The Influence of Extracellular Algal Products on the Surface Tension of Water

Abstract

By means of laboratory experiments and field investigations in Lake Zürich, the influence of extracellular algal products on the surface tension of water was investigated. Of interest to us was the question of whether a reduction in the surface tension, i.e. surface pressure, is dependent on (i) algal species or phytoplankton and phytoneuston community, (ii) the growth phase of the species or community concerned, and (iii) the abundance or concentration of phytoplankton and phytoneuston biomass. A dependence was ascertained in the case of the first two points. The laboratory experiments showed that extracellular products originating from diatoms give rise to a distinctly higher surface pressure than those originating from green and blue-green algae; and that the change in surface pressure occurs during the later part of the stationary algal growth phase. In Lake Zürich, high values of surface pressure were measured at the time of the collapse of the diatom bloom, and comparatively low values during the period of dominance of the blue-green alga Oscillatoria rubescens in the winter months. Changes in surface pressure established during the course of a year can thus be explained partly in terms of the phytoplankton and phytoneuston succession.