Transcript Biogeochemical Cycles

What are these cycles?
 Cycling of atoms, molecules, and ions from
the non-living environment to the living
organisms and back again.
 Connect the past, present, and future
forms of life.
 Obey Law of Conservation of Mass
 Provide for recycling of materials
 Prevent accumulation of wastes
 Prevent essential nutrients from running out
What is the water/hydrologic cycle?
 The steps involved in the Water Cycle
 Evaporation – liquid water in rivers, lakes, oceans, etc. is
converted into water vapor
 Transpiration – the evaporation of water from the leaves of
plants
 Condensation – as water vapor in the air rises with warm air, it
cools and forms liquid water, resulting in cloud formation.
 Precipitation– rain or snow falling from clouds
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Runoff – precipitation runs over land into bodies of water
Groundwater – precipitation infiltrates the ground and ends up in
aquifers
Ice – precipitation freezes for varying periods of time resulting in
glaciers, etc.
What are the benefits of the
Hydrologic Cycle?
 Water supplies are replenished
 Since water is the universal solvent and so many
substances dissolve in it, it helps to transport nutrients
 When water is evaporated, only the water becomes a
gas, pollution and particulates are left behind. So this
is a natural purification process for water.
How do humans affect the Water
Cycle?
 Remove groundwater supplies faster than can be
replenished resulting in water shortages.
 Runoff from erosion pollutes water by adding
nutrients (eutrophication) which cause excessive plant
growth and fish kills
 Runoff brings pollutants from land into water like oil
and pesticides (non-point source pollution)
 Removal of forests and other vegetation alters normal
rain patterns
What is the Sulfur Cycle?
 It is the cycling of sulfur containing compounds and
ions through the atmosphere and rocks.
 S naturally enters the atmosphere by weathering,
volcanic eruptions, sea spray, and sea floor vents.
 H2S (hydrogen sulfide) is released from the anaerobic
(without oxygen) breakdown of organic matter by
bacteria in swamps, bogs, and tidal flats. (Smells like
rotten eggs). H2S is a greenhouse gas.
 Sulfur circulates through plants in the form of sulfate
(SO42-) or sulfur dioxide (SO2)
Where is Sulfur found?
 It is found in amino acids, insulin, fool’s gold,
oceanic deposits, sulfur dioxide, etc.
How does sulfur contribute to acid
rain?
 When certain compounds are burned, sulfur dioxide
(SO2). is produced.
 SO2 released in air reacts with oxygen to produce
sulfur trioxide which then reacts with water to produce
sulfuric acid (H2SO4).
 SO2 +O2  SO3
SO3 + H2O  H2SO4
 Sulfuric acid can also form from reactions of DMS
(dimethyl sulfide) released by plankton.
 This lowers the pH of rainfall. Normal rainfall is
slightly acidic (5.6) because carbon dioxide in the air
and water react to form carbonic acid.
 Acid rain causes damage to plants, lowers the pH
in water which affects fish and other aquatic
organisms, damages building, statues, and cars,
and can decrease the pH of soils.
Acid Rain
How do humans affect the sulfur
cycle?
 Burning of fossil fuels containing sulfur causes the
release of sulfur dioxide into the air.
 Smelting (removal of valuable metal from rock) of
metal ores containing sulfur releases sulfur dioxide
into the air.
 The use of sulfuric acid in industrial and
manufacturing processes releases sulfur containing
compounds into the air.
What is the Phosphorus Cycle?
 It is the cycling of P through rocks and soil and living
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organisms.
There is no gaseous component in the P cycle.
When P is broken down from rocks and soils,
phosphate ions (PO43-) are released and this is the
form that plants will pick up through their roots.
Most compounds containing phosphate ions are
insoluble in water.
Because of this the release of P from rocks during
weathering is a very SLOW process.
As a result P is often a limiting factor (a nutrient or
needed factor in short supply) in ecosystems.
Where is P found?
