Environmental Engineering Reference
In-Depth Information
(d)
180
(e)
1,400
160
1,200
140
1,000
120
100
800
80
600
60
400
200
40
20
0
0
350
Distance to the windward forest edge (m)
300
250
200
150
100
50
0
-80
-60
-40
-20
0
20
40
60
°
N
Latitude
°
S
(f)
0
(g)
6
1978
1979
-25
1980-1995
1991
1972
1974
4
1977
-50
1980
1975
1976
1971
1973
1970
-75
2
1969
-100
1996-2000
-125
0
0 1 2 3 4 5
Proportion of lake water potentially replaced
0
0.2
0.4
0.6
0.8
Total-P (mg/L)
FIGURE 11.6
(Continued)
ecosystem might respond to future conditions, such as a warmer world. For example, cli-
matic warming may have either positive or negative feedbacks to atmospheric carbon
dioxide concentrations depending on whether warming leads to more soil respiration or
more sequestration of carbon in plants and soil (
Luo et al. 2001
;
Figure 11.7
). Because feed-
backs may operate on different timescales and yet the balance among them has profound
consequences for further change, determining what kinds of feedbacks are present in a
given system is one of the major foci in global change research.
Human Activities Control Many Ecosystems
Human activities now control many ecosystems, both locally and globally. Human
inputs of reactive nitrogen and phosphorus to the world's ecosystems are equivalent to
those from nonhuman sources (see Chapters 7 and 8). We appropriate 24% of global
terrestrial primary production (
Haberl et al. 2007
) and more than half of available runoff
of water (
Postel et al. 1996
). Our changes to land cover result in billions of tons more
