Download Biogeochemical Cycles

Biogeochemical Cycles
Water
Nitrogen
Carbon Dioxide
Phosphorus
Sulfur
Biogeochemical Cycles:
 chemical elements are required by life from
the living and nonliving parts of the
environment.
 These elements cycle in either a gas cycle or
a sedimentary cycle
 In a gas cycle elements move through the
atmosphere.
 Main reservoirs are the atmosphere and the
ocean.
 Sedimentary cycle elements move from land
to water to sediment.
Carbon
Cycle
 What are the
2 main processes
in the carbon
cycle?
Carbon Cycle
 Is an atmospheric cycle
 Carbon (C) enters the biosphere during
photosynthesis:
 CO2 + H2O  C6H12O6 + O2 + H2O
 Carbon is returned to the biosphere in cellular
respiration:
 O2 +H2O + C6H12O6  CO2 +H2O + energy
Carbon Cycle
 In the ground
 C in organic molecules in organisms is moved to C in
fossil fuels over millions of years by pressure, heat
and bacterial action.
 C in limestone (CaCO3) is released slowly to C in
CO2 when exposed to O2 or H2O
 Largest reservoir of C is sedimentary rock
Carbon Cycle
 Second largest reservoir of C is the ocean
 Dissolved CO2, living things in the ocean
 In Water:
 CO2 + H2O  HCO3-1 + CO3 2 Ca2+ + CO32-  CaCO3 in shells/skeletons of
aquatic organisms
 CaCO3  buried, long periods of time,
pressure  Limestone
Carbon Facts
 Every year there is a measurable difference
in the concentration of atmospheric CO2 with
changes in the seasons.
 For example, in winter there is almost
no photosynthesis ( higher CO2 )
 During the growing season there is a
measurable difference in the
concentration of atmospheric CO2
over parts of each day.
Carbon Cycle
 Human Impact:
 Removal of vegetation reduces absorption of
CO2 for photosynthesis from atmosphere.
Increases atmospheric CO2
 Burning of fossils fuels increases atmospheric
CO2
 Increase in atmospheric CO2 leads to
increased Greenhouse Effect = Global
Warming
Nitrogen cycle
Nitrogen Cycle
 Nitrogen (N) is an essential constituent of
protein, DNA, RNA, and chlorophyll.
 Is an atmospheric cycle
 Nitrogen is the most abundant gas in the
atmosphere.
 Plants and animals cannot use free N2 gas
in the atmosphere.
 Nitrogen must be fixed or converted into a
usable form.
Nitrogen Cycle
 Free N2 in atmosphere is “fixed” by nitrogen
fixing bacteria to NH3 (ammonia):
 N2 + 3H2  2NH3
 Nitrogen fixing bacteria live in nodules on
the roots of leguminous plants (soybeans,
peas, clover and alfalfa)
 Water in the soil reacts with NH3
(ammonia) to form NH41+ ammonium ion
Nitrogen Cycle
 Another species of bacteria can perform
nitrification once NH41+ has been formed
 NH41+  NO21-  NO31-
 Assimilation – absorption of NH3, NH41+,
NO31- for use by plants to make nucleic
acids and proteins.
 Animals get fixed nitrogen by eating plants
or animals
Nitrogen Cycle
 Plants and animals are broken down by still
other bacteria that convert nitrogen
containing organic molecules in organisms
to an inorganic form of nitrogen (NH3 or
NH41+) This is ammonification
 Once this ammonia is formed, still another
group of bacteria can perform denitrification:
 NH3 or NH41+  NO21 NO31-  N2 and N2O
and/or
Nitrogen Cycle
 Nitrogen is often the limiting factor in
plant growth because NH3, NH41+ and
NO31- are all water soluble and can be
leached from the soil.
Nitrogen Cycle
 Human Intervention:
 In the atmosphere:
 N2 + O2  2NO (nitric oxide) produced when burning
fuel or forests
 NO + O2  NO2 (nitrogen dioxide gas)
 NO2 + H2O  HNO3
 Nitric acid dissolved in water causes acid deposition
 N2O released from decomposition of fertilizer and
waste.
Nitrogen Cycle
 Excess nitrogen added to aquatic
systems by run off of artificial fertilizer,
farm waste and discharge of sewage.
This stimulates growth of algae.
Breakdown of algae by aerobic
decomposers depletes water of oxygen.
Oxygen Cycle (Photosynthesis)
Sources of Oxygen:
 Photosynthesis and respiration
 Photo disassociation of H2O vapor
 CO2 and O2 circulates freely throughout the
biosphere.
 Some CO2 combines with Ca to form carbonates.
 O2 combines with nitrogen compounds to form
nitrates.
 O2 combines with iron compounds to form ferric
oxides.
 O2 in the troposphere is reduced to O3 (ozone).
 Ground level O3 (ozone) is a pollutant which
damages lungs.
Phosphorus
(P) Cycle
Phosphorus (P) Cycle
 Component of DNA, RNA, ATP, proteins and enzymes
 Cycles in a sedimentary cycle – does not include the
atmosphere
 A good example of how a mineral element becomes part of
an organism.
 The source of Phosphorus (P) is rock.
 Phosphorus is soluble in H2O as phosphate (PO43-)
 Phosphate on land and in ocean sediment released by
weathering into water and taken up by plants. Can be
limiting factor for plant growth – is present in artificial
fertilizer.
Phosphorus (P) Cycle
 Animals get phosphorus by eating
plants or other animals.
 Decomposition changes organic
molecules with phosphorus back into
phosphate which dissolves in water
which returns the phosphorus to ocean
sediment or deposited as rocks.
Phosphorus (P) Cycle
 Human intervention:
 Mining of phosphate for fertilizers and soap
causes disruption to ecosystems
 Removal of phosphorus from ecosystems by
cutting down vegetation. Most phosphorus is
taken up as biomass.
 Excess phosphorus in runoff from fertilizers,
discharge of sewage, farm waste causes algae
growth, etc (same as nitrogen)
Sulfur (s) Cycle
 Component of protein
 Cycles in both a gas and sedimentary cycle but primary is an
atmospheric cycle
 The source of Sulfur is the lithosphere (earth's crust)
 Sulfur (S) enters the atmosphere as hydrogen
sulfide (H2S) during fossil fuel combustion, volcanic
eruptions, gas exchange at ocean surfaces, and
decomposition.
 H2S + O2  SO2 + H2
 SO2 + O2  SO3 (sulfur trioxide) or
 SO2 + H2O  H2SO4 (sulfuric acid) Acid deposition
Sulfur (s) Cycle
 Sulfur in soluble form is taken up by plant roots
and incorporated into amino acids such as
cysteine. It then travels through the food chain and
is eventually released through decomposition
 SO2 and water vapor makes H2SO4 ( a weak
sulfuric acid), which is then carried to Earth in the
form of acid rain.
Sulfur (s) Cycle
 Human Intervention:
 Sulfur containing coal, when burned ,
releases SO2
 Other industrial processes release SO2 into
the atmosphere.
Summary
 The building blocks of life :Water ,Nitrogen,
Carbon Dioxide, Phosphorus, Sulfur
 Continually cycle through Earth's systems,
the atmosphere, hydrosphere, biosphere, and
lithosphere, on time scales that range from a
few days to millions of years.
 These cycles are called biogeochemical
cycles, because they include a variety of
biological, geological, and chemical
processes.