Download Biogeochemical Cycles

Biogeochemical Cycles
• The cycling of chemical elements required
by life between the living and nonliving
parts of the environment. Some examples
of these chemical elements are H2O, P, S,
N2, O2 and C.
• Gas Cycles:
Sedimentary Cycles:
• Carbon
Phosphorus
Nitrogen
Sulfur
Oxygen
Carbon Cycle Basics
Egon Schiele (1890-1918)
Autumn Sun 1
All life is based on the
element carbon. Carbon is
the major chemical
constituent of most organic
matter, from fossil fuels to
the complex molecules
(DNA and RNA) that
control genetic
reproduction in organisms.
Yet by weight, carbon is
not one of the most
abundant elements within
the Earth's crust.
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Carbon Pools
Pool
Atmosphere
Terrestrial Plants
Soil Organic matter
Ocean
Fossil Fuel Deposits
Marine Sediments and Sedimentary Rocks
Amount in Billions of Met ric Tons
578 (as of 1700) - 766 (a s of 1999)
540 to 610
1500 to 1600
38,000 to 40,000
4000
66,000,000 to 100,000,000
Carbon is stored on our planet in the following major pools:
• as organic molecules in living and dead organisms found in the
biosphere;
• as the gas carbon dioxide in the atmosphere;
• as organic matter in soils;
• in the lithosphere as fossil fuels and sedimentary rock deposits such as
limestone, dolomite and chalk;
• in the oceans as dissolved atmospheric carbon dioxide and as calcium
carbonate shells in marine organisms.
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Global Carbon Cycle
Carbon is exchanged between the active pools due to various processes –
photosynthesis and respiration between the land and the atmosphere, and
diffusion between the ocean and the atmosphere.
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Atmospheric CO2 Concentration-1
Accurate and direct measurements of the concentration of CO2 in the atmosphere
began in 1957 at the South Pole and in 1958 at Mauna Loa, Hawaii.
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Historical Atmospheric CO2 Concentration
This figures shows that the concentration of CO2 has never been grater than 300
ppmv for the past 400,000 years.
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Photoautotrophs
• Ecosystems gain most of their carbon
dioxide from the atmosphere. A number
of autotrophic organisms have
specialized mechanisms that allow for
absorption of this gas into their cells. With
the addition of water and energy from
solar radiation, these organisms use
photosynthesis to chemically convert the
carbon dioxide to carbon-based sugar
molecules.
Photoautotophs
• These molecules can then be chemically
modified by these organisms through the
metabolic addition of other elements to
produce more complex compounds like
proteins, cellulose, and amino acids.
Some of the organic matter produced in
plants is passed down to heterotrophic
animals through consumption.
Sea Shells
• Carbon dioxide enters the waters of the
ocean by simple diffusion. Once
dissolved in seawater, the carbon dioxide
can remain as is or can be converted into
carbonate (CO3-2) or bicarbonate (HCO3-).
Certain forms of sea life biologically fix
bicarbonate with calcium (Ca+2) to produce
calcium carbonate (CaCO3).
Sea Shells
• This substance is used to produce shells
and other body parts by organisms such
as coral, clams, oysters, some protozoa,
and some algae. When these organisms
die, their shells and body parts sink to the
ocean floor where they accumulate as
carbonate-rich deposits. After long periods
of time, these deposits are physically and
chemically altered into sedimentary
rocks. Ocean deposits are by far the
biggest sink of carbon on the planet.
Respiration
• Carbon is released from ecosystems as
carbon dioxide gas by the process of
respiration. Respiration takes place in
both plants and animals and involves the
breakdown of carbon-based organic
molecules into carbon dioxide gas and
some other compound by products.
Decomposers
• The detritus food chain contains a
number of organisms whose primary
ecological role is the decomposition of
organic matter into its abiotic components.
Carbon and Life on Earth
• Over the several billion years of geologic
history, the quantity of carbon dioxide
found in the atmosphere has been steadily
decreasing.
• Researchers theorized that this change is
in response to an increase in the Sun's
output over the same time period. Higher
levels of carbon dioxide helped regulate
the Earth's temperature to levels slightly
higher than what is perceived today.
