Environment: Can dams be operated without killing rivers?

Glen Canyon Dam. Image courtesy NASA Earth Observatory.
Glen Canyon Dam. Image courtesy NASA Earth Observatory.

New study eyes impacts to aquatic insects

Staff Report

Using a vast sample of data collected in a citizen science project, researchers say they’ve been able to discern how hydropeaking affects aquatic insects that form the base of river food chains. The information could help resource managers develop alternative hydropower practices that aren’t as harmful to ecosystems, according to a new study published in the journal BioScience.

Hydropeaking refers to the practice of increasing river flows at times of peak demand, generally during the day. This study shows how abrupt water level changes affect aquatic insects in every stage of life. The research was done by scientists with the U.S. Geological Survey, Oregon State University, Utah State University and Idaho State University.

“For the first time, this study determines the ecological impacts of hydropeaking separated from other dam-imposed stressors, and identifies the specific cause-and-effect relationships responsible for biodiversity loss below hydroelectric dams,” said Ted Kennedy, USGS scientist and lead author of the study.

The scientists evaluated more than 2,500 insect samples taken on the Colorado River in the Grand Canyon, downstream of Glen Canyon Dam. This dataset was collected almost entirely by river guides, educational groups, and other citizen scientists. Researchers also tested the effects of abrupt water levels changes on river health by comparing insect diversity across 16 large dammed rivers in the western United States that vary in the degree of hydropeaking.

Hydropower is, of course, one of the world’s key sources of clean energy, generating about  19 percent of the world’s electricity supply. That’s much more than solar, wind, and other renewable sources combined. But when water releases drastically change river flows with huge daily fluctuations, it creates artificial tides along river shorelines to which freshwater organisms are not adapted.

Insects that lay their eggs near the shoreline of streams are particularly vulnerable to impacts from hydropower dams. Ecologically important insects groups, such as many species of mayfly, stonefly or caddisfly, lay their eggs attached to rocks or vegetation slightly below the water surface, where they soon hatch. If water levels rapidly drop and expose the eggs, they can dry out and die before hatching.

“These large daily rises and peaks in river flows due to hydropower dams are not normal. Prior to the construction of dams, there were almost no major daily changes in river levels in places like the Grand Canyon,” said David Lytle, Oregon State University professor and co-author of the paper. “This can interrupt the egg-laying practices of some species, and the impact of this was poorly appreciated. Until now, no one really looked at this aspect, and our results show that it causes serious problems for river health.”

The new study shows that daily hydropeaking operations on Glen Canyon Dam are at least partially responsible for the absence of mayflies, stoneflies and caddisflies in the Grand Canyon. Changing flow regimes by leaving water levels stable for at least a few days could give bugs a few days to lay their eggs with success.

“If mitigation flows are successful, a more diverse community of aquatic insects should improve the health of the Colorado River ecosystem in Grand Canyon, including the largest remaining population of endangered humpback chub,” said Kennedy.

“Many urgent questions in ecology remain unanswered, because scientists are bumping up against data limitations where it is impossible for them to collect sufficient data to answer complex questions across large landscapes,” said Kennedy. “This study is a powerful example of how citizen science collaborations can fundamentally advance learning and generate important new insights.”

To learn more about USGS science in the Grand Canyon, visit the USGS Grand Canyon Monitoring and Research Center’s website.

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