The Gulf of Mexico dead zone — which scientists tie to fertilizer from Midwest agriculture including ethanol production — will be slightly smaller than last year’s but still about the size of Connecticut.
The dead zone occurs when nitrogen-based fertilizer washes from Corn Belt farms into the Mississippi River and winds its way south into the Gulf, providing nutrients for a bloom of algae. When the bloom dies, it leaves oxygen-depleted water where other marine life can’t survive.
An indirect link was established between the dead zone and U.S. ethanol production when, in 2012, the dead zone contracted dramatically after an extreme drought damaged corn crops.
The annual dead zone typically peaks in July and August, and this year’s could stretch from South Texas to Alabama and cover 4,600 to 5,700 square miles, the National Oceanic and Atmospheric Administration forecasts.
That’s on par with the 5-year average but down slightly from last year’s 5,840 square miles. NOAA had predicted a larger dead zone last year because of runoff from spring flooding in Minnesota and Illinois, but windy conditions in the Gulf helped keep it in check.
The persistence of the Gulf dead zone raises concerns among some researchers that expansions of U.S. biofuel requirements could escalate harm to an area that supplies nearly one-fifth of the nation’s commercial seafood.
“None of this is happening intentionally,” said Larry McKinney, executive director of the Harte Research Institute for Gulf of Mexico Studies. “This is all the result of unintended consequences of well-meaning policies.”
Federal law mandates that an increasing amount of renewable fuels, including ethanol – pure alcohol — be blended with gasoline as a way of reducing emissions and reliance on fossil fuels. Because most U.S. ethanol is made from corn, the mandate has been a boon to ethanol makers and Corn Belt agriculture, contributing to the fertilizer flowing into the Mississippi watershed.
The oil producing and refining industries generally oppose the biofuel mandates, as do automakers and some consumer groups that argue the increasing percentage of ethanol in fuel can damage vehicle engines.
Last year, the Environmental Protection Agency, which administers the renewable fuel mandate, proposed lowering the annual volume of renewable fuel required in the nation’s fuel supply in 2014, but the agency hasn’t finalized the blending requirements.
If ethanol demand increases, however, it could prompt farmers to grow corn on marginal Midwest farmland where it hasn’t grown before, requiring more fertilizer and intensifying the downstream problems, McKinney said.
Dead zones are hard to predict because they are influenced by weather. Tropical storms and hurricanes, for example, can stir up the Gulf and add oxygen back into the water, offsetting the dead zone effects. NOAA has predicted eight to 13 storms in the Atlantic this season, including one or two major hurricanes.