Copper inhibition of phytoplankton in Saginaw Bay, Lake Huron

Abstract

Field surveys and bioassays during 1999 and 2000 demonstrated trace metal effects on the phytoplankton of inner and outer regions of Saginaw Bay, Lake Huron. Addition of as little as 1 µg·L–1 copper suppressed algal biomass, measured as particulate chlorophyll a, compared with control treatments, additions of ethylenediaminetetraacetic acid, or additions of carrier water alone. Suppression effects of copper, added alone or in combination with cadmium, lead, and thallium, were evident in inner and outer regions of Saginaw Bay during both spring and summer when phytoplankton communities were composed alternatively of diatoms and cyanobacteria. Experimental treatments were conducted in parallel with measurements of metal concentrations and metal complexation capacities of lake water collected by ultraclean trace metal techniques. Despite apparent overchelation of dissolved copper by organic ligands in Saginaw Bay, additions of a few tens of nanomoles of copper per litre strongly reduces algal biomass compared with control treatments. These results suggest that metal concentrations in some Great Lakes waters in equilibrium with natural chelators may be above the essential requirements and potentially at levels of incipient toxicity to the native phytoplankton communities.