It's that time of year again for the Gulf of Mexico: Dead Zone time. This year's dead zone is among the largest ever -- somewhere between the size of Massachusetts (10,555 square miles) or New Jersey (8,722 square miles) depending on who you ask.

The dead zone -- a region of the water chock full of oxygen-depleting algae that allow no other organisms to live -- is an annual occurrence in the Gulf (as well as in other bodies of water), caused by excess fertilizer runoff from the farms of the nation's heartland.

Because of its impact on the environment and economic livelihoods in the Gulf, the dead zone has also been the focus of some scrutiny lately. Last year, the U.S. Geological Survey found the watersheds most responsible for polluting the Gulf, almost all of which were in the Corn Belt of Illinois and Indiana.

And a report just published in the Journal of Environmental Science & Technology takes a different look at the causes of the dead zone: Which foods have the highest nitrogen and phosphorus footprints, or "eutrophication potential."

The study, by Xiaobo Xue and Amy E. Landis of the University of Pittsburgh, ranks foods on their carbon footprint and dead-zone footprint, and finds some correlation, and some surprises.

As Emily J. Gertz writes in Chemical & Engineering News:

Red meat topped both footprint lists, making it the food with the greatest impact on both climate change and eutrophication: Eating a pound of beef creates about 22 lbs. of greenhouse gases and about 2.5 oz of nitrogen pollution. Cereals and carbohydrates had the smallest footprints, with each pound of food releasing only 3 lbs. of greenhouse gases and almost no nitrogen pollution.

But many foods had diverging impacts on the climate and coastal ecosystems. Dairy products landed at the bottom of the carbon footprint list with carbohydrates, but sat second only to beef in eutrophication potential, releasing 1.1 oz of nitrogen pollution for every pound of food produced.

The takeaway, then: Carbs good, cows bad.

Once again, with less snark: Landis told Gertz in the article linked above, "We showed that carbon footprints are not necessarily the best metric in evaluating the sustainability of a product."

It's a good point, and one that applies well beyond food: Measuring sustainability of anything -- food, your shoes, an entire company -- is highly complex and reducing any metric to a single element is an oversimplification that hides the true impacts.

In this case, looking solely at greenhouse gas emissions hides the water impacts of products. If you're looking just at CO2e, dairy products are a fine, greenish product, but coming as they tend to do from livestock, the dead-zone impacts are all the way up at the top.

To some extent, these high impacts are endemic to industrial agriculture -- large-scale farming and ranching serve to concentrate all this pollution, and it ends up being bad for animals and bad for the environment, as the picture below, from Farm Sanctuary, shows.

 

 

Of course, just to bring it back to snark one last time, if we could just genetically modify cows like we can with pigs, we could negate all those harmful environmental impacts of factory farms...