SECTION 15 



STRUCTURAL AND FUNCTIONAL CHARACTERISTICS OF SESTON 

 AS INDICES OF WATER POLLUTION 



A. P. Ostapenya 



Plankton has long been a traditional part of ecological investigations 

 related to water pollution. Accumulated data show convincingly that ses- 

 ton, including planktonic, detrital and mineral suspensions are an impor- 

 tant, distinct structural component of aquatic ecosystems, functioning as 

 a single entity. Seston actively influences the quality of water. This 

 influence is diverse, and is evident by its action on the production and 

 destruction stages of the biotic circulation. 



Structural and functional characteristics of the seston are suffi- 

 ciently sensitive for use as an indicator in the evaluation of water pol- 

 lution. 



The concentration of suspended substances in unpolluted waters may 

 vary within a rather wide range. A survey of literature values shows 

 that the concentrations of seston in unpolluted lakes, depending on 

 trophic type, varies from 0.1 to 70 mg dry wt/1. In rivers, even greater 

 concentrations of the suspensions may be observed. However, in spite of 

 differences in content of suspended materials, each may be characterized 

 by definite mean concentrations of seston. Since, in general; the influx 

 of nontoxic pollutants causes an increase in the content of suspended 

 substances in water, the zones of pollution within a water-body may be de- 

 lineated by the increase in concentration of the seston. The River 

 Svisloch serves as a typical example of a polluted stream. As a result 

 of year round observations in 1973, it has been demonstrated that at all 

 stations situated both above and below the source of pollution, no regu- 

 lar seasonal changes in concentration of seston are observed. This 

 apparently suggests that autochtonous suspension plays a minimal role, 

 since its concentration is closely associated with seasonal changes in 

 the production processes. On the cleaner parts of the river, the concen- 

 tration of seston varied from 7 to 25 mg/1 . Below the outfall, the con- 

 centration was greatly increased. Further downstream, approximately 50 

 kilometers, the content of the seston in the water continued to increase, 

 apparently at the expense of heterotrophic synthesis. During all seasons, 

 seston concentrations were approximately three times greater than the 

 unpolluted sections of the river. The distribution of seston at various 

 stations on the River Svisloch during August of 1973 is shown in Figure 1. 



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