Most people are familiar with the concept of a carbon footprint, the amount of carbon dioxide an individual or entity produces. Our transportation, food, manufacturing, building, and land use choices all affect the amount of carbon dioxide released to the atmosphere. Ever since the start of the Industrial Revolution, humans have had a major impact on the carbon cycle on Earth, resulting in climate change, accelerated melting of glaciers, rising sea levels, acidification of the oceans, etc. Another element whose cycle we have disrupted in a major way is nitrogen (N), and with impacts that may be similarly serious.
In the 1800s there was concern that agriculture soils were losing their N, an essential plant nutrient, in unsustainable amounts. The only way to return N to the soil was through organic material, primarily animal manure. But this was an insufficient source for the growing population. Nitrogen gas (N2) is the most common gas in the atmosphere (78.09%), but it is relatively inert. Early in the 20th century, Fritz Haber, a German chemist, first developed what would come to be known as the Haber-Bosch Process, which produced ammonia (NH3) from atmospheric nitrogen. It has been called the most important invention of the 20th century, leading to the mass production of synthetic fertilizers and great gains in crop yields.
No good deed goes unpunished, of course. Almost all of the N applied to crops ends up in the environment. Some of the N leaches directly to groundwater and surface water. Livestock and humans consume the N taken up by the crops, and that N eventually returns to the environment as animal and human waste. Excess N in the hydrologic cycle can cause a number of problems, including acid rain, coastal ‘dead zones’, algal blooms, and fish kills. Nitrate is also a drinking water contaminant. Other environmental problems associated with excess N include smog, forest dieback, biodiversity loss, stratospheric ozone depletion, and an enhanced greenhouse effect.
Recently a colleague of mine at the University of Virginia (where I got my Ph.D.), Jim Galloway, has developed a Nitrogen Footprint calculator, similar to Carbon Footprint calculators. According to the web site, the average individual in the U.S. has an annual N footprint of 91 pounds. There are four main components of our N footprint: food consumption, housing, transportation, and goods and services, with food consumption accounting for close to ¾ of the total. I calculated my N footprint to be about 79 pounds, mainly because I bike to work and don’t eat a lot of red meat. Still, that is well above the averages in Germany and The Netherlands, the other two countries currently available; their average footprints were less than 60 pounds per year.
If you want to calculate you N footprint, you’ll need to be able to estimate your weekly eating and driving habits. You’ll also need to have your power bill handy so that you know your average electricity and gas usage. (FYI, one therm is equal to approximately 100 cubic feet of natural gas.) The web site offers suggestions on how to reduce your N footprint.
Fritz Bosch is one of the fascinating people in history. In addition to being responsible for helping feed the world, he also helped invent poison gases that were used to such devastating effects during WWI. In a sickening irony, one of the gases he helped invent was Zyklon B, which was used in Nazi extermination camps. Haber was Jewish.
