The extent of the polluted zone is evident from the concentrations of sus- 

 pended material in the river. Approximately 160 km below the source, ses- 

 ton values again achieve levels characteristic of non-polluted portions 

 of the river. 



Depending on the intensity of the production processes and the pre- 

 sence of nontoxic substances in waters, the correlation between dissolved 

 and suspended organic matter varies markedly. Usually, dissolved organic 

 substances in unpolluted waters greatly exceed suspended materials. The 

 processes of eutrophication and pollution of waters leads to a consider- 

 able increase in suspended organic matter. Thus, in mesotrophic water 

 bodies, suspended organic matter constitutes about 10 percent of dissolved 

 materials, while in eutrophic waters, the relative content of suspended 

 matter reaches 80 percent or higher. In heavily polluted streams, the 

 content of suspended substances may greatly exceed the content of dis- 

 solved organic matter. 



In the unpolluted part of the Svisloch River, the seston makes up 39 

 percent of the dissolved organic matter. In a significant part of the 

 river below the source of pollution, the relative content of seston rises 

 to 14 percent of dissolved organic matter (DOM). As a result of self- 

 purification processes, within 60 m, the relative content of the seston 

 drops to 17 percent. Thus, the correlation between dissolved and sus- 

 pended organic matter may serve as a convenient indication of the zones 

 of eutrophication and pollution. 



Relative chlorophyll content in seston is also a rather sensitive in- 

 dex of pollution, and may be used for evaluation of the influence of pol- 

 lution on aquatic ecosystems. Generally, the relative chlorophyll con- 

 tent in the seston of the polluted zone is higher than in a clean part of 

 the river. Table 1 shows data on the relative chlorophyll content in the 

 seston of three rivers in Belorussia. All the three streams are moder- 

 ately polluted by domestic and industrial wastes. The relative chloro- 

 phyll content in the seston below the source of pollution increased in the 

 Pripyat, Western Dvina, and Neman by 25, 100, and 70 percent, respec- 

 tively. 



Under the stress of heavy pollution by waste waters, the relative 

 chlorophyll content in the seston may notably decline as a result of large 

 quantity of allochtonous suspensions. Data on the relative chlorophyll 



TABLE 1. RELATIVE CHLOROPHYLL CONTENT OF SESTON IN CLEAN AND 



POLLUTED PARTS OF RIVERS 



Chlorophyll in Seston, % 



River Clean Part - Pol luted Part 



Pripyat 0.040 0.050 



Western Dvina 0.052 0.108 



Neman 0.224 0.390 



151 



