I recently read "The Evolution and Future of Earth’s Nitrogen Cycle" in Science. Just as we have "broken into" the carbon cycle and revved it up by digging up and burning millions of tons of coal, gas and oil that had been locked out of harm’s way underground, we have, similarly, caused a major "disequilibrium" of the nitrogen cycle by our activities.
This cycle is the flow of nitrogen -- in its various forms of nitrogen, ammonia, nitrite, nitrate, proteins, amino acids, et cetera -- in and out of animals, plants, the sea, fresh water, ground and air.
Nitrogen gas forms around four-fifths of the earth’s atmosphere, but it is very difficult for any normal chemical reaction to change it from N2 (very unreactive, almost inert) to ammonia, nitrite or nitrate, all of which animals and plants can use to make protein.
Happily, we have lightning flashes that "burn" nitrogen into nitrogen oxides that can be used; and we have, miracle of miracles, some extraordinary bacteria -- most of which form a cozy, mutually beneficial relationship with plants -- which can, thanks to a remarkable enzyme they possess, pull nitrogen out of the air and "fix" it as ammonia.
There are other bacteria and other organisms that process the ammonia and still others that cycle it back into nitrogen.
Okay, this cycle was working just fine. Farmers were quite content fertilizing their crops with manure, and there was a steady balance. Then some genius -- and I am using that word in its sincere and also its sarcastically pejorative meaning -- came up with the Haber-Bosch process (okay, it was actually three geniuses).
It was discovered how to make ammonia from hydrogen and nitrogen -- with a considerable energy input and new catalysts. The "inert" nitrogen from the air is transformed, ultimately, into fertilizer (and also explosives, which you must admit is quite a double-edged sword).
Now, it would be difficult to deny that the advent of cheap nitrogen-containing fertilizer has been a boon for mankind. The green revolution that fed so many millions in Asia owes its success to brilliant plant-breeding skills creating new types of very productive rice, which were sustained by copious amounts of man-made nutrients.
However, the creation of ammonia through the Haber process traps a huge quantity of nitrogen that would not otherwise have entered the cycle. We have to add to that the large amount of nitrogen oxides caused while burning coal and gasoline. According to the Science article, the sum total of human intervention from these sources contributes 45% of the total fixed nitrogen produced each year. So we have almost doubled it.
So?
Well, of course, the nitrogen has to go somewhere. A lot of it grows crops, which is not a bad thing. Yet because of its relatively low cost, excessive amounts of nitrogen-containing fertilizer are added to lawns and agricultural land across the world. Rain leaches this excess into rivers, lakes and streams. And the effect of this is quite dramatic: the surplus nutrients encourage unnatural microorganism "blooms" that suffocate almost every other living thing. We end up with dead zones -- like the six thousand square mile one in the Gulf of Mexico where all this left-over fertilizer ends up having traveled down the Mississippi (good reviews here and here).
The Science article concludes, "Humans may have produced the largest impact on the nitrogen cycle since the major pathways of the modern cycle originated some 2.5 billion years ago." And as I have been careful to point out, a lot of this extra nitrogen is genuinely excessive -- it is just money (and pollution) down the drain.
So how can you and I make a difference? I guess this seems as ridiculous as you and I making a difference fighting global warming, but we believe that’s worth a go. (Visit Climate Stewards and Carbon Fund, for example.) So, can an individual become nitrogen neutral? Or a company?
Thankfully, people are looking at this. For example, for those in the Northeast United States, you can visit the Chesapeake Fund website and you can sign up to help with "nitrogen reduction projects" to protect the beautiful Chesapeake Bay. This organization’s site has a sophisticated calculator to assess how polluting your home’s sewer system is, how much nitrogen oxide pollution your cars cause, and so on. You can reduce your footprint and offset the rest with interventions that aim to trap fertilizer runoff with trees, reeds and other plants.
Live nowhere near the Chesapeake? Then find out the state of the waterways you live by -- and start your own nitrogen reducing initiative.
