October 2006, Vol. 18, No.10

Waterline

Waterline - Beaver Dams Create Healthy Downstream Ecosystems

 Beavers are much more than cute critters with impressive building skills. Long known for their beneficial effects on the environment near their dams, beavers are also critical to maintaining healthy ecosystems downstream, according to recent research. Researchers have found that ponds created by beaver dams elevated downstream groundwater levels in the Colorado River valley, keeping soil water levels high and providing moisture to plants in the otherwise dry valley bottom. The results were published in the June 8 issue of Water Resources Research, a journal of the American Geophysical Union (AGU; Washington, D.C.).

Cherie Westbrook of Colorado State University (Fort Collins), her colleagues, and scientists from the U.S. Geological Survey conducted a 3-year study in northern Colorado’s Rocky Mountain National Park, examining valley ecosystems downstream in the Colorado River. They noted that water diverted by beaver dams is forced out of the natural stream channel and spreads across and down the valley for hundreds of meters. In addition, beaver dams built on the river changed the direction of groundwater flow in the valley. The changes caused water to infiltrate the river banks and flow underground toward the sides of the valley, instead of down the center of the valley, an AGU press release states.

The researchers suggest that the elevated moisture levels found in soil surrounding the dams would otherwise require water from a very large natural flood, which they estimate as the 200-year flood, to achieve the same expansive water availability to the valley bottom. Additionally, beaver dams built away from natural river channels further redirect water across the valley, enhancing the depth, extent, and duration of inundation associated with smaller floods. Dams also elevate the water table to sustain plant and animal life during the dry summer season, the press release notes.

“The beaver dams greatly enhanced hydrologic processes during the peak flow and low flow periods, suggesting that beavers can create and maintain environments suitable for the formation and persistence of wetlands,” Westbrook said.

The study comes as the beaver population in Rocky Mountain National Park is dwindling, AGU states. Approximately 30 of the animals currently live there, down from a high of nearly 600 estimated in 1940. The authors caution that additional reductions in the population could harm the current hydrologic balance in the river valley and affect the area’s water cycle and soil conditions, potentially changing plant species and influencing the overall diversity of the ecosystem in the future.
For more information, see www.agu.org, or contact Westbrook at cherie.westbrook@usask.ca.

Curtain May be Closing on Scientific Water Controversy

If you thought water was just an “H” and a couple of “O”s, you were right.

According to the U.S. Department of Energy’s Lawrence Berkeley National Laboratory, the scientific controversy regarding the structure of water is coming to an end.

Two years ago, scientists at Stanford University (Palo Alto, Calif.) reported a series of experiments, using X-ray absorption spectroscopy and X-ray Raman scattering techniques, that indicated a radically different molecular arrangement for water, a Berkeley Lab press release states. They reported that in the liquid state, more than 80% of the hydrogen bonds between water molecules were broken. On average, they found each liquid water molecule formed only two hydrogen bonds — one electron donor and one electron acceptor. From this, they concluded that in the liquid state, water molecules form a network of large rings or chains, rather than tetrahedrons.

However, a new study by scientists at the Berkeley Lab provided further evidence that the traditional structure of liquid water, in which the average water molecule is hydrogen-bonded to approximately four other water molecules in a tetrahedral arrangement, is correct, according to the press release.

Teresa Head–Gordon and Margaret Johnson, bioengineers in Berkeley Lab’s Physical Biosciences Division and the University of California, Berkeley–San Francisco Joint Graduate Group in Bioengineering, characterized the static structural organization of liquid water by analyzing data collected by Head–Gordon’s research group in 2002 using the ultrabright X-ray beams at Berkeley Lab’s Advanced Light Source (ALS).

The pair found that while the “rings and chains” alternative model of liquid water may exist for the briefest of instants, the average structure is that of the familiar tetrahedral network.

