Degradação biológica da matéria orgânica dissolvida em seis reservatórios tropicais

Abstract

Heterotrophic bacteria play a central role in the degradation of dissolved organic matter (DOM) and nutrient cycling in aquatic ecosystems. Their metabolism can be affected by several factors, such as origin and quality of DOM, concentration of organic nutrients, temperature, concentration of dissolved oxygen, among others. Reservoirs are artificial ecosystems built for specific purposes, such as water suppliers and electricity generation. Reservoirs have different compartments with unique characteristics, named as river, transition and dam. Our hypothesis is that DOM degradation is higher in the dam region and into the reservoirs with the highest trophic status, as they present more labile carbon sources for bacterias. To test this hypothesis, two experiments were carried out: one of short time incubation, to assess the degradation of DOM through oxygen consumption, and one of long time incubation, to evaluate the nutrients cycling over time. Neither the trophic state nor the compartmentalization had any effect on the analyzed parameters, possibly due to the influence of the relatively low hydraulic retention times, making the influence of the river greater in relation to the other compartments. However, in two experiments, we observed that both DOM degradation and the nutrient cycling were greater in the accumulation reservoirs compared to the run-of-river reservoirs, possibly due to the fact that the more labile DOM found in the first reservoirs used has undergone internal recycling processes, such as humification.