A hole in Huron

[Spiel]

A hole in Huron

Newly discovered sinkholes sustain unusual bacteria at the bottom of the Great Lake

 

 

Tuesday, March 10, 2009

Kevin Mayhood / THE COLUMBUS DISPATCH

 

 

Tiny, ancient life forms that thrive in ice-covered lakes in Antarctica and at thermal vents deep on the ocean floor have been discovered in saltwater percolating through the floor of Lake Huron.

 

Mats of bright white and purple algae abound in sinkholes close to the freshwater plants and fish that teem through much of the lake.

 

"We're seeing organisms and biochemical processes we're not supposed to be seeing in the Great Lakes," said Bopaiah Biddanda, an aquatic microbial ecologist at the Annis Water Resources Institute at Grand Valley State University in Michigan.

 

His colleague, Stephen Nold, a biology professor at the University of Wisconsin-Stout, said scientists are getting their first glances at this discovery.

 

"It's like a rain forest on the bottom of Lake Huron; we don't know what species are there."

 

Or, for that matter, what might lurk at the bottom of Erie and the other Great Lakes.

 

"It's strange that salt-savoring bacteria from deep in the ocean would be in the lake," said Eugene Braig, assistant director of the Ohio Sea Grant program.

 

"It certainly is of interest to me."

 

Scientists from several Wisconsin and Michigan universities and the National Oceanic and Atmospheric Administration recently made the discoveries and plan to look for the sinkholes and unique ecosystems in Lake Erie and Lake Michigan in the next couple of years.

 

But first things first. How in the world do salt-tolerant species exist in a freshwater lake?

 

To crack this mystery, you have to go back hundreds of millions of years, when an ocean covered the area.

 

Eventually, the ocean dried up. Later, the Great Lakes formed.

 

Today, there are freshwater aquifers beneath the lakes.

 

In Huron, water bubbles from such an aquifer rise through the old sea floor, eroding and absorbing minerals left behind in the ancient limestone and dolomite, said Steve Ruberg, an observing systems researcher at NOAA's Great Lakes Environmental Research Laboratory.

 

This denser water pools in the sinkholes there, creating the right environment for the microbes.

 

The sinkholes, which are about a yard deep and stretch in length from a few yards to 100 yards, were discovered in 2001 by scientists looking for shipwrecks.

 

After several years of preparation, the team of researchers began exploring with both divers and submersibles.

 

Two weeks ago, the team announced that it had found unique ecosystems that include species normally found half a world away. "It looks like the bacteria have mechanisms to distribute themselves worldwide," Nold said. "They find a niche -- a spot where they can grow."

 

After examining the DNA of one of the finds, cyanobacteria, researchers found that it is a close cousin of genus Oscillatoria, bacteria found at the bottom of clear, frozen lakes in Antarctica and at the bottom of a lake in Switzerland that is fed by sulfur springs.

 

The purple microbes can feed through standard photosynthesis and anoxygenic photosynthesis. In the absence of oxygen, the microbes use hydrogen sulfide instead of water as a source of electrons for the process.

 

The researchers found mats of white bacteria in deep, dark sinkholes where oxygenated lake water meets the high-sulfur water.

 

The bacteria appear to be related to Beggiatoa, which live deep in the ocean near geothermal vents and cold seeps.

 

These microbes feed off hydrogen sulfide through chemosynthesis, a lightless process akin to photosynthesis.

 

The bacteria make carbohydrates from the oxidation of sulfur compounds.

 

"In a true sense, this is a look at ancient times," Biddanda said. "Only microbes existed at the beginning of the Earth.

 

"The conditions are similar: shallow seas, water very rich in sulfate and carbonate and chloride and almost depleted of oxygen."

 

Monitors set up in two of the sinkholes will run through the summer to determine whether the flow of water through the floor is constant and how much it contributes to the water in the lake.

 

Biddanda said they will try to gauge the age of the water by studying its radionuclides.

 

Although the findings are unprecedented, researchers say the discovery in Lake Huron might not be unique. "We've heard from people that there are sinkholes in Lake Erie," Ruberg said.

 

The same kind of aquifer that abuts Lake Huron also surrounds Lake Erie and much of Lake Michigan.

 

And there are sinkholes on land associated with the aquifers.

 

For example, the Blue Hole of Castalia is a spring that pumps more than 7,500 gallons per minute of fresh, oxygen-poor water into Cold Creek and nearby Sandusky Bay.

 

Similar holes are reported in Sandusky Bay as well, making it a likely spot to look, said John Hageman, lab manager of Ohio State University's Stone Laboratory on Put-in-Bay.

 

Mark Jones, a scientist with the Ohio Geological Survey, said he'd be surprised if no sinkholes are found in Lake Erie. However, he said he doesn't expect to learn of isolated microclimates.

 

"Consider the western basin averages 10 or so meters in depth, maybe less," Jones said.

 

He said the shallow lake is influenced more by sunlight and the warmth of the air than the rest of the Great Lakes, and that might make the lake inhospitable to the fauna seen in Huron.

 

Nold said that makes further research all the more interesting.

 

"A change in pH or temperature or any number of factors would make a difference," he said.

 

"What's there may be the same as what's been found in other habitats or something completely different."

 

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