Despite water’s ubiquitous presence in people’s lives, it remains a mystery, the news release notes. Whereas most substances contract when they solidify, water expands, making it less dense as a solid than as a liquid. Our lives depend on liquid water, but — considering its light molecular weight — water at room temperature should be a gas, according to Berkeley Lab. The key to understanding the strange but vital properties of liquid water is understanding its structure fully, the news release says.

A single water molecule is V-shaped, but because the oxygen atom is more electronegative than the hydrogen atoms, the electrons in the molecule tend to gather toward the oxygen end, creating a slightly negative pole there and a slightly positive pole on the hydrogen side. The polarity of each water molecule results in a weak attraction between it and other water molecules, called a hydrogen bond. In the traditional scientific picture of water in the solid ice state, every individual water molecule forms four hydrogen bonds — two that are electron acceptors and two that are electron donors — through which it connects to its nearest neighbors. The result is a network of tetrahedrons. When ice melts, these bonds may become distorted and up to 20% of them broken. Despite these thermal distortions, liquid water still retains its tetrahedral network. This tetrahedral structure, coupled with strong hydrogen bonding, has long been thought to be the source of liquid water’s unusual properties.

For more information, contact Head–Gordon at tlhead-gordon@lbl.gov.  

World’s Largest Marine Reserve Established

 On June 15, U.S. President George W. Bush established the 360,000-km2 (139,00-mi2) Northwestern Hawaiian Islands Marine National Monument. According to The Ocean Conservancy (Washington, D.C.), the action will help preserve one of the last intact marine ecosystems in the world — one that is home to sharks, whales, extensive coral reefs, and the endangered Hawaiian monk seal. The marine reserve will be free from commercial and extractive activities, enabling the entire marine ecosystem to continue to thrive for future generations.

In 2004, the U.S. Commission on Ocean Policy delivered a series of recommendations to the president and the U.S. Congress on ways to improve management of the oceans. These recommendations include ending overfishing, reforming the ocean governance structure, and adopting a national ocean policy with conservation as its main directive.

“The marine ecosystem around the Northwest Hawaiian Islands is truly a national treasure on par with Yellowstone and the Grand Canyon, and a National Monument designation is the strongest level of enduring protection we can provide,” said Morgan Gopnik, senior vice president of The Ocean Conservancy. “Whether we are talking about additional Marine National Monuments or other bold action, it’s time to make this conservation ethic the norm, not the exception.”

For more information on the Northwestern Hawaiian Islands Marine National Monument, see www.hawaiireef.noaa.gov.

Researchers Propose New Hypothesis on the Evolution of Hot Springs Microorganisms

Studies of a unique microorganism may reveal more secrets to the evolution of life, according to a University of Georgia (UG; Athens) news release.

Since discovering the microorganisms known as archaea in the 1970s, scientists have been amazed by their ability to thrive where no other life can — in conditions that are extremely hot, acidic, or salty.
However, in the 1990s, scientists discovered that archaea occur widely in more mundane, low-temperature environments, such as oceans and lakes, according to the news release. Now, researchers from UG and Harvard University (Cambridge, Mass.) find evidence that these low-temperature archaea might have evolved from a moderate-temperature environment, rather than from their high-temperature counterparts as most scientists had believed. The results appear in the June 2006 issue of the journal Applied and Environmental Microbiology.

“Archaea represent one of the three domains of life on Earth,” said Chuanlun Zhang, lead author of the study and associate professor of marine sciences at UG. “Understanding their evolution may shed light on how all life forms evolve and interact with the environment through geological history.”

Zhang and his colleagues examined a common group of archaea known as Crenarchaeota. He explains that the Crenarchaeota’s low-temperature success may involve a unique molecule known as crenarchaeol that allows the organism’s cell membrane to remain flexible in cooler environments.
The commonly held theory was that the crenarchaeol is a fairly new feature by evolutionary standards, evolving 112 million years ago during the Cretaceous period, the same period in which dinosaurs became extinct.

