By Linda Fresques
Program aims to take riparian renewal methods to the city
By Linda Fresques
NMSU civil engineering Professor Salim Bawazir is using nature to restore itself. He is investigating natural methods to return native vegetation to riparian zones that have been damaged through the introduction of the infamous salt cedar, a highly invasive shrub that consumes valuable water supplies and strangles native vegetation.
Bawazir’s research in the management of salt cedar, also known as tamarisk, dates back to 2005, working with the U.S. Bureau of Reclamation and the USDA New Mexico Sierra Soil and Water Conservation District.
He now plans to apply what he has learned to improve and conserve water quality and habitat to urban settings as part of a National Science Foundation-funded, multi-university effort to reinvent America’s aging and inadequate water infrastructure.
New Mexico, along with the surrounding states of Colorado, Arizona and Texas, has been waging battle with salt cedar, a highly invasive species originating from Eurasia and Africa that was introduced in North America as an ornamental shrub in the 19th century.
“The salt cedar has readily adapted and replaced native vegetation, such as cottonwood and salt grass, diminishing the diversity of the ecosystem and impeding the growth of plants that support wildlife. It becomes so dense that deer cannot walk through it,” says Bawazir. “Additionally, it uses a lot of water.”
For many years, the U.S. Bureau of Reclamation has been managing the growth of salt cedar by mowing, plowing and spraying with herbicides. Together, BOR and NMSU are using three test bed sites totaling about 600 acres that are located between the Caballo Reservoir and Elephant Butte Dam to study salt cedar management and riparian restoration. They have installed shallow wells to monitor depth to ground water and are also using ground stations and satellite imagery to measure evapotranspiration of the vegetation.
These methods, however, have garnered limited success.
Mowing is successful only in the short term as salt cedar grows rapidly: Bawazir reports that one year’s growth exceeds six feet. Spraying with herbicides is expensive and is effective only for several years. Plowing removes the plant, but leaves behind seeds that will germinate with the next rain and also causes erosion.
“It’s very challenging,” said Bawazir. “It’s a never-ending battle.”
Instead, Bawazir, along with co-project lead Richard Luthy, Stanford University civil engineering professor; Phil King, NMSU civil engineering professor; Brent Tanzy of the BOR; and several graduate students, are developing geo-engineering methods to ameliorate the problem.
“We hope to take what we’ve learned and engineer zones using native plants within urban settings that will have multiple functions,” said Bawazir. “Such areas create microenvironments that support wildlife and are aesthetically pleasing, which might encourage more development and support the economy. They use less water than non-native vegetation and their root systems filter the water, to some extent, removing some of the impurities that would eventually reach the groundwater.”
Bawazir has had success at his restoration test plots with the reintroduction of inland saltgrass, native vegetation that can grow with shallow ground water and survive in areas around the river where salt has accumulated.
“It grows like a carpet. It prevents salt cedar seeds from reaching the ground to germinate. Once the salt grass takes over, it naturally reduces the growth of salt cedar,” said Bawazir.
Perhaps even more important, inland saltgrass uses about half the amount of water that is used by salt cedar.
A fully mature and dense salt cedar stand uses four to four and one-half acre feet of water per acre of land per year, as opposed to saltgrass which uses only two and one-half acre feet of water per year. A savings of 1 acre foot of water per acre per year from 600 acres of salt cedar, if transferred for municipal use, could support more than 200 four-bedroom households per year. Or, it could be left to replenish the groundwater.
There are other benefits as well. In an urban setting, salt grass would be ideal for schools and walkways where there is a lot of traffic, as it is very rugged. It brings diversity to the ecosystem, supporting wildlife. And it naturally filters the runoff of water, whether it is in the city and goes into a canal system or in the desert, traveling through gullies and arroyos to the river.
Bawazir is also investigating the use of zeolite for arid land restoration. This project has shown promising results at establishing riparian vegetation without the need for irrigation.
Zeolite, a naturally occurring, porous material that he obtains from the nearby St. Cloud Mine, is used in many products such as cat litter and cosmetics. Its wicking ability is helpful in bringing shallow groundwater to a plant’s root system when rain is not available. It can also filter salts from the water.
Bawazir drills six-inch diameter holes to the groundwater, fills them with zeolite, and plants native vegetation in the holes. Using sensors to monitor moisture, he’s found that, depending on the depth of the groundwater, in some cases enough moisture reaches the plant to sustain it without irrigation. “We’ve had about a 75 percent success rate,” he said.
He hopes to work with the cities of Las Cruces and El Paso to incorporate these methods into their landscaping schemes, using native vegetation rather than concrete and rock.
He added, “I’m very excited about taking the knowledge that we’ve developed over the years studying the riparian zones and applying it to urban areas. It’s a whole new way of thinking.”
The Engineering Research Center for Re-inventing the Nation’s Urban Water Infrastructure (ReNUWIt), comprising NMSU, along with Stanford University, Colorado School of Mines and University of California, Berkeley was formed in 2011 under a National Science Foundation grant. ReNUWIt’s mission: identify new ways to supply urban water and treat wastewater, with greater efficiency, resource recovery and environmental mitigation as the foremost goals.
NMSU civil engineering Professor Nirmala Khandan is co-principal investigator of ReNUWIt.
“At this level of collaboration, we can achieve much more than any one individual campus could alone,” he said. “We are starting with a clean slate and developing entirely new philosophies about how to recreate our urban water systems.”
For more information, visit the Engineering Research Center on Reinventing Urban Water Infrastructure website at http://urbanwatererc.org.