Item

Abstract

Heterotrophic parameters of a black water lake (Lago Tupé) and four different Várzea lakes of the Janauacá region (L. Castanho, L. Muru-Murú, L. Jacaré and L. Jutaí Grande) were studied during high and low water phases. Besides heterotrophic planktonic bacterial populations, saprobic bacterial
populations, chlorophyll-a content, and dissolved organic carbon concentration were determined because of their possible relationship to chemoorganotrophy. Saprobic bacterial numbers of black water lake (L. Tupé) ranged from 2.7 to 1.3 x 10^4/l and a maximum uptake velocity (Vmax) ranged from
0.09 - 9.3 pg glucose/l/h. Várzea lakes receive water from Rio Solimões have higher bacterial numbers.
The saprobic bacterial varied between 4 x 10^3 - 2.2x 10^5 during high water phase and 1.1 - 9 x 10^5/l
during low water phase. The maximum velocity of uptake (Vmax) for the Vârzea lakes varied between 0.039 and 0.662 pg glucose/l/h during high water phase and 1.36 - 2.944 pg glucose/h during low water phase. Comparison of kinetic data from several lakes suggests a relationship between the bacterial
uptake rate of glucose and phytoplankton production. Both saprobic bacterial numbers and activity in L. Tupé may be close to the minimum recorded in the freshwater environment. In the Várzea lakes
studied, the relationship between Vmax and phytoplankton biomass was quite evident (r = 0.963). The total bacterial populations of Várzea lakes were very high and ranged from 2.1 - 11.6 x 10^8/l during high water phase and 4,2 - 15.6 x 10^9/l during low water phase. The dynamics of the bacteria in the
Amazon lakes is characterized by high bacterial numbers, large seasonal fluctuations, and very slow turnover times (Tt) for the available organic matter. There is a good evidence that water level fluctuations is a very important ecological parameter which regulates the microbiological productivity of
aquatic ecosystem in the Central Amazon lakes. Such observations were also made earlier on the primary production of algae (SCHMIDT 1973) and on the production of floating meadows (JUNK 1970).