After the unprecedented release of over 650 million gallons of water into the Rio Grande this summer, researchers have found the surge had a noticeable effect on trees closest to the riverbank.
In September, because of a deadly combination of stubbornly persistent drought and historic heat, several groups came together to dump hundreds of millions of gallons of water from the Abiquiu Reservoir into the parched Rio Grande in a quick-ditch effort to save wildlife and distressed cottonwoods.
While a number of water researchers are still trying to grasp the broader effects of the pulse two months later, one impact is obvious: the Albuquerque bosque got greener.
“There's a ‘greenness index’ that is available through satellite imagery that tells you how green something is, and it's a good indicator for the health of the trees in a situation like this,” said Paul Tashjian, director of freshwater conservation at Audubon Southwest, who helped put together the so-called “environmental flow.”
This research index leans on reflected light captured by drones, satellites, or digital cameras to determine how healthy and green plants are. Scientists use this method to track overall tree growth and the creation of leaves.
“The greenness index improved from the pulse flow with the trees that were close to the river,” Tashjian said.
Tashjian says they also noticed that wilting trees teetering on the edge of mortality seemed to make a slight rebound, especially as late monsoon rainfall brought flowing water back to the river.
For now, it’ll be unclear how many trees died until the springtime – when tree mortality can be better assessed – but Tashjian said there might be a 20 or 30% loss.
“This has been a kick in the gut, in terms of the bosque’s health and a warning,” Tashjian added.
In addition to paying close attention to the greying cottonwoods, groups mobilized to set up groundwater logging instruments to monitor how Albuquerque’s aquifer reacted to the special water release. They are still monitoring it now.
Normally, these trees are able to survive bouts of extreme drought by relying on a layer of shallow, saturated soils – but, because of how dry it was, that crucial pocket of water largely disappeared. Trees near private homeowner wells were noticeably hit hard.
Bouncing back is a harder question to answer, as cottonwoods have a difficult time recovering from round after round of multi-year drying. Less-established, younger trees are the first to keel over.
The lack of river surface water over the summer forced Albuquerque to tap its underground aquifer water reserve for all of its drinking water needs, further depleting crucial water resources for nature.
But, thanks to a mountain of rainfall filling the San Juan and Chama rivers – which feed naturally and artificially into the Rio Grande – the city has since transitioned back to river water at the San Juan-Chama Surface Water treatment plant, allowing groundwater to slowly replenish.
Although there is a state-run program that aims to buy or lease water for environmental benefits, the significant summer pulse flow happened after the Audubon Southwest, the Middle Rio Grande Conservancy District, and the Albuquerque Bernalillo County Water Utility Authority came together to pool water from the Colorado River.
Tashjian will speak to the public about this effort to save the Rio Grande beginning at 5:30 p.m. Nov. 11 at the Marble Brewery NE Heights Taproom in Albuquerque for the New Mexico Wildlife Federation’s “Wildlife Wednesday” lecture series.
