January 2010, Vol. 22, No.1


NASA Satellites Identify Declining Groundwater in Northern India

Groundwater levels in northern India are declining rapidly, dropping by as much as 0.3 m/yr (1 ft/yr) in the past decade, according to research conducted by NASA scientists. Using satellite data, a team of hydrologists led by Matt Rodell of NASA’s Goddard Space Flight Center in Greenbelt, Md., found that human activities are draining aquifers faster than natural processes can replenish them, according to a NASA news release.

 The findings are based on data from NASA’s Gravity Recovery and Climate Experiment (GRACE), a pair of satellites orbiting 483 km (300 mi) above Earth’s surface. The satellites sense changes in Earth’s gravity field and mass distributions, including water masses stored above or below Earth’s surface, the release says. Data collected showed that more than 108 km3 (26 mi3) of groundwater disappeared from aquifers in the Indian states of Haryana, Punjab, and Rajasthan, as well as near the city of Delhi, between 2002 and 2008.

The satellites’ positions change in response to variation in the pull of gravity. Changes in underground water masses affect gravity enough to provide a signal that can be measured by the satellites, the release says. The satellites’ findings enable NASA scientists to “observe and monitor water storage changes” around the world from their desks, said Isabella Velicogna of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and the University of California–Irvine.

Since groundwater levels respond slowly to changes in weather, it can be take months or years to replenish that water which has been pumped for irrigation or other uses, the release says. While India’s Ministry of Water Resources provided data to NASA researchers suggesting countrywide use of groundwater exceeding the rate of replenishment, regional data were unknown. Rodell and his colleagues analyzed 6 years worth of monthly data from GRACE for northern India to produce a timeline of water storage changes beneath India, the release says.

“We don’t know the absolute volume of water in the northern Indian aquifers, but GRACE provides strong evidence that current rates of water extraction are not sustainable,” Rodell said. The region’s dependence on irrigation is cited as one of the top sources of water use, the release says. No changes in typical factors affecting aquifer levels, along with a slightly above normal level of rainfall, led researchers to conclude that reduction in water levels is due to human activities, the release says.

This technology enables scientists to track changes in freshwater availability across large areas in regions where ground-based data are sparse or hard to access, said James Famiglietti of the University of California–Irvine, a collaborator on the project.


Scientists Use Poultry Litter To Produce Activated Carbon

Scientists at the U.S. Agriculture Research Service (ARS) have been awarded a patent for a new way to produce activated carbon that begins with poultry litter. Despite the “yuck factor,” the method represents a sustainable improvement on traditional activated carbon, which generally is made from nonrenewable coal and from plant materials, such as coconut shells and wood, according to an ARS news release.

To make the product — called biochar — scientists begin with poultry byproducts that contain wood shavings, peanut shells, poultry droppings, and feathers. They grind the waste into a fine powder. After grinding, it is turned into pellets and heated in an oxygen-free furnace at temperatures up to 816°C (1500°F). This process converts the pellets into biochar and sanitizes the product.

Biochar has a relatively high phosphorus concentration, giving it a negative charge. This makes it apt to attract positively charged ions in metals. The biochar-activated carbon, which is highly porous, then can be used to absorb pollutants in both liquids and gases.

However, the high phosphorus levels also can lead to excessive amounts of the nutrient in water streams.

Unlike the nonrenewable coal that most activated carbon is made from, it is estimated that U.S. broiler chickens produce 13.6 million Mg/yr (15 million ton/yr) of litter, the release says.

According to the release, biochar can be made for about $1.43/kg ($0.65/lb) of poultry waste, making it competitive with traditional activated carbon products. It is also suitable for any waste cleanup process in which activated carbons are used.


Using Submerged Wetlands as Alternatives to Septic Tanks

On a quest to find an alternative to septic tanks, Joe Yelderman and Margaret Forbes constructed five different submerged gravel wetlands and tested their ability to filter pollutants at the Baylor Wastewater Research Program research site at the Waco (Texas) Metropolitan Area Regional Sewerage System.

Yelderman, a professor of geology at Baylor University (Waco), and Forbes, a research associate of biology at Baylor, tested to see what dosing system works best with each wetland. Submerged wetlands rely on gravel and plants to remove contaminants by mirroring the pollutant removal ability they have in nature, according to a Baylor news release.

“Our goal was to improve the water quality coming out of the septic tank so residents could dispose of the treated wastewater into thinner soil or places where the water table is higher,” Yelderman said in the news release. “It would just provide more options.”

Following septic tank treatment, the effluent flows into a drain field, where the soil further decomposes the pollutants in the water and makes it safer for the environment, the release says. In many areas, the water table is too high and so does not allow effluent to decompose fully, or the type of soil does not absorb the effluent adequately, resulting in contaminants entering the groundwater.

The study’s results show that the majority of the wetlands significantly reduced biochemical oxygen demand and reduced the levels of such nutrients as phosphorus and ammonia, Yelderman explained.

Wetlands with gravel and plants performed better during batch dosing than during more continuous dosing. Batch dosing performs better because of the wetland's interaction with the air in between the dosings, Yelderman said. When the wetland dried and was rewetted, the gravel and plants oxidized the wastewater and enabled aerobic bacteria to decompose the organic matter. The plants used during batch dosing were stressed by the process, not growing as large as possible, but they adapted by sending roots deeper, Yelderman added.

The research was funded by the Texas Onsite Wastewater Treatment Research Council (Austin).


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