BGSU research looks at effects of dam removal

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Innovative research out of Bowling Green State University is highlighting the effects of removing long-standing dams from water-based ecosystems and providing a blueprint for future conservation efforts.

BGSU Biological Sciences Professor Paul Moore has been taking students to the Maple River, located in the northern Lower Peninsula of Michigan, just south of the Mackinac Bridge, for nearly 30 years to teach aquatic ecology.

When talks began more than a decade ago about removing the aging Lake Kathleen Dam that connects to the river’s system, a research team led by Moore began conducting exhaustive sampling of the river.

He led a team of researchers – including more than 100 students over 10 years – to study the river’s complete habitat rather than just one species or variable, and to do so at several different biological organization levels.

An initial lack of funding, however, stalled the dam removal project as the team continued to study the river’s ecosystem. Eventually, the project received the green light and work was completed in 2019.

By the time the river stabilized in the following years, the research team had compiled a full decade of data that tracked the Maple River’s ecology before, during and after the dam removal, marking what is likely the most comprehensive longitudinal study ever completed on the topic.

“Usually for a study, people focus on one thing – fish, water flow or sediment – and it’s typically a two or three-year sample that covers that one thing prior to the dam removal and after the dam removal,” Moore said. “Well, we had a 10-year period prior to the dam removal, during the dam removal and three years after the dam removal.”

The project was a collaboration between BGSU and the University of Michigan Biological Station, through which students from both universities studied, observed and sampled the river from 2012-21.

The resulting research, published in Science of the Total Environment, already has drawn wide praise from other scientists due to its comprehensiveness on an issue of significant importance.

As expected, the team’s findings revealed that removing a dam had significant consequences for the river’s habitat. Without the dam, the river’s temperature and pH changed, then stabilized at new levels.

One of the primary concerns about removing a dam is that water flow increase can cause a sudden, dramatic increase in sediment, which can carry undesirable substances like lead, mercury and pesticides upstream.

Sediment washing away algae can have grave consequences for the lower food web, but Moore said the company that performed the dam removal largely mitigated these effects by slowly changing water levels and building sediment traps.

“All these rocks are covered with algae, microbes and all these things that are really critical to the ecology of the stream, and releasing all this sediment can be like taking sandpaper and scrubbing it all out,” Moore said. “But we saw virtually no scouring.”

The lower food web – which includes macroinvertebrates like worms, snails, beetles and crayfish – serves as a vital food source for fish and birds, which is especially of note due to the Maple River’s status as a “blue ribbon” trout stream that is highly popular for fishing.

Due to the dam’s removal, researchers observed changes in how the lower food web is now composed. Macroinvertebrates such as crayfish that subsist on matter like grass and leaves are thriving, while the river-wide decrease in pH brought notable changes to the algae available for the species that rely upon it.

“Because we saw changes in temperature and pH, we’ve seen community compositions change,” Moore said. “What was there previously was green algae, but what’s there now is brown algae. The brown algae are actually more nutritious, so we’re seeing the ecology get enhanced because we’re changing the food sources.”

The dam removal did bring worrisome erosion – researchers observed the increase in water flow cutting into banks, which can deposit sediment and even whole trees into the river – but overall, saw a remarkable recovery for the Maple River.

One of the primary conclusions of the research is that an ecosystem has the propensity to recover quickly so long as it is allowed to regenerate without interference.

“One thing we were surprised about is how quickly the river recovered,” Moore said. “As soon as the dam comes out, there are changes in flow and everything’s decimated. But a year after the work, the algae were there, the macroinvertebrates were there, colonization was there. The recovery of the stream – if left alone – was really quick.”

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