Removing a Dam Can Cause Incredible Initial Recovery for River Ecosystems

Removing a dam could mean all the difference for ecosystems. Scientists have found that river ecosystems show an incredible initial recovery after dam removal.

In this latest study, the researchers focused on a songbird species that flourishes on the salmon-rich side of dams in the western United States. This songbird, though, struggles when it tries to nest on the side closed off from fish and the nutrients that they leave behind.

The bird itself is called the American dipper, which has an unusual feeding style. The bird is equipped with a transparent second eyelid which it uses to see beneath the river's surface as it walks the riverbed, scouring the rocky floor for meals. These mostly include aquatic insects in their larval stages. The birds also eat small fish, including juvenile salmon when they're available.

In this study, the researchers looked at the effects of dams and dam removal on the dipper. The Elwha River, which winds through Washington's Olympic National Park, has had a dam for years. However, starting in 2011, crews started tearing down the dam, which allowed researchers to study how the area and ecosystem changed.

With the removal of the dam, salmon were able to travel the river. The researchers found that birds with salmon access had more marine-derived nutrients and were 20 times more likely to attempt multiple broods. They were also 13 times more likely to stay year-round and had an annual adult survival rate that was 11 percent higher than their salmon-deprived peers.

"It's exciting to be able to show a real positive outcome in conservation," said Christopher Tonra, one of the researchers, in a news release. "We don't always get that. That these rivers can come back within our generation is a really exciting thing. Watching it happen was just incredible."

The findings are published in the journal Ecography.

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