Nitrogen in West Africa: the regional cycle
A nitrogen cycle budget has been calculated for West Africa south of the northern Sahara that quantifies biologically important pools of nitrogen in the region and major fluxes associated with these pools. Major compartments of the model include noncultivated systems broken down by vegetation zone, successional status, and plant components, annual and perennial crops each broken down by crop species and plant and harvest components; wetlands; anthropic systems, and soils and sediments. Base reference year is 1978. Biological nitrogen fixation and precipitation fluxes dominated nitrogen inputs to West Africa in 1978. Approximately 12 x 10/sup 9/ kg were fixed in noncultivated systems; about half of this was fixed in early successional (0-6 yr) rain forests, and much of the rest in grazed or fallow savanna grasslands and woodlands. Less than 0.7 x 10/sup 9/ kg were fixed in cultivated systems; legumes accounted for approx. = 25% of this. Total anthropic sources (fossil fuel combustion, fertilizer production, and agricultural commodity imports) were minor (< 0.3 x 10/sup 9/ kg). Precipitation inputs to the region were approx. = 0.4 x 10/sup 9/ kg. Most nitrogen leaving West Africa did so volatilized by fire (approx. = 8.3 x 10/sup 9/ kg), principally in non-cropped systems. Major losses also occurred via hydrologic export to the Atlantic Ocean (1.5 x 10/sup 9/ kg) and via denitrification (1.1 x 10/sup 9/ kg). Total N losses from West Africa exceeded 11.0 x 10/sup 9/ kg. The overall budget balances within 1%, despite independent calculations of all major fluxes. The balance portrays a nitrogen cycle dominated by pools and fluxes in noncropped systems. Indirect human influences, however, mainly through effects on vegetation cover, appear to be a major determinant of both the rates at which nitrogen is cycled in West Africa and the relative importance of most pools and fluxes.
- Research Organization:
- Royal Swedish Academy of Sciences, Stockholm
- OSTI ID:
- 5328132
- Journal Information:
- Ecol. Monogr.; (United States), Vol. 56:1
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
NITROGEN
AVAILABILITY
AFRICA
BIOGEOCHEMISTRY
ENERGY BUDGETS
MINERAL CYCLING
NITRIFICATION
NITROGEN CYCLE
NITROGEN FIXATION
NUTRIENTS
SOILS
CHEMICAL REACTIONS
CHEMISTRY
ELEMENTS
GEOCHEMISTRY
NONMETALS
510200* - Environment
Terrestrial- Chemicals Monitoring & Transport- (-1989)