Carbon and Life on Earth
These moderate temperatures allowed for the
flourishing of plant life despite the lower
output of solar radiation. An enhanced
greenhouse effect, due to the greater
concentration of carbon dioxide gas in the
atmosphere, supplemented the production of
heat energy through higher levels of
longwave counter-radiation. As the Sun grew
more intense, several biological mechanisms
gradually locked some of the atmospheric
carbon dioxide into fossil fuels and
sedimentary rock.
Lithosphere
• Carbon is stored in the lithosphere in both
inorganic and organic forms. Inorganic
deposits of carbon in the lithosphere include
fossil fuels like coal, oil, and natural gas, oil
shale, and carbonate based sedimentary
deposits like limestone. Organic forms of
carbon in the lithosphere include litter, organic
matter, and humic substances found in soils.
Volcanoes
Some carbon dioxide is released from the interior
of the lithosphere by volcanoes. Carbon dioxide
released by volcanoes enters the lower
lithosphere when carbon-rich sediments and
sedimentary rocks are subducted and partially
melted beneath tectonic boundary zones.
Industrial Revolution
Since the Industrial Revolution, humans have
greatly increased the quantity of carbon dioxide
found in the Earth's atmosphere and oceans.
Atmospheric levels have increased by over
30%, from about 275 parts per million (ppm) in
the early 1700s to just over 365 PPM today.
Scientists estimate that future atmospheric
levels of carbon dioxide could reach an amount
between 450 to 600 PPM by the year 2100. The
major sources of this gas due to human
activities include fossil fuel combustion and the
modification of natural plant cover found in
grassland, woodland, and forested ecosystems.
Other CO2 Sources
• Emissions from fossil fuel combustion
account for about 65% of the additional
carbon dioxide currently found in the
Earth's atmosphere. The other 35% is
derived from deforestation and the
conversion of natural ecosystems into
agricultural systems. Researchers have
shown that natural ecosystems can store
between 20 to 100 times more carbon
dioxide than agricultural land-use types.
http://www.windows.ucar.edu/earth/climate/carbon_cycle.html
N Cycle
Facts
• Ultimate source of nitrogen to organisms is
N2 from the atmosphere. Many temperate
zone ecosystems limited by availability of
Nitrogen
• Nitrogen fixation is the chemical
transformation of N2 to NH3
• Nitrogen fixation is energetically costly
• Nitrogen fixation is done by microbes, often
in a symbiosis with plants
N’s Role in Life
• The nitrogen cycle represents one of the most
important nutrient cycles found in terrestrial
ecosystems. Nitrogen is used by living
organisms to produce a number of complex
organic molecules like amino acids, proteins,
and nucleic acids. The store of nitrogen found
in the atmosphere, where it exists as a gas
(mainly N2), plays an important role for life. This
store is about one million times larger than the
total nitrogen contained in living organisms.
N Stores
• Other major stores of nitrogen include
organic matter in soil and the oceans.
Despite its abundance in the atmosphere,
nitrogen is often the most limiting nutrient
for plant growth. This problem occurs
because most plants can only take up
nitrogen in two solid forms: ammonium
ion (NH4+ ) and the ion nitrate (NO3- ).
Most plants obtain the nitrogen they need
as inorganic nitrate from the soil
solution.
Uses of N
• Ammonium is used less by plants for
uptake because in large concentrations it
is extremely toxic. Animals receive the
required nitrogen they need for
metabolism, growth, and reproduction by
the consumption of living or dead organic
matter containing molecules composed
partially of nitrogen.
N Cycle
Decomposers
• In most ecosystems nitrogen is primarily stored
in living and dead organic matter. This organic
nitrogen is converted into inorganic forms when
it re-enters the biogeochemical cycle via
decomposition. Decomposers, found in the
upper soil layer, chemically modify the nitrogen
found in organic matter from ammonia (NH3 )
to ammonium salts (NH4+ ). This process is
known as mineralization and it is carried out
by a variety of bacteria, actinomycetes, and
fungi.
N Cycle Processes
Processes involve chemical oxidation and are
known as nitrification. However, nitrate is very
soluble and it is easily lost from the soil system by
leaching. Some of this leached nitrate flows
through the hydrologic system until it reaches
the oceans where it can be returned to the
atmosphere by denitrification. Denitrification is
also common in anaerobic soils and is carried
out by heterotrophic bacteria. The process of
denitrification involves the metabolic reduction of
nitrate (NO3- ) into nitrogen (N2) or nitrous oxide
(N2O) gas. Both of these gases then diffuse into
the atmosphere.
