September 2007, Vol. 19, No.9

Waterline

Cell Splits Water Via Sunlight to Produce Hydrogen

 Engineers at Washington University in St. Louis have developed a unique photocatalytic cell that splits water to produce hydrogen and oxygen in water using sunlight and the power of a nanostructured catalyst, according to a university press release.

The group is developing novel methodologies for synthesis of nanostructured films with superior optoelectronic properties. One of the methods, which sandwiches three semiconductor films into a compact structure on the nanoscale range, is smaller, more efficient, and more stable than current photocatalytic methods, according to the news release. Current methods require multiple steps and can take from several hours to a day to complete.

According to Washington University, the discovery provides a new, low-cost, and efficient option for hydrogen production and can be used for a variety of distributed energy applications.

Pratim Biswas, the Stifel and Quinette Jens Professor and chair of the Department of Energy, Environmental, and Chemical Engineering, and his graduate student Elijah Thimsen recently developed the well-controlled gas phase process and have demonstrated it for synthesizing a variety of oxide semiconductors, such as iron and titanium dioxide films, in a single step process. It is based on a simple, inexpensive flame aerosol reactor and consists of four mass flow controllers to regulate process gases, a standard bubbler to deliver a precursor, a metal tube that acts as a burner, and a water-cooled substrate holder.

“We put these films in water and they promote some reactions that split water into hydrogen and oxygen,” Biswas said. “We can use any oxide materials such as titanium dioxide, tungsten oxide, and iron oxide in nanostructures sandwiched together that make very compact structures. The process is direct and takes only a few minutes to fabricate. More important, these processes can be scaled up to produce larger structures in a very cost-effective manner in atmospheric pressure processes.”

The research is among the first wave of news out of the new Washington University Department of Energy, Environmental, and Chemical Engineering, which performs research on energy and environment, including alternative fuels and energy sources, air quality research, nanoparticle technology and particle emission control, among other topics.

Some of the department faculty — currently 14 members and expected to double in five to 10 years — are active in the university’s BioEnergy Initiative, which is focused on the development of technologies for the production of next-generation biofuels. The adoption of a systems approach will not only enable development processes for large volume production of liquid fuels from plant-based sources, but also at a low cost, and most importantly, in an environmentally benign manner — not only during production, but also during actual usage.

Contact Biswas at pratim.biswas@wustl.edu.

NASA Satellites Watch as China Constructs Giant Dam

Some call it the eighth wonder of world. Others say it’s the next Great Wall of China. Upon completion in 2009, the Three Gorges Dam along China’s Yangtze River will be the world’s largest hydroelectric power generator and one of the few manmade structures so enormous that it’s actually visible to the naked eye from space.

National Aeronautics and Space Administration (NASA) Landsat satellites have provided detailed, vivid views of the dam since construction began in 1994, according to a NASA news release. The Yangtze River is the third largest river in the world, stretching more than 6275 km (3900 mi) across China before reaching its mouth near Shanghai. Historically, the river has been prone to massive flooding, overflowing its banks about once every 10 years. During the 20th century alone, Chinese authorities estimate that 300,000 people were killed from Yangtze River floods, NASA reports.

The dam is designed to greatly improve flood control on the river and protect the 15 million people and 1.5 million ha (3.7 million ac) of farmland in the lower Yangtze floodplains. Observations from the NASA-built Landsat satellites provide an overview of the dam’s construction. The first image shows the region prior to start of the project. By 2000, construction along each riverbank was under way, but sediment-filled water still flowed through a narrow channel near the river’s south bank. The 2004 images show limited development of the main wall and the partial filling of the reservoir, including numerous side canyons. By mid-2006, construction of the main wall was completed, and a reservoir more than 3 km (2 mi) across had filled just upstream of the dam.

The sheer size and power of the dam is mind-boggling. At a construction cost of at least $625 billion, it is roughly 2.3 km (1.4 mi) long and 185 m (607 ft) tall, five times larger than Hoover Dam on the Arizona–Nevada border.

