Gulf’s ‘dead zone’ is biggest ever

Scientists just measured the largest 'dead zone” ever recorded for the Gulf of Mexico, a whopping 8,776 square miles, massive enough to cover all of New Jersey.

And only dramatic shifts in farming practices are likely to prevent even bigger problems in the future, experts say.

Dead zones, which disrupt fishing industries and threaten aquatic species, are caused by industrial and agricultural runoff. Every spring, the Mississippi River funnels a rush of nutrients into the gulf that fuels an explosion of growth of microscopic algae called phytoplankton.

But the bloom of life for the algae is short lived, and their corpses sink to the depths below. Their decomposition gives rise to a burst in bacterial growth. The microbes rapidly consume not only the plankton but also all of the oxygen dissolved in the deep.

At the same time, the incoming river water forms a layer on the surface of the gulf, preventing new oxygen from dissolving and mixing with the depleted waters below. Fish that do not flee suffocate, as do all stationary species and plant life.

The size of the Gulf of Mexico dead zone fluctuates annually, but increased precipitation this year amplified runoff. The result is an oxygen-depleted area almost 50 percent larger than what has been seen on average for the past five years.

Although oxygen depletion occurs naturally in some parts of the ocean, the Gulf of Mexico's dead zone is caused by humans. The nutrients these algae blooms feed on come from synthetic fertilizers and animal manure, human and industrial waste.

It is one of the reasons water quality has become such an issue in Iowa. Although many farmers are adopting practices to reduce runoff pollutants, legislators continue to balk over approving a dedicated funding source for broader water quality improvements in the state.

Matt Liebman, who studies cropping systems at Iowa State University, is hopeful that a shift in agricultural practices in the Midwest could make a big difference for the Gulf of Mexico.

In a study published this year, his team showed that runoff could be reduced by 60 percent if farmers growing corn and soybean rotated in one or two more crops.

Half of the nitrogen and a quarter of the phosphorous that runs into the gulf comes from corn and soybean fields in the Midwest, he said. In Iowa alone, those crops cover 65 percent of the state. Both plants have shallow roots and are green for only part of the year, unlike the native grasses that once colonized the Corn Belt.

Liebman's group compared two different management systems. In the first, corn and soybeans were grown in alternating years with fertilizers applied at typical levels. In the second, alfalfa and oats were rotated in, manure was applied once, and fertilizer was used restrictively as needed.

Despite using nearly 90 percent less fertilizer, corn and soybean yields increased, soil quality improved and soil erosion decreased by 25 percent - all without decreasing profitability.

In addition to rotating crops, Liebman found, 'less productive areas could be converted into crop and non-crop vegetation that provides conservation benefits.”

A previous ISU study showed that converting just 10 percent of farmland to native prairie grass could reduce nitrogen and phosphorous runoff nearly 90 percent.

'I'm optimistic that we have a lot of technical answers,” he said, but 'we need a market pull and a policy push.”

Such policy changes could include regulations, financial incentives for farmers to adopt conservation practices, and technical assistance to help farmers incorporate the changes.

Yet even with a dramatic shift in reducing runoff, Robert Magnien, an algae bloom expert with the National Oceanic and Atmospheric Administration, warns that it could be 10 to 20 years before the gulf shows visible improvement.