Influence of stratification on the growth of planktonic Chlorophyceae in a small body of water

Abstract

Growth of chlorophycean algae occurred during summer and autumn in the phytoplankton of Abbot's Pool. both motile and non-motile species were recorded during summer stratification and turbulent conditions in autumn. The largest standing crop in terms of biomass was produced by the growth of Pandorina and concurrently nitrate levels in the epilimnion decreased to below the level of chemical detection. Although nitrate-nitrogen and inorganic phosphorus levels in the epilimnion were severely depleted from July onwards, further growth of phytoplankton including Chlorococcum and Chlamydomas occurred. It is suggested that such nutrients may have become available from the hypolimnion via the process of eddy diffusion. From consideration of the biology of Chlorococcum and Chlamydomonas it is suggested that Chlamydomonas is at a selective advantage during the summer, yet during mixed water conditions with higher levels of nutrients growth of Chlorococcum is favoured. This hypothesis is supported by consideration of the specific rates of population increase of these two algae in Abbot's Pool during summer and autumn.