Abstract
The aim of this research was to study the flood pulse influence and the anthropic impact caused by bauxite tailings on the chemical composition of O. glumaepatula in Batata lake (PA, Brazil). Sampling was carried out in stands of O. glumaepatula in the low-water, filling, high-water, and drawdown periods in impacted and natural areas of Batata lake. During the low-water and drawdown periods the stands of O. glumaepatula were exposed, and in the filling and high-water periods the water depth was respectively 1.4 and 3.8 m. The collected material was dried at 70 degrees C, ground, and concentrations of total phosphorus, total nitrogen, organic carbon, and energy content were determined. The results indicate that the biomass increase, caused by the rise in water level, has a dilution effect on nitrogen and phosphorus concentrations in O. glumaepatula. The energy contents did not present significant differences in any of the studied periods. The results suggest that from the low water to filling period, nitrogen becomes more limiting to O. glumaepatula in the impacted area, whereas phosphorus becomes more limiting in the natural area. The population of O. glumaepatula contributes to the recovery of the impacted area of Batata lake as the detritus from this species accumulates over the sediment. This accumulation impedes future re-suspension of the bauxite tailings and increases the organic matter and nutrient concentrations in the impacted sediment.
Highlights
Aquatic macrophytes play an important role in the biogeochemical cycles of Amazonian ecosystems due to their capacity to store large amounts of nutrients in comparison with sediment and water (Howard-Williams & Junk, 1977)
The nitrogen and phosphorus concentrations in O. glumaepatula decreased as the individuals of this species grew as the water level increased in the two studied areas
The organic carbon concentrations, which increased with the growth of individuals of O. glumaepatula, presented a pattern contrary to the that of the phosphorus and nitrogen concentrations (Fig. 1)
Summary
Aquatic macrophytes play an important role in the biogeochemical cycles of Amazonian ecosystems due to their capacity to store large amounts of nutrients in comparison with sediment and water (Howard-Williams & Junk, 1977). This characteristic is even more pronounced in ecosystems with low nutrient concentrations, such as the clear and black water Amazonian ecosystems (Sioli, 1984; Setaro & Melack, 1984; Esteves et al, 1990). Chemical composition analysis of aquatic macrophytes is fundamental in determining the influence of this community on water column characteristics (Nogueira et al, 1996; Camargo, 1991). It allows calculating nutrient amounts stored in this community (Barbieri et al, 1984). Wetzel (1992) has pointed out the importance of the aquatic macrophyte biomass and chemical composition in understanding the food chain and nutrient cycling in shallow aquatic ecosystems
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