The growth of phytoplankton populations in nature and in culture

Abstract

An investigation over a period of more than two years of phytoplankton,and physical and chemical conditions of the River Thames and the Wraysbury Reservoir in Southern England has indicated seasonal occurrence of phytoplankton populations with diatoms (chiefly Stephanodiscus ref. hantzschii Grun.) forming a large percentage of the populations. During 1984,1985 and 1986, phytoplankton populations occurred most abundantly during the spring (mainly diatom populations) and during the summer (diatoms and green algae in the River Thames,and blue-green algae in the Wraysbury Reservoir). Selected algal taxa were isolated and grown in culture in the laboratory and experiments carried out in which culture conditions have been manipulated in various ways.Such experiments included those involving suspected nutrient limiting factors (e.g.phosphate) as well as physical factors especially those of temperature and light.Ecological records and experimental cultures indicate that the occurrence and growth of diatoms is encouraged by the increasing water temperatures and light intensity during the spring,and by higher levels of nutrient concentrations (i.e.nitrate-nitrogen,phosphate-phosphorus and silica) at all times.On the other hand, the growth of green algae (Chlorophyceae) and blue-green algae (Cyanophyceae) wasinfluenced by the maximum water temperatures and light intensity of the summer period and despite lower nutrient concentrations.Thus,differences in physical and nutrient requirements by phytoplankton populations help to explain the presence of diatoms during the spring and green algae (in the River Thames) and blue-green algae (in the Wraysbury Reservoir) during the summer. Simple investigation of the growth responses of the River Thames and Wraysbury Reservoir phytoplankton populations to River Thames and Wraysbury Reservoir water as natural culture media were performed.The results indicated that the River Thames and Wraysbury Reservoir are potentially able to support considerable crops of phytoplankton populations,and that the potential is present throughout the year.