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What's in your water?

Above: ASU Professor Nancy Grimm examines what happens when city dwellers alter the natural environment.

Scientist Nancy Grimm wonders what’s percolating in our urban aquafers

By Scott Seckel

At home, your yard is landscaped to look like the desert. The house faces an artificial lake. Your kids release pet turtles into the lake when they get too big. You have a swimming pool. When it gets dirty you backwash it into your yard.

Your home, and the city it sits in, are ecosystems, like a marsh or a forest. Unlike marshes and forests, urban ecosystems haven’t been studied for long — only about 25 years.

At a time when cities are growing in size and number, no one really knows how the world around them works.

That’s what drives the research of Nancy Grimm, Virginia M. Ullman Professor of Ecology in the School of Life Sciences at Arizona State University. How do cities function from an ecological standpoint?

In 2006, the world became urbanized with more than half the population living in cities. Projections are for the world to be 80 to 90 percent urbanized by the end of the century.

“I’m interested in these ecological questions associated with cities and how cities work as ecosystems,” Grimm says. “What are the ecological phenomena that are occurring in them and how do they compare to nonurban systems? What is it that people do or bring to the equation that is so different?”

If there are 10 billion people on the planet, what’s the best configuration for them to persist? And other species as well?

“I think cities have an important role to play in that,” Grimm says.

Everything you see in Phoenix was created. We may have built it, but we don’t really understand how it works. One of Grimm’s favorite sayings is, “Things aren’t always as they seem.”

Your desert landscaping, for instance.

“You can make it look like what’s out there, but it’s not going to behave the same way,” she says. “It may have the same parts, in terms of structure of the ecosystem, but in terms of function and what kinds of things you see there, it’s different … What is it we’re not putting into the soup that would make it the same kind of soup you would get in the desert?”

Retention basins have been around the Valley since the 1970s, when cities mandated all developments of a certain size have a retention basin that can handle a 100-year flood. After a big rain, stormwater drains down to the aquifer.

“That’s the idea,” Grimm says. “I don’t know that we know for sure that’s actually happening.”

Ground water is, on average, 300 feet under Phoenix.

“Are there pollutants that are accumulating in these retention basins, which are often used as soccer fields?” Grimm asks. “We haven’t looked at that in great detail, but it could be interesting to look at an older one and a younger one and look at the soil profiles and what kinds of materials are accumulating in the soils.”

Urban ecology questions are beginning to be asked by environmental organizations. Sandy Bahr is director for the Grand Canyon Chapter of the Sierra Club. She says the work being done by Grimm at ASU is significant.

“Urban ecology is an important field of study as we all need to better understand the places in which we live and the impacts of our everyday actions,” Bahr says.

“What’s in stormwater and where it goes helps us to better understand why merely dumping something on the ground or planting potentially invasive plant species is a huge problem. The study of urban ecology drives home how connected we are to our neighbors and to the coyotes, birds, insects and other creatures with whom we share our communities.”

After Tempe Town Lake was built, wetlands sprung up in the Salt River bed, surprising everyone. Egrets, herons, even beaver have been spotted.

Grimm discovered that these accidental wetlands perform many of the same functions of a naturally occurring wetland, like removing nitrogen and phosphorus. “Once you put water in this environment, things grow,” she says.

You nod your head as she speaks, because you honestly have never thought about what stormwater runoff impregnated with chemicals from lawns, whatever you washed your car with in the driveway, and the gunk you backwashed out of your pool might be doing to the urban environment we all live in.

“See? There’s more questions than one person could answer in a lifetime.” She laughs.

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