Dead Zone Entrée
Which foods contribute the most to eutrophying nitrogen pollution?
You already know your carbon footprint. How about your “nitrogen footprint”? Researchers have calculated how much nitrogen pollution is produced by the production of common foods. Ultimately, they hope the approach might help consumers curb nutrient pollution that is creating oxygen-poor “dead zones” in many coastal seas.
Over the last few decades, researchers have documented an alarming increase in so-called dead zones, where oxygen levels become too low to support marine life. Such extreme “eutrophication” now affects more than 400 areas around the globe, researchers estimate, and is often linked to nearby farming. Perhaps the best known dead zone grows and shrinks seasonally off the mouth of Mississippi River in the Gulf of Mexico, sometimes covering more than 8,000 square miles. There, nitrogen and phosphorous running off Corn Belt farm fields fuel massive algae blooms in the Gulf. After the algae die, they sink to the seafloor, sparking a feeding frenzy by microbes that use up the available oxygen.
To get a clearer picture of how eating choices might be linked to eutrophication, two researchers at the University of Pittsburgh, Pennsylvania — Xiaobo Xue and Amy E. Landis – decided to tally the nutrient pollution associated with the production of different foods. They used “life cycle assessments” to estimate the amount of nitrogen, phosphorous and other nutrients created at every step, including farming, processing, packaging, and transport. Ultimately, they used the totals to create a comparable “nitrogen footprint” for each food.
Topping their dead zone menu was red meat, which generated the equivalent of more than 150 grams of nitrogen per kilogram of flesh. Next in line – with nitrogen footprints of 50 to 100 grams — were dairy products, chicken and eggs and fish. Cereals and carbohydrates had the lowest footprint, of just 2.6. Overall, farming activities were responsible about 70% of the emissions in every food group, the researchers report in a July 23 paper published online by Environmental Science & Technology.
The researchers also looked at how a food’s nitrogen footprint compared to its carbon footprint – the amount of carbon dioxide emitted during the production process. Meat had both the biggest carbon and nitrogen footprints – and cereals the smallest. Some foods, however, left big nitrogen prints but relatively small carbon tracks, including dairy products, fish, and chicken. In contrast, sugars, oils, fruits and vegetables had small nitrogen footprints but big carbon tracks.
Such inconsistencies pose difficulties to consumers – and policymakers – trying to promote eco-friendly diets, the authors note, since a diet that minimizes carbon might not necessarily reduce nitrogen. One lesson is clear, however. “If people consume less red meat and dairy products, the nitrogen usage for food production will decrease,” the authors note. Lentils, anyone? – David Malakoff
Source: Xue, X., & Landis, A. (2010). Eutrophication Potential of Food Consumption Patterns. Environmental Science & Technology DOI: 10.1021/es9034478
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