BIOGEOCHEMICAL CYCLES
- The cycle wherein the elements and compounds that make
up nutrients move continually through air, water, soil, rocks
and living organisms within ecosystems.
- Life-earth-chemical cycles or nutrient cycles.
WATER CYCLE
Water is an amazing substance that is necessary for life on the
earth and there is a fixed supply of it in our planet. The hydrologic
or water cycle, collects, purifies, and distributes this supply of
water.
The water cycle is a continuous movement of water from the
atmosphere to the earth and from the earth back to the
atmosphere.
Four major processes:
1. Evaporation – changes liquid water into water vapor in the
atmosphere.
2. Condensation – the process by which water vapour in air
cools and condenses into droplets of water forming clouds.
3. Precipitation – movement of water from the atmosphere to
the earth.
4. Transpiration – the loss of water from plants due to
evaporation.
Human beings alter the water cycle by withdrawing large
quantities of freshwater faster than it can be replaced and by
clearing the vegetation. We also cover land with buildings and
pavement, which reduces the recharge of aquifers by holding
water above ground and increase runoff, which in turns increases
flooding and soil erosion.
CARBON CYCLE
Role of Carbon
1. Carbon is a major building block in organisms as it is a
component of carbohydrates, fats, proteins, ATP, and nucleic
acids.
2. Carbon forms carbon dioxide (CO2), a component of the
atmosphere which acts as a major storage “bank” for the
recycles carbon in the biosphere.
3. Carbon dioxide enters the plant body as a raw material for
photosynthesis.
4. Carbon is stored in the earth’s crust, in the limestone shells of
marine organisms, and as fossil fuels or deposits of coal, oil,
and natural gas.
Role of Oxygen
1. Oxygen is one of life’s building blocks. About every fourth
atom in the body of an organism is an oxygen atom.
2. Oxygen serves as an acceptor of hydrogen atoms in the
respiration process.
3. Together with hydrogen atoms, oxygen forms water
molecules during respiration.
4. Oxygen enables heterotrophic cells to transform energy
through oxidation of food materials.
Processes involved:
- Photosynthesis – use of CO2 along with water and the sun’s
energy to produce glucose and release O2.
- Respiration – both plants and animals use O2 to breakdown
glucose. The by products are carbon dioxide and water.
- Decomposition – process by which organisms like bacteria
break down the tissues and excretions of other organisms to
simple substances. This process of decay releases carbon
dioxide from the compounds retained in the bodies of
organisms when they die.
Human beings are altering the carbon cycle mostly by adding
large amounts of carbon dioxide to the atmosphere when we
burn carbon-containing fossil fuels and clear carbon-absorbing
vegetation forests (especially tropical forests) faster than it can
grow back.
NITROGEN CYCLE
- Involves green plants and several kinds of bacteria, and may
or may not involve animals.
- the major reservoir for nitrogen is the atmosphere.
Chemically unreactive nitrogen makes up 78% of the volume
of the atmosphere. Nitrogen is crucial component of proteins,
many vitamins, and nucleic acids such
as DNA
(deoxyribonucleic acid ). However, N2 cannot be absorbed
and used directly as a nutrient by plants and animals.
- Two natural processes convert or fix N2 into compounds that
can be used as nutrients – electrical discharges or lightning
taking place in the atmosphere and nitrogen-fixing bacteria.
Processes involved:
1. Ammonification. The process of releasing ammonia (NH3)
from decaying protein by means of bacterial action.
2. Nitrification. The action of a group of bacteria on ammonia,
producing nitrates (NO3).
3. Denitrification. This process is carried out by denitrifying or
anaerobic bacteria which breaks down ammonia, nitrates,
and nitrites (NO2), liberating free nitrogen.
4. Nitrogen Fixation. This refers to the process by which bacteria
in the soil or in the roots or leguminous plants converts free
N2 into compounds that the plants can use.
Human beings have more than doubled the annual release of
nitrogen from the land into the rest of the environment. Most of
this is from the greatly increased use of inorganic fertilizer to
grow crops.
A problem brought about by human input is eutrophication – a
process by which lakes or any freshwater ecosystems slowly
become shallow by the accumulation of dead plant materials. In
such a process, as contaminants are dumped into the body of
water, there is an increased quantity of nitrate or phosphate ions
causing a rapid multiplication of algae population. The condition
in which the algae either cover the water of color it with their
presence is called algal bloom.
Algal bloom increases the number of decomposers which use up
the oxygen needed by other animals as well as other
decomposers. As an effect, the water animals and the
decomposers die, accumulating at the bottom of the body of
water.
PHOSPHORUS CYCLE
The major reservoir for phosphorus is phosphate salts containing
phosphate ions (PO4-3) in terrestrial rock formation and ocean
bottom sediments. The phosphorus cycle is slow as compared to
to other cycles and does not include the atmosphere.
As water runs over exposed phosphorus-containing rocks, it
slowly erodes away inorganic compounds that contain phosphate
ions. The dissolved phosphate can be absorbed by the roots of
plants and by other producers. Phosphorus is transferred by food
webs from producers to consumers, eventually including detritus
feeders and decomposers.
Phosphorus can be lost from the cycle for long periods when it
washes from the land into streams and rivers and is carried to the
ocean. There it can be deposited as marine sediments and remain
trapped for millions of years. Someday, geological processes may
uplift and expose these seafloor deposits from which phospahet
cn be eroded to start the cycle again.
Human activities are affecting the phosphorus cycle which
includes removing large amounts of phosphate from the earth to
make fertilizer and reducing phosphorus in tropical soils by
clearing forests.
Soil that is eroded from fertilized crop fields, lawns, and golf
courses carries large quantities of phosphates into streams, lakes
and oceans where it stimulates the growth of producers.
Phosphorus-rich run-off from the land can produce huge
populations of algae, which can upset chemical cycling and other
processes in lakes.
SULFUR CYCLE
Sulfur enters the atmosphere - as hydrogen sulfide, a colorless
gas, highly poisonous gas with a rotten-egg smell and as sulfur
dioxide, a colorless and suffocating gas. Both gases are released
by volcano. Particles of sulphate enters the atmosphere from sea
spray, dust storms and forest fires. Plant roots absorb sulphate
ions and incorporate sulphur as an essential component of
proteins. Specialized bacteria converts sulphate ions to sulphide
ions. Sulfide ions can react with metal ions to form insoluble
metallic sulfides which are deposited as rocks or metal ores and
the cycle continues.
Human activities have affected the sulfur cycle primarily by
releasing large amounts of sulfur dioxide into the atmosphere.
Ways of adding sulfur dioxide into the atmosphere: Burning of
sulphur-containing coal and oil to
produce electric power.
Refining sulfur-containing petroleum to make gasoline.
Conversion of sulfur-containing metallic mineral ores into free
metals such as copper, lead and zinc.