A murky question: What does groundwater have to do with lake algal blooms?

The causes of troublesome lake algae are not always clear, but an interdisciplinary research project with W.K. Kellogg Biological Station researcher Elena Litchman and a colleague from Michigan State University have identified one factor: colder groundwater that feeds some inland lakes. Their finding could help predict the formation of harmful algal blooms, or HABS, to mitigate their impact on drinking water, tourism, fishing and fish toxicity.

“I have been monitoring the HABs in Gull Lake in Michigan for many years,” said Elena Litchman, an MSU Foundation professor of aquatic ecology in the Department of Integrative Biology in the College of Natural Science. “We want to understand the processes that lead to HABs.”

A lake could have HABs one year and the next year, the lake is clear. The processes that trigger HABs are complex, making it difficult for researchers to identify a clear answer.  

Toward a better understanding

Litchman collaborated with Phanikumar Mantha, a professor in the Department of Civil and Environmental Engineering in the College of Engineering, combining their expertise in aquatic ecology and hydrological engineering respectively, to create a hydrodynamic model of Gull Lake with the help of Mantha’s former graduate student, Ammar Safaie.

Their research was published Sept. 1 in the Journal of Geophysical Research: Biogeosciences.

To create the model, Safaie crisscrossed Gull Lake to measure varying lake depths as part of a bathymetric survey in which sound waves are transmitted from the boat to the lake bottom. Instruments also measure—at varying depths—lake temperature, dissolved oxygen, nutrients, and phytoplankton. All the data were combined into the model, but one piece was amiss.

“The observed (deep) lake temperatures weren’t matching the models,” Mantha said. “The model’s temperatures were warmer, and it wasn’t making any sense initially.”

The impact of groundwater

After several months, the research team figured out the source of that anomaly: groundwater. Gull Lake is fed with groundwater, which cools deep lake temperatures during summer months. That may inhibit bloom formation.  

“This is an important finding because groundwater levels are declining worldwide,” Mantha said. “Less groundwater means that the deep waters in similar inland lakes may warm, triggering the growth of algae at some depths and depleting oxygen at other depths with implications for the survival of cold-water fish species.”  

This could mean more frequent algae outbreaks in lakes around the world when groundwater is depleted. The team plans to use the model to help predict the chances of HABs in other inland lakes.

This research was supported by the grants from the National Science Foundation 10-27061, 13-31852 and 17-54250. Read the original research article.

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