Influence of limnological characteristics of water in the occurrence of Salvinia molesta and Pistia
stratiotes in rivers from the Itanhaém River basin (SP, Brazil)
CAMARGO1,2, A.F.M. & BIUDES1,2, J.F.V.
1 Departamento de Ecologia, Instituto de Biociências, UNESP, Avenida 24-A, 1515. CEP: 13506-900, Rio Claro/SP, Brazil.
2 Programa de Pós Graduação em Aqüicultura, Centro de Aqüicultura da Universidade Estadual Paulista (CAUNESP), UNESP, Via de Acesso Prof. Paulo Donato Castellane, s/n. CEP: 14884-900, Jaboticabal/SP, Brazil.
ABSTRACT: Itanhaém River basin is located in the South Coastal Plain of São Paulo State (Brazil) and is formed by many small rivers and streams with low water flow and meandered beds. Pistia stratiotes and Salvinia molesta are the most abundant species of floating aquatic macrophytes that occur in different rivers of the basin. Although the water flux can transport these species for different rivers, these two species do not coexist in the same stand. In this work we measure some physical and chemical characteristics of the water from four stands (2 of P. stratiotes located in rivers Guaú and Aguapeú and 2 of S. molesta located in rivers Preto and Branco) with the objective to identify favourable conditions for occurrence of these species and understand why the two species do not coexist in the same stand. The Principal Component Analysis (PCA) showed that the stands located in rivers Branco and Guaú have very distinct limnological characteristics while the stands located in rivers Aguapeú and Preto have similar limnological characteristics. Between stands located in rivers Aguapeú and Preto, only phosphorus concentrations were significantly (p<0.05) higher in Aguapeú River. Mean concentrations of total P in water from stand of P. stratiotes in Aguapeú River (111.2 mg.L-1) was similar to water from stand of P. stratiotes in Guaú River (110.9 mg.L-1) and significantly (p<0.05) higher than in water from stands of S. molesta in Preto River (53.5 mg.L-1) and Branco River (63.3 mg.L-1). We concluded that the concentration of phosphorus, probably, is an important factor that determines the distribution of these two species of floating aquatic macrophytes in rivers from the Itanhaém River basin.
Key-words: Limnological characteristics, phosphorus, Pistia stratiotes, Salvinia molesta.