3: Our incremental understanding of nitrogen
element of the periodic table was named ‘nitrogene’
in 1790 by Jean Antoine Claude Chaptal (1756–1832).
By 1850, the fundamental role of nitrogen in living systems
and its beneficial role in crop production became clear: it
was a common element in plant and animal tissues, indispensable
for plant growth, underwent constant cycling between organic
and inorganic compounds, and was an effective fertilizer.
Knowledge on the negative impacts of nitrogen compounds on
people and ecosystems also grew with time. The contribution
of nitrogen compounds to air pollution was certainly known
by the late 19th century, as was the impact of excess nutrients
(including nitrogen) on coastal marine ecosystems, although
for the latter, the focus was on the positive impacts of nutrients
marine productivity. It was not until the mid- 20th century
that negative impacts of excess nutrients were recognized
as a serious international problem.
|Source: Nixon and Buckley 2002
Although the environmental significance
of nitrogen has been studied for at least 150 years (Box 3) scientists
have only recently documented how reactive nitrogen ‘cascades’
through ecosystems, creating environmental and human health problems
all along the way (Galloway and others 2003). We have also recently
come to a better understanding of the magnitude of the problem: human
production of reactive nitrogen is now greater than the amount created
by natural processes on land, leading to a large increase in the amount
of nitrogen moving within the environment. Globally, humans create about
160 million tonnes of reactive nitrogen per year, compared to natural
rates of terrestrial biological nitrogen fixation, which are between
90–120 million tonnes annually. However, we have not similarly
increased de-nitrification processes which convert nitrogen primarily
back to non-reactive N2. Reactive nitrogen is, therefore, accumulating
in the environment.