SECTION 10 



DETERMINING THRESHOLD AND BIOLOGICALLY DANGEROUS 

 CONCENTRATIONS OF BLUE-GREEN ALGAE IN WATER BODIES 



L.A. Sirenko, A.Ya. Malyarevskaya, and T.I. Birger' 



The economic activities of man have caused eutrophication in many water 

 bodies. One of the significant results of this is a change in the species 

 composition and number of aquatic organisms in an affected area. This often 

 causes a disturbance in the regulation processes in the ecosystem of the 

 water body. The blue-green algae bloom may be the most important example 

 of disturbance in the ecological balance under the influence of anthropo- 

 genic factors. In this case, excessive development of individual species 

 of algal flora determines the whole complex of the internal water body pro- 

 cesses and the ecosystem's final biological productivity. As is known, in 

 their vital processes algae excrete into the environment about 30% of the 

 total carbon absorbed by them during 24 hours or about 40% of the daily 

 pure photosynthesis production. 



Excreted products include: Organic acids which determine the environ- 

 mental buffer action and its pH; amino acids and peptides, which contribute 

 to the formation of the complex and lower the toxicity of heavy metals; 

 polysaccharide substances which adsorb on their surface the most varied 

 types of ions, aldehydes, terpenes, polyphenol compounds; and also other 

 biologically active substances which dominate biological activity. 



Toxins found in individual species of algae (blue-green, flagellateae, 

 peridium) also play a very important role among exogenous metabolites. 



Blue-green algae excreting some substances during life processes, and 

 decomposition not only form a definite biotic environmental background, but 

 also change the hydrochemical indices of the environment if their accumula- 

 tion is considerable. In this case, the quantity of oxygen diminishes, the 

 content of carbonic acid increases and the environmental reaction changes. 

 In other words, the effect of algae on the aquatic organisms depends on a 

 whole complex of biotic and abiotic factors. 



In addition to this direct influence, blue-green algae may also affect 

 the aquatic organisms indirectly. Namely, the substances they excrete may 

 intensify or weaken to a considerable degree the action of different chemi- 



Institute of Hydrobiology, Academy of Sciences, Ukrainian SSR. 



105 



