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Chapter 5
The Biogeochemical Cycles
In all things there is a law of cycles.
-Pubilus Cornelius Tacitus
(Roman Historian)
Lake Washington
5.1 How Chemicals Cycle
Chemical- an element like C or P or a
compound like NH3.
 Biogeochemical cycle- complete path a
chemical takes through Earth’s major
reservoirs (bio- involves life; geo- include atmos., water, rock,

soil; chemical- chemicals are cycled)
– Atmosphere
– Hydrosphere (ocean, lake, river, groundwater,
glacier)
– Lithosphere (rock & soil)
– Biosphere (plants & animals)
© 2008 John Wiley and Sons Publishers
© 2008 John Wiley and Sons
Publishers
Rate of transfer/flux: the amount per unit time of a
chemical that enters or leaves a storage compartment
 Sink: the compartment that receives the chemical

– Ex: forests (measured in units – billions of metric tons)

Residence time: the average length of time that an
atom is stored before its transfered
5.3 Biogeochemical Cycles and Life:
Limiting Factors

Macronutrients
– Elements required in large amounts by all life
– Include the “big six” elements that form the fundamental
building blocks of life:

Micronutrients
carbon
oxygen
hydrogen
phosphorus
nitrogen sulfur
– Elements required either in
 small amounts by all life or
 moderate amounts by some forms of life and not all by others

Limiting factor
– When chemical elements are not available at the right times, in
the right amounts, and in the right concentrations relative to
each other
Micronutrients (human body)
5.4 The Geologic Cycle

The Geologic Cycle:
– The processes responsible for formation and
change of Earth materials
– Best described as a group of cycles:
 Tectonic
 Hydrologic
 Rock
 Biochemical
Geologic cycle
© 2008 John
Wiley and Sons
Publishers
Tectonic Cycle

Tectonic cycle:
– Involves creation and destruction of the solid outer
layer of Earth, the lithosphere
 Lithosphere: 100 km (60 mi) thick and is broken into
plates

Plate tectonics:
– The slow movement of these large segments of
Earth’s outermost rock shell
– Boundaries between plates are geologically active
areas
 Float on denser material and move 2-15 cm/year (as fast
as fingernails grow)
© 2008 John Wiley and Sons Publishers
Tectonic Cycle: Plate Boundaries

Divergent plate boundary:
– Occurs at a spreading ocean ridge, where
plates are moving away from one another
– New lithosphere is produced (seafloor
spreading)
Divergent…
Tectonic Cycle: Plate Boundaries

Convergent plate boundary
– Occurs when plates collide
 Produces linear coastal mountain ranges or
continental mountain ranges
Result: upfolded mountains
Example: Himalyas and Appalacian Mts.
Result: trench and volcanic island arcs
Example: Aleutian Trench and Aleutian
Islands
Tectonic Cycle: Plate Boundaries

Transform fault boundary
– Occurs where one plate slides past another
 San Andreas Fault in California
Offset
100 yards
Wallace Creek- Carrizo Plains
All 3…
Hydrologic Cycle
“Water Cycle”
Water Cycle

Role of Water?
– Terrestrial ecosystems: major factor determining
distribution of organisms
– Aquatic ecosystems: literally matrix that surrounds
& serves as environment of aquatic organisms
– Flows of water are major means for material &
energy transfer
– Water Is critical for human activities: agriculture,
industry, and municipal use
Water is the driver of nature.
- Leonardo da Vinci
Water Cycle: Main Processes
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Evaporation: conversion from liquid to vapor
(surface to atmosphere)
Transpiration: evaporation of water from leaves
Condensation: conversion of vapor to liquid (ex:
water droplets of water on cold soda can)
Precipitation: movement as rain, sleet, hain, & snow
(atmosphere to surface)
Infiltration: movement into soil
Percolation: downward flow through soil to aquifers
Runoff: surface flow down slope to ocean, river, or
lake.
Water Cycle
Withdraw large quantities of freshwater- water
diversion, ground water depletion, wetland
drainage
 Clear vegetation- increase runoff, decrease
infiltration & groundwater recharge, increase
flooding & soil erosion.
 Modify water quality- add nutrients (P, N, K,…)
and pollutants