Engineered to store more than 18.9 billion m³ (5 trillion gal) of water, the Three Gorges Dam is designed to produce more than 18,000 MW of electricity when all 26 turbines become operational in 2009 — twenty times the power of Hoover Dam, according to the news release. The reservoir also will allow 9100-tonne (10,000-ton) freighters to enter the nation’s interior, opening a region burgeoning with agricultural and manufactured products, and increasing commercial shipping access to China’s cities.

Despite these anticipated advantages, construction of the dam has not been free of controversy. While the reservoir's flood storage capacity will lessen the frequency of major downstream floods in the future, the dam’s reservoir will eventually be flooded to 175 m (574 ft) above sea level, submerging about 632 km² (244 mi²) of land — including the three gorges that give the dam its name: the Qutang, Wu Xia, and Xiling. As a result, more than 1 million people have been or will be relocated. Dozens of architectural and cultural sites will also disappear under the reservoir.

There are also environmental concerns, NASA reports. The dam is designed to weather floods of a once-in-a-century severity, but some researchers say a greater concern is earthquake activity in the area, which might result in a breach of the dam.

In April 2007, China’s Xinhua news agency reported that the dam’s reservoir is polluted by pesticides, fertilizers, and wastewater. According to a joint study by the Chinese Academy of Sciences, the World Wildlife Fund (Gland, Switzerland), and the Yangtze River Water Resources Commission, nearly 30% of the Yangtze’s major tributaries are seriously polluted.

While Landsat is a premier research tool for observing changes on Earth’s surface, other NASA satellites also are being used to determine how changing land cover and use may influence climate and the environment. Just as transforming forested lands into cities can change the local climate, scientists have found evidence that Three Gorges Dam and its enormous reservoir might have a similar effect.

In a recent study, researchers used computer models and data from NASA’s Tropical Rainfall Measuring Mission satellite to estimate how the dam’s construction affected area rainfall. Information from NASA’s Terra and Aqua satellites also revealed the dam’s effect on land surface temperatures.

“The satellite data and computer modeling clearly indicate that the land use change associated with the dam’s construction has increased precipitation in the region between the Daba and Qinling mountains,” said lead author Liguang Wu of NASA’s Goddard Space Flight Center (Greenbelt, Md.), and the University of Maryland, Baltimore County (Ellicott City). The land changes also reduced rainfall in the region immediately surrounding Three Gorges Dam after the dam’s water level abruptly rose in June 2003.

The researchers were surprised to see that the dam affected rainfall over such a large area — a 161-km² (62-mi²) region — rather than the 9.6 km (6 mi) projected in previous studies.

Land surface temperature changes were also found to occur in the area where more rain fell, the news release notes. In the daytime, temperatures between the Daba and the Qinling mountains decreased by an average of 0.67 C (1.2 F). Where there was more rainfall, there were more clouds, which reduced the amount of sunlight and heat that reached the land surface, creating cooler daytime temperatures.

The study suggests that the cause of these temperature changes was the expansion of the width of the Yangtze River and the formation of the dam’s reservoir. After construction, a 1039-km² (401-mi²) reservoir formed in the mountainous area. Before the dam, the Yangtze River was only 0.54 km (0.34 mi) in width. The larger mass of water created a “lake effect,” causing cooler temperatures and increased rainfall between the Daba and Qinling mountains but less rainfall in the immediate vicinity of the reservoir, according to the NASA news release.

When the dam becomes fully operational in 2009 and the reservoir reaches its peak size, scientists predict these regional temperature and precipitation changes may increase even more.

Predators Shape Rivers by Affecting Grazing Behaviors

 Large carnivores not only play a pivotal role in the health of ecosystems, they can also affect the shape of the landscape, according to recent research by two Oregon State University (OSU; Corvallis) forestry professors.

Where predators such as wolves and cougars are absent, river channels are apt to widen and erode as deer and other browsers, free of fear, devour and trample streamside vegetation, according to an OSU news release. These riparian plant communities — willows, cottonwoods, sedges — help anchor soils, hold sediments and maintain riverbanks.

