In A Revived Arizona River, A Wildlife Oasis Is Remade

Nov 29, 2019
Originally published on November 12, 2019 9:34 am

Much of the Santa Cruz River is a dry, desert wash, only flowing after heavy monsoon rains. As Tucson Water hydrologist Dick Thompson and I walk along the river south of Starr Pass Boulevard, he points out how brown the vegetation looks.

"Dry as a bone," he says.

We walk down the dry riverbed, toward the stretch of the Santa Cruz that does have water. Since June, a pipe in the side of the embankment has been releasing treated effluent — wastewater — into the channel. As we get closer, the vegetation changes from brown to green. Soon, we can hear, and see, the shallow rock-bottomed pond surrounded by grassy plants.

We're joined by aquatic ecologist and University of Arizona professor Michael Bogan.

"The wetland vegetation is really starting to come in here, so we see things like cattails and sedges, and this yerba manza. So it's starting to look more like a natural cienega, or marsh," he says.

Bogan has been studying the Santa Cruz. He says as soon as the water started to flow, bugs and animals started to show up, flying or hopping in from other areas nearby.

"Day one, we saw seven species of dragonflies within hours of the water being released."

And more soon followed. At last count Bogan says they've seen 41 species of dragonflies here, which represent 80% of those native to the lower Santa Cruz River. It's not just insects though. Toads, birds and other wildlife also visit the little oasis.

Many of those species rely on a permanent water source, which this revived stretch of the Santa Cruz has now become.

"The species that we're seeing here so far are still a subset of all the species that could be here or that probably historically were here. But the river is essentially only four months old at this point, right? So that's not a surprise," he says.

"This is an artificial river," says Dick Thompson, lead hydrologist at Tucson Water. "We're supplementing the water that's gone now. It used to be, over 100 years ago ... there was enough rainwater and groundwater that you had intermittent flows in the Santa Cruz River and some places stayed wet all year 'round. That's all gone, due to overpumping of the aquifer."

Thompson says this project offers a couple benefits. First, a new location for groundwater recharge. The city needed a new place to store treated wastewater because its Sweetwater recharge basins are full. They hold 26,000 acre-feet of water, a portion of which is pumped out and replaced annually to supply clients who use the reclaimed water on golf courses and parks.

"You could think of recharge basins and the river as a bank, where you're putting money in your bank. Some time in the future when you need that water, you can pump it back out," he says.

A change in law as part of the drought contingency plan allows water utilities to get the same amount of credit for water put into a riverbed as into a recharge basin. Previously, river recharge had only earned half the credit. Along with creating new riparian habitat, the other major benefit, says Thompson, is reconnecting people with a flowing river.

"The public gets to see it, and see how just a little bit of water makes such a profound difference," he says. "And then when they hear about the different problems with the different watersheds around Arizona, they can think back to this and say: 'I've seen that. I've seen what a little water does. I can't imagine that they're drying out other places.'"

Today, ecologist Michael Bogan is squelching through the marshy grasses, on the hunt for damselflies.

"I think they're all hunkered down because of the wind, but you can see them, all these little toothpicks flying around," he says, pointing to what look like blue toothpicks hovering in the air.

The prevalence of all these insects is directly tied to improvements Pima County wastewater has made to its treated wastewater quality in 2013, says ecologist Claire Zugmeyer with the Sonoran Institute.

"As years go on, the science and technology improves and we know how to better treat our wastewater," she says. "So the big change that made a difference for aquatic life is the removal of ammonia and other forms of nitrogen that are very, very common in wastewater but weren't being removed well enough before. And we've seen tremendous improvements in the aquatic life as a result of the improved water quality."

Zugmeyer says before the wastewater treatment upgrades, the average concentration of ammonia was 20 milligrams per liter. In the 2018 water year, that had dropped to just 2 milligrams per liter. "So, huge difference," she said.

Zugmeyer says the Sonoran Institute has been tracking changes and improvements on the two other effluent-fed flowing stretches of the Santa Cruz for the last decade. She's excited about this latest stretch even while it may not be a totally natural river system.

"This stretch of the river used to flow year-round, so it has this great cultural, historical meaning too. And even if it can't be exactly what it was, we have a little glimpse into the past," she says.

After a couple minutes of searching, Bogan returns with a beautiful discovery: a common green darner dragonfly that's still emerging out of its larval skin.

He says the colorful dragonfly is probably 3 or 4 months old, born here at this riparian oasis.

Thompson says they're still calibrating the amount of water to keep it within the bounds of their permit, which limits the flow to the Congress Street bridge. But they're already working on phase 2 of this project, to see if and where they might be able to add more water back to the river in the next few years.

This story is part of a project covering the Colorado River, produced by Arizona Public Media and KUNC, and is supported through a Walton Family Foundation grant. The project is solely responsible for its editorial content.

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