The Water
Cycle
Transport overland: net movement of water vapor by wind
Condensationconversion of
gaseous water vapor into liquid
water
Precipitation
(rain, sleet, hail, snow, fog)
Rain clouds
Evaporation
from inland
lakes and rivers
Precipitatio
n to land
Transpiration
Evaporatio
n from the
land
Precipitation
Precipitation
over the
ocean
Surface
runoff (rapid)
Transpiration
from plants
Evaporation
Evaporation
from the
ocean
Rivers
Water locked up
in snow and ice
Lakes
Infiltration:
movement of water
into soil
Percolation:
downward flow of
water
Ocean storage
97% of total water
Aquifers:
groundwater storage
areas
Groundwater movement (slow)
Water Transformations
The hydrological (water) cycle,
collects, purifies, and distributes the
Earth’s water.
Precipitation
Over the oceans, evaporation
exceeds precipitation. This results
in a net movement of water vapor
over the land.
On land, precipitation exceeds
evaporation. Some precipitation
becomes locked up in snow and ice
for varying lengths of time.
Most water forms surface and
groundwater systems that flow back
to the sea.
Rivers and streams
The Demand for Water
Hydroelectric power generation…
Humans intervene in the water cycle by
utilizing the resource for their own needs.
Water is used for consumption, municipal use,
in agriculture, in power generation, and for
Irrigation…
industrial manufacturing.
Industry is the greatest withdrawer of water
but some of this is returned. Agriculture is the
greatest water consumer.
Washing, drinking,bathing…
Using water often results in its contamination.
The supply of potable (drinkable) water is
one of the most pressing of the world’s
problems.
© 2008 John Wiley and Sons Publishers
The Rock Cycle

The rock cycle:
– Numerous processes that produce rocks and
soils
– Depends on other cycles:
 tectonic cycle for energy
 Hydrologic cycle for water
– Rock is classified as
 Igneous
 Sedimentary
 Metamorphic
© 2008 John Wiley and Sons Publishers
Element
Carbon
(C)
Nitrogen
(N)
Phosphorous
(P)
Sulfur
(S)
Main nonliving
storehouse
Main forms in
Other nonliving
living organisms
storehouse
Atmospheric:
Carbon dioxide (CO2)
Carbohydrates:
organic molecules
Hydrologic: dissolved
carbonate (CO32-) and
bicarbonate (HCO3-)
Sedimentary: carbon
containing minerals in
rocks
Atmospheric:
Nitrogen gas (N2)
Proteins and other
nitrogen-containing
organic molecules
Hydrologic: dissolved
ammonium (NH4+) and
nitrate (NO2-) in water
and soils
Sedimentary:
Phosphate (PO43-)
containing minerals in
rocks
DNA. Other nucleic
acids (ATP) and
phospholipids
Hydrologic: dissolved
phosphate (PO43-)
Sedimentary: rocks
(e.g., Iron disulfide &
pyrite) and minerals
e.g., sulfate [SO42-])
Sulfur- containing
amino acids in most
proteins, some
vitamins
Atmospheric: hydrogen
sulfide (HgS), sulfur
dioxide (SO2), sulfur
trioxide (SO3), and sulfuric
acid (H2SO4)
Hydrologic: sulfate
(SO42-) and sulfuric acid
Carbon Cycle
Carbon Cycle
Building block of organic molecules
(carbohydrates, fats, protein, & nucleic acids)essential to life
 Currency of energy exchange- chemical energy
for life stored as bonds in organic compounds
 Carbon dioxide (CO2) greenhouse gas- traps
heat near Earth's surface & plays a key role as
“nature’s thermostat”

Carbon: Main Processes
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Movement in atmosphere: atmos. C as CO2
(0.036% of troposphere)
Primary production: photosynthesis (=carbon
fixation) moves C from atmos. To organic molecules in
organisms
Movement through food webs: C movement in
organic form from organism to organism
Aerobic respiration: organic molecules broken down
to release CO2 back to atmos.
Combustion: organic molecules broken by burning
down to release CO2 back to atmos.
Dissolving in oceans: C enters as to form carbonate
(CO32-) and bicarbonate (HCO3-)
Movement to sediments: C enters sediments,
primarily as calcium carbonate (CaCO3)
Carbon- Terrestrial
Carbon- Aquatic
Processes in Carbon Cycling
Carbon cycles between the living (biotic) and
Burning fossil fuels
non-living (abiotic) environments.
Gaseous carbon is fixed in the process of
photosynthesis and returned to the
atmosphere in respiration.
Carbon may remain locked up in biotic or
abiotic systems for long periods of time, e.g.
in the wood of trees or in fossil fuels such
as coal or oil.
Petroleum
Humans have disturbed the balance of the
carbon cycle through activities such as
combustion and deforestation.
The Carbon
Cycle
Carbon: Human Influences?
Removal of vegetation- decreases primary
production (decrease carbon fiation)
 Burning of fossil fuels & biomass (wood)increase movement of carbon into the atmos.
 The resulting increase concentration of atmos.
CO2 is believed to be sufficient to modify world
climate through global warming

