April 2007, Vol. 19, No.4

Water Line

How Trees Manage Water in Arid Environments

The scarcity of water in the southwestern United States is no secret to Constance Brown. But when Brown, a micrometeorologist in the Atmospheric Science Program of the Indiana University (Bloomington) Department of Geography, moved from Arizona to Indiana 2 years ago, she was struck by how people in Indiana don’t think about water every day the way people in Arizona do.

In semi-arid environments, such as the southwestern United States, humidity is so low that water is scarce and hard to retain when there is a rare rain event, according to a University of Indiana press release. Rain that collects in puddles is quickly sucked up by evaporation into the dry air, and most of the rest runs off before it can soak into the ground.

One way to make better use of scarce water resources would be to retain more of the water that falls during a heavy rain, the release states. To accomplish this, better understanding is needed about how water behaves in the environment, and Brown is one of the scientists working to provide this understanding.

In a paper in the Journal of Arid Environments, Brown reports the first results of a study designed to characterize the surface exchanges of water and carbon dioxide in a forest in the Santa Catalina Mountains near Tucson, Ariz.

Understanding surface–atmosphere interactions is important to understanding a range of water resource phenomena, including predictions about water supplies, Brown said.

“This research seeks to characterize the explicit relationship between water availability and photosynthetic activities of the vegetation,” Brown said. “This paper is the first step in that process, and it illustrates the seasonal characteristics of the forest vegetation–water relationship as observed during a 3-year period during which there were extreme drought conditions in the semi-arid southwestern United States.”

Brown’s measurements showed that in this environment, there is a predominant, direct, and immediate correspondence between water availability and photosynthetic activity of the vegetation, according to the press release. This is different from what happens in most coniferous forests, where the seasonal behavior of the trees is significantly influenced by temperature changes: The trees are largely dormant in winter and have a summer growing season. The mountaintop forest that Brown studied was in some ways the opposite. The winter has a significant impact on the primary growing season for these mountain trees. Since moisture is continually available from rain or snow, the tree root zones don’t freeze, and there is enough sunlight for photosynthesis. The trees slow down during the premonsoon dry season in May and June, when water is scarce, and then quickly respond to the sudden availability of water at the onset of the monsoon in July.

For more information, contact Brown at combrown@indiana.edu.

New Tide Gate Designs Enhance Fish and Water Passage

Tides gates — fixtures of Oregon coastal farming — are coming under new scrutiny because of their environmental effects.

Essentially hinged metal doors at the ends of culverts, tide gates have been used for centuries to prevent flooding and help drain low-lying coastal lands, making it possible for people to farm and build on land that otherwise would be under water. But in many cases, the devices have also compromised or destroyed critical fish and wildlife habitat, according to a news release from Oregon State University (OSU; Corvallis).

“Tide gates tend to be effective at maintaining low water levels on the upland side of dikes,” said Guillermo Giannico, a fisheries specialist at OSU Extension Service, an educational outreach program. “Unfortunately, by altering water flow they also have some undesirable side effects.”

Among these side effects, Giannico said, are elimination of upland tidal marshes and changes in water temperatures, sediment transport, nutrient concentration, and fish passage.

The effects of tide gates on estuaries and wildlife were the focus of a symposium held last year at the South Slough National Estuarine Research Reserve in Charleston, Ore. Also discussed were the potential benefits and problems associated with removing or replacing existing tide gates to help restore habitat and encourage fish passage. Giannico organized the symposium.

Jon Souder of the Coos Watershed Association (Charleston), a co-organizer of the event, noted that significant concern with tide gates is that “flooding can be exacerbated rather than mitigated by tide gates, both above and below the gates.”

Both regulatory agencies and private industry are looking to engineering solutions that can enable landowners to continue using tide gates. Tide gate designer and builder Leo Kuntz of Nehalem Marine (Nehalem, Ore.) demonstrated several new tide gate designs and discussed their respective features and effectiveness. One of his designs, he said, allowed for a “30% increase in water flow” in both directions, enhancing the exchange of saltwater and fresh water and thus improving the natural marshland conditions.

Giannico was encouraged by the symposium’s attendance and what he sees as a general increase in awareness among both professionals and the public. “The importance of protecting and restoring these ecosystems has finally appeared on the radar screen,” he said.

For more information, contact Giannico at giannico@oregonstate.edu.

Roof-Collected Rainwater Fails Health Test

More than half of 560 samples from private dwellings in New Zealand exceeded the minimal standards for contamination and 30% showed evidence of heavy fecal contamination.

“I’m utterly amazed at the number of roof water supplies that fail the New Zealand drinking water standards,” said Stan Abbott, a microbiologist at the Institute of Food, Nutrition and Human Health at Massey University (Wellington, New Zealand).

Roof-collected rainwater consumption is popular because the public believes that rainwater is pure and safe to drink, said Abbott, who is director of the Roof Water Research Centre at Massey. More than 400,000 New Zealanders depend on roof-collected rainwater systems for their drinking water, especially those who are not served by town water supplies, he said.

