The effect of environmental parameters and cyanobacterial blooms on phytoplankton dynamics of a Portuguese temperate Lake

Abstract

The increasing occurrence of cyanobacterial blooms in freshwaters is of great concern due to the ability of many cyanobacteria to produce cyanotoxins. In the present work, the eutrophied Vela Lake (Central Portugal), used for recreational purposes and as a water source for agriculture, was monitored every fortnight between 2000 and 2001. Phytoplankton diversity and densities were measured and correlated to environmental parameters. A seasonal phytoplanktonic succession was observed and it was mainly correlated with conductivity, temperature, total suspended solids and nutrients availability (particularly phosphorus). Diatoms were dominant during winter months (inferior temperatures and higher nutrients availability) followed by green algae in early spring and then cyanobacteria from late spring until early autumn (less nutrient availability and higher temperatures). A massive cyanobacterial bloom of Aphanizomenon flos-aquae occurred early in May 2001 and was preceded by the lowest nitrogen levels measured in the water during all the study period. At the time of this bloom senescence, dissolved oxygen was severely depleted and a massive death of ichthyofauna was recorded. A Microcystis aeruginosa bloom was also detected in July 2001 and it occurred following a rapid decrease in abundance of green algae and diatoms. By considering not only the environmental parameters but also the occurrence of cyanobacterial blooms as explanatory variables in a canonical correspondence analysis, the variance explained for the phytoplanktonic assemblage during the study period was increased in about 7% achieving a total of 61.0%, indicating a correlation that may be due to the known competitive advantage and/or allelopathy of the bloom-forming cyanobacteria towards microalgae.

Controlling factors of spring–summer phytoplankton succession in Lake Taihu (Meiliang Bay, China)

“…Large cladocerans often cannot grow and reproduce fast enough to prevent bloom formation, and they always disappear when the bloom becomes dense (ChowFraser, 1986;Gliwicz, 1990). In a canonical correspondence analysis, de Figueiredo et al (2006) indicated the occurrence of cyanobacterial blooms was an important explanatory variable for the phytoplankton assemblage due to the competitive advantage and/or allelopathy of the bloom-forming cyanobacteria toward microalgae. The mechanisms by which environmental factors affect the phytoplankton succession are complex (Reynolds, 1999).…”

Synergistic allelochemicals from a freshwater cyanobacterium

“…The presence of competitors (29)(30)(31) and coexisting heterotrophic bacteria that degrade allelochemical substances (32) have been identified among biotic factors. Light intensity (33), temperature (34), nutrient levels, and pH (35) have been shown to control allelochemical production in some species of cyanobacteria.…”

Short-term dynamics of cladocerans in a eutrophic shallow lake during a shift in the phytoplankton dominance

“…The phytoplankton is dominated by cyanobacteria, Bacillariophyceae (e.g., Cyclotella spp.) and Chlorophyta (de Figueiredo et al, 2006). Submerged macrophytes are scarce and the macrophyte community is dominated by Nymphaea alba .…”

“…Lake Vela, located at the west coast of Portugal, is no exception. Massive cyanobacteria blooms (e.g., Aphanizomenon flos-aquae and Microcystis aeruginosa blooms) have become increasingly frequent and large fish kills have occurred in recent years in Lake Vela de Figueiredo et al, 2006). Moreover, the native fish community has been completely replaced by alien fish (mainly pumpkinseed sunfish).…”