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Nitrates and Ammonium – The Big Ideas Network

Nitrogen is the seventh most abundant element in the Milky Way, and forms an impressive 78% of the Earths atmosphere. Most nitrogen originates in planetary nebulae, where low mass stars have expelled their outer layers of gas.

Nitrogen atoms usually bond with other nitrogen atoms, creating a ‘dinitrogen’ molecule with a powerful triple bond (NN). Cells need this nitrogen to create amino acids (and proteins), nucleic acids (like DNA), and a number of other important things. But for any nitrogen to be used by plants and animals, this triple bond must be broken and the nitrogen converted to other compounds.

Other compounds include Ammonium (NH4), ammonia (NH3), nitrite (NO2), nitrate (NO3), nitrous oxide (N2O), and Nitric oxide (NO). The conversion of dinitrogen to these more useful compounds is called nitrogen fixation. In nature it is carried out by bacteria and within lightning strikes, but in the first half of the 20th Century we discovered an industrial means of producing large quantities of ammonia. We called it the ‘Haber process’, and it’s one of the most important and least appreciated discoveries in human history.

Life requires a wide variety of nutrients to thrive, and in nature nitrogen tends to be a bit of a struggle to find. Nitrogen compounds tend to be highly soluble in water, which means that rain is constantly washing them out of soil and out towards the oceans. Its availability is often the main factor restricting plant growth in an ecosystem.

The discovery of the Haber process was a landmark development in chemistry and industry, as it led to nitrogen-fixed fertilizers applied on an industrial scale. From the Wikipedia page Haber process:

The Haber process now produces 450 million tonnes of nitrogen fertilizer per year… Three to five percent of the worlds natural gas production is consumed in the Haber process (around 12% of the worlds annual energy supply). In combination with pesticides, these fertilizers have quadrupled the productivity of agricultural land.

Emphasis on that last part. Nitrogen fixed fertilisers have played a pivotal role in quadrupling the productivity of agricultural land. It’s not an exaggeration to say that this discovery created the modern world as we know it today. The page continues:

Due to its dramatic impact on the human ability to grow food, the Haber process served as the detonator of the population explosion, enabling the global population to increase from 1.6 billion in 1900 to todays 7 billion. Nearly 50% of the nitrogen found in human tissues originated from the Haber-Bosch process.

Nitrogen-fixed fertiliser

Such a dramatic development has naturally brought side effects. The actual efficiency of absorbtion and use of nitrogen compounds by plants is only about 50%. The rest of the nitrogen in the fertiliser is absorbed by the soil and runs off into the ocean, where it acidifies the water and can asphyxiate entire coastal ecosystems.

The unintentional introduction of so much nitrogen in these natural environments usually creates an enormous bloom of algae (small, floating marine plants). The bloom is always short lived, up until the excess of nitrogen washes away. Among other effects that the algae bloom has, the masses of algae soon die. The large volumes of decaying plant matter absorbs all of the oxygen in the surrounding water, leaving none for any kind of marine animal.

Image credit: National Ocean Service,

Harmful Algal Blooms

At times the blooms can be so extensive that they can be seen from space.

An algae bloom in Lake Eyrie, caused by nitrogen fixed fertilisers and torrential rains. Image credit: NASA

In the picture above, the green swirling shapes in the water are algae in hugely unnatural proportions. The algae will die and asphyxiate the entire local marine system.

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