Southwest Environment

Stories written by University of Arizona students

Department of Soil, Water and Environmental Science
The Stories

Shorebirds frequent Tucson sewage treatment facility

By Matthew Jewell

Santa Cruz River
Photo by Matthew Jewell
The Santa Cruz River just south of the Ruthrauff Bridge was flowing in mid-October, thanks in part to effluent from the nearby sewage treatment plant
The smell of sewage water drifts over with the wind at the Sweetwater Wetlands facility on a mid-October afternoon. The scent is subtle, not strong enough to keep away the birds, or the local and international birdwatchers, that visit the site.

“Between 1 million and 1.8 million gallons of backwash water flow daily through the wetlands. This creates a sanctuary for over 250 different bird species,” explained Joaquim Delgado, a hydrologist and who serves as a tour guide for the Sweetwater treatment plant.

In the series of ponds that receive the backwash, or treated sewage, mallard ducks congregated on and near the water, while sandpipers stood one leg peering down for their next meal, and quail families ran in and out of the salt bush cover at the outer edge of the pond area.

Before delivering the effluent to the ponds, Tucson Water treats the incoming domestic wastewater chemically, physically, and biologically to remove contaminants and produce “an environmentally safe fluid,” Delgado said.  Effluent from this plant and others provides water to parks, schools grounds, golf courses, and other grass turf areas, Delgado said. The Sweetwater facility began delivering effluent to this newly created wetlands area in 1996.

The treatment plant is surrounded by three different transitional zones of vegetation. The effluent flows first into an aquatic area, with a water surface completely covered with algae. Next the water flows into the wetland area, which is dominated by cattails and other non-native wetland species. The outer edge is dominated by native salt brush, mesquite and palo verde trees.

Throughout the wetland ponds, solids (heavy metals, nitrates, and phosphates) accumulate at the bottom of the pond, according to one of the many educational signs found throughout the wetlands. Plants can remove these compounds from the water as they grow. Plants also provide the oxygen necessary for many microbes. These microbes in the water and on plant surfaces transform complex, sometimes harmful substance, into simpler forms. The simpler compounds then become available as nutrients for other microbes and plants.

The Santa Cruz area near the Sweetwater Treatment plant has “one of the biggest diversity of birds in Arizona,” according to Ethan Beasley, an experience birder who has worked with the Tucson Audubon Society for the past 10 years. The thick vegetation and the flowing water in the Santa Cruz create bird habitat from the Sweetwater Treatment plant north to where the flow stops in Avra Valley.

The wildlife habitat aspect of the Sweetwater plant is slightly urbanized, complete with cement roads and buildings throughout the facility, with trees in neat rows fringing the riparian area. This riparian park provides habitat for a wide variety of animals, including javelina, Mexican free-tailed bats, rabbit, and even bobcats.   
The species of birds here can be heard more than seen due to the thick brush on the outer layer of the site. Bird species found in this area that make this a permanent home include quail, mourning doves, some warblers and English sparrows. Others just make it a stop during migration.

A green heron (Butorides virescens)
Photo by Alan Goulet
A green heron (Butorides virescens)
Some unexpected visitors arrived this migratory season, Beasley said. The black bellied plover, greater yellowlegs, cattle egrets, and a green heron were seen Oct. 7 on the Santa Cruz River not far from the Sweetwater treatment plant. The sandbars in the river make nice resting points as the birds travel from the northeast to their eventual destination around the Gulf of Mexico.

Many migratory species “fly from northern Alaska and the Arctic and are stopping over here for the winter,” Beasley said, while some tropical species are here more temporarily and leave in early October.

Downstream from the plant, birds can be seen and heard in large arching tamarisk stands and sporadic desert willow trees. Alongside the Santa Cruz here, the vegetation differs from the typical Sonoran Desert plants. It changes from cacti and creosote bush vegetation to huge desert willows, tamarisks, and grasses.

Plants such as tamarisk were brought in decades ago for erosion control and now dominant the landscape in the Santa Cruz west of the Sweetwater. Deeply eroded soils are present along the outer most banks of the Santa Cruz, which makes it extremely difficult to drive along at some points, even in a four-wheel drive truck.

The Lower Santa Cruz Recharge Project started operations in June 2000. It consists of three basins totaling approximately 30 acres of recharge basins. The Pima County Department of Transportation and Flood Control District works with the Central Arizona Project on this recharge program.

Cattails at Sweetwater wetlands
Photo by Matthew Jewell
Cattails, which provides good cover for birds, fringe a pond at Tucson’s Sweetwater Wetlands.

Tucson Water and affiliates are looking to restore some of these historical flood plains in an effort to increase the height of the water table in Tucson. These areas are becoming increasingly important as wildlife habitat is becoming scarce do to human encroachment.

“Constructed wetlands” such as those surrounding the Sweetwater facility offers a rare opportunity for Tucsonans to view shorebirds in action on their journeys to the south, Delgado said.

Ethan Beasley said that he suspects that more shorebirds than usual visited the Sonoran Desert in 2011. The reasons for these increased visitations are not exactly clear, but he speculated that “migration patterns are changing more towards the Southwest.” The patterns can change from year to year, though, he noted. Other factors can also contribute.

“I think one important factor to consider is that there are more observers, today, than ever before,” Beasley said. More people observing can mean more birds get counted and identified. “ID skills, technique, and equipment are better, today, than ever, as well.”

More birds could be attracted to this area now that the wastewater is restoring the flow for the Santa Cruz from just south of Ruthrauff Bridge to Twin Peaks Bridge. Birds overhead see a flowing river with increased vegetation, thanks in part to the effluent.

In the future, these two factors could lead to increased migratory birds stopping by, Beasley indicated, giving people the opportunity to sight these birds for pleasure and give serious birdwatchers opportunities to learn more about the shorebirds’ mysterious migratory patterns.


Matthew Jewell is in rangeland ecology and management in the University of Arizona’s School of Natural Resources and the Environment. He is particularly interested in invasive plants and the effects they have on ecosystems


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