OSU researchers William Ripple and Robert Beschta have found evidence, both historical and contemporary, of significant impact from predation on the width, depth, and meanders of the Gallatin River in Yellowstone National Park.

Archival photos show dramatic — and deteriorating — changes in the river’s path from the mid-1920s, when wolves were wiped out, through the latter decades of the 20th century, OSU reports. In contrast, an image from the early 2000s, after wolves had once again gained a foothold in the park, shows signs of renewal.

“It appears that the presence or absence of this apex predator can impart important effects upon lower trophic levels: first to elk, then to willows, and finally to … processes associated with floodplain systems,” professors Beschta and Ripple explain in the May 2006 issue of the journal Earth Surface Processes and Landforms.

The ecological consequences of catastrophic channel transformations are profound, according to the OSU news release.

As their banks crumble, rivers flow faster and sediments get finer, while water temperatures grow warmer and water tables sink deeper. Plant communities shift from moisture-loving to dry-land species. On the over-browsed sections of the Gallatin floodplain, for instance, shrubby cinquefoil and lodgepole pines replaced the lush willow thickets and dense sedges characteristic of healthy riparian zones.

Animal communities across the food web — from birds to aquatic insects, butterflies, fish, frogs, toads, and lizards — shrink or disappear along with the vegetation they depend on.

In studies across the western United States, the researchers have been amassing evidence of the predator–vegetation–biodiversity link. The stream channel study takes the linkage still further, connecting the carving of landscapes by river systems to the prowling of these landscapes by large carnivores.

The researchers said that wolves and cougars could, under certain circumstances, be important management tools for restoring riparian zones — essentially, reviving the natural stasis of a system that has been out of balance since predators were extirpated.

For more information and a slide show, see www.oregonstate.edu/terra.

Understanding River’s History Important to Today’s Water Managers

  epic drought during the mid-1100s dwarfs any drought previously documented for a region that includes areas of Arizona, Colorado, New Mexico, Utah, and Wyoming, according to a University of Arizona (UA; Tucson) study.

The six-decadelong drought was remarkable for the absence of very wet years, a UA news release notes. At the core of the drought was a period of 25 years in which Colorado River flow averaged 15% below normal.

The new tree-ring-based reconstruction documents the year-by-year natural variability of streamflows in the upper Colorado River basin back to the year 762, said the tree-ring scientists who led the research team. The work extends the continuous tree-ring record of upper Colorado streamflows back seven centuries earlier than previous reconstructions, according to the news release.

“The biggest drought we find in the entire record was in the mid-1100s,” said team leader David M. Meko, an associate research professor at UA’s Laboratory of Tree-Ring Research. “I was surprised that the drought was as deep and as long as it was.”

Meko contrasted that with the last 100 years, during which tree-ring reconstructed flows for the upper basin show a maximum of 5 consecutive years of below-normal flows.

The Colorado supplies water for cities and agriculture in seven western states in the United States and two states in northwestern Mexico. Los Angeles, Las Vegas, Denver, Phoenix, Tucson, and Albuquerque, N.M., are among the many cities dependent on Colorado River water. The Intergovernmental Panel on Climate Change predicted in a recent report that the southwestern United States will become hotter and drier as the climate warms, according to the news release.

“We have natural variability that includes this time in the 1100s,” said co-author Connie A. Woodhouse, a UA associate professor of geography and regional development and dendrochronology. “If we have warming it will exacerbate these kinds of droughts.”

The newly documented droughts “could be an analogue for what we could expect in a warmer world,” Woodhouse said.

Meko, who was asked by the California Department of Water Resources to pursue the research, said understanding more about natural variability in the Colorado is important to the region’s water managers. “Water managers rely on wet years to refill reservoirs,” he said.

At press time, the team’s research article, “Medieval Drought in the Upper Colorado River Basin,” was scheduled to be published May 24 online in the American Geophysical Union’s journal Geophysical Research Letters.

