Silicon Consumption and Population Density Changes of Dominant Planktonic Diatoms in Lake Constance

Abstract

(1) Interactions between silicon concentration and diatom growth have been studied in Lake Constance with data on number and volume of cells per unit volume of water and concentration of dissolved reactive silicon. (2) Concentration of dissolved reactive silicon was found to decrease markedly during the spring and summer growth period of diatoms in 1979 and 1980. (3) Amounts of silicon taken up per cell and per unit cell volume have been calculated from the changes in silicon concentration and the increases in population density for several diatom species. The silicon to cell quotient (mg per million cells) varied over a wide range from 0.005 for Stephanodiscus hantzschii to 0.72 for Synedra acus, while that of silicon per unit cell volume (mg mm-3) varied over a narrower range from 0. 10 for Stephanodiscus hantzschii and Fragilaria crotonesis to 0.36 for Synedra acus. (4) A four-compartment model, that allows estimates of the rates of growth and of loss of diatom populations to be calculated, is outlined. (5) Summer succession from Asterionellaformosa to either Fragilaria crotonensis (in 1979) or Stephanodiscus binderanus (in 1980) is explained by interspecific differences in the effects of silicon concentration on growth and death. For Asterionellaformosa, silicon depletion did not stop cell-division but led to the death of most of the population. For Fragilaria crotonensis and Stephanodiscus binderanus cell division stopped but cells did not die and population growth continued after the concentration of dissolved silicon had increased again