A glimpse of how humans impact the environment

Research conducted at South Center Lake gains national attention—

Toward the end of the Jan. 15 Chisago County Board of Commissioners meeting, Commissioner George McMahon mentioned, with a little laugh, that “We made the New York Times.” What he was referring is the well-known paper’s coverage of scientific research, also published Jan. 8 in Ecology Letters, conducted at South Center Lake near Lindstrom by Lawrence J. Weider, Punidan D. Jeyasingh — both professors, Weider from the University of Oklahoma and Jeyasingh from Oklahoma State University — and other researchers.

A Daphnia pulicaria clone isolated from 60-64 cm sediment layer in South Center Lake. The estimated age of the Daphnia is 600-700 years old. Photo by Dagmar Frisch

A Daphnia pulicaria clone isolated from 60-64 cm sediment layer in South Center Lake. The estimated age of the Daphnia is 600-700 years old. Photo by Dagmar Frisch

What they found could amount to a breakthrough discovery when it comes to studying how human activity impacts other species.

Starting in 2009, the researchers began collecting sediment samples from the depths of the lake.

Inside the sediment was the organism they were looking to study: Daphnia, which are tiny, shrimp-like creatures that are commonly referred to as “water fleas,” even though they’re really crustaceans.

The researchers took a boat out on the lake and repeatedly lowered a tube about 3 feet into the sediment.

Weider, reached by phone Monday, said he thought the collection might yield Daphnia that were a couple decades old, but preliminary estimates have the Daphnia being far older than his initial estimate.

He said Lead-210 dating puts the Daphnia at about 700 years old, but the researchers will have a better idea of their exact age when Carbon-14 dating information becomes available in about a year.

“They’re definitely centuries old,” Weider said. “Whether they’re 700 years old or not, we’ll have to wait to determine that.”

The normal lifespan of a Daphnia is about eight weeks, so that raises the question: How did these Daphnia survive for so long?

Weider explained that the Daphnia found in the sediment had not yet hatched. Essentially, they were in a state of suspended animation, and Weider and his colleagues brought them to life in a lab by exposing them to heat and light conditions that they would experience during a spring season.

Larry Weider (standing) and Ryan O’Grady taking sediment core from South Center Lake in July 2010. Photo by Punidan Jeyasingh

Larry Weider (standing) and Ryan O’Grady taking sediment core from South Center Lake in July 2010. Photo by Punidan Jeyasingh

What allowed the Daphnia to survive so long were the thick shells that covered their eggs.

“These eggs are enclosed in this very resistant casing, kind of like a pea pod,” Weider said.

With Daphnia about a decade old, Weider said they typically hatch at a level of about 90 percent.

But with Daphnia that are much older, like the ones brought up from the bottom of South Center Lake, the probability of “resurrecting” them is around 1 percent.

“You have to have a fairly large sample size of eggs, and the success rate of hatching is really quite small,” Weider said.

What the research means

Weider said the history of South Center Lakes and two other lakes he and his colleagues are researching — Hill Lake in Aitkin County and Madison Lake in Blue Earth County — has been documented for decades, which is one of the reasons that the researchers were attracted to this area.

The other reason they came to these lakes is they fit the depth parameters the team was looking for, and there is a good amount of history available about human settlement in those areas.

Weider said by comparing the centuries-old Daphnia to research conducted at the lakes in the past couple of decades, the scientists can learn how Daphnia have reacted to increased pollutants that have been introduced into their ecosystems.

“Daphnia, over the years, have been a very important bioassay organism,” Weider said. “So, for example, a lot of toxicology laboratories around the world, including the Environmental Protection Agency, use Daphnia as one of their bioassay species to look at the sensitivity (of the organism) to different chemicals.”

In South Center Lake, the amount of phosphorus and other chemicals has increased over centuries, and Weider said the Daphnia, in the researchers’ interpretation, have changed to account for the increased amount of chemicals.

“The genes that we looked at indicated that this species was evolving,” he said.

Weider said it’s interesting to see that the Daphnia are adapting to human impact, but he added a caveat.

“If changes occur too quickly, there is the high probably (of some species) going extinct,” he said.  Weider said the particular species of Daphnia he has been studying probably won’t go extinct due to human activity — he noted there are billions in any given lake — but seeing how they react to that impact provides a window to look through when it comes to thinking about how humans impact other aquatic or land species.

“I think it’s really important that we scientists have outreach to the public and to let folks know that their tax dollars are important for supporting research,” Weider said. “And hopefully the research can come back and provide valuable information so all of us can understand, in our case, how freshwater systems might be changing.”

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