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The Biogeochemical Cycles
Fig 4.5 Periodic table of the elements.
© 2003 John Wiley and Sons Publishers
D. T. Krohne, General Ecology
Fig 4.6 Idealized
diagram of the
geologic cycle, which
includes the tectonic,
hydrologic, rock and
biogeochemical cycles.
© 2003 John Wiley and Sons Publishers
CO2 & CH4
15%/year
Modified from D. T. Krohne, General Ecology
The Carbon Cycle
Fig 4.14 The Carbon Cycle.
© 2003 John Wiley and Sons Publishers
Fig 4.15 Idealized diagram illustrating
photosynthesis for a green plant (tree) and
generalized reaction.
© 2003 John Wiley and Sons Publishers
Fig 4.17 Global flux of carbon, 1850-1990.
© 2003 John Wiley and Sons Publishers
50% fertilizer
(Bacteria)
Modified from D. T. Krohne, General Ecology
Microbial mediated
processes in the nitrogen
cycle
Nitrogen fixation
Microbes fix
nitrogen gas
into
ammonia
that is
incorporated
into plant
tissue
Cyanobacteria
live everywhere
in the aquatic
environment
Nitrogen fixing bacteria
in plant root nodules
Ammonification (Mineralization)
Refers to the
breakdown of
organic matter in
order to release the
organically bound
nitrogen as
inorganic (mineral)
nitrogen in the form
of ammonia
Decomposition is
the biological
process that allows
for the process
Nitrifying bacteria (Nitrosomonas and Nitrobacter)
Occurs in oxygen poor or anaerobic
environments usually deep in the soil
or in muddy sediments
NO3- → NO2- → NO → N2O → N2 gas
The complete denitrification
process can be expressed as a
redox reaction
2NO3- + 10e- + 12H+ → N2 + 6H2O
Mangrove swamps are areas where
denitrification happens
From http://www.epa.gov/maia/html/nitrogen.html
Fig 4.19 The global nitrogen cycle.
© 2003 John Wiley and Sons Publishers
Critical Thinking Issue – How are Human Activities
Affecting the Nitrogen Cycle?
Effects of increased use of
nitrogen fertilizer:
• Increased nitric acid in soil:
• Leaching of magnesium and potassium
• Increased aluminum levels
• Plant root damage
• Changes in microbe communities
• Fish kills
• Eutrophication of water bodies
• Nitrates in drinking water
• Global effects on plant based CO2 uptake
© 2003 John Wiley and Sons Publishers
Gaseous
phase
D. T. Krohne, General Ecology D. T. Krohne, General Ecology
Modified from D. T. Krohne, General Ecology
Phosphorous cycle in water
Fig 4.20 The global phosphorus cycle.
© 2003 John Wiley and Sons Publishers
Ecosystems and the Gaia Hypothesis
Ecosystem defined: a community of
organisms and it’s corresponding abiotic
environment through which matter cycles and
energy flows
• Wide
variation in ecosystems
• Boarders can be well defined or vague
• Can be natural or artificial, managed or wild
• Wide range in scale
• Common to all ecosystems: energy flow and
cycling of matter
Gaia Hypothesis(es)
• Life has greatly affected the planetary environment
• This alteration has allowed life to persist
• The Earth is a “super-organism” - Life controls the
environment in a fashion that is equivalent to the way
an organism controls its various systems
• Evolution?
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