The likely sources of the contamination were fecal material deposited by birds, frogs, rodents, and opossums, as well as dead animals and insects, either on the roof, gutters, or water tank. Contamination can lead to gastrointestinal diseases from pathogens, including Salmonella, Campylobacter, Giardia, and Cryptosporidium.

“Simple steps such as installing down-pipe debris screens and a first-flush diverter will reduce the risk of contracting waterborne diseases,” Abbott explained. A first-flush diverter is a device that reduces contamination of the tank water by diverting the first flush of contaminated water after a rainfall event so that contaminants do not enter the tank. Recent research at Massey University has shown significant improvements in water quality in the storage tanks linked to first-flush diverters.

While relatively few disease outbreaks linked to contaminated roof-collected rainwater have been reported in New Zealand, Abbott said there is massive underreporting of illnesses associated with contaminated roof water.

“The lack of evidence linking illness and poor quality roof water inhibits moves to improve systems delivering rainwater for consumption,” Abbott said. Although it is the homeowner’s responsibility to ensure that drinking water is clean, he said, information on the safe collection and storage of roof-collected rainwater seems not to be reaching many people.

New Zealand’s Building Act requires premises to be provided with potable water for consumption, oral hygiene, utensil washing, and food preparation. Under Sec. 39 of the Health Act, it is illegal to let or sell a house unless there is a supply of potable water.

Contact Abbott for more information at s.e.abbott@massey.ac.nz.

Absence of Water in Distant Planet’s Atmosphere Surprises Astronomers

This just in: Planet HD 189733b has no water.

A team of astronomers led by Carl Grillmair of the Spitzer Science Center (Pasadena, Calif.) and David Charbonneau of the Harvard–Smithsonian Center for Astrophysics (Cambridge, Mass.) announced that they have directly measured the first spectrum from a known planet orbiting a distant star. Two other teams made a similar measurement of a different extrasolar planet, according to a news release from the Harvard–Smithsonian Center. Taken together, this pioneering work opens a new field of planetary exploration, enabling astronomers to analyze directly the atmospheres of worlds beyond our solar system.

“We expected to see common molecules like water, methane, or carbon dioxide,” Grillmair explained. “But we didn’t see any of those. The spectrum was flat, with no molecular fingerprints that we could detect.”

The planet studied by Charbonneau and his colleagues is known as HD 189733b. It orbits a star slightly cooler and less massive than the sun located about 60 light-years from Earth in the direction of the constellation Vulpecula.

The team studied HD 189733b using the infrared spectrograph instrument aboard the space-based Spitzer Space Telescope of the U.S. National Aeronautics and Space Administration. The telescope detects infrared light, or light beyond the red end of the visible light spectrum. When light is split into a rainbowlike spectrum, certain atoms or molecules can leave “fingerprints” in the spectrum, the news release states. These fingerprints tell astronomers what molecules are there, just as crime scene investigators use real fingerprints to determine what person was in the area.

Theoretical calculations by different teams unanimously predicted that water vapor should be the most obvious spectral feature. However, the fingerprint of water was missing from HD 189733b. Astronomers also expected a prominent signature of methane, but that also was missing.

“The most fundamental thing we predicted was wrong,” Grillmair said.

Since planet formation works the same way everywhere, and since the molecules in question should be just as abundant on a distant world orbiting a sunlike star as they are in our solar system, astronomers speculate that something is hiding the molecules from sight.

One clue comes from the spectrum of a second planet, HD 209458b, which orbits a different star.
“We think that both planets may be cloaked in dark silicate clouds,” said Charbonneau. “These worlds are blacker than any planet in our solar system.”

The best way to clear up the mystery is to study comparable planets to determine if they show similar signs in their atmospheres. Astronomers also will continue to study HD 189733b and HD 209458b in more detail.

“Right now, it’s a puzzle,” Charbonneau said. “With a few more puzzle pieces, the picture should become clearer.”

Contact Charbonneau at dcharbonneau@cfa.harvard.edu.

U.S. EPA Cultivates Water-Efficient Landscapes

The U.S. Environmental Protection Agency (EPA) is issuing its first WaterSense label for landscape irrigation. As part of the agency’s new water-efficiency partnership program, two certification programs for landscape irrigation professionals received the WaterSense label for their adherence to water-saving techniques. WaterSense is a voluntary public–private partnership that identifies and promotes high-performance products and programs that help preserve the nation’s water supply, according to an EPA news release.

“Landscapes can use less water and still be beautiful and healthy,” said EPA Assistant Administrator for Water Benjamin H. Grumbles.

The first WaterSense label has been issued to the Certified Irrigation Designer and Certified Irrigation Contractor programs of the Irrigation Association (Falls Church, Va.). To earn the WaterSense label, the association’s certification programs must test for the ability to design, install, and maintain water-efficient landscape irrigation systems, including tailoring systems to the surrounding landscape, selecting water-efficient equipment, tracking local climate conditions, and developing appropriate schedules for watering.

To read more about WaterSense, see www.epa.gov/watersense.