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Aquatic biology resurfaces at Cedar Creek

Ecology Professor Robert Sterner has launched a study of nutrient composition in the reserve’s lakes to better understand how excess nutrients cause toxic algae blooms.

In the early 1940s, aquatic biology made a big splash at Cedar Creek Ecosystem Science Reserve when Raymond Lindeman’s research at Cedar Bog Lake showed how energy moved through ecosystems.

For several decades, faculty have focused on land-based environmental research at the University of Minnesota field station. But aquatic biology is resurfacing thanks to Bob Sterner, professor of ecology, evolution and behavior. Sterner recently launched a long-term study of nutrient composition in the reserve's many lakes.

The project is funded by the Long-Term Ecological Research (LTER) network, a group of 26 field research sites managed by the National Science Foundation. Most ecological experiments end after a few years, but LTER supports research that runs for decades. This can help scientists understand how ecosystems respond to slow processes like climate change.

Cedar Creek Ecosystem Science Reserve is one of LTER's research sites. Owned by the University of Minnesota since the 1940s, the reserve marks the site where three great ecosystems in North America – prairie, pine forest, and oak forest – converge. As a result it has high biological diversity, which creates unique research opportunities.

Sterner and his lab started their field research last summer, making frequent trips to the field station, where they paddled kayaks onto Cedar Bog Lake, Fish Lake, Ice Lake, Beckman Lake Bog, and Cedar Creek itself to scoop up water samples. Back in the lab, they tested the water for the presence of algae and several kinds of phosphorus and nitrogen.

By monitoring nitrogen and phosphorus in the lakes over the long term, the team hopes to resolve an ecological debate about pollution management. “To feed the world’s growing population, we have to apply nutrients to crops, but to make agriculture sustainable, we need to prevent run-off from polluting our waters,” Sterner says. Historically, government agencies have tightly controlled phosphorus run-off from lawns and agricultural fields to prevent toxic algal blooms in lakes and streams. But is phosphorus the only nutrient that matters? Do others, like nitrogen, contribute to blooms?

It could depend on the timescale. On a short scale, many nutrients could affect algae, but over a period of many years, the larger ecosystem could compensate for many of these, leaving only one nutrient to limit algae. Sterner's project will ultimately measure nutrients and algal blooms on both short and long-term scales.

In a sense, Sterner’s research picks up where Lindeman left off, he says. Long an admirer of Lindeman, Sterner wrote a short biography of the pioneering ecologist published by the Association for the Sciences in Limnology and Oceanography in 2012.

"Lindeman built a comprehensive picture of an ecosystem based on energy flow. He knew about nutrients, but there was no good way to measure them at the time," Sterner says. "It's not a straight line, but what we're doing is a natural next step."

So far, the Sterner lab has only one season of data. It will take many years for long-term patterns to emerge, but the lab has already found short-term differences in the nutrient levels in these lakes.

In the future, this research could lead to more targeted water pollution management. But Sterner cautions that if one nutrient limits algal blooms over the long term, this does not mean we can ignore the others. "Whether they matter or not locally is different from whether they matter or not downstream," he says. "The smarter we are about the way we control nutrients, the more efficient our management will be."

— Margaret Taylor