February 20, 2008

Ethanol's Effect on the Gulf of Mexico Dead Zone

The USGS recently completed a report on the factors effecting the Gulf of Mexico Dead Zone. As has been known for some time the Dead Zone is caused by nutrients, particularly nitrogen and phosphorus entering the Mississippi River system. This study attempted to answer the question of where these nutrients are coming from.

As you can see corn and soybean farming is a significant contributer, but it also shows that if all corn and soybean farming were ended not even half of the problem would go away.

But the real question is how much is ethanol effecting the situation. Well with a little math we can figure that out.

First let's see how many acres of corn and soybeans were planted in 2007.

Corn - 93,600,000 acres
Soybeans - 63,631,000 acres
Total - 157,231,000 acres

Now let's see how many acres of corn went to ethanol production. The final numbers aren't out for 2007 yet, but it looks like about 6.5 billion gallons of ethanol will have been produced in 2007. The average yield of ethanol per bushel of corn is about 2.8 gallons. The average yield per acres of corn in 2007 was 151 bushels.

6,500,000,000 / 2.8 / 151 = 15,373,700 acres

Now to find out what percentage of the total acreage was devoted to ethanol production.

15,373,700 / 157,231,000 x 100 = 9.8%

So 9.8% of all the acres planted in corn and soybeans went to ethanol production.

So using the chart above, if 52% of all nitrogen was from corn and soybean farming and 9.8% of that was from ethanol that would mean that 5.1% of all the nitrogen delivered to the Gulf of Mexico was because of ethanol production.

And if 25% of the phosphorus was from corn and soybeans farming and 9.8% of that was from ethanol that would mean that 2.5% of all phosphorus delivered to the Gulf of Mexico was because of ethanol.

That would mean that if all the acres that produced corn for ethanol in 2007 were taken completely out of production, 5.1% less nitrogen and 2.5% less phosphorus would be delivered to the Gulf of Mexico.


Ethanol Production Statistics
USDA: Crops and Plants
USGS : Nutrient delivery to the Gulf of Mexico


EJ said...

Wouldn't it be wrong to assume that all 93.6M corn acres drain into the Mississippi River System?

Michael A. Gregory said...

Not only that but last year not all ethanol came from corn. Although a small amount, some ethanol is made from other sources such sorghum, beverage wastes and cellulosic. So the numbers I presented would be "at best" numbers. In other words if all the acres that grew corn for ethanol last year were taken out of production, the levels of nitrogen reaching the Gulf would go down by at best 5.1%.

Many media source have singled ethanol out as the source of the problem with the Gulf of Mexico dead zone, and this was just to show that at most it is a very small contributer.

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