The effects of cadmium on the successional stages of a freshwater protozoa community.

Microcosms containing protozoan were used to observe the differential effects of cadmium on the successional stages of a community. After 7, 14, and 21 days, 500 micrograms/liter cadmium was added. Some environmental parameters such as pH, conductivity, and nutrient levels affect metal toxicity. The effect of cadmium on diversity, density, and biomass was evident 48 hr after the addition of the metal. The pollutant caused a transition period in each treatment, of a different duration, followed by a recovery of the community. In both the control and the treatments, trophic structure was defined by bacterivore-detritivore, nonselective, and photoautotroph organisms.