Steve Colman, Large Lakes Observatory: Great Lakes Sediment Holds Clues to Freshwater Threats

December 12, 2011

Many parts of the ocean are better understood than some of the Earth's large lakes, despite the fact that these are key reservoirs for much of the fresh water on the planet. Since 1994, scientists at the Large Lakes Observatory (LLO) have been working to change that. With support from the National Science Foundation (NSF), LLO scientists study the biology, chemistry, physics and geology of large lakes around the world.

"As I started doing work in Lake Superior, I came to realize that there had been very little done in the way of scientific study of these lakes beyond the biology of the fish," says LLO founder and oceanographer Tom Johnson. "The University of Minnesota Duluth decided that they wanted to have an institute in Duluth, and the idea was to have expertise locally to look after the welfare of Lake Superior. When I was interviewed for the job, I was interested in those objectives, but also wanted to see the Large Lakes Observatory be global in outlook."

LLO director Steve Colman says there are a wide variety of impacts to large lakes. "In the United States, they range from Lake Erie, which is the most impacted and has had pollutant problems both with nutrient loading and invasive species, to Lake Superior, whose waters are mostly in pretty good shape," explains Colman.

Currently there are 10 fulltime faculty and approximately 30 graduate students and technicians working at the LLO, plus a team that runs the Research Vessel (R/V) Blue Heron. This 27-meter ship accommodates up to 11 crew and scientists and can operate up to 21 days without a stop in port.

On a short research cruise in July, scientists retrieved tools including a robotic glider, which had been gathering data for about a week on Lake Superior.

"Before it goes out, we give it a set of locations and different mission parameters, such as how deep we want it to go and how often we want it to come up, and we can watch how the physics and the biology of the lake change during that period," explains physicist Jay Austin. "We're looking at things such as chlorophyll fluorescence, turbidity, dissolved oxygen, dissolved organic matter--a whole suite of physical, chemical and biological indicators."

Colman is a geologist and he's focusing on lake sediments.

"In lake basins, you almost invariably are accumulating fine-grain sediments in deep water. Those sediments pile up year after year and each increment is like a little time capsule. The analogy I like to use is that the sediments are like a tape recorder, as they accumulate, they're recording something about the climate, the hydrology, the energy of the lake," says Colman. "Now, it's not always very straightforward to play back that tape. We have to use some pretty fancy chemical and biological analyses to try to figure that out, but, in principle, we have a tape recorder that's recording past history of any place there are lakes in the world."

Colman also says scientists have tried to reconstruct what conditions were like in lakes that were adjacent to ancient civilizations, such as those in the Mayan area of the Yucatan and Guatemala.

"We can actually go back in the lake sediments to see whether there was a big climate shift when the empire fell or environmental problems or soil erosion, for instance, and we can reconstruct some of that to give us more insight about human history," he says.

This summer, the R/V Blue Heron completed a 17-day research cruise on Lakes Superior, Huron and Erie--focused on how a buildup of nitrates may impact the ecology of all the Great Lakes.

"This was a unique sampling trip for us," says University of Minnesota professor Jacques Finlay, who studies the ecology of aquatic ecosystems. "We reached many sections of the lakes that we don’t normally see."

Another big project for the LLO looks at changes underway at Lake Malawi in Africa. Lake levels there could drop sharply as agricultural demand for water intensifies in the coming decades, unless policies on water allocation are developed with care.

"We currently have an extensive project in Lake Malawi in East Africa, which is a lake that a developing country depends on for its livelihood, not just for protein from the extensive fisheries there, but for power," says Austin. "The lake level is very sensitive to small changes in climate and if the lake were to just drop another two meters, which it has done in the last century, it would shut off power production for them. So we're very interested in the energy balance and the water balance on that lake. That's an example of a lake where the more we can develop an understanding of how it works, the more likely we are going to be able to help to protect and more carefully manage it."

The LLO has attracted scholars and students from several countries, with research opportunities for those who want to understand the science of large lakes and inland seas.

"Just as comparative anatomy advances our knowledge of human health, so too do our studies of large lakes in different settings," says LLO founder Tom Johnson. "We have to compare how a big lake works in a temperate system versus tropical or sub polar. Through those kinds of comparisons, we gain insights into the dynamics of these lakes and the processes that are really responsible for maintaining their ecosystems."

"We're interested in the fundamental underpinnings of lakes," adds Austin. "Our focus is on how they function from a scientific perspective rather than how to manage and restore them. But, you need those fundamental underpinnings in order to produce effective management."