The Mineralization of Plankton

Abstract

The rate and the thoroughness of the decomposition of plankton remains are important factors in the cycles of some nutrients in lakes. Experimental data on the mineralization of plankton in vitro are available, especially of marine organisms, but quantitative observations on this process in nature are not mentioned in the literature. This paper presents the results of such observations, made in Lake Lauzon, Montcalm County, P.Q., by means of a sediment collector described in an earlier paper. The chemical composition of plankton, of sediment collected at the 11-meter level, and of surface bottom sediments are studied. Most of the decomposition of the sinking detritus takes place in the epilimnion of the lake. Sediment collected at the 11-meter level, in weekly intervals, shows a remarkable resemblance in composition with the surface bottom sediments. Most of the nitrogen is liberated in the upper 11 meters of water. The liberation of phosphorus seems to be slower and the surface bottom sediments are actually enriched with this element. Silica is enriched at both the 11-meter level and the bottom of the lake, mainly through the settling of diatom frustules. Hydrolysis of organic matter in the upper 11-meter column of the lake decreases in the course of the summer. Mineralization seems to be practically halted in the oxygen-poor hypolimnion.