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."