Environmental Engineering Reference
In-Depth Information
Active Figure 3-25
Natural capital:
simplified model of the global
carbon cycle.
Carbon moves
through both marine ecosystems
(left side) and terrestrial ecosystems
(right side). Carbon reservoirs are
shown as boxes; processes that
change one form of carbon to an-
other are shown in unboxed print.
See an animation based on this fig-
ure and take a short quiz on the con-
cept.
(Cecie Starr,
Biology: Concepts
and Applications,
4th ed., Pacific
Grove, Calif.: Brooks/Cole, © 2000)
Diffusion between
atmosphere and ocean
Combustion of fossil fuels
Carbon dioxide
dissolved in
ocean water
Marine food webs
Producers, consumers,
decomposers, detritivores
Marine sediments, including
formations with fossil fuels
In
denitrification,
nitrogen leaves the soil as special-
ized bacteria in waterlogged soil and in the bottom
sediments of lakes, oceans, swamps, and bogs convert
NH
3
and NH
4
back into nitrite and nitrate ions, and
then into nitrogen gas (N
2
) and nitrous oxide gas
(N
2
O). These gases are released to the atmosphere to
begin the nitrogen cycle again.
14
13
12
High
projection
11
10
Low
projection
9
8
Effects of Human Activities
on the Nitrogen Cycle
We add large amounts of nitrogen-containing
compounds to the earth's air and water and remove
nitrogen from the soil.
We intervene in the nitrogen cycle in several ways.
First,
we add large amounts of nitric oxide (NO) into
the atmosphere when N
2
and O
2
combine as we burn
any fuel at high temperatures. In the atmosphere, this
gas can be converted to nitrogen dioxide gas (NO
2
)
and nitric acid (HNO
3
), which can return to the earth's
surface as damaging
acid deposition,
commonly called
acid rain
.
Second,
we add nitrous oxide (N
2
O) to the atmo-
sphere through the action of anaerobic bacteria on
livestock wastes and commercial inorganic fertilizers
7
6
5
4
3
2
1
0
1850
1900
1950
2000
2030
Year
Figure 3-26
Natural capital degradation:
human interference in
the global carbon cycle from carbon dioxide emissions when fos-
sil fuels are burned, 1850-2004, and projections to 2030 (dashed
lines). (Data from UN Environment Programme, British Petroleum,
International Energy Agency, and U.S. Department of Energy)
