(Aug. 22, 2019) EPA Great Lakes National Program Office (GLNPO) scientists aboard the EPA Research Vessel Lake Guardian annually monitor the dissolved oxygen levels in Lake Erie’s central basin. Periodically measuring dissolved oxygen levels throughout the summer helps scientists determine whether there is enough oxygen in the water to support life and to assess trends in Lake Erie’s dissolved oxygen levels.
Dissolved oxygen (DO) in the water is essential for aquatic plants and animals to survive. However, during the warm summer months, the central basin of Lake Erie experiences hypoxia, or low DO levels, near the bottom of the lake. In most years, the DO decreases until there is not enough oxygen to support life – a condition termed anoxia – which creates a “dead zone” at the bottom of the lake.
The size, shape, and onset of this dead zone varies from year to year, but it has formed annually for the last several decades. The dead zone is caused by the geographic shape and location of Lake Erie’s central basin and excess nutrient inputs that overstimulate algal growth. Algae that aren’t consumed by animals die and sink to the bottom of the lake. Decomposition of the dead algae by bacteria depletes the oxygen in the bottom water.
EPA scientists use the Lake Guardian to conduct water sampling in support of GLNPO’s Lake Erie Dissolved Oxygen Monitoring Program. From June to September each year, GLNPO routinely monitors the DO levels in Lake Erie’s central basin waters during six surveys, conducted approximately every two to three weeks. DO concentrations and water temperature data are collected at 10 different long-term sampling sites throughout the basin and are used to track changes throughout the summer.
GLNPO has been monitoring DO concentrations in the central basin of Lake Erie since 1983 to assess the status and trends of hypoxia and inform environmental management decisions. GLNPO and its activities, such as the Lake Erie Dissolved Oxygen Monitoring Program, are funded under the Great Lakes Restoration Initiative.