Spring 2021 eNewsletter

Spotlight: Lake Erie’s ‘Dead Zone’ Fuels Sediment Phosphorus Release

Lake Erie central basin sediment core experiment set up in the laboratory. Photo Credit: CIGLR.

New research led by CIGLR graduate student Hanna Anderson and her advisors, Drs. Thomas Johengen and Casey Godwin, is helping to reveal the relationship between two of the most perplexing water quality issues in Lake Erie: hypoxia and it’s consequences for the lake’s biogeochemical cycles. Excessive phosphorus, largely from agricultural sources, fuels annual HABs in Lake Erie’s western basin and contributes to hypoxia. This seasonal hypoxia, defined as a shortage of dissolved oxygen in water, degrades water quality, affects water column redox conditions and biogeochemical cycling, and can be fatal to fish and macroinvertebrates.

The hypoxic conditions in the central basin are believed to drive the release of even more phosphorus from Lake Erie sediments in a widely-recognized process called internal phosphorus loading, which has been documented in Lake Erie since the 1970s. Hanna Anderson, a recent alumna of the University of Michigan School for Environment and Sustainability (SEAS) graduate program, led a monitoring study focused on this seasonal phenomenon. To address her research questions, Hanna worked with her advisors to determine the location and timing of Lake Erie’s internal phosphorus loading and how much this process contributes to the overall nutrient concentration. “Our team used two complementary approaches in our research,” says Anderson. “We used controlled, replicated sediment core incubation experiments and in situ phosphorus analyzers placed in Lake Erie’s central basin to generate a time series of data. The analyzers measured phosphorus concentrations every 6 hours, as well as temperature and dissolved oxygen levels at two sites. As the overlying water in both the lab and field experiments lost total oxygen and became anoxic, we were able to observe and compare the behavior of the sediment-bound phosphorus.”

Hanna Anderson (left) and Russ Miller (right) collecting sediment cores in Lake Erie’s central basin. Photo Credit: CIGLR.

“What’s interesting was that phosphorus was not yet released from the sediments when the water turned hypoxic, when dissolved-oxygen concentrations in the surrounding waters are very low. But, when oxygen in Lake Erie’s central basin was depleted completely and the water became anoxic, a rapid increase in phosphorus was observed,” says Anderson. The observations from this study have helped define the bounds of phosphorus flux relative to oxygen levels in the central basin.

Anderson’s interest in large-scale ecosystem research and the Great Lakes led her to the graduate program at SEAS and CIGLR. “I wanted to apply my laboratory skills and broaden my experience in the environmental sciences,” says Anderson. “I’ve always been interested in the connectivity of environmental processes, and am fascinated by what you find looking at ecosystems and landscapes from the bottom up. My experience at the University of Michigan and CIGLR has exposed me to a plethora of environmental research and monitoring techniques, and has given me the opportunity to make connections with the researchers who work in both an academic and government research setting. I had so much fun doing my fieldwork on the research vessels, cruising around Lake Erie, and getting messy while collecting sediment cores!”

What’s next for Anderson? She was recently accepted into the Ph.D. program at Columbia University’s Earth and Environmental Science department, focusing on oceanic microbes. Best of luck to you, Hanna!

Related Resources:

  • Anderson, H.S., T.H. Johengen, C.M. Godwin, H. Purcell, P.J. Alsip, S.A. Ruberg, and L.A. Mason. 2021. Continuous In Situ Nutrient Analyzers Pinpoint the Onset and Rate of Internal P Loading under Anoxia in Lake Erie’s Central Basin. Environmental Science & Technology: Water. (DOI:1021/acsestwater.0c00138).

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