Breweries, cough syrup, toothpaste, paints, polishes, … concrete, animal feed, fertilizers, … dynamite. It is astounding where the remains of diatoms can be found. One might say that many of the wheels making modern life go 'round are studded with the vacant shells of these tiny phytoplankton, which are used as filters, fillers, insulation, and mild abrasives.

The crystalline beauty of diatom shells whipped Victorian era microscopists into giddy covetousness; their durability aids modern research.

"Diatoms are the most powerful tool in our arsenal," said Euan Reavie, Senior Research Associate with the University of Minnesota Duluth’s Natural Resource Research Institute. Reavie is an aquatic ecologist that specializes in paleolimnology — the historical study of lakes and rivers using what they find in sediment.

With funding from Sea Grant and other agencies, Reavie and his colleagues have been examining sediment cores to reveal the extent to which they have captured the story of Great Lakes water quality over the past several centuries. “The most compelling stories are told by diatoms,” Reavie said.

Diatom shells (more correctly called frustules) are composed of silica, the essence of glass. Single frustules are typically smaller than the period at the end of this sentence but they tend to persist for millions of years.

Populations of various species of these tiny glassy-cased phytoplankton are so sensitive to changes in water quality that, by looking at the population trends, the Sea Grant researchers could see that water quality in the western arm of Lake Superior:

• degraded with initial European settlement;
• worsened when the watershed was logged and developed;
• improved as wastewater management modernized.

Victoria Chraïbi, a recent Sea Grant graduate working with Reavie said by examining sediment cores, it appeared that the diatom community reorganized due to nutrient enrichment and then again as people took action to reduce nutrient loads. The cores also revealed trace metal profiles that tracked a period of mining and ore processing which temporarily increased metal loads to the lake in the mid- to late-20th century. Chraïbi suggests that water quality as seen through the lens of diatoms is currently being influenced by atmospheric deposition and changes in the lake's physical and chemical processes associated with climate change.

The human impact story as told through the glass shells of diatoms broke out of the laboratory and into the Great Lakes Aquarium in Duluth, Minnesota. A diatom display intrigues visitors and shares the research story that speaks to human influences on the largest lake in the world by surface area. "For many visitors, this is the first time they have heard about or seen diatoms," said Sarah Erickson, Director of Education at the Great Lakes Aquarium. "They spark an interesting conversation."

What good is a diatom? Diatoms supply the oxygen in every fourth breath you take. Diatoms are critical in the ecological food chain of streams, lakes and oceans. Scientists have suggested that seeding the ocean with iron to stimulate diatom reproduction could help remove atmospheric carbon dioxide, thus slowing Earth's current warming trend. Diatoms can tell the story of our past. See for yourself; watch these short videos:

Diatoms: Collecting a Core Sample in Lake Superior with Amy Kireta. www.youtube.com/watch?v=Xm7tP-zZ3UA&list=UU62Dxe2pV75obJzzmFkRRtg

Diatoms: Euan Reavie. www.youtube.com/watch?v=ejqbdHhnXCQ&index=11&list=UU62Dxe2pV75obJzzmFkRRtg

Diatoms: Victoria Chraibi.

https://www.youtube.com/watch?v=XxYu2QBEVe4&index=10&list=UU62Dxe2pV75obJzzmFkRRtg

Scientific articles:

Reavie, E.D., and Allinger, L.E. (2011) What have diatoms revealed about the ecological history of Lake Superior? Aquatic Ecosystem Health & Management 14: 396-402. www.ingentaconnect.com/content/tandf/uaeh/2011/00000014/00000004/art00008.

Reavie, E.D., Heathcote, A.J., Shaw Chraïbi, V.L. (2014) Laurentian Great Lakes phytoplankton and their water quality characteristics, including a diatom-based model for paleoreconstruction of phosphorus. PLoS ONE 9(8): e104705. doi:10.1371/journal.pone.0104705