By Peter Montague
A new global environmental problem has emerged from an unexpected source: nitrogen. Nitrogen makes up 78% of Earth's atmosphere. In its atmospheric form, nitrogen is an unreactive gas, unavailable to most living things. Now a new peer-reviewed report from the Ecological Society of America (ESA) portrays nitrogen as a triple threat: warming the planet via the greenhouse effect, damaging the Earth's protective ozone layer and reducing biodiversity.
ESA is the US professional organisation for ecologists.
Nitrogen problems arise when human activities — mainly industrial agriculture and combustion of fossil fuels — "fix" nitrogen out of the atmosphere by combining it with hydrogen or oxygen. In its fixed forms, nitrogen becomes biologically active.
Other human activities (burning grasslands and forests, draining wetlands, clearing land for crops) move nitrogen out of long-term storage, making it available to living things.
Two big natural forces fix nitrogen from the atmosphere: lightning and micro-organisms, many of which work together with legumes and algae.
Nitrogen fixation in the oceans is poorly understood; on the land, natural forces fix somewhere between 90 and 140 million tonnes of nitrogen per year. Of this, lightning accounts for perhaps 10 million tonnes and micro-organisms for the rest.
Human activities now fix something just over 140 million tonnes per year, thus doubling the amount of biologically active nitrogen on the land, according to ESA. Doubling a natural flow of a chemical like nitrogen is "an enormous effect on a global cycle", says Dr William H. Schlesinger of Duke University, one of the authors of the new ESA report.
Until 1940, human industrial activities fixed almost zero nitrogen. Indeed, a study in 1990 found that half of all the nitrogen ever fixed by industrial processes has been produced after 1980.
Many of the Earth's plant species are adapted to — and function best in — soils and waters containing low levels of available nitrogen. By doubling the amount of available nitrogen, and increasing the movement of nitrogen from place to place, humans are disrupting ecosystems on a grand scale.
"No place on earth is unaffected", says the ESA report. Here are some of the problems identified by the ESA report:
- Nitrous oxide (N2O) added to the atmosphere is a potent greenhouse gas. Nitrous oxide presently accounts for "a few per cent" of the global greenhouse gas problem, says the ESA report.
- When it reaches the stratosphere, nitrous oxide contributes to the destruction of the Earth's ozone shield.
Nitrous oxide is increasing in the atmosphere at the rate of 0.2% to 0.3% per year. It comes from many sources: fertilisers, nitrogen-enriched ground water, nitrogen-saturated forests, burning of grasses and forests, land clearing for crops and manufacture of nylon.
- Nitric oxide (NO) plays a key role in creating toxic ozone near the ground. Ozone is the most harmful common air pollutant to humans and vegetation. Ozone and other nitrogen compounds are key components of the smog that now envelopes large areas, especially urban areas.
- The final product of oxidising NO is nitric acid, a key component of acid rain, which is damaging forests in Canada, the US and Europe. Combustion of fossil fuels is the main source of nitric oxide (20 million tonnes per year), followed by biomass burning (8 million tonnes per year). Human sources now account for 80% of all atmospheric NO.
- NH3, or ammonia, injected into the atmosphere is a major source of nitrogen movement between ecosystems. Each year, fertiliser contributes 10 million tonnes of ammonia to the atmosphere; domestic animal wastes contribute 32 million tonnes; biomass burning adds 5 million tonnes. Humans contribute 70% of all the ammonia reaching the atmosphere.
- As a result of all these contributions of fixed nitrogen to the atmosphere, fixed nitrogen is deposited back on land and oceans at an increased rate. In the midwestern and eastern US, nitrogen deposition from the atmosphere is more than 10 times as great as the natural rate. In parts of northern Europe, it is now more than 100 times as great as the natural rate.
- Nitrogen deposited on land tends to move into nearby waters, carrying with it calcium and magnesium from the soil. Both the soils and the receiving waters tend to become more acidic. After calcium in the soil has been depleted, then aluminium begins to move into nearby waters with the nitrogen. Aluminium is toxic to many aquatic species.
As sulfur dioxide emissions have been curbed in recent years, nitrogen has become better recognised as a source of acidification in lakes. As areas of land become nitrogen-saturated, nitrogen run-off and consequent acidification are increasing.
Another effect is to create nutrient imbalances in trees. Such imbalances can lead to reduced photosynthesis, reduced forest growth and even to increased tree deaths.
- Ecologists in Minnesota treated 162 plots of land with varying amounts of nitrogen and examined the results. After 12 years they found three important changes:
1. Some plant species disappeared completely, driven out by others that thrived better in a high-nitrogen environment. The result was a loss of biodiversity as "weedy" species took over.
2. When these weedy species died, their higher nitrogen content put more nitrate into the soil. Nitrate is highly soluble in water and moves readily into local streams. In high concentrations, nitrate is toxic to humans; at lower concentrations it can cause blooms of algae, depleting oxygen and upsetting the balance of aquatic ecosystems.
3. Because the weedy plants were rich in nitrogen, bacteria and fungi that feed on nitrogen decomposed them rapidly. Because of the rapid decomposition, these plants did not capture and retain any more carbon than the plants they had displaced. Ecologists had hoped that, by encouraging plant growth, high nitrogen levels would capture increased carbon, thus reducing the threat of global warming from carbon dioxide. It turns out not to work that way.
- The nitrogen content of the Mississippi River has more than doubled since 1965, and nitrate concentrations in the major rivers of the north-eastern US have increased three to 10-fold since 1900. The same is true of European rivers. Nitrogen from rivers is now reaching the Atlantic Ocean at rates two to 20 times as great as during pre-industrial times. Around the North Sea, the increase has been six to 20-fold.
- Nitrogen entering the oceans is causing fertilisation and eutrophication of estuaries and coastal seas: "... it represents perhaps the greatest threat to the integrity of coastal ecosystems", says the ESA report. Eutrophication is the excessive growth of plants.
Nitrogen-fed algae blooms have been identified as the source of a major outbreak of cholera in South America in 1991. The algae harbour the cholera-causing bacterium.
These nitrogen problems are not going to be easy to solve. The ESA report says, "The momentum of human population growth and increasing urbanization ensure that industrial N[itrogen] fixation will continue at high rates for decades."
The report suggests that, by 2020, industrial agriculture will be contributing 134 million tonnes per year, up from the 80 million tonnes it contributes annually today. By 2020, fossil fuel combustion will be contributing 46 million tonnes per year, about twice its present contribution.
Obviously these projections could prove wrong if the corporations promoting industrial agriculture and fossil fuel combustion could be brought under control. The ESA's report does not consider this possibility. Under "Future Prospects and Management Options", the report only considers slightly less wasteful ways of using nitrogen fertiliser on industrial farms.
Disappointingly, ESA's report never acknowledges the really viable alternative to industrial farming, which is ecological farming that seeks to mirror and maintain the natural ecology in which it is practised.
As the ESA report documents to a dismaying degree, the industrial farming model is leading to widespread deterioration of global ecosystems. It is not sustainable.
[From Rachel's Environment & Health Weekly. Like Green Left Weekly, Rachel's is a non-profit publication which distributes information without charge on the internet and depends on the generosity of readers to survive. If you are able to help keep this valuable resource in existence, send your contribution to Environmental Research Foundation, PO Box 5036, Annapolis, Maryland 21403-7036, USA. In the United States, donations to ERF are tax deductible.]