Factors influencing phytoplankton growth and succession in Farmoor Reservoir

Weekly observations were made at the Thames Water Authority's Farmoor reservoir during the development of the spring bloom of phytoplankters from November 1973 to March 1974. Counts were made of the phytoplankters, their fungal parasites and the zooplankters. Analyses were made of those chemical parameters which it was thought might exert an influence on phytoplankton growth. Physical and meteorological measurements were also made. The development and decline of four phytoplankton populations were observed. The growth of Asterionella formosa Hass. was interrupted in December when 43·5% of the cells were parastiized by Zygorhizidium affluens Canter. Stephanodiscus astraea (Ehr.) Grün. and Stephanodiscus hantzschii Grün. were not similarly affected. All three diatoms were apparently limited finally by silica depletion. The desmid, Closterium peracerosum Gay. became 66% parasitized by an undescribed chytrid and declined rapidly. Light, turbulence, zooplankton grazing and nutrients other than silica appeared to be unimportant.