Grant to help ASU researchers improve soil moisture measurements

November 29, 2012

Fresh produce at the supermarket, running water and the daily weather forecast are everyday conveniences that rely on soil moisture measurements.

Soil moisture, a term not heard in everyday conversation, is the water found in the top soil layers in the ground. This water is a key component of the hydrological cycle, the Earth’s system of moving water from the oceans to the atmosphere to the ground and back again. Download Full Image

Until now, the accuracy and applicability of soil moisture measurements obtained from space has been limited. However, an Arizona State University research team is working to change that.

Led by Enrique Vivoni, the team recently received a $220,000 NASA grant for the development of a way to increase the utility of satellite-based soil moisture measurements.

Vivoni is a professor in ASU’s School of Earth and Space Exploration in the College of Liberal Arts and Sciences and in the School of Sustainable Engineering and the Built Environment, one of ASU’s Ira A. Fulton Schools of Engineering.

The other team member is research engineer Giuseppe Mascaro, in ASU’s School of Sustainable Engineering and the Built Environment in the Ira A. Fulton Schools of Engineering.

“Soil moisture is the most important variable in the hydrological cycle of the land surface,” Vivoni said. “We’re talking about the water that can be used by plants and the water that’s in direct contact with the atmosphere.”

Who it affects

Before water makes its way into streams, lakes or reservoirs it exists as soil moisture.

Because soil moisture directly impacts the amount of water that is available in a particular region, water managers rely on soil moisture data to determine how much water can be released to cities and agricultural areas.

Eric Kamienski, a water resources manager in Tempe, Ariz., said water managers spend much of their time collecting data and monitoring the amount of water that is available to their area.

In years of drought, water managers need to know how severe the drought is and be able to predict how long it will persist. This information is partly based on soil moisture data, Kamienski said.

“The amount of water in storage determines how they allocate water,” he said. “When there are years with prolonged drought and you see reservoir levels fall, water managers have to take immediate action.”

The data also help scientists make weather and climate predictions.

“The amount of soil water in the landscape has a big effect on atmospheric conditions,” Vivoni said.

The dryness or wetness of an area impacts the amount of rainfall the area is likely to experience.

If an area is dry and has little soil moisture, there is little water that can be evaporated and recycled back as rainwater. This feedback loop helps scientists predict if a dry spell in that area is likely to continue.

Similarly, an area with large amounts of soil moisture is likely to flood when it rains. If government agencies know that an area is prone to flooding, they can ensure that appropriate emergency response measures are in place, Vivoni said.

Current measurements

Over the last ten years, a sensor aboard the NASA satellite Aqua collected soil moisture data by recording microwave emissions from the land surface. This sensor reported a failure and stopped working in October.

The instrument collected data at resolutions of about 25 square kilometers (about 10 square miles) per sample, Vivoni said. The data are too coarse to be useful for people like farmers or reservoir operators who manage plots of land that can be less than half a mile across, he said.

“Twenty-five kilometers is larger than Tempe. This means that there is a single soil moisture value for the entire city. That’s a big limitation,” he said.

The project

A new sensor, which is set to launch in November 2014 aboard the Soil Moisture Active Passive satellite, will provide data representing 10 square kilometers (4 square miles).  But Vivoni and Mascaro want to refine even those results. 

Vivoni and Mascaro developed and are testing a mathematical model that can provide detailed information on soil moisture data based on the less detailed satellite data.

Mascaro explained that the model will take the satellite’s data point representing 10 square kilometers and simulate the statistical variability of soil moisture values for each square kilometer within the larger area. This means that the model will be able to provide information on the soil moisture values for each square kilometer based off of the satellite’s coarser data. One square kilometer is about 0.4 square miles.

“Imagine having this bird’s eye view of soil moisture over the entire country,” Vivoni said. “It would give us an idea of how weather systems impact soil moisture and how our actions affect the landscape’s soil moisture.”

Vivoni and Mascaro proposed to include the model in the satellite’s computer system. This way the onboard calculations would be available to all scientists who use NASA data, not just to the team.

With this data available to others, Kamienski said he believes the project will benefit water managers and those whom they service.

“This is one more tool that they could use to determine overall watershed conditions,” he said. “It will help them know what the next season may look like so they can start planning reservoir operations accordingly.”

Story written by Kristen Hwang

Associate Director, Media Relations & Strategic Communications


What are you drinking?

November 29, 2012

When people think about water contamination, images of oil spills or gunk spurting out of a kitchen faucet might jump to mind. But contaminants in our water are often undetectable to the naked eye.

Researchers at Arizona State University are working to identify these unseen contaminants and to measure their effects on human and environmental health. Water pouring into a glass Download Full Image

Some of those unnoticed pollutants are directly linked to consumer practices. Chemicals in the products we use often end up in the water supply. For example, many stain and stick resistant products are made with something called perfluorinated compounds. Their chemistry, which makes them useful in the home, also makes them persistent in the environment. They simply do not degrade.

Nature is full of hydrocarbons – strings of carbon atoms that hold onto hydrogen atoms. In perfluorinated compounds, those hydrogen atoms get replaced with fluorine. These new chemicals are not seen in nature.

