Hydropeaking of river water levels is disrupting insect survival, river ecosystems

The research was based in part on a huge citizen science project with more than 2,500 samples taken on the Colorado River in the Grand Canyon, and collaboration of researchers from the U.S. Geological Survey, Oregon State University, Utah State University and Idaho State University.

It raises serious questions about the current practice of raising river volumes up and down every day -- known as hydropeaking -- to meet hour-by-hour electricity demand, which has nearly wiped out local populations of some insects that feed local river ecosystems.

"Insects have evolved to live with occasional extreme floods and droughts, and gradual or seasonal changes in river levels," said David Lytle, a professor of integrative biology in the OSU College of Science.

"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. This can interrupt the egg-laying practices of some species, and the impact of this is poorly appreciated. Until now no one really looked at this, and it's a serious problem."

Hydropeaking is used around the world and is particularly common with hydropower dams in the American West. Rivers are some of the most extensively altered ecosystems on Earth, the researchers wrote in their study, and more than 800,000 dams exist globally. Hydropower provides 19 percent of the world's electricity supply and far exceeds the generation of all other renewable sources combined.

Lytle is a national expert on how organisms and communities are shaped by disturbances such as floods, droughts, and dams, with much of his research focused on aquatic insects. Hydropower dams, in this case, have a particular impact on insects that lay their eggs near the shore of streams, such as a mayfly, stonefly or caddis fly. Given normal water conditions, the eggs are laid slightly below the water surface and soon hatch. But if the water level drops suddenly, they can be stranded, dry out and die before hatching.

In this study, the researchers found a clear correlation between hydropeaking and the number of insect species present, and an almost complete absence of certain insects in some parts of rivers where they should have been present -- including the Colorado River downstream of Glen Canyon and Hoover Dams. A majority of aquatic insects are vulnerable to this phenomenon, the scientists said in their report, and they can be "subject to acute mortality."

Some of these insects, Lytle said, are the food base for fish, birds, bats, and other wildlife.

"The loss of these aquatic insects can have a major impact on fisheries and other aspects of ecosystem health," Lytle said.

The researchers did point out in their study that one possible way to address the problem might be to leave river levels stable for several days at a time -- possibly on weekends when electricity demands did not vary as much -- so that insects could lay their eggs with success. This might help address but not totally solve the problem, Lytle said.

It's been known that dams can impose serious environmental problems, including alterations of flow, temperature, sediment regimes and migratory fish barriers. However, the researchers called the impact of dams on aquatic insects a "hitherto unrecognized life history bottleneck."

"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, a USGS scientist and lead author of the study. "These results may help resource managers improve river health while still meeting societal needs for renewable hydroelectricity."

Funding for this study was provided by the Bureau of Reclamation's Glen Canyon Dam Adaptive Management Program, the U.S. Geological Survey's Southwest Biological Science Center, and the Department of Energy's Western Area Power Administration.