Anderson Medeiros dos Santos

Primary production and mortality of Eleocharis interstincta in response to water level fluctuations

This study evaluated the net aboveground primary production (NAPP) of Eleocharis interstincta in response to water level fluctuations. Sampling was carried out every 2 weeks from June 1997 to June 1998 in the littoral region of the Jurubatiba (coastal) lagoon (Rio de Janeiro), where three 0.0625 m 2 study plots were selected for cohort observation. Three quadrats from the same area were also harvested. In the laboratory, stems were oven-dried at 70 ◦ C for 3 days to reach constant weight, their heights measured and their weights taken to determine biomass. The water level fluctuated seasonally, with two periods when the water failed to cover the macrophyte stand—the end of winter (natural dry out) and in summer (artificial breaching of the sandbar). Cohort average height and mean water level in the stand were positively correlated (r = 0.91, P< 0.01). The relative growth rate of E. interstincta was not influenced by water level fluctuations, since different growth rates were observed even when the water level was stable ( P< 0.05). Stem mortality and herbivory occurred throughout the year and accounted for 14.8 and 1.8% of net annual aboveground primary production (NAAPP), respectively. NAPP varied from 0.5 to 1.8 g dry weight m −2 per day, and there was a significant correlation with average water level ( P< 0.05), indicating that water level has an important role in E. interstincta dynamics.

Metabolism and Gaseous Exchanges in Two Coastal Lagoons from Rio de Janeiro with Distinct Limnological Characteristics

The global metabolism and exchange of gases with the atmosphere were measured during a diel cycle in two tropical coastal lagoons, using the curves of carbon dioxide and dissolved oxygen. Heterotrophic metabolism (net CO2 production and net O2 consumption) was observed in a black water lagoon (Comprida), and autotrophic metabolism (net O2 production and net CO2 consumption) in a clear water lagoon (Imboassica). These differences were attributed to the limnological characteristics of both ecosystems, especially to dissolved organic carbon and the attenuation coefficient of light, which are much higher in the first environment. During the diel cycle analyzed there was a net release of carbon dioxide into the atmosphere in the first lagoon and a net uptake by the water in the second one. Thus, the importance of coastal lagoons for the global carbon budget deserves further study.

Effects of spatial and environmental factors on benthic a macroinvertebrate community

Interactions between terrestrial and aquatic systems influence the structure of river habitats and, consequently, affect their benthic macroinvertebrate composition. The aim of this study was to evaluate the effects of spatial and environmental variables (local physical and chemical variables of water and regional landscape characteristics) on the benthic macroinvertebrate community of the Pandeiros River Basin. Biotic and abiotic variables were evaluated at 20 sampling sites distributed across the primary sub-basins of the Pandeiros River Basin. We found that the macroinvertebrates were primarily affected by environmental variables. The most important environmental variables were pebble proportion and water conductivity at the local scale (7.2% of explained variation) and elevation and nonforest areas at the regional scale (6.9% of explained variation). The spatial variables were representative only in shared explained variation with the environmental matrices (local-spatial = 0.2% and regional-spatial = 2%; all matrices combined = 4.4%). Sampling sites with higher non-forest areas, lower elevations, and steeper slopes presented low pebble fractions and higher electrical conductivities. Habitat diversity was lower when the percentage of pebbles decreased, resulting in decreased taxonomic richness and diversity in macroinvertebrate communities. High electrical conductivities and non-forest areas also had negative effects on macroinvertebrate density due to the loss of habitat diversity. We conclude that higher proportions of pebbles in the substrate and higher altitudes were likely the primary variables for positive effects on the taxonomic richness and density of macroinvertebrate communities.

Short term fluctuations and succession trends in tropical floodplain vegetation measured by correspondence analysis

The aim of this work was to study the aquatic macrophytes community development to distinguish the fluctuations from succession trends at different temporal and spatial scales in the Upper Parana River floodplain. The samples were collected quarterly from May 2000 to March 2002 in seven lakes with different degrees of connectivity from the main river channel and analyzed by between-class correspondence analysis. It was difficult to establish any pattern of community development at local scale but at a higher level of organization, disconnected lakes were characterized by fluctuation of the floristic composition. Connected lakes showed a straight trajectory, indicating that succession was occurring at these sites. Probably the income of propagules and diaspores from the river into connected lakes was the driving force of the observed change in community composition.

Aspects of the uptake of dissolved oxygen in Cabiúnas and Imboassica Lagoons (Macaé, RJ)

In this work, we describe qualitative and quantitative aspects of the cycling of detritus of aquatic macrophytes and carbohydrates in two coastal lagoons of the northeastern part of the State of Rio de Janeiro. Samples of water of the Imboassica and Cabiunas lagoons were enriched with sucrose. Samples of water of the Cabiunas lagoon were also utilized to arrange mineralization 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 laboratory) for a period of 8 days. The concentrations of dissolved oxygen, the pH, the electrical conductivity and the temperature were daily measured. The 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 the organic matter was dominant. In the short term, maximum oxygen uptake occurred in the mineralization of N. ampla, followed by the mineralization of P. stenostachys and of T. domingensis. However, it was estimated that in long term the mineralization of P. stenostachys showed a greater oxygen uptake.