This is Scientific American's 60-second Science, I'm Jason Goldman.In the 1800s, many rivers in the American West were diverted for irrigation or dammed for generating electricity.So rapidly expanding cities began tapping into groundwater. Add climate change into the mix, and you can see how an already arid desert can become even more parched.The banks of the Santa Cruz River in southeastern Arizona were described in 1855 as “covered with poplars and willows, ash trees and plantains, oaks and walnut trees.” But a century later the river was gone.“But It was the original river of Tucson and the reason the city is here.”Ecologist Michael Bogan from the University of Arizona.Seventy years after it ran dry, the city of Tucson decided to release treated wastewater back into the riverbed―around 2.8 million gallons each day.Bogan went to participate in the festivities when the valves were opened in June 2019.“Everybody was splashing around in the water, excited to see water back in the river. And what I immediately got sidetracked with was the number of dragonflies that I was seeing.”Within a few hours, Bogan counted seven different species of dragonflies. He even saw dragonflies and damselflies mating and laying eggs―at a river that had not existed earlier that day.
