Egeria najas PLANCHON (HYDROCHARITACEAE) E O BALANÇO PARCIAL DE NITROGÊNIO E FÓSFORO EM UM RESERVATÓRIO TROPICAL NO SUDESTE DO BRASIL

• DOI: https://doi.org/10.22533/at.ed.71024040412

• Palavras-chave: macrófita, nutrientes, vazão, eutrofização

• Keywords: macrophyte, nutrients, flow, eutrophication

• Abstract: The species with largest distribution in Volta Grande Reservoir (MG/SP, Brazil) is Egeria najas, which influences the dynamics of nitrogen and phosphorus. To assess this influence, a deterministic interpolation of concentrations of total nitrogen and phosphorus was performed for dry and rainy seasons, as well as the content of such nutrients in water column, E. najas and sediment. With time series it was also possible to calculate the partial mass balance of total nitrogen and phosphorus for Volta Grande Reservoir in the studied period. Mean concentrations of total nitrogen were higher in rainy season (388.9 μg.L-1) than in dry season (174.26 μg.L-1). Otherwise, mean concentrations of total phosphorus were higher in dry season (17.03 μg.L-1) than in rainy season (9.15 μg.L-1). Higher mean contents of total nitrogen were observed in E. najas (32.1 ppm), while phosphorus contents were higher in sediment (29.8 ppm). During the study period (July/2013 to May/2015) Volta Grande Reservoir retained 3,690.35 tons of nitrogen and 150.06 tons of phosphorus. Despite the accumulation of nutrients, the lacustrine region of Volta Grande Reservoir still maintains low concentrations of total phosphorus and nitrogen, probably due to sedimentation and incorporation by Egeria najas, respectively.