Further Observations on the Seasonal Cycle of Melosira Italica (EHR.) Kutz. Subsp. Subarctica O. Mull.

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Abstract
The changes in the abundance of the diatom in the plankton of two lakes from week to week or even day to day have been followed for a year. Evidence is brought forward to show that these changes are almost always caused by concomitant changes in certain physical and chemical factors which have previously been shown to control the general periodicity of this diatom over a period of 7 1/2 years. The main factor is turbulence, itself a function of wind action on, and temperature distribution within, the water mass. Under stratified conditions, the cells, by virtue of their high rate of sinking, pass rapidly to the deposits. However, large loss of cells by sedimentation can also occur under isothermal conditions if almost dead calm conditions persist for several days. The amount of loss of cells by outflow is also important. Limitation of growth by nutrient shortage occurred in one lake. It is suggested that silica was the nutrient responsible. The abundance of the diatom differed in the two lakes. This may be related to the number of live cells left on the deeper deposits in the previous summer and to differences in the morphology and location of the lakes.

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