Egeria densa em reservatório do semiárido e relação com cianobactéria tóxica

Abstract

Submerged macrophytes act on the complexity of nutrient dynamics in the coastal regions of aquatic systems by mobilizing phosphorus in the various environmental compartments. They also act in interactions with other producers such as macrophyte-phytoplankton allelopathy interactions, this mechanism is pointed out as a potential factor of inhibition of phytoplankton by submerged macrophytes during the dominance phase of these plants. The first chapter of this thesis aimed to evaluate the influence of submerged macrophytes on phosphorus in the water, sediment and water-sediment interface compartments in the semi-arid eutrophic reservoir, as well as to evaluate the relationship between the concentration of this nutrient present in the macrophyte tissues and the available in the different compartments of a reservoir. We observed a difference in the phosphorus concentration inside and outside the macrophytes banks, being this difference determined by the abundance and intensity of the processes of growth and decomposition of these plants. The entrance of new waters originated from the transposition of a river was an important factor that influenced the abundance of the macrophytes during the study. The main source of phosphorus for the macrophytes was the water-sediment interface. The second chapter had as objective to verify the effects of the physical presence of the submerged macrophyte E. densa on the growth and production of cyanotoxins of the cyanobacteria C. raciborskii. It was hypothesized that the E. densa submerged macrophyte may act as a stressor for the C. raciborskii population, causing a decrease in cyanobacteria biomass and boosting cyanotoxin production. It was tested t he presence of higher biomass and lower biomass of macrophytes on cyanobacteria. As a result, the reduction of Cylindrospermopsis raciborskii grown with Egeria densa as well as the release of toxins in the treatments with presence of Egeria densa was verified, corroborating with the work hypothesis, that reduction of the biomass of cyanobacteria occurred in the treatments with larger biomass and less macrophytes. The values of dissolved phosphorus decreased significantly among the treatments, this reduction was observed in the treatments of greater macrophyte biomass. The results presented in this thesis contribute to the understanding of how submerged macrophytes exert effects on the availability of phosphorus in the various compartments of a system. In addition, it was recorded the entry of water into the studied reservoir, which made it possible to study the effects of this phenomenon on the population of macrophytes and consequent impacts to the environment. In addition, it was possible to observe deleterious actions of submerged macrophytes on C. raciborskii. These findings are closely related to eutrophication processes, since they show the relationship of macrophytes with phosphorus assimilation or phosphorus release events, as well as showing the negative relationship between toxin producing cyanobacteria.