Nitrogen Fixation
Almost all nitrogen found in any terrestrial
ecosystem originally came from the atmosphere.
Significant amounts enter the soil in rainfall or
through the effects of lightning. The majority,
however, is biochemically fixed within the soil by
specialized micro-organisms like bacteria,
actinomycetes, and cyanobacteria.
Legumes
• Members of the bean family (legumes)
and some other kinds of plants form
mutualistic symbiotic relationships with
nitrogen fixing bacteria. In exchange for
some nitrogen, the bacteria receive from
the plants carbohydrates and special
structures (nodules) in roots where they
can exist in a moist environment.
Scientists estimate that biological fixation
globally adds approximately 140 million
metric tons of nitrogen to ecosystems
every year.
Nitrogen Fixation
Nodules on plant roots
Human Impact
• The activities of humans have severely altered
the nitrogen cycle. Some of the major
processes involved in this alteration include:
• The application of nitrogen fertilizers to crops
has caused increased rates of denitrification
and leaching of nitrate into groundwater. The
additional nitrogen entering the groundwater
system eventually flows into streams, rivers,
lakes, and estuaries. In these systems, the
added nitrogen can lead to eutrophication.
Human Impact
• Increased deposition of nitrogen from
atmospheric sources because of fossil fuel
combustion and forest burning. Both of these
processes release a variety of solid forms of
nitrogen through combustion.
• Livestock ranching. Livestock release a large
amounts of ammonia into the environment from
their wastes. This nitrogen enters the soil
system and then the hydrologic system through
leaching, groundwater flow, and runoff.
• Sewage waste and septic tank leaching.
• A source of energy for some microbes, and a
source of N for plants and microbes
Ammonification is the conversion of amino acids
to NH3
Nitrification is the oxidation of ammonium:
• ammonium (NH4+) to nitrite (NO2-)
• nitrite (NO2-) to nitrate (NO3-)
Denitrification is the reduction of NO3- to nitric
oxide (NO), to nitrous oxide (N2O), and finally to
molecular nitrogen (N2)
• NO3- => NO => N2O => N2
The Hydrologic (Water) Cycle
•
The hydrologic cycle is a conceptual
model that describes the storage and
movement of water between the
biosphere, atmosphere, lithosphere,
and the hydrosphere (see Figure 8b-1).
Water on this planet can be stored in any
one of the following reservoirs:
atmosphere, oceans, lakes, rivers,
soils, glaciers, snowfields, and
groundwater.
Hydrologic Cycle
Movement of Water
• Water moves from one reservoir to another by
way of processes like evaporation,
condensation, precipitation, deposition,
runoff, infiltration, sublimation,
transpiration, melting, and groundwater
flow. The oceans supply most of the
evaporated water found in the atmosphere. Of
this evaporated water, only 91% of it is returned
to the ocean basins by way of precipitation. The
remaining 9% is transported to areas over
landmasses where climatological factors induce
the formation of precipitation.
Movement of Water
• The resulting imbalance between rates of
evaporation and precipitation over land and
ocean is corrected by runoff and groundwater
flow to the oceans.
• The planetary water supply is dominated by the
oceans. Approximately 97% of all the water on
the Earth is in the oceans. The other 3% is held
as freshwater in glaciers and icecaps,
groundwater, lakes, soil, the atmosphere, and
within life.
Water Reservoirs
Reservoir
Oceans
Volume
Percent
(cubic km x
of Total
1,000,000)
1370
97.25
Ice Caps and Glaciers
29
2.05
Groundwater
9.5
0.68
Lakes
0.125
0.01
Soil Moisture
0.065
0.005
Atmosphere
0.013
0.001
Streams and Rivers
0.0017
0.0001
Biosphere
0.0006
0.00004
Cycle of Water
• Water is continually cycled between its various
reservoirs. This cycling occurs through the
processes of evaporation, condensation,
precipitation, deposition, runoff, infiltration,
sublimation, transpiration, melting, and
groundwater flow. Table 8b-2 describes the
typical residence times of water in the major
reservoirs. On average water is renewed in
rivers once every 16 days.
Cycle of Water
• Water in the atmosphere is completely
replaced once every 8 days. Slower rates
of replacement occur in large lakes,
glaciers, ocean bodies and groundwater.
Replacement in these reservoirs can take
from hundreds to thousands of years.
