Water securityColorado River’s Low-Flow Sheds Light on Eventual New Normal for Grand Canyon
The Colorado River follows a 1,450-mile route generally southwest from north central Colorado to just east of Las Vegas. From there it turns south to form Arizona’s western border with Nevada and California, and then the border between Mexican states Sonora and Baja California before emptying into the Gulf of California. Between the U.S. and Mexico, 40 million people depend on water from the Colorado.As the climate continues to warm and the amount of water available for humans continues to drop, low flows may become the new normal, he added.
Researchers from Oregon State University say ecological data gathered during a recent low-flow experiment in the Grand Canyon is a key step toward understanding Colorado River ecosystems as the amount of water in the river continues to decline.
Dave Lytle, professor of integrative biology, and Ph.D. students Angelika Kurthen and Jared Freedman teamed with scientists from the United States Geological Survey during the March 2021 project to examine the quantity and diversity of invertebrates in the river. Monitoring aquatic invertebrates is an important tool for keeping track of stream health.
“The Colorado River and its dams are important to cities throughout the Southwest, and as a result of that management the river experiences some pretty unusual flows,” Lytle said. “During the day in the Grand Canyon, river levels can rise several feet, then they can drop down several feet, stranding your boat if you’re not careful. That’s because there’s high electricity demand during the day and lower demand at night.”
The high flow during times of heavy demand for power is known as hydropeaking.
“Hydropeaking can cause trouble for ecosystems downstream, and with our collaborators we’re experimenting with ways to change river flows to make them more compatible with productive ecosystems,” Lytle said. “Invertebrates are food for fish, birds and bats, and we want to enhance that food base by testing out different flow regimes that mesh with management ideas.”
During the low-flow event, releases from Lake Powell through the Glen Canyon Dam were restricted so that the Colorado ran at 4,000 cubic feet per second compared to its usual flow of 8,000 to 15,000 CFS. Lytle’s team took samples to measure the quantity of invertebrates stranded by the low flows and environmental DNA samples to analyze the diversity of invertebrates in the water.
“During this spring’s low flow, gravel bars and parts of channels that had been submerged were exposed for the first time in decades,” Lytle said. “We saw really large areas of vegetation and invasive species like New Zealand mud snails and quagga mussels, which are there in high numbers at the expense of native invertebrates such as black flies, mayflies and midges that are better food sources for native fish.”
