Fate and effects of cadmium on the development of North Sea coastal plankton communities, enclosed in plastic bags containing 1.5 m3 natural water, were studled in 2 experiments.Both experiments were carried out in summer-autumn and lasted 11 and 7 weeks respectively.Cadmium chloride was added to different bags in single doses of 1, 5 and 50 pg Cd I-'; in the first experiment additional doses of 100 and 250 pg Cd 1-' were added in the middle of the experiment to 2 of 6 bags.At the end of the experiments 4-9 % of the added cadmium was recovered in the sediment, the remainder was still in the water phase.Addition of 5 or 50 pg Cd I-' resulted in slightly higher phytoplankton concentrations in one experiment.The mortality of copepods was increased by addition of 250 or 100 pg Cd I-'; addition of 50 pg Cd 1-' resulted in a much lower zooplankton biomass.Due to differences in the sensitivity of different species, a d d ~t i o n of 50 pg Cd I-' caused a change In species compos~tion of the zooplankton community compared to controls.Growth of Pleurobrachia p ~l e u s was inhibited at 5 and 1 pg Cd I-', leading to differences in the numbers of copepods between controls and treated bags.At concentrations of 50 pg C d I-' or higher no P. pileus were found.Concentrations of 1-5 pg Cd 1-' occur locally in polluted waters.The first experiment lasted more than 3 months and showed that nutrient regeneration rates in the bags are large enough to enable the system to persist without artificial nutrient additions.
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Jan Jurjen Kuiper (1981) studied this question.