Some of these resources (especially
groundwater) are being used by humans
at rates that far exceed their renewal
times. This type of resource use is making
this type of water effectively
nonrenewable.
Typical residence times of water
found in various reservoirs.
•
•
•
•
•
•
•
Glaciers: 20 to 100 years
Seasonal Snow Cover: 2 to 6 months
Soil Moisture: 1 to 2 months
Groundwater: Shallow 100 to 200 years
Groundwater: Deep 10,000 years
Lakes: 50 to 100 years
Rivers: 2 to 6 months
Evaporation
• Evaporation can be defined as the process
where liquid water is transformed into a
gaseous state. Evaporation can only occur
when water is available. It also requires that the
humidity of the atmosphere be less than the
evaporating surface (at 100% relative
humidity there is no more evaporation). The
evaporation process requires large amounts of
energy. For example, the evaporation of one
gram of water requires 600 calories of heat
energy.
Transpiration
• Transpiration is the process of water loss from
plants through stomata. Stomata are small
openings found on the underside of leaves that
are connected to vascular plant tissues. In most
plants, transpiration is a passive process largely
controlled by the humidity of the atmospheric
and the moisture content of the soil. Of the
transpired water passing through a plant only
1% is used in the growth process.
Transpiration
• Transpiration also transports nutrients from the
soil into the roots and carries them to the
various cells of the plant and is used to keep
tissues from becoming overheated. Some dry
environment plants do have the ability to open
and close their stomata. This adaptation is
necessary to limit the loss of water from plant
tissues. Without this adaptation these plants
would not be able to survive under conditions of
severe drought.
Infiltration
• Infiltration refers to the movement of water into
the soil layer. The rate of this movement is
called the infiltration rate. If rainfall intensity is
greater than the infiltration rate, water will
accumulate on the surface and runoff will
begin.
• Movement of water into the soil is controlled by
gravity, capillary action, and soil porosity.
The burrowing of worms and other organisms
and penetration of plant roots can increase the
size and number of channels within the soil.
The amount of decayed organic matter found
at the soil surface can also enhance infiltration.
Runoff
• If the amount of water falling on the ground is
greater than the infiltration rate of the surface,
runoff or overland flow will occur. Runoff
specifically refers to the water leaving an area
of drainage and flowing across the land surface
to points of lower elevation. It is not the water
flowing beneath the surface of the ground. This
type of water flow is called throughflow.
Runoff
• Runoff involves the following events:
• Rainfall intensity exceeds the soil's infiltration
rate.
• A thin water layer forms that begins to move
because of the influence of slope and gravity.
• Flowing water accumulates in depressions.
• Depressions overflow and form small rills.
• Rills merge to form larger streams and rivers.
• Streams and rivers then flow into lakes or
oceans.
Throughflow and Groundwater
Storage
•
Throughflow is the sporadic horizontal flow of
water within the soil layer (Figure 8m-1). It
normally takes place when the soil is
completely saturated with water. This water
then flows underground until it reaches a river,
lake, or ocean. Rates of water movement via
throughflow are usually low. Rates of maximum
flow occur on steep slopes and in pervious
sediments. The lowest rates of flow occur in
soils composed of heavy clays, which can be
less than 1 millimeter per day.
Water Movement
• Hydrologic movement of water beneath
the Earth's surface. Water usually enters
the surface sediments as precipitation.
This water then percolates into the soil
layer. Some of this water flows horizontally
as throughflow. Water continuing to flow
downward eventually reaches a
permanent store of water known as the
groundwater. The movement of
groundwater horizontally is called
groundwater flow.
Throughflow & Groundwater
Throughflow and Groundwater
• Precipitation that succeeds in moving from the
soil layer down into the underlying bedrock will
at some point reach an area of permanent
saturation that is known as the groundwater
zone. The top of this zone is called the water
table. Groundwater tends to flow by way of
gravity to the point of lowest elevation. Often
groundwater flow discharges into a surface
body of water like a river channel, lake, or
ocean.
Groundwater
• Rock formations that store groundwater water
are known as aquifers. Rock formations that
cannot store groundwater are called
aquicludes.
• Groundwater occurs in two main forms.
Unconfined groundwater occurs when the
flow of subterranean water is not confined by
the presence of relatively impermeable layers.
Springs that flow from underground to the
Earth's surface are often formed when a
perched (impermeable) water table intersects
the surface.
