Fertilizer + Rainforests = More Carbon Emissions

By David L. Brown

What could nitrogen and phosphorus fertilizer, drought in Africa’s Sahel region along the southern edge of the Sahara Desert, the Amazon Basin rainforest, and carbon emissions have in common? Well, quite a lot apparently and this is an interesting example of the unforeseen connections of nature that are being routinely disrupted by human activity and the on-going effects of global warming.

According to a news item in the 21 June 2006 issue of New Scientist magazine, when fertilizer is added to rain forests, a disproportionately large release of carbon results. Two scientists with the University of Colorado at Boulder added phosphorus fertilizer to a test plot in a tropical forest in Costa Rica for two years. They found that the amount of CO2 released was 18 percent higher than before. Adding nitrogen fertilizer to another plot had a similar result, raising emissions by 22 percent. A mixture of the two yielded a 14 percent increase in emissions.

The study, published in the Proceedings of the National Academy of Sciences, noted that “since tropical forests contain 40 percent of the world’s terrestrial carbon, the impact on global warming could be large” if more of that carbon is released into the atmosphere as greenhouse gas.

So what’s the connection with the Sahel region of Africa and the Amazon? Here is the explanation as reported in the New Scientist news story, which is titled “Fertilizers Give the Lungs of the Planet Bad Breath”:

Although no one deliberately adds fertiliser to rainforests soils, the amount of airborne phosphorus and nitrogen reaching tropical forests is increasing because of human activity, especially agriculture.

“Easterly winds carry significant quantities of phosphorus-containing dust from Africa to the Amazon basin, and are increasing due to desertification of the Sahel,” says [Cory] Cleveland [who did the study along with Alan Townsend]. Levels of nitrogen in the air are rising because of increased fossil fuel and fertiliser use. The researchers suggest that even small amounts of fertiliser can have a damaging effect. (Read article; subscription may be required.)

We have written before about how the complex interactions of nature make the Law of Unintended Consequences an important consideration in trying to figure out the future of climate change (see my article “Actions and Reactions in Nature,” posted June 14, 2006). This latest revelation about the effect of windborne nitrogen and phosphorus is merely another small but potentially important example of just how interconnected the global ecosystem is, and how changes in one place can have unexpected consequences elsewhere.

Taken as a whole, the influence of human activity on our planet’s environment is creating widespread disruption in natural balances of nature that have developed over millions of years. To predict the final result is far beyond our knowledge, and there are no doubt a vast number of effects of which we are not even yet aware. It does seem safe to say that there are many ominous trends and surprises awaiting as humankind continues to go boldly and blithely into the future.

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