The city of Pelotas is located on the shores of the São
Gonçalo Channel in the state of Rio Grande do Sul, in
southern Brazil. This channel connects the Patos and Mirim
lagoons, which are the largest ones in Brazil. This region
has a humid subtropical climate, which is suitable for the
development of some floating aquatic macrophytes species
such as Spirodela sp, (giant duckweeds), Pistia stratiotes
(water lettuce) and Salvinia sp.
The Macrophytes form an important group in the shallow
freshwater ecosystems and these systems are common
throughout the coastal plain of Rio Grande do Sul (Vieira &
Rangel, 1988). This category of plant has a great potential for
reducing or removing water pollutants, including phosphorus,
nitrogen and heavy metals. On the other hand, these plants
are regarded as weeds because they have high rate of biomass
production setbacks, which may cause obstruction and
changes in aquatic environments (Bini & Thomas, 2003).