Garbage Patches--in the Desert?
Garbage patches foul not only oceans, but deserts, too, according to study published this month in the Journal of Arid Environments. Study author Erin Zylstra found more windblown plastic bags and latex balloons than desert tortoises and western diamondback rattlesnakes in Saguaro National Park in Arizona’s Sonoran Desert. Like marine trash, desert debris could threaten wildlife and ecosystems.
Zylstra originally went to the desert to conduct fieldwork on desert tortoises. At the same time, she and her colleagues spotted not just tortoises, but litter — lots of it. “We just started to notice that there were a lot of these balloons and plastic bags around,” said Zylstra, a Ph.D. student at the University of Arizona.” That’s when the researchers figured that while surveying tortoises, they might as well survey the trash, too.
So for two summers, Zylstra and colleagues surveyed selected tracts of desert from two study areas on opposite sides of Tucson. They used a technique called distance sampling, which allowed them to closely estimate the density of trash in each tract, even if they missed a few pieces. They recovered refuse ranging from fully intact bags and balloons to dried-up fragments. Most balloons turned up as deflated bouquets tied with string, some so disintegrated they looked like lichens growing on rock.
Contrary to what she expected, Zylstra didn't find more trash alongside roads than she did further away. Her results suggested that wind could carry plastic bags and balloons more than two kilometers into remote wilderness. She also observed that dispersal of the trash followed seasonal winds.
“I think it at first it surprised me,” she said. “When I started thinking about it, it’s not rare to see those plastic bags flying around.” She also remembered balloon releases, which can send hundreds of balloons adrift.Although the latex in balloons can biodegrade, no one knows for certain how long that takes in the desert. Plastic bags made of polyethylene decompose only when exposed to sunlight — but not completely. They break down only into small shards that penetrate the water and soil, where they could persist for centuries and become ingested by wildlife. Scientists have yet to characterize the long-term effects of these synthetic materials.
Listed as a candidate species under the Endangered Species Act, the desert tortoise is prone to eating latex balloons and getting entangled in balloon strings. Garbage could pose similar dangers to other desert animals, possibly even ending up in precious watering holes shared among myriad species.
Other researchers have surveyed desert
trash, but their numbers reflected only the trash they had seen, without
necessarily accounting for any they overlooked. Some trash might lie hidden
beneath vegetation, for example. The distance sampling technique is not only
simple, but it also accounts for imperfect human detection.
With data showing that discarded plastic bags and balloons accumulate to high levels in protected desert areas and could threaten desert wildlife, Zylstra’s study might affect policy on trash disposal in the inner U.S. She pointed out that while coastal cities, especially in California, have banned plastic grocery bags and releasing balloons en masse, inland states like Arizona have yet do so, although Tucson has discussed levying a tax on plastic bags and restricting their distribution. “Potentially this could be some kind of evidence that would support that,” Zylstra said.
Because Zylstra’s desert survey is the only published, comprehensive survey of trash in a desert area to date, it sets a baseline for future studies that could further support policy changes. Given the simplicity of distance sampling, scientists could collect trash data in concert with their current studies. “There’s a lot of research going on in Saguaro,” Zylstra added. “If people collect data incidentally, they can see whether the numbers went up over time and that could be some good incentive to make some kind of policy decision.”
For now, individuals can take steps to keep trash from wafting to natural habitats, such as limiting plastic bag use and turning to alternatives to balloon release. “It’s really easy” for the wind to disperse plastic bags and balloons, Zylstra said. “It’s a good reminder that they don’t necessarily stay where we leave them.”
This week, we’ll suggest ways you can dispose your trash to minimize harm to wildlife, no matter what their habitat.
Image by iStockphoto/Julia Nelson
Melissa Pandika is an editorial intern at Sierra and a graduate journalism student at Stanford University. Her interests include environmental health and justice, urban environmental issues, and conservation biology. She has a soft spot for cetaceans.