The Colorado River’s unexpected carbon footprint

Flooding a dry riverbed restored vegetation, but released significant amounts of methane and carbon dioxide.

 

When water rushed over the dry riverbed of the Colorado River Delta for the first time in two decades, thousands of bubbles popped up in the sand. Alongside the bank, a group of scientists stood in awe, theorizing that oxygen and nitrogen trapped in the sediment were the cause. But nearly two years later, in early 2016, the team discovered those bubbles were actually composed of  greenhouse gases – methane and carbon dioxide – that dissolved into the water, traveled downstream, and eventually made their way into the air.

The Colorado River supplies water to 40 million people. It is used so heavily by farms and communities in the West that it rarely reaches the ocean, so where the river should meet the Gulf of California, only a dry delta exists. In 2012, Mexico and the U.S. hashed out the Minute 319 pact to allow for a one-time pulse flow to restore water in the Delta so scientists could study the regenerative capability of the floodplain ecosystem. So in 2014, the U.S. released over 100,000 acre-feet of water at Morelos Dam near Yuma, Arizona, to restore wildlife and native plant habitats in the Delta downstream. But a new study by University of Florida, University of Arizona, Yale University and University of Washington researchers shows the water also caused the ground to rapidly emit carbon stored for years beneath the riverbeds, which could have an impact on the global carbon cycle and affect future river restoration.

A view of the Colorado River Delta where it meets the Sea of Cortez.

“It’s still a big unknown on the true magnitude of these fluxes, but these large river(beds) are turning out to have really high concentrations of carbon dioxide and methane,” says David Butman, an environmental science and engineering professor at the University of Washington who worked on the study. “Looking at the exchanges of carbon gasses between landscapes, the atmosphere, and water as we look to restore these disturbed ecosystems may be important.”

The study, funded in part by the National Science Foundation, is a step toward understanding carbon balance in water systems and the impact it could have on carbon levels on land and in the ocean. It’s still unclear why carbon was released, but the study documented that 30 percent more greenhouse gases came out of the riverbed and dissolved into the water at one site during the Minute 319 flow than before it (they’re still working to determine how much was released into the atmosphere). Several researchers who worked on this study say most of the gas was stored underground in sediment, and sand-dwelling microbes created the rest when the water reached them. The riverbed normally releases greenhouse gases gradually as part of the typical carbon cycle, but the Delta released a significant amount in a matter of just eight weeks during the pulse flow, though the researchers aren’t yet sure exactly how much.

The consequences of that are still tough to quantify, says Karl Flessa, a co-author of the study and co-chief scientist of Minute 319, but he doesn’t think the risks of emitting greenhouse gases outweigh the benefits of watering a parched ecosystem and growing new plant life. Since the pulse flow event, vegetation has thrived in the riparian zone where the land meets the river in the Colorado River Delta – cottonwoods and willows have turned the space greener than it had been in years.

The U.S. and Mexico are currently in negotiations about more restoration efforts when this one expires in 2017. And now, the researchers plan to look into how the duration of floods like this one affects water chemistry, how controlled flooding could support coastal stability, and how the consequences of flood pulses compare to a steady, minimum water flow in rivers like the Colorado.

This study may actually strengthen the case for consistent flow of the Colorado River. Keeping the Delta wet is something advocates have long been fighting for because it could help with wildlife protection, water access for those who live near the Delta in Mexico, and irrigation and water rights throughout the region. If a significant release of greenhouse gases happened because the riverbed was dry for so many years, “the costs of drying out rivers are greater than we knew,” says Jennifer Pitt, director of the Colorado River Project at the Audubon Society. She also said a more holistic view of the carbon in river ecosystems — specifically, how much carbon is sequestered and restored by new plant life — is necessary to quantify the full impact. 

Butman and some U.S. Geological Survey scientists are already running similar tests in the Columbia and Mississippi Rivers using new tools to map methane and carbon dioxide (similar to how methane plumes from oil wells are mapped on land). In some parts of the riverbed of the Columbia River, they’re finding methane at three to five times the concentration in the atmosphere; in others, it’s up to almost 1,000 times.

What they’re finding could end up having big impacts on water management: As humans manipulate their water sources in times of drought, the impacts those tweaks have on the carbon cycle could become a part of planning, too. “What’s really interesting,” Flessa says, “is getting people to start thinking about rivers and having a carbon budget. It’s a whole new way of thinking about rivers.”

Lyndsey Gilpin is an editorial fellow at NewTowncarShare News. She tweets

NewTowncarShare News Classifieds
  • This newly created position with The Nature Conservancy's Colorado River Program will play a key role in the development and implementation of strategies to achieve...
  • The Foundation NoVo Foundation acts from the original meaning of philanthropy: the love of humanity. The Foundation is dedicated to catalyzing a global social transformation...
  • A new generation of monkey wrenchers hits the Front Range?
  • The Tanner Humanities Center and the Environmental Humanities Program of the University of Utah seek an environmental writer to offer classes in Utahs Environmental Humanities...
  • The Wilderness Society works to protect Wildlands and inspire Americans to care for our public lands. We seek to hire a strategic, experienced leader who...
  • The Idaho Conservation League (ICL) seeks an individual to lead this 45-year-old organization as executive director, to carry on ICLs work as Idahos leading voice...
  • 2+ acres, 400+ feet on Snake River, 2800 sf residence, NWF-certified wildlife habitat, excellent hunting, fishing, birdwatching, stargazing, sunsets & panoramic views. In the heart...
  • Guardians is expanding and looking for a few great people to join us in protecting and restoring the wildlife, wild places, wild rivers, and health...
  • Organic grocery/cafe at Glacier Bay needs a vibrant leader. Love good food, community, and Alaska? Join us!
  • Ouray County, Colorado, a popular tourist destination, has dramatic mountains and amazing winter ice climbing. Challenging terrain and high altitude can push visitors to their...
  • National conservation organization seeks a regular, full-time California Program Associate-Tahoe Area. Position works closely with California-based program staff and National Forest Foundation staff to provide...
  • National conservation organization seeks a regular, full-time California Program Coordinator-Tahoe Area. Position works closely with California-based program staff and National Forest Foundation staff to provide...
  • National conservation organization seeks a regular, full-time California Program Manager-Tahoe Area. Position works closely with California-based program staff and National Forest Foundation staff to provide...
  • National conservation organization seeks a regular, full-time California Program Associate-Southern CA. Position works closely with California-based program staff and National Forest Foundation staff to provide...
  • Collector's Item! The story of barley, the field crop. 50 years of non-fiction research. www.barleybook.com
  • Are you a climber and a writer who is passionate about mountain literature? Do you love searching through old alpine journals for stories of esoteric...
  • 1400 sf of habitable space in a custom-designed eco-home created and completed by a published L.A. architect in 1997-99. Nestled within its own 80-acre mountain...
  • Great Old Broads for Wilderness seeks a full-time grassroots leadership director to oversee all aspects of the Grassroots Leadership Program. This includes ongoing development of...
  • Colorado Canyons Association (CCA) is a growing nonprofit organization fostering community stewardship of our National Conservation Lands with a focus on Dominguez-Escalante, Gunnison Gorge and...
  • Colorado Canyons Association (CCA) is a growing nonprofit organization fostering community stewardship of our National Conservation Lands with a focus on Dominguez-Escalante, Gunnison Gorge and...