Zhang said the problem with this theory is that it puts the arrival of the organisms that contain crenarchaeol, Crenarchaeota, relatively late in geologic history and doesn’t explain how they arose.
By analyzing 17 samples from springs in California, Nevada, and Thailand, as well as examining data published by other researchers in different environments, Zhang and his colleagues found that crenarchaeol was most commonly found at temperatures of about 40°C (104°F). This is well above even the warmest sea surface temperatures during the Cretaceous period, leading the researchers to conclude that the crenarchaeol — and by extension the groups of Crenarchaeota that have the molecule — evolved much earlier than previously thought.

Zhang’s study puts the evolution of Crenarchaeota at 3.5 billion years ago, shortly after life began to emerge on Earth.

Zhang said understanding these ancient organisms is important to the planet’s future. Most scientists believe that Crenarchaeota play an important role in fixing carbon dioxide, helping sequester greenhouse gases from the atmosphere. Having a better understanding of how abundant Crenarchaeota are and how much carbon they remove can help scientists more accurately model the effects of global warming.
The study was supported by the U.S. National Science Foundation and the U.S. Department of Energy. For more information, contact Zhang at zhang@srel.edu.  

El Niño Phenomenon Could Help Reforest Semiarid Regions

 Universitat Autònoma de Barcelona (Spain) scientists recently participated in an international cooperation project, “ELNIÑO,” to study the El Niño phenomenon and its effects on vegetation. El Niño is a temperature fluctuation of the Pacific Ocean’s surface waters that has an impact on the climate of the southern hemisphere, and according to the National Weather Service, such fluctuations come in cycles lasting to 9 to 12 months. By observing the relationship between the development of two species (Prosopis pallida and Prosopis chilensis) and the El Niño cycles (which have varying intensity), they concluded that the increase in precipitation could be used to recover semiarid zones through reforestation programs.

Arid and semiarid systems worldwide have lost a large part of their woody vegetation and biodiversity due to the overuse of wood cutting, cattle grazing, and subsistence agriculture, according to a news release issued by the university. These systems are used for cattle production, but their productivity is usually very low, and erosion of the unprotected soil is often a major problem. According to the release, this is a problem not only because of the poor productivity but also because it is the start of the path toward desertification. Countries such as Peru and Chile have been suffering these effects for many years, the news release states.

The El Niño phenomenon is the main cause of Earth’s climate variability, according to the news release. The frequency of El Niño varies between 3 and 6 years. Its intensity also varies and, therefore, so do its effects. On the Latin American Pacific Coast, the effects can be seen in increased rainfall, with varying intensities depending on the location. Rainfall in Peru, for example, can increase up to 25 times, as happened in 1983 and 1998; in Chile, however, the increase in rainfall is much lower, and sometimes nonexistent, the press release states.

The main mission of the recent international “ELNIÑO” cooperation project was to study how the decrease in herbivores and the increase in water availability due to El Niño could be used to stimulate the regeneration of trees and shrubs in semiarid ecosystems in Chile and Peru. Those participating in the program chose two species that can be found in large quantities in Latin America and are used frequently by rural communities — the Prosopis pallida in Peru and the Prosopis chilensis in Chile — and took samples using a latitudinal gradient from northern Peru to the center of Chile.

The results show that, despite the distance between the distributions of the two species, both gave similar responses. The growth of the two species is positively correlated with precipitation but not temperature. In northern Peru, precipitation and growth of the species occur in 3-year cycles and coincide with El Niño. Furthermore, in southern Peru and central Chile, precipitation, growth of the species, and El Niño also have the same cycle, but here the cycle lasts more than 3 years.

On a local level, it has been demonstrated that these species respond positively and significantly to precipitation. This means that when the intensity of El Niño is only moderate, zones protected from herbivores can be recovered through reforestation programs, and the intensity of the phenomenon can be forecast months earlier.

Global warming could cause an increase in precipitation in many semiarid zones worldwide. El Niño could cause the frequency and intensity of precipitation to increase, according to these models. This means that although semiarid zones currently play an almost insignificant role in global carbon balance, the expected increase in vegetation in these zones, due to climatic change, could turn these systems into important consumers of carbon.