We compared the values of the biomass, chemical composition and nutritive value of the emergent aquatic macrophyte S. alterniflora in a river affected by the discharge of domestic sewage (Guaú River) and in an unpolluted river (Itanhaém River). S. alterniflora, water and sediment samples were obtained in the two rivers in November, 2001. The Guaú River presented the highest levels of Total-N and Total-P in the water (415 and 674 µg.L-1, respectively) and in the sediment (0.25 e 0.20% of the Dry Mass, respectively), when compared to the water (TN = 105 µg.L-1; TP = 20 µg.L-1) and the sediment (NT = 0.12% DM; PT = 0.05% DM) of the Itanhaém River. Aerial (316 g DM.m-2) and subterraneous (425 g DM.m-2) biomass of S. alterniflora were significantly higher in the Guaú River than in the Itanhaém River (146 and 115 g DM.m-2, respectively). In addition, the values of TN, protein, TP, lipids and soluble carbohydrates were significantly higher in S. alterniflora biomass from the Guaú River. On the other hand, the values of the polyphenols and the cell wall fraction were significantly higher in the biomass of S. alterniflora from the Itanhaém River. We concluded that domestic sewage discharge in water bodies may increase the biomass and change the chemical composition of S. alterniflora. The high N and P availability in the water of the Guaú River is probably the cause of the higher biomass, TN, TP, protein, lipids and soluble carbohydrates measured in S. alterniflora in this river.
biomass; chemical composition; nutritive value; Spartina alterniflora
