Seasonal and annual variation of virioplankton abundance in rivers running through an industrial city (City of Cherepovets, Upper Volga)

The total abundance of virioplankton and the total abundance and biomass of bacterioplankton were determined in two small rivers and in the large Sheksna River in April to October 2009–2011. A high positive correlation is found between the abundance of viruses and bacteria. The abundance of planktonic viruses in small rivers exceeds their abundance in the Sheksna River. In 2010, in all rivers with extremely high water temperatures in summer, the abundance of planktonic viruses was significantly higher than in years with a normal water temperature in summer.