Artesian Water
• In some cases, groundwater can become
confined between two impermeable layers.
This type of enclosed water is sometimes called
artesian. If conditions are right, a confined
aquifer can produce a pressurized ground to
surface flow of water known as an artesian
well. In an artesian well, water flows against
gravity to the earth's surface because of
hydrostatic pressure. Hydrostatic pressure is
created from the fact that most of the aquifer's
water resides at an elevation greater than the
well opening. The overlying weight of this water
creates the hydrostatic pressure.
The Oxygen Cycle
Definition of Oxygen
• Oxygen – a colorless, odorless, tasteless gas
• Denser than air
• Poor conductor of heat and electricity
Step One of Oxygen Cycle
• Plant release oxygen into the atmosphere as
a by-product of photosynthesis.
oxygen
Step Two of Oxygen Cycle
• Animals take in oxygen through the
process of respiration.
• Animals then break down sugars and food.
Step Three in Oxygen Cycle
• Carbon dioxide is released by animals and
used in plants in photosynthesis.
• Oxygen is balanced between the atmosphere
and the ocean.
History of Oxygen
• Early evolution of Earth, oxygen released from
H2O vapor by UV radiation and accumulated
in the atmosphere as the hydrogen escaped
into the earth's atmosphere
• Photosynthesis became a source of oxygen
• Oxygen released as organic carbon and gets
buried in sediments.
Photosynthesis
•Definition- process in which green plants use the energy
from the sun to make carbohydrates from carbon dioxide
and water in the presence of chlorophyll.
How is Photosynthesis Carried
Out?
•Photosynthesis only occurs in plants containing
chlorophyll:
•Water is absorbed by the roots and carried to
the leaves by the xylem
•Carbon dioxide is obtained from air that enters
the leaves through the stomata and diffuses to the
cells containing chlorophyll.
•Chlorophyll is uniquely capable of converting
the energy from light into a dormant form that
can be stored and used when needed.
Steps in Photosynthesis
•
•
•
•
•
The light energy strikes the leaf, passes into the leaf and
hits a chloroplast inside an individual cell
The light energy, upon entering the chloroplasts, is
captured by the chlorophyll inside a grana.
Inside the grana some of the energy is used to split water
into hydrogen and oxygen.
The oxygen is released into the air.
The hydrogen is taken to the stroma along with the
grana's remaining light energy.
Steps Continued:
• Carbon dioxide enters the leaf and passes into the
chloroplast.
• In the stroma the remaining light energy is used to
combine hydrogen and carbon dioxide to make
carbohydrates.
• The energyrich carbohydrates are carried to the plant's
cells.
• The energyrich carbohydrates are used by the cells to
drive the plant's life processes.
Respiration
• Process by which an organism exchanges
gases with its environment
• Process → oxygen is abstracted from air,
transported to cells for the oxidation of
organic molecules while CO2 and H2O, the
products of oxidation, are returned to the
environment
Today
The Earth’s atmosphere
consists of:
• 21% Oxygen
The Earth’s lithosphere
consists of:
• 99.5% Oxygen
The Earth’s hydrosphere
consists of:
• 46.60% Oxygen
The Earth’s biosphere
consists of:
• 0.01% Oxygen
Biological Importance of Oxygen
• Humans need it to breathe
• Needed for decomposition of organic
waste
• Water can dissolve oxygen and it is this
dissolved oxygen that supports aquatic
life.
Ecological Importance of Oxygen
• Without oxygen at the bottom of the water body,
anaerobic bacteria (those that live without oxygen) produce
acids. These acids not only increase acidity, but also cause a
massive release of phosphorus and nitrogen, two major
fertilizers, from the organic sediment and into the water
column.
• These same anaerobic bacteria put toxic gases in the water
including hydrogen sulfide (that rotten egg smell),
ammonia, carbon dioxide and methane. These gases are all
toxic to fish, beneficial bacteria and insects.
• Lack of bottom oxygen is the cause of odors produced by
anaerobic bacteria.
Ecological Importance of Oxygen
Cont.
• Lack of fish enables disease-hosting mosquitoes
to thrive, as mosquitoes are natural food for
fish.
• Without oxygen at the bottom at all times,
beneficial bacteria and insects cannot biodegrade
the organic sediment. Large accumulations of
organic sediment follow.