Research▼Watch Forests acquire most of their mineral nutrients from precipitation or atmospheric dust deposited on topsoil rather than through the weathering of rocks as was previously thought, according to new research reported by Martin Kennedy from the University of California–Riverside (UCR) and colleagues at Princeton and Cornell Universities. The finding suggests that the nutrient budget for trees is tighter than scientists had assumed, making the effects of acid rain much more serious. Analyzing the natural strontium isotope composition of soils, streams, rain, and plants in a rainforest of southern Chile, the healthiest ecosystem they could find, Kennedy and colleagues found that close to 90% of the strontium—and therefore similar nutrients such as magnesium, calcium, and potassium—was brought in by rain. Moreover, nutrients were moving through the soil and into the trees in as little as 3 years. “We thought there would have to be a long residence time, a very tight recycling of these nutrients over a prolonged period in order to make the ecosystem work,” Kennedy says. Instead, “they’re moving through much faster than we feared.” In areas disturbed by acid rain deposition, these nutrient bases are leached away more quickly, resulting in nutrient deficiencies in soils and plant systems. The implication is that old-growth hardwood forests may be closer to the brink than anyone thought. “So, what we might expect to see is not just a linear decrease, but a step decrease as soils are exhausted and whole forests begin to feel the effects,” Kennedy says. (Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 9639–9644)
Thinning glaciers and rising seas Melting mountain glaciers may be contributing more to rising sea levels than previously thought, according 376 A
■
to a new analysis by University of Alaska scientists. The data point to glaciers in Alaska and Canada as the world’s largest glaciological contributors to rising sea levels, with annual losses in volume estimated to be nearly twice that of the entire Greenland Ice Sheet. Because large glaciers in remote locations like the high latitudes of Alaska and Canada are difficult to access, their contribution to sea level rise has previously received little at-
data and contour data from topographic maps made from aerial photographs by the U.S. Geological Survey from the 1950s to the 1970s. From the 1950s to the mid-1990s, the average change in thickness of the glaciers was –0.52 m/yr. By extrapolating to all glaciers in Alaska and Canada, the researchers estimated a contribution to sea level rise of 0.14 mm/yr. Over the last decade, however, the data suggest that the average change in thickness of the glacPHOTODISC
Forests even closer to the brink
Shrinking glaciers in Alaska and Canada are large contributors to sea level rise, as indicated by new airborne laser altimetry data.
tention. Although there are more than 160,000 glaciers worldwide, only about 40 are routinely monitored for changes in volume and area. Those tend to be glaciers that are easily accessible and small in size, which may not contribute much to sea level rise. To overcome this bias toward small glaciers, Anthony Arendt and colleagues estimated the changes in volume and area of 67 glaciers in Alaska and Canada using 40 years worth of data. They used a combination of new airborne laser altimetry
ENVIRONMENTAL SCIENCE & TECHNOLOGY / OCTOBER 1, 2002
iers increased to –1.8 m/yr, which, when extrapolated to all glaciers in the region, corresponds to a sea level rise of 0.27 mm/yr. Although glaciers in Alaska and Canada represent only about 13% of the Earth’s mountain glacier area, they form the largest glaciological contribution to sea level rise measured to date. Previous reports based on observations and computer model simulations have estimated the total contribution of all mountain glaciers to sea level rise to be 0.2–0.4 mm/yr. (Science 2002, 297, 382–386)