About a year ago, Woodhouse, Meko and colleagues published a continuous tree-ring record for the upper Colorado River Basin that went back to 1490, the longest record for the area until now.

Contact Meko at dmeko@ltrr.arizona.edu or Woodhouse at conniew1@email.arizona.edu.

Deep-Sea Mining May Pose Serious Threat to Fragile Marine Ecosystems

 Undersea habitats supporting rare and potentially valuable organisms are at risk from sea-floor mining scheduled to begin within this decade, says a new study led by a University of Toronto at Mississauga geologist.

According to a university news release, the mining of massive sulfide deposits near “black smokers” — undersea hydrothermal vent systems that spew 350°C (662°F) water into the frigid deep-sea environment and support sulfur-loving bacteria and bizarre worm and clam species — could smother and contaminate these communities, which some biologists argue may represent the origins of life on Earth.

“We need to act now to establish scientific and legal methods to protect these sensitive ecosystems and minimize the potential environmental impact of this industry,” said lead author Jochen Halfar, an assistant professor of earth sciences at University of Toronto. “Imposing regulations after operations begin would prove very difficult, and some of the governments in the jurisdictions targeted by this industry have a poor record of mining oversight,” Halfar said. “The prospects for regulation of underwater mining are not good.”

A Canadian-based company is currently planning the world’s first commercial undersea exploration for high-grade gold and copper. They are targeting an area known as the Manus backarc basin off the coast of Papua New Guinea. The active hydrothermal vents in these areas occur where new oceanic crust is formed through undersea volcanic activity, the news release states. Until the late 1970s, scientists had assumed that life required sunlight, but the discovery of these vent communities showed that life could exist on thermal and chemical energy. Since oceans have existed, more or less, since the beginning of Earth’s history, these deep sea hydrothermal vents could be the most ancient sites of life on Earth. Yet the vents are not only of scientific interest, since the organisms may have pharmaceutical and biotechnological applications, the news release notes.

Mining companies first turned their attention to the oceans in the 1970s, and interest grew in manganese nodules that exist on the surface of the ocean floor. However, high projected costs and the regulatory restrictions on deep-sea mining in international waters through the United Nations Convention on the Law of the Sea currently have put those projects on hold, according to the University of Toronto. In particular, Halfar said, restrictions by the International Seabed Authority, which oversees environmental protection and demands that profits from mining in international waters be shared with developing nations, redirected prospecting and exploration of the sea floor into areas under national jurisdiction, where regulations are often weaker or nonexistent.

“The demand for metals is growing rapidly, and along with the sharp rise in metal prices, we have seen the depletion of metal-rich terrestrial mines,” Halfar said. “For mining companies and their investors, undersea mining offers high concentrations of ore at relatively low production costs.”

The mining operations will use a strip-mining approach to remove deposits within the top 20 m (66 ft) of the sea floor, using remotely operated underwater mine cutters and a hydraulic pump system to transfer roughly 1.8 million tonne (2 million ton) of ore per year to the surface. These strips would be located approximately 500 m (1640 ft) to 2 km (1.2 mi) from the active vents, but Halfar argues that the cutting and pumping process will disgorge considerable amounts of fine sediment into the water column — a serious problem for vent organisms that feed by filtering the water in their habitat.

The process also will raise the concentrated nutrients from the deep sea to the relatively nutrient-poor surface waters of the ocean, causing algal blooms and potentially contaminating waters that support Papua New Guinea’s commercial fishing industry, as well as local subsistence fishers, according to the press release. Depending on ocean currents, these nutrients could drift widely, disrupting the food chain and potentially damaging ecosystems that lie within other countries’ economic zones or in international waters. This poses additional problems, because while a state has the right to exploit its own resources, international environmental law decrees that it cannot damage the environment beyond its boundaries, the news release states.

The study appears in the May 18 issue of the journal Science.

For more information, contact Halfar at jochen.halfar@utoronto.ca.