Dynamics of Cadmium-Stressed Plankton Communities

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Abstract
Structural and functional responses of plankton communities to Cd stress were studied during 1977 in Lake Michigan [Michigan, USA] using small-volume (8 l) completely sealed enclosures, and in Canada''s Experimental Lakes Area (ELA) Lake 223 using large-volume (1.5 .times. 105 l) open-surface enclosures. In Lake Michigan, reductions of the average abundance of microcrustaceans by Cd were significantly greater in light or shallow epilimnetic incubations than they were in dark or deep epilimnetic incubations. Measurements of dissolved O2 indicated that this interaction with light (depth) was an indirect effect due to a reduction of photosynthesis and primary production. Zooplankton density and species diversity were not significantly affected within 21 days by Cd concentrations .ltoreq. 0.6 and .ltoreq. 1.2 .mu.g Cd/l, respectively; final dissolved O2 concentration and percentage similarity (PS) of the crustacean zooplankton community were significantly reduced by .gtoreq. 0.2 .mu.g Cd/l. In the ELA lake 223 experiment, the reducing effect of Cd on zooplankton density increased up to 31 days after Cd enrichment and then decreased, probably due to decreasing Cd concentrations in the water. Values of PS on day 24 for the ELA enclosures enriched with 1 and 3 .mu.g Cd/l were within the 95% confidence limits for individual values predicted from a regression of PS on Cd for the 21-day Lake Michigan experiments.