Botkin Environmental Science Earth as Living Planet 8th txtbk

122 CHAPTER 6 The Biogeochemical Cycles
Numbers in
Numbers in
Land biota
500
10
Rock
Mine
represent stored amounts in millions of metric tons (10 12 g)
represent flows in millions of metric tons (10 12 g) per year
100
Soil to freshwaters
Fertilizer
100 22
Soils
50
10
Erosion
30
Ocean
Industrial wastes
Freshwaters
0.1
2
Urban
3
Atmospheric
deposition
30
0.01
4
Fish harvest
Islands
Guano birds
Mineable
15,000
Earth's crust
20,000,000,000
FIGURE 6.19
Global phosphorus cycle.
Values are approximated with errors
20%. Note the amount mined (22) is about
equivalent to the amount that is eroded from the
land and enters the oceans by runoff (25).
95,000
Tectonic
uplift
1000
30
1000
200
100,000,000
(Sources: Data from 5 mil, 2000 Phosphorus in the environment: Natural flows and
human interference. Annual Review of Environment and Resources 25:53–88.)
20
Marine biota
Ocean sediments
(a)
FIGURE 6.20 Guano Island, Peru. For centuries the principal source of phosphorus fertilizer was guano
deposits from seabirds. The birds feed on fish and nest on small islands. Their guano accumulates in this
dry climate over centuries, forming rocklike deposits that continue to be mined commercially for phosphate
fertilizers. On the Peruvian Ballestas Islands (a) seabirds (in this case, Incan terns) nest, providing some of
the guano, and (b) sea lions haul out and rest on the rocklike guano.
(b)