Nitrogen Cycles: Past, Present, and Future
Abstract
This paper contrasts the natural and anthropogenic controls on the conversion of unreactive N2 to more reactive forms of nitrogen (Nr). A variety of data sets are used to construct global N budgets for 1860 and the early 1990s and to make projections for the global N budget in 2050. Regional N budgets for Asia, North America, and other major regions for the early 1990s, as well as the marine N budget, are presented to Highlight the dominant fluxes of nitrogen in each region. Important findings are that human activities increasingly dominate the N budget at the global and at most regional scales, the terrestrial and open ocean N budgets are essentially disconnected, and the fixed forms of N are accumulating in most environmental reservoirs. The largest uncertainties in our understanding of the N budget at most scales are the rates of natural biological nitrogen fixation, the amount of Nr storage in most environmental reservoirs, and the production rates of N2 by denitrification.
- Publication:
-
Biogeochemistry
- Pub Date:
- September 2004
- DOI:
- Bibcode:
- 2004Biogc..70..153G
- Keywords:
-
- nitrogen;
- Haber-Bosch;
- fertilizer;
- fossil fuel combustion;
- denitrification;
- nitrogen fixation