Increased global cultivation of legumes and other crops that harbor nitrogen-fixing bacteria also adds to the influx. The burning of fossil fuels provides the third major source of newly available nitrogen compounds. The clearing of wildlands liberates perhaps another 70 million metric tons of nitrogen that had been stored in biomass. The nitrogen glut is evident throughout the biogeochemical cycle, according to the report. Other nitrogen compounds contribute to smog and acid deposition.
Researchers now think that the excess nitrogen is diminishing biological diversity in some areas.
European heathlands, long adapted to nitrogen-poor conditions, are giving way to Eurasian grasses under the fertilizing effects of nitrogen. The trends are likely to continue, in step with the growing, urbanizing world population, the ecologists say. They see a need for more efficient fertilizer use and greater control of nitrogen emissions. Pollution helps weeds take over prairies. When nitrate reigns.