 Living organisms
 DNA
 Fats
 Bones, shells, teeth
 Rocks
 Both terrestrial and oceanic formations
What is Organic Phosphorus?
 Inorganic (does not contain C). Organic (contains C).
 Plants absorb inorganic P in the form of phosphate
and convert it to organic forms (such as DNA).
 Animals take in organic P through the food chain (and
use it for making bones, shells, teeth, DNA, etc.).
 Organic P is broken down by bacteria during cellular
respiration. It is then released in urine and wastes.
 There are large concentrations of P in guano (sea bird
poop) since their diet is high in fish which naturally
have higher levels of P.
How do humans affect the P Cycle?
 Phosphorus is mined from rocks for use in
fertilizers and detergents.
 Mining phosphate rocks damages the land and
pollutes groundwater.
 P is found in limited quantities in tropical soils so
removing forests for agriculture helps to wash
away P
 Runoff from farms and fertilized areas and sewage
runoff containing excess P leads to eutrophication
in waterways. Results in algae blooms and fish
kills.
What is the Nitrogen Cycle?
 It is the cycling of nitrogen and nitrogen
containing compounds and ions through the air,
soil, water, and living organisms.
 In living organisms, nitrogen is found in DNA,
RNA, proteins, and amino acids.
 It’s a gaseous cycle.
 78% of the atmosphere is N2.
What are the steps of the
Nitrogen Cycle?
 Nitrogen fixation – conversion of N2 in the
atmosphere into a form usable by plants.
 N2 cannot be taken up by plants.
 It must be “fixed”: converted to NH3 or NH4
 N2 + H2 ---> NH3
 What fixes N2?
 Lightening
 cyanobacteria
 Rhizobium bacteria which live in root nodules on legumes
(peas, soybeans, alfalfa)
 Humans use the Haber process
Legumes and
Rhizobium
 Nitrification
 NH3 or NH4+ are converted to nitrate (NO3-) or
nitrite (NO2-) ions.
 Nitrates are easily taken up by plants, while
nitrites are toxic.
 Assimilation
 Inorganic forms of nitrogen are converted to
organic forms in plants
 Animals pick up organic forms of nitrogen by
eating plants directly or by eating other animals.
 Ammonification
 Animal/plant waste or dead organisms are
broken down by bacteria.
 Bacteria convert the organic nitrogen forms
back into simpler inorganic forms such as
ammonium (NH4+) or ammonia(NH3).
 Denitrification
 The “final” process
 Converts ammonia and ammonium first into
nitrates or nitrites and then back into
atmospheric nitrogen (N2) or NO2.
How do humans affect
the Nitrogen Cycle?
 Humans now control more of the nitrogen
cycle than natural processes.
 3 human activities have the greatest
impact:
 Use of commercial fertilizer.
 Increased cultivation of legumes and crops that
have nitrogen fixing bacteria.
 Burning of fossil fuels.
 HOW DOES NITROGEN IN FERTILIZER HAVE
AN IMPACT ON AQUATIC ECOSYSTEMS?
 Draining of wetlands, burning of forests, etc.
also release N
 Burning fossil fuels releases nitrogen in the
form of NOx into atmosphere which reacts
with water in the air to form nitric acid
(HNO3), a component of acid rain.
 NOx + H2O  HNO3
 Nitrous oxide gas (N2O) in the air is a greenhouse
gas. Forms by the breakdown of animal waste and
commercial fertilizer.
 Excess N entering waterways can lead to
eutrophication, algae blooms, and fish kills.
 Overfertilization of crops can lead to a decrease in
biodiversity.
 Fixed nitrogen entering ground water and drinking
water is a health risk particularly to pregnant
women and young children. Prevents blood from
taking up enough oxygen. Known as
Methemoglobinemia or Blue Baby Syndrome
Methemoglobinemia
What can be done to decrease
human impact on the N cycle?
 Reduction of commercial fertilizer use and change
to more “natural forms” of fertilizers.
 Reduction in fossil fuel consumption.
 Methods of removing nitrates from water.
 Preservation of wildlands.
