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Zusammenfassung:
The present study was performed in Lake Batata, a clear water Amazonian floodplain ecosystem, located
on the right bank of the Trombetas river (Pará State, Brazil). For a period of 10 years (1979-1989), the
lake received a large quantity of bauxite tailings from a nearby mine. These tailings originally covered
about 30 % of the lake sediments, but resuspension and redeposition have resulted in an even wider
distribution of the tailings. Phytoplankton production was measured at dìfferent sites in natural and impacted
areas at different hydrological phases. Incubations were exposed at 5 light depths using (14)C as tracer. All
vertical profiles of primary production exhibited ca. 13 % light inhibition in the surface. The maximum
primary production rates (Pmax) were always found near the surface at approximately 30 cm. Production
rates ranged from 9 to 664 mgC m^(-3) d^(-1), being the higher rates found during low water and lower rates
during high water periods. Transparency measurements were good predictors of phytoplankton attributes.
A strong predictive capacity of the turbidity effect was shown. An increase in turbidity of 3.6 times could
reduce the carbon production in the lake by 51 %. In areal terms, it was estimated that Lake Batata
produces ca. 122 g C m^(-2) per year. Our data reveal that although being poorer in nutrients, clear water
systems are as productive as decanted white water systems. The results suggest that phytoplankton
production is regulated by solar radiation and not nutrient. Despite the turbidity increase caused by
resuspension of tailings, phytoplankton production remains relatively high and still plays a central role to
the carbon flux in Lake Batata, especially during low water hydrological periods.
