Benthic Macroinvertebrates Modify Copper and Zinc Partitioning in FreshwaterSediment Microcosms

The effects of bioturbation on metal dynamics in freshwater–sediment systems were examined. In general, benthic macroinvertebrates caused significant changes in Cu and Zn partitioning among physicochemical forms in the sediment. The proportion of cation-exchangeable and specifically adsorbed Cu observed in Chub Lake (Muskoka–Haliburton) microcosms colonized by chironomids and chaoborids was greater than that for uncolonized sediment. The same relationship held for Cu in Lohi Lake (Sudbury) microcosms supporting a similar benthic community and for Cu and Zn in Port Credit (Lake Ontario) sediments inhabited by tubificids. The ability of tubificid worms to increase sediment E h was recorded and related to Cu and Zn dynamics. We conclude that macroinvertebrate communities have the potential to increase metal concentrations in the water column, particularly during short episodes of high burrowing activity, and that in situ studies are warranted to verify this potentiality.