Effet de l'enrichissement continu en nitrates sur les populations de Diatomées isolées à l'aide d'enceintes expérimentales placées dans un étang oligotrophe

The influence of nitrates (NH₄NO₃ KNO₃ and Ca(NO₃₎₂) on Diatom populations has been studied. These populations were isolated by enclosures with transparent walls, without bottom or lid, placed in an oligotrophic pond. The addition of NH₄NO₃ generally resulted in a decrease in the number of Diatoms and the disappearance of some species. The addition of KNO₃ and Ca(NO₃₎₂ was followed, during some periods, by a very important increase of Achnanthes minutissima, Fragilaria construens and Gomphonema parvulum.