were cultured in 2,000-l outdoor concrete tanks. Triplicate tanks, with a continuous flow of effluent from culture ponds containing Nile tilapia, were used for each plant type (n = 3). The plant material was collected monthly from 0.25 m 2 floating quadrats, at the two ends of the tanks (higher nutrient concentrations near the inflow and lower nutrient concentrations near the outflow). In low nutrient concentrations, the maximum relative growth rates (RGRs) for E. crassipes (0.016/day) and P. stratiotes (0.016/day) were significantly lower (P B 0.05) than for S. molesta (0.029/day). There were no significant differences between the RGRs of S. molesta in the different nutrient concentrations.Eichhornia crassipes and P. stratiotes had their growth limited by nitrogen and phosphorus concentrations. The increase in plant density during the experiment probably also affected the growth of these species. In this context, E. crassipes and P. stratiotes can cause problems in nutrient-rich waterbodies, but under these experimental conditions their growth was limited by nitrogen and/or phosphorus concentrations. The growth of S. molesta was not influenced by the different nutrient concentrations.

The effluents from fish farming can increase the quantity of suspended solids and promote the enrichment of nitrogen and phosphorus in aquatic ecosystems. In this context, the aim of this work was to evaluate the efficiency of three species of floating aquatic macrophytes (Eichhornia crassipes, Pistia stratiotes and Salvinia molesta) to treat effluents from Nile tilapia culture ponds. The effluent originated from a 1,000-m 2 pond stocked with 2,000 male Nile tilapia Oreochromis niloticus. The treatment systems consisted of 12 experimental tanks, three tanks for each macrophyte species, and three control tanks (without plants). Water samples were collected from the: (i) fish pond source water, (ii) effluent from fish pond and (iii) effluents from the treatment tanks. The following water variables were evaluated: turbidity, total and dissolved nitrogen, ammoniacal-N, nitrate-N, nitrite-N, total phosphorus and dissolved phosphorus. E. crassipes and P. stratiotes were more efficient in total phosphorus removal (82.0% and 83.3%, respectively) and total nitrogen removal (46.1% and 43.9%, respectively) than the S. molesta (72.1% total phosphorus and 42.7% total nitrogen) and the control (50.3% total phosphorus and 22.8% total nitrogen), indicating that the treated effluents may be reused in the aquaculture activity. Key words: Eichhornia crassipes, Pistia stratiotes, Salvinia molesta, aquaculture, nutrients EFICIÊNCIA DE MACRÓFITAS AQUÁTICAS NO TRATAMENTO DE EFLUENTES DE VIVEIRO DE TILÁPIA DO NILORESUMO: Os efluentes de piscicultura podem aumentar a quantidade de sólidos em suspensão e promover o enriquecimento de nitrogênio e fósforo nos ecossistemas aquáticos. Neste contexto, o objetivo deste trabalho foi avaliar a eficiência de três espécies de macrófitas aquáticas flutuantes (Eichhornia crassipes, Pistia stratiotes e Salvinia molesta) no tratamento de efluentes do viveiro de tilápia do Nilo. O efluente foi proveniente de um viveiro com 1000 m 2 contendo 2000 machos de tilápia do Nilo (Oreochromis niloticus). Os sistemas de tratamento consistiram de 12 taques experimentais, três tanques para cada espécie de macrófita estudada, e três tanques sem plantas (controle). Amostras foram coletadas da água de abastecimento do tanque de tilápia do Nilo (i); do efluente do viveiro com tilápia do Nilo (ii) e dos efluentes tratados pelas macrófitas aquáticas (iii). As seguintes variáveis foram determinadas: turbidez, nitrogênio total, nitrogênio dissolvido, N-amoniacal, N-nitrato, N-nitrito, e fósforo total e fósforo dissolvido. E. crassipes e P. stratiotes foram mais eficientes na remoção de fósforo total (82,0% e 83,3%, respectivamente) e nitrogênio total (46,1% e 43,9%, respectivamente) do que quando comparadas com S. molesta (72,1% de fósforo total e 42,7% de nitrogênio total) e com o controle (50,3% de fósforo total e 22,8% de nitrogênio total). Pode-se concluir que as macrófitas aquáticas, principalmente E. crassipes e P. stratiotes foram eficientes na remoção de nitrogênio e fósforo dos efluentes de criação de t...

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-Changes in land cover, especially the replacement of forest by agricultural activities affect the hydrological processes of river catchments, resulting in physical and chemical compositional changes of water draining from affected basins. The aim of this study was to evaluate landscape influences at different spatial scales (catchment and riparian) on the physical and chemical composition of stream water in 15 agricultural catchments, belonging to the Corumbataı´basin (Brazil). We calculated the average slope (%), average elevation (m), soil classes (%), major land use classes (%), average distance from the forest cover in relation to the hydrographic network (m), largest patch index (%) at the catchment scale and riparian zone of drainage network scale within a 30 m buffer. Water samples were collected in two seasons (dry and rainy) to characterize physical and chemical properties: turbidity, suspended solids, total nitrogen, nitrate and total phosphorus. Our results showed higher concentration of nitrate in sugarcane fields and larger amount of suspended solids and turbidity in pasture areas. We concluded that degraded and highly fragmented forests may not be effectively contributing toward the protection of aquatic ecosystems.

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ABSTRACT

RESUMO Treatment of shrimp effluents by free-floating aquatic macrophytesABSTRACT -The efficiency of systems composed of two species of floating aquatic macrophyte (Eichhornia crassipes and Pistia stratiotes) to treat effluents from shrimp culture was evaluated in this research. The effluent originated from a pond populated with Macrobrachium amazonicum. Treatment systems consisted of 12 experimental tanks with aquatic macrophyte and three tanks without plants (control). Water samples were collected from the fresh water supply and before and after passing through the treatment systems. There are no differences in the removal of nutrients between the two species. The higher nutrient removal was observed for total phosphorus (41.9% by control; 71.6% by E. crassipes; 69.9 by P. stratiotes; 72.5% by E. crassipes + P. stratiotes and 72.1 by P. stratiotes + E. crassipes) and turbidity (30.6% by control; 80.2% by E. crassipes; 75.2 by P. stratiotes; 79.8% by E. crassipes + P. stratiotes and 81.5 by P. stratiotes + E. crassipes).The systems containing aquatic macrophytes were efficient in nitrogen and phosphorus removal from M. amazonicum culture.