Research Update

Lake Michigan ‘Doughnut Effect’ Linked to Deep Water Production

Using recent advances in remote sensing technology, researchers at Michigan Technological University are examining the formation and food web implications of a late winter “doughnut” pattern in the open waters of southern Lake Michigan.

Driven by winter storms, the circular ring of chlorophyll a persists for several weeks in March and April. With Sea Grant funding, W. Charles Kerfoot is leading a team of investigators to document the occurrence and magnitude of this unusual event, which temporarily circulates sediment and nutrients.

According to researchers, the circular pattern coincides with a late-winter distribution pattern of phytoplankton and zooplankton. The winter productivity pulse marked by the “doughnut” helps explain how certain native zooplankton species can successfully over-winter through what was previously thought to be a very unproductive period.

Cross-lake profiles confirmed the chlorophyll a pattern and revealed an underlying vertical structure. Phosphorus-rich coastal sediments were detected at key areas and are believed to enhance deep-water production.