2003 Volume 89 Issue 4 Pages 446-453
In two series of the culture experiments to observe responses of a natural phytoplankton assemblage to enrichment with different steelmaking slags, de-Si slag and de-P slag temporal change of the assemblage in abundance and taxonomic composition was recorded. Phytoplankton chlorophyll a and abundance of diatoms attained their maxima on the 13th day in the first series, whereas on the 5th day in the second series. Among diatoms Skeletonema costatum was benefited most strikingly by the enrichments, particularly with the de-P slag. After the maxima, phytoplankton and diatoms as well readily decreased without forming a stationary state. Such a rapid initiation of decrease might be cased by the following three reasons, which were not directly caused by the slag enrichment. 1) Grazing by microheterotrophs such as amoebae, 2) physiological death caused by severe nitrogen depletion, and 3) sinking accelerated by coagulation with, fibrous exudate and filamentous bacteria.