Government Watch Stephenson, a research ecologist with the U.S. Geological Survey. Now, dense stands of young trees create a ladder for ground fires to climb into the crowns of large trees, which leads to hot, out-ofcontrol fires. "Both mechanical thinning and prescribed burns are needed to restore western forests," Stephenson emphasizes. Some forests have so much fuel that prescribed burns can run out of control if the weather suddenly changes, such as the spring blaze that torched Los Alamos, NM. In some areas, the trees must first
be thinned by chainsaw, he says. But logging small trees is not always economical and often cannot be done in remote areas or on steep slopes, Stephenson says. Although prescribed burns can restore wetter forests, such as those below 7000 ft on the western slope of the Sierra Nevadas, their use may be limited because of air quality concerns, he says. Stephenson emphasized that not all forests, especially high elevation ones such as those in Yellowstone National Park have been altered by fire suppression JANET
PELLEY
Cropland net emitter of greenhouse gases High soil nitrogen levels are causing U.S. cropland to release more greenhouse gases (GHG) to the atmosphere than crops remove, according to research presented at the Ecological Society of America meeting in August and reported in Science (2000, 289, 1922-1924). The findings affect U.S. and Canadian hopes that soil carbon sequestration on farms could receive international credit for slowing global warming. The research shows that practices such as reduced tillage and fertilizer use lower GHG generation, but the potential of farmland to act as a carbon sink may be less than officials at the U.S. Department of Agriculture (USDA) anticipated. Previous studies only looked at capture and release of carbon on cropland. The new research calculates a complete budget for carbon dioxide (C02), methane (CH4), and nitrous oxide (N20), says Phil Robertson, an ecosystem scientist at Michigan State University. The budget balances carbon stored in the soil against C0 2 released during manufacture and transport of fertilizer, and natural soil generation of N 2 0. The long-term study (1991-1999) compares conventional, no-till, and organic crops to unmanaged ecosystems in the Midwest. For all die cropping systems, N 2 0 is the greatest single source of global warming potential, Robert-
son says. N 2 0 has a global warming potential 310 times that of C0 2 and is produced by soil bacteria from fertilizer components such as ammonium (NH4+) and nitrate (N03~). "Accelerated N 2 0 production depends on having lots of nitrogen in the soil, which can come from fertilizer, organic matter in the soil or biological fixation of nitrogen gas by alfalfa or clover," Robertson explains. Conventional fields have the highest global warming potential, due to fertilizer-driven N 2 0 flux from soils and the vast amounts of COz produced during the manufacture and transport of fertilizer. No-till agriculture reduces that potential by more than 80% by storing the carbon from crop residues in the soil, according to Robertson. Other practices, such as organic agriculture and planting cover crops like annual rye grass in the fall, slash global warming potential by half by lowering fertilizer use and better tailoring nitrogen application to crop needs. These practices combined with no-till could neutralize U.S. agriculture's annual release of 60 million metric tons of C0 2 equivalents, says Robertson. Moreover, abandoned farm fields have a negative global warming potential because they have low rates of N 2 0 emissions that are more than offset by the large amounts of
allow the Canadian government to step in and force Ontario, which along with the province of Quebec is Canada's major source of smog, to meet U.S. emissions standards if the province does not act on its own, he claims. N0 X emissions from Ontario's coal-fired power plants are three times higher than what would be allowed under U.S. regulations proposed for 2003 (Environ. Sci. Technol, 1999, 33 (3), 64A). Final negotiations were expected to take place in October, and the treaty is expected to be signed by the end of this year.
Full disclosure on bottled water? Bottled water may have to carry labels proving its purity if the U.S. Food and Drug Administration (FDA) has its way. In a Federal Register notice (2000, 65(166), 51,833-51,839), FDA recommends that bottled water reveal the same information on contaminants that water utilities are required to provide to their customers under the Safe Drinking Water Act. These annual reports describe the source of the tap water and disclose the levels of a host of regulated contaminants. Unlike the tap water reports, however, bottled water labels would not have to include explanatory information on recommended maximum levels of contaminants and their reduction targets. Although FDA's recommendation has not yet been enacted, it is a blow to the bottled water industry, which maintains that additional labeling requirements are unnecessary. More than half of all Americans drink bottled water, making it a $4 billion-peryear business. In contrast to its image of crystal-clear purity, about one-fourth of bottled water Continued on Page 457A
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Environmental News carbon stored in soil from rapidly growing grasses and trees. In addition to cutting GHG emissions, retiring marginal farmland and implementing no-till and best management practices reduces erosion and nonpoint source pollution, says Rattan Lai, a soil scientist at Ohio State University. What impact these practices could have on global warming is questionable. Practiced across the country, these techniques could sequester 100-300 million metric tons of carbon per year, according to Lai and USDA figures. This would bring the United States nearly one-third of the way to its commitment under the 1997 Kvoto Protocol an international treatv to emissions of GHG to 5% below does not consider N O e m i s s i o n s a n d p r n h a b l y over
