No silver lining.Scientists have long recognized that trees require calcium for healthy growth. More recently they have speculated that acid rain robs trees of this vital nutrient nutrient /nu·tri·ent/ (noo´tre-int) 1. nourishing; providing nutrition. 2. a food or other substance that provides energy or building material for the survival and growth of a living organism. by leaching it from the soil and by mobilizing aluminum, which interferes with calcium uptake by roots. However, a lack of soil data from before the acid-rain era--which began after World War II--frustrated attempts to trace the connection. That impediment A disability or obstruction that prevents an individual from entering into a contract. Infancy, for example, is an impediment in making certain contracts. Impediments to marriage include such factors as consanguinity between the parties or an earlier marriage that is still valid. was removed a few years ago when U.S. Geological Survey The term geological survey can be used to describe both the conduct of a survey for geological purposes and an institution holding geological information. A geological survey scientist Greg Lawrence learned of the Dokuchaev Central Soil Museum, near St. Petersburg, Russia, a unique repository of soil samples that date back nearly a century. "We've known that acid rain acidifies surface waters, but this is the first time we've been able to compare and track tree growth in forests that include soil changes due to acid rain," says Lawrence, who led an international study based on the Dokuchaev collection. The results suggest that acid rain may have serious implications for forest health in affected areas. The researchers selected archived soils from 1926 and 1964, which had been stored in wooden boxes as intact three-foot-deep profiles, and dug replicate pits to obtain modern samples. Their analysis revealed a trend of decreasing concentrations of calcium in a "root-available" form and increasing concentrations of "root-available" aluminum. Examination of cores taken from Norway spruce spruce, any plant of the genus Picea, evergreen trees or shrubs of the family Pinaceae (pine family) widely distributed in the Northern Hemisphere. The needles are angular in cross section, rather than flattened as in the related hemlocks and firs. growing near the sampling sites showed that the soil changes coincided with decreased diameter growth. In about 50 years, acid rain had so severely degraded de·grad·ed adj. 1. Reduced in rank, dignity, or esteem. 2. Having been corrupted or depraved. 3. Having been reduced in quality or value. the previously fertile soil that the trees could no longer maintain normal growth rates Growth Rates The compounded annualized rate of growth of a company's revenues, earnings, dividends, or other figures. Notes: Remember, historically high growth rates don't always mean a high rate of growth looking into the future. . What's more, this decline in tree health occurred despite the regional climate becoming warmer and wetter, a situation that should have increased growth. Although the research was conducted in Europe, Lawrence says the findings are relevant to North America North America, third largest continent (1990 est. pop. 365,000,000), c.9,400,000 sq mi (24,346,000 sq km), the northern of the two continents of the Western Hemisphere. , where large areas of eastern forests, such as those in New York's Adirondack and Catskill regions, have soils that are likely more sensitive to acid rain than those studied in Russia. |
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