Aspects of the uptake of dissolved oxygen in Cabiunas and Imboassica lagoons (Macae, RJ)

In this work, we describe qualitative and quantitative aspects of the cycli ng of detritus of aquatic macrophytes and carbohydrates in two coastal lago ons of the northeastern part of the State of Rio de Janeiro. Samples of wat er of the Imboassica and Cabiunas lagoons were enriched with sucrose. Sampl es of water of the Cabiunas lagoon were also utilized to arrange mineraliza tion chambers with fragments of three species of aquatic macrophytes found in these lagoons (Typha domingensis, Potamogeton stenostachys and Nymphaea ampla). Following that, the bottles were aerated and incubated (in the labo ratory)for a period of 8 days. The concentrations of dissolved oxygen, the pH, the electrical conductivity and the temperature were daily measured. Th e anaerobic processes were inhibited by periodical aeration of the bottles. The results suggested that the mineralization process in Imboassica lagoon was more efficient; in Cabiunas lagoon the process of immobilization of th e organic matter was dominant. In the short term, maximum oxygen uptake occ urred in the mineralization of N. ampla, followed by the mineralization of P. stenostachys and of T. domingensis. However, it was estimated that in lo ng term the mineralization of P. stenostachys showed a greater oxygen uptak e.