“The fluorine-carbon bond is the strongest bond in organic chemistry. There is no organism known that can make a living pulling these fluorines back off the carbon skeleton. And we’ve decided to mass produce these chemicals and put them into the environment, where they will linger for decades, centuries, if not millennia,” says Rolf Halden, director of the new Center for Environmental Security in the Biodesign Institute at ASU.

Perfluorinated compounds are found in grease-resistant food packaging, non-stick cookware and water-resistant clothing. Halden describes these compounds as “schizophrenic” in their behavior, which makes it difficult to predict their environmental fate.

“One half of the compound repels water, while the other embraces it; and the high fluorine content renders the compound almost indestructible,” says Halden. “It’s beautiful chemistry, really. But if you don’t use it prudently, you create pollution that’s impossible to clean up.”

Other pollutants that have proved resistant to degradation are antimicrobial compounds. These are designed to kill or stop the growth of bacteria and fungi. Like perfluorinated compounds, polychlorinated antimicrobials do not break down easily and instead simply accumulate in the environment.

By taking sediment cores from the Chesapeake and Jamaica Bays and dating them using radioactive fallout from atmospheric nuclear tests conducted in the ‘50s, Halden and his colleagues were able to find antimicrobials used and disposed of by Americans as far back as the 1960s.

“The stuff is still there, awaiting degradation,” says Halden. “There are organisms living in these aquatic environments now, including many microbes, that have been exposed to antimicrobials throughout their entire lifecycle and over multiple generations. How do they react to that pressure?”

Since these compounds don’t break down, they create an environment that fosters the emergence of drug-resistant bacteria. As they build up in the environment, these antimicrobials cycle back to us, first accumulating in algae and worms and then in fish that people eat.

In a 2007 study published in the journal Food and Chemical Toxicology, the chemical triclosan was found in 60 out of 62 breast milk samples collected from women in California and Texas. Triclosan is an antibacterial and antifungal agent that is widely used in deodorants, soaps, toothpaste and cleaning supplies.

“These polychlorinated antimicrobials are everywhere,” says Halden. “If I swipe up dust on my finger, it can contain up to two parts per million of triclosan.”

Other than successfully combating gingivitis, there is no evidence that triclosan provides any other health benefits, according to a consumer update by the U.S. Food and Drug Administration. The New York Times reported in August 2012 that Johnson & Johnson, a personal care product company, is phasing out the use of triclosan in their products. But many companies resist making changes.

While manmade pollution is an evolving problem, many natural contaminants still get into our water sources, as well. Some of these natural chemicals can cause pretty serious problems, says Paul Westerhoff, a professor in the School of Sustainable Engineering and the Built Environment in the Ira A. Fulton Schools of Engineering. He studies water contamination and its impact downstream.

Westerhoff notes that a wide range of natural contaminants exist. Arsenic can naturally occur in surface and ground water, and presents a host of health risks. And algae that grow in water can make toxic byproducts. Algae also produce compounds that can make water taste and smell funky.

“The two that we’ve been focused on in the Phoenix metro area for the last 15 years are called Methylisoborneol, or MIB, and Geosmin. These are produced by algae in the reservoirs and the canals and are responsible for making our drinking water have an earthy-musty taste or odor,” says Westerhoff.

Other contaminants actually come from our efforts to purify water. When chlorine is added to the water to kill bacteria and pathogens, it can react with dissolved organic matter to form carcinogens.

“Things like chloroform, bromoform and a large list of other regulated compounds are formed, as well as many that aren’t regulated,” says Westerhoff. “They regulate about nine of these chemicals out of about 900. These all are derived from reactions of disinfectants with natural organic matter.”

While it may seem that our water is chock full of deadly toxins, it’s important to remember that exposure to something does not automatically create a health risk. For example, passing a smoker on the street and inhaling a puff of second-hand smoke is much different from the constant exposure of living with a smoker. We need more information about what effects certain chemicals have on humans and what levels of exposure we can tolerate without risk.

As an engineer, Westerhoff also examines the effectiveness of methods to filter and purify drinking water, such as activated carbon. Activated carbon is processed to be porous and absorb unwanted contaminants, acting as a filter.

“If you have activated carbon under your sink, it removes the flavors of MIB, Geosmin and chlorine, but only a few of the chlorinated organics” says Westerhoff. “If you did that on a municipal treatment scale, say for the city of Phoenix, it’s far more cost-effective. So we’ve been looking at the efficiency of activated carbon to remove a broad range of chemicals beyond those that are currently regulated.”

While some methods are available to clean up our drinking water, perfluorinated and antimicrobial compounds have permeated the environment and present significant hurdles in cleaning them up. Halden believes the best route to dealing with these resilient chemicals is informing the public about what’s in the products they use.

“What’s needed is a combination of more foresight in the way we pick and produce chemicals and then education of the consumers,” says Halden. “Right now, people are completely in the dark – they don’t even know what they’re buying. If you work with pollution control, the best, most effective way to deal with pollution is to not create pollution.”

Rolf Halden is also a senior sustainability scientist in the Global Institute of Sustainability, and a professor in the Ira A. Fulton Schools of Engineering.

Written by Pete Zrioka, Office of Knowledge Enterprise Development. This article first appeared on ASU Research Matters.

Director, Knowledge Enterprise Development