A diel study in a water column of Lake Maarsseveen I

Abstract

A study was made of vertical distribution of phytoplankton and zooplankton, primary production and grazing in a stratified lake, over a period of 24 hours. Photoresponse curves, made at sunrise and noon, showed great differences. Phytoplankton sampled from 0–5 m and from 5–10 m reacted more or less in the same way, but phytoplankton sampled from the meta- and hypolimnion between 10–18 m showed a low photosynthetic activity. The daily production could for 95% be ascribed to algae smaller than 30 μm. Grazing byDaphnia longispina, Bosmina spec. andEudiaptomus gracilis, The dominant grazers, was concentrated on this small size fraction phytoplankton, especiallyCryptomonas species. At sunrise and at sunrise the next day, phytoplankton species abundancies were determined. A particular great increase was found forCryptomonas cf. erosa. Since other species had been at approximately constant population densities for days before as well as after the particular date, or were rapidly disappearing from the plankton, primary production was supposed to be due largely toC. erosa. A carbon balance over 24 h was made, comparing primary gross production, respiration and grazing with changes in carbon content based on algal cell counts.