Phosphorus, nitrogen, and carbon contents of macrophytes in lakes lateral to a tropical river (Paranapanema River, São Paulo, Brazil)

Abstract

AIM: The aim of this paper was to determine the phosphorus, nitrogen, and carbon contents of aquatic macrophyte species during two periods of the year in the land-water transition zone of three lakes lateral to the Paranapanema River (Sao Paulo); METHODS: Plants, water, and sediment were collected during two distinct periods (August 1998 and February 1999) in three transects perpendicular to littoral zones of the sampled sites. For the determination of the phosphorus, nitrogen and carbon contents of aquatic macrophyte species, aerial and submerged plant structures (leaves, roots, and stems) were used; RESULTS: In Camargo Lake, which has a poor connection with the river during the dry period (August 1998), the highest nitrogen content was obtained for Salvinia auriculata Aublet, while the highest phosphorus contest was observed for Eichhornia azurea (Swartz) Kunth. During the rainy season (February 1999), Echinochloa polystachya (H.B.K.) Hitch was the species with the highest phosphorus, nitrogen, and carbon contents. In Coqueiral Lake (a lake with great connectivity to the river), the highest phosphorus and nitrogen concentrations during the dry period were observed for Cyperus esculentus L. Similar carbon contents were found for both C. esculentus and Eichhornia azurea. During the rainy season, the species with the highest phosphorus and nitrogen concentrations were E. polystachya, Ludwigia octovalvis (Jacq.) P.H.Raven, and Polygonum spectabile Mart. Considering the plants recorded during the dry period in Cavalos Lake, which is isolated from the river, Myriophyllum aquaticum (Vellozo) Verdcourt was the species with the highest phosphorus and nitrogen concentrations. During the rainy period, C. esculentus and E. azurea had the highest nitrogen concentration. All the aquatic macrophyte species presented similar carbon contents. The highest phosphorus concentration was that of C. esculentus; CONCLUSIONS: The bottom of Camargo and Coqueiral Lakes (both with permanent connection with the river) and some sites of Cavalos (an isolated lake) can be considered similar. They were characterized by sediment with more phosphorus, organic matter, silt, and clay than other sites, which can affect the macro-nutrient content of macrophytes. In the isolated lake, the degradation of submerged plants at the land-water interface contributed to the nutrient pool of aquatic macrophytes after rainfall.