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Sediment Samples to Reveal Duluth Harbor History

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Sediment Samples to Reveal Duluth Harbor History

Euan Reavie slid his gloved hand under the open end of a 5-foot plastic cylinder filled with muck and smiled. There, in his arms, was about 300 years of history, sucked from the bottom of Superior Bay in the St. Louis River estuary.

“We’ve got a goo record in this one,” Reavie proclaimed to this research team members and a few onlookers.

Reavie is an aquatic ecologist at the Natural Resources Research Institute (NRRI) at UMD who specializes in paleolimnology — the study of historic sediment in lakes and rivers.

The three feet of muck and other sediment Reavie pulled form the harbor contains thousands of dead algae and other diatoms, mostly single-cell phytoplankton. Scientists already know that certain diatoms do well when water is clean and ecosystems healthy. Others thrive when rivers are choked with organic matter, sewage and other pollution.

While many other scientists have taken core samples out of the harbor sediment, most are only 6-18 inches deep, and most were aimed at looking for specific toxic hot spots. In these much deeper samples, each layer of sediment will offer a snapshot of water quality for the year in which it settled on the bottom.

“This is going to give us 200, maybe 300 years of water quality history,” Reavie said. “The different species (of diatoms) will tell us what the water conditions are.”

Reavie and his team members were out on the harbor ice, about halfway between Park Point and Superior. They’ll take the core back to the NRRI lab and slice it very thin, with scientists checking not just diatoms but also chemistry, looking for things like legacy mercury and other pollutants that stacked up over time.

Lisa Allinger - research fellow at the NRRI - and Meagan Aliff - graduate research assistant - help Euan Reavie - NRRI senior research associate assemble and prepare the equipment needed to gat
Lisa Allinger, research fellow at the NRRI, and Meagan Aliff, graduate research assistant, help Euan Reavie, NRRI senior research associate, assemble and prepare the equipment needed to gather the sediment sample.

They’ll even look for wild rice seeds deep in the sediment sample to see if the plant was once a major component of the estuary ecosystem before industrialization.

They picked a spot to pull the sediment sample where the harbor hadn’t been dredged in the past and that hadn’t been piled on or filled in — a rare location in an otherwise greatly altered estuary that runs about 20 miles from Lake Superior to the Fond du Lac dam.

Reavie manned the ice auger while his team – including Lisa Allinger, a research fellow on the project – measured the water depth (about 13 feet), the ice thickness (about 24 inches), and then helped assemble the sediment-sucking cylinders.

The goal is to find out exactly how clean and healthy the river was before settlement, before industry and dredging and shipping, before the Clean Water Act, before the Western Lake Superior Sanitary District removed nasty stuff from human and industrial waste, before the Great Lakes Restoration Act and before the growing effort to restore problem areas like the Sr. Louis River Area of Concern.

The $298,000 project will pull and analyze sediment core samples at seven sites along the river and one just off the mouth in Lake Superior. The effort was funded through the federal Great Lakes Restoration program and the Minnesota Clean Water Land and Legacy fund.

“We need to know how far we’ve com from the days when the river was choked with organic matter and fish were dying because there wasn’t enough oxygen. And we need to know how far we still need to go,” said Dianne Desotelle, who coordinates restoration of the St. Louis River Area of Concern for the Minnesota Pollution Control Agency. “We know the river is cleaner now than it was in the late 1970s. But we don’t know how clean it was before settlement, before the pollution got so bad.”

Tracey Ledder of the Superior-based Lake Superior National Estuarine Research Reserve program, said government reports as early as the 1930s already listed the harbor as a heavily polluted area. But there was little or no information before that.

“We only have date back to when we (humans) had already started to pollute it. What we want to know is what it was like pre-pollution,” Ledder said.

It could be a year or longer before all the results are analyzed, although some data, such as chemical makeup of the sediment, will be available before then.

There’s no rush. But state, federal and local officials have set a goal of “de-listing” the St. Louis River estuary as an area of concern by 2025. The sediment history project is just one of a half-dozen projects now underway across the estuary to restore fish habitat, identify and cap or clean toxic hot spots and otherwise restore the river into a thriving ecosystem to benefit nature and people.

“We don’t know if we can make that timeline. We don’t know if we can solve all the problems,” Desotelle said. “But maybe we can reach a point where the river is as good as we can bring it back, That’s what we’re trying to do.”

Sediment samples to reveal Duluth Harbor history 1
Euan Reavie sets the equipment that will take sediment samples which they hope will reveal Duluth Harbor’s history.


Article written by John Myers of the Duluth News Tribune; “Sediment samples to reveal Duluth Harbor history”; March 17, 2014