Abstract
AIM: This study examines the short-term changes of phytoplankton in an oxbow lake on the floodplain of the Acre River, Amazonia, Brazil. METHODS: Samples were taken with a Van Dorn bottle, at three depths (surface, middle and bottom), in two periods (low waters and high waters), for seven consecutive days in two schedules, night and morning. RESULTS: Phytoplankton was represented by 198 taxa and the Class Euglenophyceae, with 62 taxa, was the best-represented group in both periods. There were abrupt changes in the community during the high waters (potamophase). During this period, in conditions of partial atelomixis, we recorded higher values of phytoplankton biovolume and dominance of Gonyostomum semen (Ehr.) Dies. (Raphidophyceae). CONCLUSIONS: In the low waters (limnophase), conditions in the lake were more stable, the diversity and rate of change in the community were lower, and the frequent periods of stratification and mixing were responsible for the dominance of Geitlerinema sp. (Cyanobacteria).
Highlights
Floodplains are complex, highly dynamic and heterogeneous ecosystems, which contain flooded land areas and lakes and channels associated with the major rivers and their tributaries
Tropical floodplain lakes pass through two distinct phases, potamophase and limnophase which mainly depend on hydrologic dynamics of tributary-headwaters
The greater species richness detected during the potamophase was possibly related to the prolonged thermal stratification and greater availability of nutrients from the influx of allochthonous material into the lake, caused by the flood pulse. These results agree with those reported by other studies focusing on the phytoplankton of Brazilian floodplain lakes (Ibañez, 1998; Train and Rodrigues, 2004; Melo et al, 2005; Bovo-Scomparin and Train, 2008; Phlips et al, 2008)
Summary
Floodplains are complex, highly dynamic and heterogeneous ecosystems, which contain flooded land areas and lakes and channels associated with the major rivers and their tributaries. These aquatic habitats differ in their physical and chemical characteristics and are subject to periodic disturbances that promote high spatial and temporal variability, changing the successional processes of their aquatic communities and resulting in high diversity (Ward et al, 1999). This variability occurs at smaller scales, resulting from stochastic events (such as rain and wind) that outweigh the predictable annual cycles and govern the structure of freshwater aquatic habitats. The river-floodplain concept of Junk et al (1989) gives emphasis to the interactions and exchanges between the main channel of the river and adjacent water bodies as well as terrestrial environments subject to flooding, so that distinct connectivity among rivers and lentic environments, changing the physical and chemical properties of the environment and is considered as the main structuring force in these environments.
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