Quantification of Factors controlling the Development of Anabaena Circinalis Blooms

Report No WSAA 88

January 1995

 

SYNOPSIS

 

The Algal Bioassay technique has enabled the quantification of several factors of major importance in the development of Anabaena circinalis, a potentially toxic cyanobacterial species. A combination of high water temperature (optimum 35°C) and saturating light intensity (120 mE/m²/sec), comparable to summer conditions, resulted in optimum growth rate. At lower water temperatures, photoinhibition of algae occurred at approximately 10% of optimum surface light intensity (approx. 2000 mE/m²/sec), indicating that surface blooms are less likely to persist during winter. Increased growth rate was found to occur at a total nitrogen (N) to phosphorus (P) ratio of about 10:1 at constant P and with increasing P concentration at constant N, although luxuriant uptake of P was found to be very efficient in maintaining algal cells. This cyanobacterium is a freshwater species displaying inhibition in growth at approximately 7 ppt salinity. Silica too, was found to inhibit the growth of A. circinalis at concentrations above 5 mg/L. Finally, tripton particles were found to influence growth rate by the adsorption of P and essential trace elements required by cyanobacteria for growth.

 

In order to prevent the development of cyanobacterial blooms, total catchment management (TCM) must be applied whereby a combination of factors are manipulated to select against this troublesome group of algae from flourishing in our waterways. Quantification of Anabaena circinalis growth at the environmental parameters selected in this study may aid in enabling the most efficient TCM applications to be made.

 

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