SECTION 12 



BALANCE OF ORGANIC MATTER IN THE 

 ECOSYSTEM OF THE RYBINSKIY RESERVOIR 



V.I. Romanenko' 



The Rybinskiy reservoir and its drainage basin are located in the south- 

 ern "taiga" zone, within the boundaries of three districts: Yaroslavskiy, 

 Vologodskiy and Kalininskiy. It was constructed in 1941, and it is one of 

 the largest man-made water bodies in the world with a surface area of 4450 

 km 2 , water volume of 25.4 km 3 and mean depth of 5.6 m. Water inflow, 

 according to data taken over a period of several years, is around 37 km 3 /- 

 year. The Volga, Mologa and Shekana River inflows amount to 2/3 of total 

 inflow, with the rest supplied by small rivers. 



The reservoir freezes in November and thaws (melts) in April or the be- 

 ginning of May. According to Secchi disc readings, transparency during the 

 summer is 1-3 m. The content of particles in water is 3-7 mg/liter. The 

 water is of bicarbonate-calcium type according to chemical analysis. The 

 pH is 7.0-7.5, content of organic matter is around 15 mg C/liter, total N 

 is 1.2 mg N 2 /liter, total phosphorus is 0.04 mg P/liter, and bicarbonate is 

 10-20 mg C/liter (monograph "Rybinskiy reservoir and its life", 1972). 



Data presented below are based on results of long term observations, 

 for some parameters 5-10 years, up to 20 years for others. Analyses were 

 carried out at 15 day intervals from May through November at six stationary 

 stations distributed along the base area of the reservoir (Figure 1). 



INPUT OF ORGANIC MATTER 



In the Rybinskiy reservoir, as in all water bodies, there are two basic 

 sources of organic matter: Internal (authocthonous) and external (alloch- 

 thonous). The photosynthetic production of organic matter by phytoplankton 

 and macrophytic vegetation, which is not large in this reservor (Belavskaya 

 and Kutova, 1963) (approximately 1.8% in the input balance), are the main 

 sources of authocthonous organic matter. Diatoms (Melosira and Aterionella) 



Institute for Biology of the Inland Waters, Academy of Sciences, USSR. 



121 



