August 14, 2008
Ocean Dead Zones Growing Around The World

Want some meat on part of the argument for why a Scripps researcher expects big ocean extinctions? Here's a pretty impressive indicator of bad trends in the oceans: the hypoxic (oxygen deficient) dead zones are growing in size.

A global study led by Professor Robert Diaz of the Virginia Institute of Marine Science, College of William and Mary, shows that the number of "dead zones"—areas of seafloor with too little oxygen for most marine life—has increased by a third between 1995 and 2007.

How much of that dead zone size growth is due to expanded use of nitrogen fertilizers? All of it? The only development I can see on the horizon that will change this trend is Peak Oil. Declining availability of fossil fuels will push up the cost of nitrogen fertilizer made using natural gas. But at some price of fertlizer the use of wind, solar, or nuclear electric power will become competitive for nitrogen fertilizer production. So I do not expect a permanent shift toward lower nitrogen fertilizer usage.

Diaz and collaborator Rutger Rosenberg of the University of Gothenburg in Sweden say that dead zones are now "the key stressor on marine ecosystems" and "rank with over-fishing, habitat loss, and harmful algal blooms as global environmental problems."

The study, which appears in the August 15 issue of the journal Science, tallies 405 dead zones in coastal waters worldwide, affecting an area of 95,000 square miles, about the size of New Zealand. The largest dead zone in the U.S., at the mouth of the Mississippi, covers more than 8,500 square miles, roughly the size of New Jersey.

Diaz began studying dead zones in the mid-1980s after seeing their effect on bottom life in a tributary of Chesapeake Bay near Baltimore. His first review of dead zones in 1995 counted 305 worldwide. That was up from his count of 162 in the 1980s, 87 in the 1970s, and 49 in the 1960s. He first found scientific reports of dead zones in the 1910s, when there were 4. Worldwide, the number of dead zones has approximately doubled each decade since the 1960s.

As China develops, the US population grows by 50%, and other areas grow in population and industry this these dead zones will grow much larger. Is it possible for farmers to maintain high levels of crop production without nitrogen fertilizer run-off so high that it causes dead zones at the mouths of rivers?

Diaz and VIMS colleague Linda Schaffner estimate that Chesapeake Bay now loses about 10,000 metric tons of carbon to hypoxia each year, 5% of the Bay's total production of food energy. The Baltic Sea has lost 30% of its food energy—a condition that has contributed to a significant decline in its fisheries yields.

From 1974 to 2000 world nitrogen fertilizer usage grew by about a factor of 2.5. The economic development of China, southeast Asia, and India creates the possibility of a far larger growth in nitrogen fertilizer demand in the next 25 years. How big will the dead zones become?

The outlook for fertilizer demand is up up up.

The FAO report estimates that world fertilizer supply (nitrogen, phosphate and potash nutrient) will increase by some 34 million tonnes representing an annual growth rate of 3 percent between 2007/08 and 2011/12, comfortably sufficient to cover demand growth of 1.9 percent annually.

Total production is expected to grow from 206.5 million tonnes in 2007/08 to 241 million tonnes in 2011/12. Fertilizer demand will increase from 197 million tonnes today to 216 million tonnes in 2011/12.

World nitrogen supply is forecast to rise by 23.1 million tonnes by 2011/12; world phosphate fertilizer supply will increase by 6.3 million tonnes and potash supply by 4.9 million tonnes.

The Daily Telegraph has a worldwide map of hypoxic areas.

Update: A Time article reports use of winter wheat crops could catch nitrogen released by spring thaws. But that costs money and the incentive isn't there to do this.

Share |      Randall Parker, 2008 August 14 05:39 PM  Trends Extinction


Comments
Dave said at August 16, 2008 9:46 AM:

How about using some of this nutrient rich runoff as feedstock for algae-to-oil production?

Randall Parker said at August 16, 2008 9:55 AM:

Dave,

Algae-to-oil isn't ready yet for other reasons. But my guess is that even if algae biodiesel was ready it would use only a small fraction of the dissolved fertilizer in rivers. The Mississippi in particular is massive.

For the Mississippi I am wondering whether efforts to channel silt toward Mississippi delta land replenishment would also reduce the amount of dissolved fertilizer that would make it into the Gulf of Mexico.

Randall Parker said at August 16, 2008 2:10 PM:

Dave,

Algae-to-oil isn't ready yet for other reasons. But my guess is that even if algae biodiesel was ready it would use only a small fraction of the dissolved fertilizer in rivers. The Mississippi in particular is massive.

For the Mississippi I am wondering whether efforts to channel silt toward Mississippi delta land replenishment would also reduce the amount of dissolved fertilizer that would make it into the Gulf of Mexico.

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