Abstract
The aim of this study was to characterize phytoplankton associations, as well as discuss controlling factors determining algal dominance in a eutrophic tropical reservoir, Mundaú, Pernambuco, Brazil. Water samples were collected during the dry period (January/2005) and the rainy period (June/2005). The samples were collected from both limnetic and littoral regions, and the phytoplankton assemblages identified from current literature after preservation in formaldehyde 4%. At the same time as sampling was done, in situ measurements of water temperature, transparency, dissolved oxygen, and pH were also taken. Total phosphorus, total nitrogen concentration and the Trophic State Index were subsequently determined in the laboratory. Phytoplankton density (ind. L-1) was estimated using an inverted Zeiss microscope. Grouping of the phytoplankton associations was carried out using the Reynolds phytosociological classification. During the dry period, reservoir water showed low dissolved oxygen concentrations, alkaline pH and was relatively turbid compared to the situation during the rainy season. Reservoir water is limited by nitrogen during both seasonal periods. The Trophic State Index is classified as determining eutrophic conditions. Phytoplankton was represented by 70 infrageneric taxa grouped in 16 functional associations, with the majority typical of eutrophic systems. This fact is supported by quantitative analysis, which shows the dominance of S associations comprising exclusively R-strategist cyanobacteria.
Highlights
Aquatic ecosystems show spatial and temporal variability promoted by high levels of uncertainty in relation to phytoplankton communities
Several recent studies have correlated phytoplankton composition with environmental factors in an attempt to propose models and patterns for lakes and reservoirs under distinct trophic states. This advance was motivated by a presupposition worked out by Hutchinson (1961), that phytoplankton community behavior is at variance with the Competitive Exclusion Principle, in eutrophic systems
Other taxons were sub-dominated in the ecosystem with densities higher than 5% (Tab. 3)
Summary
Aquatic ecosystems show spatial and temporal variability promoted by high levels of uncertainty in relation to phytoplankton communities. This variability, a result of biotic and abiotic factors, causes constant reorganization in both relative abundance and composition of phytoplanktonic associations. Several recent studies have correlated phytoplankton composition with environmental factors in an attempt to propose models and patterns for lakes and reservoirs under distinct trophic states. This advance was motivated by a presupposition worked out by Hutchinson (1961), that phytoplankton community behavior is at variance with the Competitive Exclusion Principle, in eutrophic systems
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