Control of cadmium levels in Holopedium gibberum (crustacea, cladocera) in canadian shield lakes

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Abstract
Cadmium concentrations (Cd‐h) of Holopedium gibberum (Crustacea, Cladocera) collected from 26 Canadian Shield lakes with positive alkalinity ranged from 0.9 to 31 μg/g. Levels were positively correlated with aqueous Cd concentrations (Cd‐aq) and negatively correlated with clutch size. Animals collected from acidified lakes did not have elevated Cd‐h concentrations despite elevated Cd‐aq levels. In three intensive study lakes, the presence of eggs lowered Cd‐h concentrations and Cd‐h levels frequently increased with increases in body size. In two of these lakes, many H. gibberum occupied waters rich in particulate iron just above the anoxic interface. Cd‐h levels fell when animals were experimentally confined to this layer, presumably because much of the Cd‐aq was adsorbed by the particulate iron and was unavailable for uptake. We suggest that the behavior of animals, specifically their movement to light‐scattering layers just above the anoxic interface, influences the accumulation of Cd by H. gibberum in Canadian Shield lakes.