© 2008 John Wiley and Sons Publishers
Carbon Sink
Units are PgC.- One Pg [petragram]= on ebillion metric tonnes=1000 x one bilion kg
Carbon-Silicate Cycle
The Carbon-Silicate Cycle

The carbon-silicate cycle:
– A complex biogeochemical cycle over time scales as
long as one-half billion years.
– Includes major geological processes, such as:

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Weathering
Transport by ground and surface waters
Erosion
Deposition of crustal rocks
– Believed to provide important negative feedback
mechanisms that control the temperature of the
atmosphere.
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The Archean atmosphere was a mix of gases
including nitrogen, water vapor, methane (CH4),
and CO2.
"Atmospheric Oxygen," free oxygen did not
accumulate in the atmosphere until more than
two billion years after Earth was formed.
Volcanoes emitted CO2 as a byproduct of
heating within the Earth's crust.
But instead of developing a runaway greenhouse
effect like that on Venus, Earth's temperatures
remained within a moderate range because the
carbon cycle includes a natural
This sink involves the weathering of silicate
rocks, such as granites and basalts, that make
up much of Earth's crust.

4 basic stages:
– First, rainfall scrubs CO2 out of the air, producing carbonic
acid (H2CO3), a weak acid.
– Next, this solution reacts on contact with silicate rocks to
release calcium and other cations and leave behind
carbonate and biocarbonate ions dissolved in the water.
 This solution is washed into the oceans by rivers, and then calcium
carbonate (CaCO3), also known as limestone, is precipitated in
sediments. (Today most calcium carbonate precipitation is caused by
marine organisms, which use calcium carbonate to make their shells.)
– Over long time scales, oceanic crust containing limestone
sediments is forced downward into Earth's mantle at points
where plates collide, a process called subduction.
– Eventually, the limestone heats up and turns the limestone
back into CO2, which travels back up to the surface with
magma. Volcanic activity then returns CO2 to the
atmosphere.
© 2008 John Wiley and Sons Publishers
Nitrogen Cycle
Nitrogen cycle

Role of Nitrogen?
– Building block of various essential organic
molecules- especially proteins & nucleic acids
– Limiting nutrient in many ecosystemstypically addition of N leads to increased
productivity
How is Nitrogen Cycled?
Nitrogen Cycle: Main Processes
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Nitrogen fixation: conversion of N2 (nitrogen gas) to
NH4+ (ammonuim), atmospheric by lightning,
biological by bacteria & blue-green algae (anaerobic),
e.g., Rhizobium in legumes
Nitrification: conversion of NH4+ to NO2- (nitrite) to
NO3- (nitrate) by microbes
Uptake by plants, forms proteins and other N
containing organic compounds, enters food chain
Ammonification: returned NH4+ inorganic forms by
saprophytes (fungi) and decomposers
Denitrification: conversion of NH4+ to N2 by
combustion or microbes
FUNGI -all are heterotrophs, and eukaryotes (they contain a nucleus), they
can be most are multi-cellular, most are decomposers and feed on dead
things (saprophytes). http://www.ucl.ac.uk/Pharmacology/dc-bits/fungipics1-04m.jpg
Nitrogen in the
Environment
Nitrogen cycles between the biotic and abiotic environments. Bacteria play an
important role in this transfer.
Nitrogen-fixing bacteria are able to fix atmospheric nitrogen.
Nitrifying bacteria convert ammonia to nitrite, and nitrite to nitrate.
Denitrifying bacteria return fixed nitrogen to the atmosphere.
Atmospheric fixation also occurs as a result of lightning discharges.
Humans intervene in the nitrogen cycle by producing and applying nitrogen
fertilizers.
Nitrogen Transformations
The ability of some bacterial species to fix
atmospheric nitrogen or convert it between states is
important to agriculture.
Nitrogen-fixing species include Rhizobium,
which lives in a root symbiosis with leguminous
plants. Legumes, such as clover, beans, and
peas, are commonly planted as part of crop
rotation to restore soil nitrogen.
Nitrifying bacteria include Nitrosomonas and
Nitrobacter. These bacteria convert ammonia to
forms of nitrogen available to plants.
NH3
NO2Nitrosomonas
NO3Nitrobacter
Root nodules in Acacia
Nodule close-up
Nitrogen
Cycle
Nitrogen Cycle: Human Influences?
Emit nitric oxide (NO), which leads to acid rainhuge quantities of nitric oxide emitted;
contributes to photochemical smog; forms
nitrogen dioxide (NO2) in atmosphere, which
can react with water to for nitric acid (HNO3) &
cause acid deposition (“acid rain”)
 Emit nitrous oxide into the atmosphere- nitrous
oxide (N2O) is a potent greenhouse gas & also
depletes ozone in stratosphere

