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-of-control 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 eleva-tion 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 C02 released during manufacture and transport of fertilizer, and natural soil generation of N20. The long-term study (1991-1999) compares conventional, no-till, and organic crops to unmanaged ecosystems in the Midwest.

For all die cropping systems, N20 is the greatest single source of global warming potential, Robert­

son says. N20 has a global warm­ing potential 310 times that of C02

and is produced by soil bacteria from fertilizer components such as ammonium (NH4

+) and nitrate (N03~). "Accelerated N20 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 N20 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 C02 equiva­lents, says Robertson. Moreover, abandoned farm fields have a negative global warming potential because they have low rates of N20 emissions that are more than offset by the large amounts of

Government Watch

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. N0X 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-per-year business. In contrast to its image of crystal-clear purity, about one-fourth of bottled water

Continued on Page 457A

NOVEMBER 1, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 4 5 5 A

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 emiss ions and prnhably over<stafe<; w h a t is achievable savs Bill Schlpsinppr a h ineporhemis t at Dirkp llniversitv

Researchers measure the release of the greenhouse gas N20.

"Robertson's work confirms USDA research that shows land management can reduce emis­sions of greenhouse gases," says Bill Hohenstein, Director of US-DA's global change program of­fice. The research "demonstrates the technical potential for cuts, but what turns out to be econom­ically feasible might be a subset of that," he added.

"Robertson's study helps ex­plain the whole agricultural emissions system and should influence the November nego­tiations at the Hague for the Kyoto Protocol," predicted Gregg Marland, a geochemist with the Oak Ridge National Laboratory. U.S. and Canadian officials have been pushing for talks at the November meeting to establish a program that allows countries to receive greenhouse gas reduc­tion credits for storing carbon in agricultural soils JANET PELLEY

Disconnect between Kyoto Protocol and clean energy? The Kyoto Protocol's clean devel­opment mechanism (CDM) is regularly associated with renew­able energy projects like wind farms and solar power plants. However, if the experience of the World Bank's nascent Prototype Carbon Fund (PCF) is any indica­tion, the first CDM projects may not include as many renewable technologies as hoped.

The goal of the PCF, which was launched in January, is to demon­strate how the CDM can foster collaborations between industri­alized and developing countries by mobilizing private and public resources to combat climate change. It is one of several efforts under way to harness the CDM by allowing countries and busi­nesses to obtain credit for reduc­ing the world's greenhouse gas burden by helping developing nations invest in technologies that produce less CO than tradi­tional fuels like coal and oil.

The negotiations at the Sixth Conference of Parties (COP 6) of the U.N. Framework Convention

on Climate Change (UNFCCC), which is scheduled to take place in the Netherlands at The Hague later this month, could result in renewable technologies being more viable, says Ken Newcombe, PCF's manager.

"The problem in the Kyoto Protocol is knowing for what part of the life of a project you're likely to get creditworthy emis­

sions reductions," Newcombe explains. At present, the protocol does not make clear how long investments in renewable tech­nologies can be amortized. The only firm date is 2012, so the six governments and 17 multina­tional companies investing in PCF projects currently want to be able to recoup their invest­ments in a decade, he says.

Carbon costs for alternative energy technologies Unless the parties to the Kyoto Protocol clarify the time frame for which climate-friendly projects can earn emissions reduction credits, renewable energy tech­nologies with long payback times like wind and small-scale hydro are likely to be too expensive to benefit from the protocol's clean development mechanism.

Source: World Bank.

4 5 6 A • NOVEMBER 1, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS