Environmental▼News curve, generating more sewage and exhaust gases,” he warns. The nutrient overload, which has nearly tripled the amount of nitrogen delivered to vulnerable coastal seabeds through natural processes, generates low oxygen zones that range in size up to 70,000 km2, the report says. Fisheries are destroyed when oxygen concentrations drop below 2 milliliters of oxygen per liter because adult fish suffocate and their spawning habitat is ruined, says Bob Diaz, a marine biologist at the College of William and Mary and a coauthor of the report. “In the 20th century, loss of fish stocks from over-fishing was the biggest marine issue, but in the 21st century the key factor affecting fish stocks will be oxygen depletion,” he says. Since the 1960s, the number of
oxygen-depleted ecosystems worldwide has doubled every 10 years to a total of 146, the report says. Climate change could compound the problem in areas where increased rainfall flushes more nutrients into coastal waters and strengthens the stratification of the water column, which cuts off fresh oxygen inputs to bottom waters. For example, the report predicts that a doubling of carbon dioxide levels would boost Mississippi River discharge into the Gulf of Mexico by 20%, leading to a 50% increase in algal production, a 30–60% decrease in oxygen, and expansion of the Gulf’s dead zone. Precision agriculture, matching fertilizer applications to plant needs, and removing nitrogen from exhaust gases of power plants and cars are part of the solution, Nuttall says.
Sustainable sanitation, composting toilets, and biological sewage treatment systems are a must, especially in light of the UN’s goal to halve the number of people without hygienic sanitation by 2015, he adds. Nutrient loads have dropped in some watersheds, revealing long lag times prior to recovery, says Don Boesch, oceanographer at the University of Maryland’s Center for Environmental Science. For instance, after the collapse of the Soviet Union, farmers couldn’t afford fertilizers, and nitrogen concentrations at the mouth of the Danube River dropped by half. In 1996, five years after inputs were cut, the dead zone in the Black Sea did not recur for the first time since the 1970s, he says. The report is at www.unep.org/ geo/yearbook. —JANET PELLEY
Simple method advances degradation studies taining particles stuck, although he had to test several resins before he found one strong enough that didn’t “creep” over the entire particle. However, even the most viscous resin would overwhelm very small particles like iron oxide. So Birkefeld also devised a way to adsorb ANDREAS BIRKEFELD
A new method for monitoring how particulate pollutants degrade in soil requires only Plexiglas, commercially available resin, and some string. Tests show the method is simple but effective. Soil scientists investigating the risk posed by pollutants such as heavy-metal-containing dusts or residues from mines have lacked a good method for studying how the particulates break down in soils. Researchers had tried burying mesh bags filled with minerals in the ground, but too many variables prevented quantitative results. Andreas Birkefeld, a doctoral candidate at the Swiss Federal Institute of Technology (ETH) in Zurich, and his advisors, Bernd Nowack and Rainer Schulin, decided to find a better approach. “We wanted the particles in direct contact with the environment to avoid any interference,” said Birkefeld, after he presented the results at the ACS national meeting held in Anaheim, Calif., in late March. To do that, he coated 2-centimeter polymethylmethacrylate polymer supports—more commonly known as Plexiglas—with a thin coat of epoxy resin. The metal-con-
A lead oxide particle fixed with epoxy resin to a Plexiglas support degraded over time in soil. Birkefeld used scanning electron microscopy images to examine the particle’s surface and analytical techniques to quantify the amount of metal lost.
such tiny pollutant particles to larger quartz surrogates before attaching them. The particles on the plates are easily analyzed for degradation and development of new mineral phases using standard methods such as X-ray fluores-
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cence, scanning electron microscopy, and Raman spectroscopy. Birkefeld tested the approach by burying the plates in an open field test site near ETH that had been previously well characterized. Over the past year and a half, he dug up two plates from the soil every other month for analysis. In these experiments, Birkefeld compared plates peppered with lead oxide particles to ones with copper concentrate mined from Chile. Overall, the copper particles were extremely slow to degrade, whereas the lead particles dissolved in acidic soils and formed new phases in calcareous soils, according to Birkefeld. His method is a big advance on the mesh bag studies because it is rugged enough for soil and is quantitative, says Janet Hering, a professor at the California Institute of Technology. And because the method works in soil, she believes it would great for sediment studies too. Nowack says that future iron oxide studies will be in collaboration with the University of Rennes in France. They hope to answer questions that arose during Birkefeld’s study, including what specific processes contributed to particle degradation. —RACHEL PETKEWICH
