Saturday, May 08, 2004

“Dead zones” on the rise

The number of oxygen-starved “dead zones” in coastal waters has doubled over the past decade to nearly 150 worldwide and is projected to become the greatest threat to marine ecosystems, according to a new report from the UN Environment Program (UNEP). The culprit is the 160 million tons of nitrogen dumped into the environment every year from fertilizers, sewage, and fossil-fuel burning, which are driving the growth of massive algal blooms that die and then consume oxygen. The nitrogen inputs must be scaled back through efficient fertilizer use, appropriate sanitation technologies, and scrubbing nitrogen from exhaust gases, UNEP says.

The report, released on March 31 as the first annual Global Environment Outlook Year Book 2003, highlights the fertilization of the planet as a spreading threat due to a rapidly growing and industrializing human population, says Nick Nuttall, a spokesperson for UNEP. “Oxygen-starved coastal waters will worsen as developing countries expand the use of industrial fertilizers and increasing human numbers put cities on a massive growth 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 sizes 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. Boesch predicts that global international treaties will be the next tool to rein in human acceleration of the nitrogen cycle.

Once again, corporate farming is destroying the world; it is not a sustainable form of agriculture.


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