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The main goal of this research was to survey information about the …

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- Uptake rates of nitrogen and phosphorus in the water by Eichhornia crassipes and Salvinia auriculata

The first studies in dynamics, cycling and storage of nutrients established the basis for studies, in wetlands, of the transformations from effluents into various kinds of biomass (Bastian & Hammer, 1993). An effluent treatment system based on aquatic macrophytes may be defined as a natural process, where the plants play the principal role in the removal and long-term storage of residues from anthropogenic origin (Brix, 1993).

Understanding of the functioning of these "natural systems" with respect to the reduction of pollutants has greatly increased in the last years (Reddy & D'Angelo, 1997). However, the basic knowledge of these systems is not yet well-developed as large amounts of data have still to be collected. These data include studies on the long-term effects on the biota, so that successful management strategies can be developed to prevent eutrophication of fresh water bodies (Knight et al., 1993).

Many coastal lagoons of an exquisite beauty distinguish the northern coast of Rio de Janeiro (Brazil). These environments are important leisure grounds for the local population, as well as having large fish and shrimp fisheries. Lagoon Imboassica is located in this region and suffer various anthropogenic impacts since the mid 1980's. The lagoon began to be utilised as a dumping site for untreated domestic sewage due to the residence construction on the shoreline.

Previous studies in this lagoon indicate that the aquatic macrophyte community is of great importance in reducing the input of domestic sewage (high nitrogen and phosphorus) into the lagoon (Lopes-Ferreira, 1995). The main goal of this study was to evaluate the capacity of E. crassipes and S. auriculata to remove nitrogen and phosphorus compounds from the water and to determine which of these species has the greatest nutrient reducing ability. In addition, the influence of the initial concentrations of NO3–N, NH4–N and PO4–P on the capacity of the aquatic plants to remove nitrogen and phosphorus from the water column in the lagoon was also observed.

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