[tt] Sci Am: Oceanic Dead Zones Continue to Spread

[Premise Checker]

Oceanic Dead Zones Continue to Spread
http://www.sciam.com/article.cfm?id=oceanic-dead-zones-spread&print=true
News -  August 15, 2008
[Thanks to Sarah for this. Big Heat continues.]

Fertilizer runoff and fossil-fuel use lead to massive areas in the ocean
with scant or no oxygen, killing large swaths of sea life and causing
hundreds of millions of dollars in damage

By David Biello

More bad news for the world's oceans: Dead zones--areas of bottom
waters too oxygen depleted to support most ocean life--are
spreading, dotting nearly the entire east and south coasts of the
U.S. as well as several west coast river outlets.
According to a new study in Science, the rest of the world fares no
better--there are now 405 identified dead zones worldwide, up from
49 in the 1960s--and the world's largest dead zone remains the
Baltic Sea, whose bottom waters now lack oxygen year-round.
This is no small economic matter. A single low-oxygen event (aknown
scientifically as hypoxia) off the coasts of New York State and New
Jersey in 1976 covering a mere 385 square miles (1,000 square
kilometers) of seabed ended up costing commercial and recreational
fisheries in the region more than $500 million. As it stands,
roughly 83,000 tons (75,000 metric tons) of fish and other ocean
life are lost to the Chesapeake Bay dead zone each year--enough to
feed half the commercial crab catch for a year.
"More than 212,000 metric tons [235,000 tons] of food is lost to
hypoxia in the Gulf of Mexico," says marine biologist Robert Diaz of
The College of William & Mary in Williamsburg, Va., who surveyed the
dead zones along with marine ecologist Rutger Rosenberg of the
University of Gothenburg in Sweden. "That's enough to feed 75
percent of the average brown shrimp harvest from the Louisiana gulf.
If there was no hypoxia and there was that much more food, don't you
think the shrimp and crabs would be happier? They would certainly be
fatter."
Only a few dead zones have ever recovered, such as the Black Sea,
which rebounded quickly in the 1990s with the collapse of the Soviet
Union and a massive reduction in fertilizer runoff from fields in
Russia and Ukraine. Fertilizer contains large amounts of nitrogen,
and it runs off of agricultural fields in water and into rivers, and
eventually into oceans.
This fertilizer runoff, instead of contributing to more corn or
wheat, feeds massive algae blooms in the coastal oceans. This algae,
in turn, dies and sinks to the bottom where it is consumed by
microbes, which consume oxygen in the process. More algae means more
oxygen-burning, and thereby less oxygen in the water, resulting in a
massive flight by those fish, crustaceans and other ocean-dwellers
able to relocate as well as the mass death of immobile creatures,
such as clams or other bottom-dwellers. And that's when the microbes
that thrive in oxygen-free environments take over, forming vast
bacterial mats that produce hydrogen sulfide, a toxic gas.
"The primary culprit in marine environments is nitrogen and,
nowadays, the biggest contributor of nitrogen to marine systems is
agriculture. It's the same scenario all over the world," Diaz says.
"Farmers are not doing it on purpose. They'd prefer to have it stick
on the land."
In addition to fertilizers, the other primary culprit is the
consumption of fossil fuels. Burning gasoline and diesel results in
smog-forming nitrogen oxides, which subsequently clear when rain
washes the nitrogen out of the sky and, ultimately, into the ocean.
Technological improvements, such as electric or hydrogen cars, could
solve that problem but the agricultural question is trickier.
"Nitrogen is very slippery; it's very difficult to keep it on land,"
Diaz notes. "We need to find a technology to keep nitrogen from
leaving the soil."
Or farmers can reduce the overall amount of nitrogen required by
employing new biotechnologies, such as the nitrogen use efficiency
(NUE) improvements offered by Arcadia Biosciences. By engineering
crops to overexpress a gene that allows roots to absorb more
nitrogen, Arcadia scientists have shown that "it's possible for NUE
crops to produce the same yield with half as much fertilizer,"
president and CEO, Eric Rey, says. "In canola, we saw a two-thirds
reduction."
Seeds bearing the technology have already been licensed to
agricultural giants Monsanto Company and Dupont's Pioneer Hi-Bred
International in the case of canola and corn, respectively--and even
grass seed from Scotts Miracle-Gro Company may one day employ it.
Although field trials over the last four years have proved the
genetic changes effectiveness, further testing and government
approval means that such crops will not be grown before 2012.
"It's a big economic benefit for farmers if they use only half as
much nitrogen as well a big beneficial impact on nitrogen runoff
into waterways," says Rey, who hopes that this product will be
adopted as quickly as herbicide-resistant crops, which only took
five years from introduction in 1998 to become nearly 70 percent of
the corn grown in the U.S., and is now nearly 90 percent. "A
reasonable expectation is that there would be a dramatic reduction,
maybe by 2018."
But that still might not solve the dead zone problem. So much
nitrogen is now reaching these coastal waters that much of it ends
up buried in sediment, Diaz says, even when new nitrogen sources are
removed those sediments release that nitrogen over time,
perpetuating the cycle.
That inability to recover is driven not only by the nitrogen buried
in the sediment but also by water layers that don't mix with one
another, despite the massive flow of rivers like the Mississippi.
Instead, warmer, fresher water on the surface sits on top of cooler,
denser, saltier water and it takes the energy of multiple powerful
hurricanes to blend the two.
For example, as Hurricane Katrina bore down on the Louisiana coast
with its powerful winds blowing faster than 130 miles (210
kilometers) per hour, the monstrous tropical storm delivered a
benefit: it mixed the warm, oxygen-rich surface waters with the
colder, almost oxygen-free waters beneath, dispelling the largest
dead zone in the U.S. for a time. Hurricane Rita followed and
finished the work, ending early the seasonal dead zone that forms
each year at the mouth of the Mississippi.
That dead zone--which last year stretched over roughly 8,500 square
miles (22,000 square kilometers), an area the size of New Jersey,
and is predicted to grow even more extensive in 2008, thanks to the
early summer floods--forms because of the rich load of nitrogen and
phosphorus the Mississippi carries down from the farm fields of the
U.S. Midwest.
Hoping for hurricanes is neither popular nor sensible, so scientists
in the Baltic Sea nations, desperate for solutions, are considering
so-called geoengineering options: large-scale human interventions
into natural systems. In this case, air would be bubbled into some
of the smaller bays to assess what happens. "If you look at
agricultural ponds, you can aerate them to prevent low oxygen," Diaz
says. "But that's a pond. We're talking about open systems with
tides. The water doesn't just stay there."
Ultimately, it may take revolutions in agriculture and
transportation, along with the energy of hurricanes to bring life
back to dead zones. "If you can't mix a dead zone with the energy of
a hurricane," Diaz adds, "I don't see how geoengineering is going to
do it."