Ecological and taxonomic studies of filter beds algae

Abstract

An investigation has been carried out on the algal flora of slow sand filter beds. Ecological field studies were made from August 1963 until December 1965 and experimental work was continued until June 1966. The filter beds studied were located at the Ashford Common works of the Metropolitan Water Board, London. The major chemical nutrients, and pH were determined throughout the period together with temperature and penetration of light into the water. Biomass, interpreted from calculated cell volumes, of the major species of algae encountered was used to express the results of cell concentrations. The periodicity end distribution of the algae in the filter beds was investigated. The algal populations present were sub-divided into planktonic, epipelic and attached bottom living species and each one was found to have a distinct seasonal periodicity. Observations suggested that the filter bed algal populations were not often limited by nutrient concentrations but the algae on the sand surface may on several occasions have been limited by low light levels. Experiments to determine the toxicity of copper sulphate to certain species of algae were carried out. The ability of algae to penetrate the sand and to survive was also investigated experimentally. These experiments showed that cells could stay alive in the filter bed sand after cleaning and act as population innocula when the bed was refilled. The flora of the sand surface was compared with that of an in-situ polythene bag to ascertain the effects of nutrient limitation. The variation in cell sizes of Stephanodiscus astraea and Asterionella formosa were investigated together with the relative growth rate, k', of S. astraea, and seasonal variations in both were found.