From The High Country News (Lyndsey Gilpin):
…a new study by University of Florida, University of Arizona, Yale University and University of Washington researchers shows the water [from the 2014 pulse flow] 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.
“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.