What is the Carbon
Cycle?
 Gaseous cycle.
 Based on carbon dioxide gas which makes up
0.036% of volume of troposphere.
 CO2 also found dissolved in water.
 CO2 helps control the earth’s thermostat.
 Terrestrial and aquatic producers remove
carbon dioxide and convert it into glucose
via photosynthesis.
 CO2 is returned to air and water through
aerobic respiration.
What is the connection
between photosynthesis and
aerobic respiration?
 Photosynthesis
 CO2 + H2O ---> O2 + C6H12O6
 Aerobic respiration
 O2 + C6H12O6 ---> CO2 + H2O
What are the sinks (place
where a nutrient is stored for
periods of time) for carbon?
1. Sedimentary rocks like limestone (CaCO3),
found in deposits on the ocean floor or on
continents.
The carbon in limestone is released slowly as CO2
by geological processes or by acid rain.
This is the largest sink for C.
 2. The oceans
 CO2dissolved in the oceans is 50x
greater than in the air.
 CO2 gets into the oceans from contact
with air, aerobic respiration and
decomposition, and breakdown of CO32 Some of the CO2 in the water is used by
producers during photosynthesis and
some will react with water to form
carbonate (CO32-)
 Some marine organisms take up the
CO32-, react it with Ca2+ and form
calcium carbonate (CaCO3) which
becomes shells and skeletons
 When these creatures die, these shells
are buried deep in the ocean where over
time they form sedimentary rock
(limestone).
3. Fossil fuels form when dead plants and
bacteria are pressed between layers of
sediment. Time and pressure eventually
create what we call fossil fuels.
 The C they contain is locked up in the fossil
fuel until it is burned and carbon dioxide is
released.
 4. Forests
 During photosynthesis, trees take in CO2
and convert it into organic matter (glucose).
 C remains bound up with the tree for long
periods of time and is not released until the
tree dies or is cut down and burned.
How do human activities
affect the carbon cycle?
 Humans increase the amount of CO2 in the
atmosphere by
 Removing vegetation.
 Combusting fossil fuels.
 CO2 in atmosphere is considered a greenhouse gas
and is linked to global climate change.
How is excess CO2 affecting
the Oceans?
 As a result of human activities, more CO2 is
entering the atmosphere and at the same time
more is entering the oceans.
 The normal pH levels of the ocean range from
7.5 to 8.5.
 When CO2 dissolves in water, it reacts with
the water to produce carbonic acid:
 H2O +
CO2 ---> H2CO3
 This creates a lowering of the pH of the ocean
(ocean acidification).
 This does not necessarily mean that the ocean
is becoming an acidic solution, but it is more
acidic than normal.
How is acidification affecting the
Ocean?
 Studies conducted have found that:
 increasing acidification of ocean water
affects the ability of organisms to make
shells.
 The problem is greatest in colder
water regions near the poles because
colder waters can hold more carbon
dioxide.
 Pteropods (a form of plankton) are an
important base of the food web in
polar regions. They cannot grow shells
as the water becomes more acidic.
May be a serious problem in the
coming decades. And in some places, it
may already be one.
Are corals also affected by
acidification?
 Coral is actually a symbiotic relationship between
the coral animal and an algae called zooxanthellae.
 Because of acidification, the coral animal itself
loses its ability to make a calcium carbonate shell.
 Because of more carbon dioxide in the water, the
symbiotic algae goes through more photosynthesis.
 The symbiotic relationship is disrupted possibly due
to greater competition for carbon between the
symbiotes.
What can be done to reduce
carbon dioxide levels?
 Reduce human activities that put excess CO2 into the
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atmosphere.
Add iron sulfate to oceans to increase phytoplankton
growth and photosynthesis
Inject carbon dioxide into the deep ocean
Direct injection of CO2 underground
Problems with injection:
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May come back up
Creates more acidic waters
Concern over earthquakes
In 1986 at Lake Nyos in Cameroon, 1700 people died when a
natural carbon dioxide bubble was released.