Phytoplankton distribution and periodicity in a series of four linked ponds

Abstract

Phytoplankton distribution and periodicity patterns were investigated in a series of four intermittently linked ponds during the period January 1984 to December 1987. The ponds, each with an area of less than one hectare, are located within the boundaries of Windsor Great Park, Berkshire. During the middle two of the four field seasons studied the ponds were subjected to mechanical disturbances which involved the dredging and enlargement of all basins. Inverted microscope counts of the algae in sedimented water samples indicated a phytoplankton succession characteristic of eutrophic bodies of water. The vernal increase was consistently dominated by the Bacillariophyceae mainly Asterionella formosa and Stephanodiscus ref hantzschii. Asterionella formosa is normally associated with larger more open water areas and may have been living at the limit of its ecological range. Diatoms were succeeded largely by species from the Chlorophyceae, Cryptophyceae and Euglenophyceae. Cyanobacteria were conspicuous only occasionally during the summer months. Changes in phytoplankton distribution and composition were observed following dredging operations, these changes suggested a reversion to less eutrophic conditions in ponds one, two and three; this was not apparent in pond four. Additionally, Stephanodiscus ref hantzschii was succeeded by Asterionella formosa as the dominant diatom during spring growth, a factor possibly associated with basin enlargement. Flagellates rather than other species were more apparent in the turbid conditions which obtained after dredging. Algae collected from the benthos indicated the presence of planktonic and bottom living species such as Caloneis silicula and Gyrosigma spencerii. These typically benthic species were not observed in sedimented samples.