Lake Erie Oxygen; The Prehistoric Record

Abstract

Periodic anoxia as a symptom of eutrophication has lasted for hundreds, maybe thousands, of years in the central basin of Lake Erie. Fossil ostracode remains in sediment cores show that a common species, Candona caudata, has been able to survive despite periodic anoxia because of its tolerance to low dissolved oxygen (as low as 2.3 mg/L at 16.5 °C) and a short life cycle of weeks to several months. These qualities have enabled it to survive despite oxygen levels below 2.3 mg/L. Two other species, Candona subtriangulata and Cytherissa lacustris, that were expected in the sediment cores were not present. They were not able to cope with periodic low oxygen levels because of their requirement for higher dissolved oxygen (5.6 mg/L at 11.5 °C, 3.0 mg/L at 12.8 °C) and a life cycle of about 1 yr. This condition appears to have been common in the lower part of some of the sediment cores examined. A time-transgressive change in carbon concentration occurred in the surficial sediments of the central basin. A decrease in carbon started in the Sandusky basin around 4000 yr ago and gradually extended itself to the middle of the central basin by 1220 A.D. The loss of carbonate in the upper part of the sediment profile probably resulted from trapping of carbon dioxide, produced by the decomposition of organic material by oxidation and bacterial activity, in the hypolimnion.Key words: Lake Erie, periodic anoxia, ostracodes, inorganic carbon, organic carbon