Anaerobic decomposition of submerged macrophytes in semiarid aquatic systems under different trophic states, Paraba State, Brazil

The macrophytes play an important role in the regulation of biological and chemical processes in aquatic ecosystems, particularly in shallow lakes. They also play an important role in storage and nutrient cycling, serving as a source of organic matter to native environments. The aim of this study was to describe the kinetic aspects of the nutrients released during the anaerobic decomposition process of Egeria densa Planch and Chara braunii Gmnel macrophytes in waters with different trophic states. The study was conducted in vitro and under anaerobic conditions for determination of both particulate and dissolved fractions of nitrogenous, phosphorus and carbon, in predetermined days in oligotrophic and eutrophic water. Mathematical models were applied to describe the macrophytes decomposition process. Both species showed the same biphasic decay pattern of organic matter and carbon mineralization. The phosphorus, nitrogen and carbon released were high for both species, regardless of the trophic water state. The loss of mass was similar for both species and the nutrients concentration in the dam water did not represent a limiting factor for the mathematical model. Key words: Chara braunii, Egeria densa, mathematical modeling, nitrogen, phosphorus.