Abstract
Cu 2+ stress was exerted on an aquatic microcosm containing green algae ( Chlorella and Scenedesmus), a filamentous blue-green alga, ciliata protozoa ( Cyclidium), two rotifers ( Philodina and Lepadella), aquatic oligochaetes (one species), and bacteria (five species or more), and the changes in population density and community metabolism were observed. Exposure to Cu 2+ in a static system in the early and middle phases of heterotrophic succession showed that the shift thus induced was greater in the early phase than in the middle phase. This shows the variations of the response to stress at successive stages. The response of the system was compared in a continuous-flow system on the basis of the amount of Cu 2+ added, at two concentration levels of organic matter (1 and 50 ppm). The shift thus induced was greater at the high nutrient level than at the low nutrient level. This indicates that in a given system containing the same biological species, the response to stress varies with the nutrient level. These characteristic responses of an ecosystem to chemical stress are one of the factors to be taken into account when the toxicity of a chemical agent on a natural ecosystem is predicted.
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