Botkin Environmental Science Earth as Living Planet 8th txtbk

126 CHAPTER 6 The Biogeochemical Cycles
Urban World
People
and Nature
Science
and Values
Our society has concentrated the use of resources in urban regions.
As a result, the release of various chemicals into the biosphere, soil,
water, and atmosphere is often greater in urban centers, resulting in
biogeochemical cycles that cause pollution problems.
Humans, like other animals, are linked to natural processes and nature
in complex ways. We change ecosystems through land-use changes and
the burning of fossil fuels, both of which change biogeochemical cycles,
especially the carbon cycle that anchors life and affects Earth’s climate.
Our understanding of biogeochemical cycles is far from complete.
There are large uncertainties in the measurement of fluxes of chemical
elements—nitrogen, carbon, phosphorus, and others. We are studying
biogeochemical cycles because understanding them will help us to solve
environmental problems. Which problems we address first will reflect
the values of our society.
KEY TERMS
biogeochemical cycle 112
biosphere 110
biota 118
carbon cycle 117
carbon–silicate cycle 119
denitrification 120
eukaryote 110
flow 112
flux 112
geologic cycle 113
hydrologic cycle 115
limiting factor 111
macronutrients 111
micronutrients 111
nitrogen cycle 120
nitrogen fixation 120
organelle 110
phosphorus cycle 121
plate tectonics 113
prokaryote 110
residence time 112
rock cycle 116
sink 112
source 112
tectonic cycle 113
thermodynamic equilibrium 108
STUDY QUESTIONS
1. Why is an understanding of biogeochemical cycles
important in environmental science? Explain your
answer, using two examples.
2. What are some of the general rules that govern
biogeochemical cycles, especially the transfer of
material?
3. Identify the major aspects of the carbon cycle and the
environmental concerns associated with it.
4. What are the differences in the geochemical cycles for
phosphorus and nitrogen, and why are the differences
important in environmental science?
5. What are the major ways that people have altered
biogeochemical cycles?
6. If all life ceased on Earth, how quickly would the
atmosphere become like that of Venus and Mars?
Explain.
FURTHER READING
Lane, Nick, Oxygen: The Molecule That Made the World
(Oxford: Oxford University Press, 2009).
Lovelock, J., The Ages of Gaia: A Biography of the Earth
(Oxford: Oxford University Press, 1995).
Schlesinger, W.H., Biogeochemistry: An Analysis of Global
Change, 2nd ed. (San Diego: Academic Press, 1997). This
book provides a comprehensive and up-to-date overview
of the chemical reactions on land, in the oceans, and in the
atmosphere of Earth.