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Ecologist: Resilience Doesn't Mean Stagnant
Nebraska Ag Connection - 08/09/2019

When one sits down to talk about water and ecosystem resiliency with Steve Thomas, river and stream ecologist with the School of Natural Resources, the conversation quickly meanders just like the streams he studies.

Resilience can mean two things to scientists, he said. Either it can mean an ecosystem is resistant to change in the face of an outside stressor; or it can mean an ecosystem has the ability to return to its previous condition quickly after a disturbance.

"Stream ecosystems in their natural state tend to be both resistant to change and recover quickly once disturbed," he said. "Flow alteration and channel simplification associated with many human activities often compromise both these aspects of ecosystem resilience."

He points out that ecosystems operating naturally are evolving, on their own and at their own pace, and left alone, they grow, change, and sometimes collapse, only to reorganize and thrive again. That cycle, often called panarchy, is drawn to look like an infinity loop or figure 8.

"Resilience doesn't mean conditions remain stagnant," Thomas said. Just look at streams and rivers where water flow changes dramatically over time but the composition of species remains relatively constant by comparison.

His research in Brazil, Trinidad and Nebraska examines waterways over time to see how different variables affect the health of streams and the ecosystems around them. He's interested in knowing how changes in watershed land use and upstream channel conditions impact downstream habitats; how far nutrients like nitrate and phosphate travel in streams and how these stresses alter the food web in downstream areas. He's interested in how these upstream impacts lead to algae blooms that are increasingly impacting water quality and human health and recreation in Nebraska, the Midwest, and across the globe.

Sometimes the research leads Thomas and colleagues to the jungle in Brazil, where they stand knee-deep in water dripping known amounts of nitrate into streams and measuring its disappearance downstream. Other times, it's comparing the diversity of species across different elevations in the Ecuadorean Andes and Rocky Mountains in Colorado.

Thomas said research has shown streams display greater resilience when their flow and the channel conditions are close to their natural condition. As activities in the watershed begin to alter the chemistry and shape of the channel, resilience can be compromised.

"We also know streams are intimately linked to their floodplain under natural conditions and that the interaction between the stream and its floodplain strongly impacts the ecology of the stream," Thomas said. In other words, the stream ecosystem doesn't operate alone, and neither does the ecosystem around the stream. They are connected.

"Streams are very dynamic ecosystems and many are really prone to disturbance," he added. The challenge for Thomas and other researchers lies in figuring out the mechanisms that allow ecosystems to maintain their condition in the face of outside stressors, or quickly return to it after disturbance such as a severe drought or flood.

Thomas is currently applying what he does know about stream and ecosystem health to research in Sao Carlos, Brazil, through a partnership fostered by the Institute of Agriculture and Natural Resources Global Engagement initiative. He's collaborating with researchers from the University of Sao Paulo to explore how restoring riparian forest and grasslands affects nutrient transport and cycling in adjacent streams. Thomas will compare and contrast nutrient retention in Brazilian streams to that of those here in Nebraska.

"We hope to understand how restoration of plant communities next to streams impacts the ability of those streams to remove and retain nitrogen and phosphorus from the water passing through them," he said. "In Brazil, this means hanging the riparian vegetation from sugar cane to native forest while in Nebraska, that often means transitioning from corn or soybeans to native grasses and shrubs."

That project, funded by the São Paulo Research Foundation and the University of Nebraska--Lincoln, runs through August 2020. Whatever the final results are, one thing is certain: The outcomes will either support or discount what scientists already know about the relationship between the two variables, and the knowledge will bring them another step closer to resilience.

To learn more about Thomas' previous research in Trinidad and Ecuador examining how species become locally adapted to their home conditions, visit bit.ly/ThomasEcuador.

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