Geoscience Reference
In-Depth Information
9
N + O
NO
ATMOSPHERE
NO
NO
N 2
Nitrogen cycle
N 2
1
10
8
11
CONTINENTAL
BIOSPHERE
N 2
N 2
EARTH
Volcano
1
12
HYDROSPHERE
(Ocean)
Ca 2+
8
7
Fossil organic
matter
4
MARINE
BIOSPHERE
NH 4 +
5
NO 2 - , NO 3 -
6
3
3
NO 2 - ,NO 3 -
2
13
SEDIMENT
12
Fossil organic matter
Continental crust
LITHOSPHERE
Oceanic crust
Figure 4.6. The nitrogen cycle occurs in a similar fashion in the sea and on land
C OMMENTS ON F IGURE 4.6.- The main steps of this cycle are: N 2
fixation by specialized bacteria, the regeneration of nitrogenous
nutrients in deep waters, the production of ammonium (NH 4 + )
by ammonification, the nitrification of NH 4 + into NO 2 - and NO 3 - by
bacteria, the use of nitrogenous nutrients and denitrification, primarily
by denitrifying bacteria, and the process of anammox (see the text).
The cycle also includes N 2 fixation by lightening in the atmosphere,
which produces NO, and the combustion of wood and fossil organic
matter (coal and hydrocarbons), which also produces NO and other
nitrogen oxides (NO x ). Full arrows represent natural flows and dotted
arrows represent flows associated with human activity; the numbers
next to the arrows refer to the flow descriptions in the text.
4.5.2. Biogeochemical cycles of nitrogen
Figure 4.6 depicts the biogeochemical flows of nitrogen between
natural reservoirs (below, numbers in italics between brackets refer to
arrows in the figure). These flows form the nitrogen cycle, which is
similar on land and in the sea, and includes the main stages described
below.
Search WWH ::




Custom Search