Limnological effects of Egeria najas Planchon (Hydrocharitaceae) in the
arms of Itaipu Reservoir (Brazil-Paraguay)
Luis M. Bini1,*, Sidinei M. Thomaz2, Priscilla Carvalho2
1
Departamento de Biologia Geral, ICB, Universidade Federal de Goiás
CP: 131, CEP: 74001-970, Goiânia, GO, Goiás, Brasil. E-mail: bini@icb.ufg.br
2
Universidade Estadual de Maringá, Nupelia, PEA-UEM
Av. Colombo, 5790, CEP: 87020-900, Maringá, PR, Brasil.
E-mail: smthomaz@nupelia.uem.br
Abstract
The limnological effects resulting from the metabolism of Egeria najas Planchon
(Hydrocharitaceae) were evaluated in the arms of the Itaipu Reservoir (Brazil). Due to local
population decline in biomass and coverage, decomposition was the main process that
accounted for the observed limnological changes. Thus, total Kjeldahl nitrogen and total
phosphorus in littoral regions were significantly higher during the periods of E. najas
occurrence. After plant stands disappeared, concentrations were lower and similar to those
measured in the pelagic regions. Probably, the nutrient pump effect explains these results and
E. najas stands act as source of nutrients, especially nitrogen. However, low concentrations
measured after above ground biomass disappearance, the similarity between pelagic and
littoral regions, and the large surface area of pelagic regions indicate that the internal loading
effect is ephemeral and restricted to the littoral regions submitted to the action of naturally
senescing populations. Underwater light regime was negatively affected by E. najas
occurrence. Since E. najas is a canopy forming species, it was inferred that self-shading, the
shading by algae growing above beds, and the high abiogenic turbidity were the factors
responsible for the decline of the local populations analyzed. This and the small areas
colonized and the range of factors that constrained the submerged vegetation expansion in the
arms of Itaipu Reservoir, indicated that ecological problems (i.e., anoxic conditions; reduction
of biodiversity) relative to E. najas metabolism could not impair reservoir uses.