Nitrogen Cycle: Human Influences?
(continued…)
Mine nitrogen- containing fertilizers, deplete nitrogen
from croplands, & leach nitrate from soil by irrigationleads to modification of nitrogen distribution in soils
 Remove N from soil by burning grasslangs & cutting
forest- leads to decreased N in soils
 Add excess N to aquatic systems- runoff of nirates &
other soluble N- containing compounds stimulates
algal blooms, depletes oxygen, & decreases
biodiversity
 Add excess N to terrestrial systems- atmospheric
deposition increase growth of some species (especially
weeds) & can decrease biodiversity

Phosphorous Cycle

Role of Phosphorous?
– Essential nutrient for plants & animals:
especially building block for DNA, other nucleic
acids (including ATP; ATP stores chemical energy),
various fats in cell membrane (phospholipids), &
hard calcium-phosphate compounds (in bone,
teeth, & shells)
– Limiting nutrient in many ecosystemstypically, addition of P leads to increased
productivity, especially for fresh water aquatic
systems
Phosphorus Cycling
Phosphorus cycling is very slow and tends to
be local; in aquatic and terrestrial ecosystems,
Deposition as guano…
it cycles through food webs.
Phosphorous is lost from ecosystems
through run-off, precipitation, and
sedimentation.
Loss via sedimentation…
A very small amount of phosphorus returns
to the land as guano (manure, typically of
fish-eating birds). Weathering and
phosphatizing bacteria return
phosphorus to the soil.
Human activity can result in excess
phosphorus entering water ways and is a
major contributor to eutrophication.
Fertilizer production
Phosphorous: Main Processes
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Weathering: P slowly released from rock or soil
minerals as phosphate (PO43-), which dissolves in H2O
& is readily leached
Uptake: by plants to form organic phosphates
Movement through food web: nucleic acids
(including DNA 7 ATP), certain fats in cell membranes
(phospholipids), bones/teeth/shells (calciumphosphate)
Break down of organic forms: to phosphate
(PO430) by decomposers
Leaching: PO43- from soil
Burial in ocean sediments: not cycled in short time
scale, only over geologic time
The Phosphorus
Cycle
Guano
deposits
Phosphorous: Human Influences?
Mine large quantities of phosphate rock:
used for organic fertilizers & detergents; can
cause local environmental effects from mining
& releases more P into environement
 Sharply decrease P available in tropical
forests & other ecosystems where P is
limiting: deforestation & certain agricultural
practices decrease available P
 Add excess P to aquatic ecosystems: leads
to excessive algal growth, depletion of oxygen,
& decrease in biodiversity; such eutrophication
(“over nourishment”) will be discussed later

Sulfur Cycle
Sulfur Cycle

Role of Sulfur?
– Component of some proteins & vitamins:
essential for organisms
– Limiting nutrient in some ecosystems
Sulfur Cycle: Main Processes
Storage in rocks: much of Earth’s S is in rock form
(e.g., iron disulfides or pyrites) or minerals (sulfates)
 Atmospheric input from volcanoes, anaerobic
decay, & sea spray: S enters atmosphere in form of
hydrogen sulfide (HS), sulfur dioxide (SO2), and
sulfates (S)42-)
 Combustion: sulfur compounds released to the
atmosphere by oil refining, burining of fossil fuels,
smelting, and various industrial activities
 Movement through food web: movement through
foor web & eventual release during decay
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Biotic flow of sulfur through ecoystems
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Abiotic flow of sulfur through ecosystems
Sulfur Cycle: Human Influences?

Contribute about 1/3 of atmospheric
sulfur emissions:
– Burning S- containing oil and coal
– Refining petroleum
– Smelting
– Other industrial processes
Rock Cycle