week9+10 chapter 3 : biogeochemical cycles dr. mohammed ajjour university of palestine 2009,

Week9+10 Chapter 3 : Biogeochemical Cycles

Dr. Mohammed Ajjour University Of Palestine

2009,

Biogeochemical Cycles The Earth is a closed system for matter, This means that all

the elements needed for the structure and chemical processes of life come from the elements that were present in the Earth's crust when it was formed billions of years ago. This matter, the building blocks of life, 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. University Of Palestine 2009, Dr. Mohammed Ajjour

Biogeochemical Cycles Together, oxygen and carbon account for 80 percent of the

weight of human beings. Because these elements are key components of life, they must be available for biological processes. Carbon, however, is relatively rare in the Earth's crust, and nitrogen, though abundant in the atmosphere, is in a form that is not useable by living organisms. The biogeochemical cycles transport and store these important elements so that they can be used by living organisms. Each cycle takes many different pathways and has various reservoirs, or pools (storage places, where elements may reside for long or short periods of time. Un)iversity Of Palestine 2009, Dr. Mohammed Ajjour

Biogeochemical Cycles How fast substances cycle depends on its chemical reactivity

and whether or not it can be found in a gaseous state. A gaseous phase allows molecules to be transported quickly.

BGC cycles are subject to disturbance by human activities when elements are extracted from their reservoirs, or sources, and deposited back into the environment (sinks). Exam: humans have altered the carbon cycle by extracting billions of tons of fossil oil that were buried deep in the Earth's crust, in addition to clearing vegetation that stores carbon. Uni(versity Of Palestine 2009, Dr. Mohammed

Ajjour

The hydrological Cycle with the evaporation of water from

the surface of oceans, moist air is lifted, it cools and water vapor condenses to form clouds. Moisture is transported around the globe until it returns as precipitation. Once the water reaches the ground, one of two processes may occur; 1) some of the water may evaporate back into the atmosphere or 2) the water may penetrate the

University Of Palestine 2009, Dr. Mohammed Ajjour

The hydrological Cycle

surface and become groundwater .Groundwater either seeps its way to into the oceans, rivers, and streams (runoff ), or infiltrate soils before it is released back into the atmosphere through pumping , irrigation and transpiration. The water that remains on the earth's surface is carried back to the oceans, where the cycle begins again. Some precipitation falls as snow and can accumulate as ice for thousands of years.


Carbon Cycle carbon is a part of seawater, rocks , such

as limestone ,the atmosphere, coal, soils, as well as all living things.

In the atmosphere carbon is attached to oxygen in carbon dioxide (co2).

Through the process of photosynthesis carbon dioxide is pulled from the air to produce food (plant tissues)

Through food chains, the carbon that is in plants moves to the animals that eat them.


Carbon Cycle When plants and animals die, their bodies, wood and leaves decays bringing the

carbon into the ground. Some is buried and will become fossil fuels in millions and millions of years.

Each time you exhale, you are releasing carbon dioxide into the atmosphere. Animals and plants need to get rid of CO2 gas through a process called respiration.

When humans burn fossil fuels to power factories, cars , ... most of the carbon quickly enters the atmosphere as carbon dioxide gas. Each year, 5.5 billion tons of carbon is released Of this massive amount, 3.3 billion tons stays in the atmosphere.

The oceans, and other bodies of water, absorb most of the carbon from the atmosphere. The carbon is dissolved into the water and stored into shells and rocks


Carbon Cycle many aquatic animals use CO2 and calcium to make shells of

calcium carbonate (CaCO3);The shells CaCO3 accumulates in mass as sediment on the ocean floor. In time the buried sediment undergoes compaction and cementation to form limestone. Perhaps millennia later to be released back into the atmosphere by the plate tectonic cycle by means of volcanic activity.

Carbon also plays a major role in the temperature on Earth. As more CO2 is released from storage areas such as: plant material, fossil fuels, and geologic process (volcanoes), more of the Sun’s energy is reflected back and forth between the surface and the atmosphere of Earth. This increased reflection and absorption of energy affects Earth, likely increasing its temperature.


Nitrogen Cycle Nitrogen comprises 78 % of the

atmosphere . It is important for the formation of organic matter like proteins. It is inaccessible to most plants and must be first “fixed”. There are four ways to convert N2 into more chemically reactive forms. 1.Biological fixation: symbiotic species( Rhizobium which live inlegume root nodules), And some free-living bacteria(Azotobacter) are able to fix nitrogen as organic nitrogen.

University Of Palestne 2009, Dr. Mohammed Ajjour

Nitrogen Cycle2.Industrial N-fixation : Under great pressure, and high temp.

atmospheric nitrogen and hydrogen (usually derived from petroleum) can be combined to form ammonia (NH3) which is used to make fertilizer and explosives. .

3.Combustion of fossil fuels : automobile engines and thermal power plants, which release various nitrogen oxides (3NOx).

4.Other processes : the formation of NO from N2 and O2 due to photons and especially lightning, are important for atmospheric chemistry,


Nitrogen Cycle Organisms that feed on the plants ingest the nitrogen and

release it in organic wastes. Denitrifying bacteria frees the nitrogen from the wastes returning it to the atmosphere

through creation of chemical fertilizers, and pollution by vehicles and industrial plants, human beings have more than doubled the annual transfer of nitrogen into biologically available forms. In addition, humans have significantly contributed to the transfer of nitrogen trace gases from earth to the atmosphere , and from the land to aquatic systems. versity Of Palestine 2009, Dr. Mohammed Ajjour

Nitrogen Cycle N2O (nitrous oxide) has risen in the atmosphere as a

result of agricultural fertilization, biomass burning, cattle and other industrial sources. N2O in the atmosphere is a greenhouse gas, currently the third largest contributor to global warming, after carbon dioxide and methane.

Ammonia (NH3) in the atmosphere has tripled as the result of human activities. It is a reactant in the atmosphere, where it acts as an aerosol, decreasing air quality and clinging on to water droplets, eventually resulting in acid rain.


Phosphorous cycle Phosphorus is an important

element for all forms of life. As phosphate (PO4), it is a component of DNA and RNA . Phosphates are also component of ATP – the energy carrier . in the human body, 80% of phosphorous is found in teeth and bones. The phosphorus cycle differs from the other major cycles in that it does not include a gas phase The largest reservoir of phosphorus is in sedimentary rock.


With rain, phosphates are removed from the rocks (via weathering) and are distributed throughout soils and water.

Plants take up the phosphate ions from the soil. It then moves from plants to animals when herbivores eat plants and carnivores eat plants or herbivores.

phosphates absorbed by animal returns to the soil through the excretion of urine and feces, as well as from the final decomposition of plants and animals after death.

Phosphates also enter waterways through fertilizer runoff, sewage seepage, and wastes from other industrial processes. phosphates tend to settle on ocean floors where they are made available to aquatic organisms . Water plants take up the waterborne phosphate which then travels up through successive stages of the aquatic food chain.


Phosphorous cycle

in surface waters an excessive concentration of phosphorus is considered a pollutant. Phosphate stimulates the growth of plankton and plants, Excess growth of these plants tend to consume large amounts of dissolved oxygen, potentially suffocating fish and other marine animals, while also blocking available sunlight to bottom dwelling species. This is known as eutrophication.

Humans can alter the phosphorus cycle in many ways, including in the cutting of tropical rain forests and through the use of agricultural fertilizers.


Phosphorous cycle

week9+10 chapter 3 : biogeochemical cycles dr. mohammed ajjour university of palestine 2009,

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