¹Department of Biological Sciences, Kent State University, Kent, OH 44242
²Fisheries and Oceans Canada, Great Lakes Laboratory for Fisheries and Aquatic Sciences, Burlington, ON L7R 4A6

*Corresponding author: ttrzebuc@kent.edu

Summary

   Areas of hypoxia and anoxia in aquatic ecosystems are often called “dead zones” because low oxygen concentrations prevent survival of higher organisms, especially fish. The purpose of this investigation was to compare two sites in Lake Erie, a central basin site with a record of hypoxia and an eastern basin site without hypoxia, in order to investigate microbial processes under oxygen-stressed conditions. This research was conducted during June, July, and August of 2004 aboard the CCGS Limnos. Phytoplankton communities in the productive surface waters appear to be meso-oligotrophic and weakly P-limited based on particulate phosphorus concentration and phosphate uptake velocities. The structure and function of the microbial community, including heterotrophic bacteria, phytoplankton, autotrophic picoplankton, and heterotrophic nanoflagellates, were analyzed. Microbial biomass and activity did not appear to be impacted by hypoxic conditions in August. Throughout the season, microbial community biomass and activity in the central basin hypolimnion was equal to or greater than that in the eastern basin. Bacterial productivity and growth efficiency peaked in July in the central basin hypolimnion, possibly as a precursor to August hypoxia. All size fractions of primary productivity were greater in the central basin. This suggests that even hypolimnetic phytoplankton remain active, thereby retaining the capability to photosynthesize. The Lake Erie “dead zone” is very much “alive” for members of the microbial community which maintain the ability to survive and thrive in the oxygen-stressed hypolimnion of the central basin. The continued use of the term “dead zone” to describe hypoxia is discouraged.