LETTERS
(continued)
and cheaper for small-scale conversion systems where the stillage needs only minimal drying before it can be used. The most serious environmental liabilities associated with the use of most forms of biomass are the environmental costs of producing the biomass residues. Collecting crop residues that are currently returned to the soil will exacerbate some of the environmental problems currently plaguing agriculture, such as erosion and the loss of humus and nutrients from agricultural soils. Intensive production of biomass will have all of the environmental liabilities of intensive agriculture. It is difficult to relate the scale of a biomass farm to its environmental costs, except that more dispersed operations will allow the environment’s natural defenses to function more effectively. It is interesting to note that some of the adverse impacts of collecting field wastes and of producing intensively grown biomass could be substantially mitigated by coupling biomass production operations with decentralized biogasification facilities.
When it comes to utilizing standing-forest biomass for energy, largescale users will exert a tremendous pressure for high-density harvesting of wood, probably by clear cutting. Decentralized users, by contrast, may be able to harvest their wood by selective harvesting operations. Selective cutting is considerably more environmentally benign, and can even be used to upgrade the timber quality on many woodlots. Thus while wood combustion produces substantially greater combustion emissions when used at small-scale decentralized facilities, it cannot be generalized that the environmental liabilities of biomass energy utilization are greater when decentralized systems are used. In many cases, the opposite is true. Biomass energy options span a broad range of technologies and applications, each with its own unique environmental characteristics. The scale of a particular biomass energy enterprise is not indicative of its environmental impact. Gregory Morris Energy and Resources Group University of California Berkeley, Calif. 94720
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November 1979, p. 1353, Figure 2. “Sulfate loading to lake water (g S04-2/ha/y)” should read “Sulfate loading to lake water (kg S04-*/ ha/ y) .” August 1980, p. 885. The name of the first author of the correspondence entitled “Accumulation of polychlorinated biphenyls in surficial Lake Superior sediments” is incorrectly reported. The correct name is Roger R . Greenburg. August 1980, p. 904. A study of nonpoint-source particles in the atmosphere was incorrectly attributed to John Cooper and co-workers a t the Oregon Graduate Center. The work was performed by Douglas W. Cooper and co-workers at the Harvard University School of Public Health.
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EnvironmentalScience & Technology
November 1979, p. 1351, col. 3. The quantity “3.8 X lo8 metric tons/y” should read “3.8 X lo6 metric tons/t” (21st line from the top). Also, the phrase “18-78 grams of S06-2/ha/y” should read “18-78 kg/ha/y” (42nd line from top).
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Corrections
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