Effects of Cadmium Stress on the Plankton Communities of Experimental Ponds

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Abstract
Experimental ponds were used to determine the impact of a single low-level addition of cadmium on naturally occuring plankton communities. Cadmium (as CdCl2) was added to two ponds to create nominal concentrations of 5 μgCd/1 and two ponds served as non-addition controls. Plankton responses were then monitored for 31 days. Cadmium concentrations declined rapidly in treated ponds to < 1 μg/1 by day 10. Biomass and productivity of the phytoplankton community were slightly lower in treated ponds immediately following cadmium addition, but by day 10 had returned to control pond levels. The zooplankton community exhibited a wide range of responses. Simocephalus serrulatus populations were virtually eliminated in treated ponds initially, but later recovered. In situ and laboratory bioassays verified this decreasing effect of cadmium with time. Populations of another cladoceran, Diaphanosoma brachyurum, were enhanced in the cadmium ponds; it appeared earlier and was more abundant on each date sampled. Copepod densities were unaffected by cadmium addition.