Biogeochemical Cycle : 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.

These elements cycle in either a gas cycle or a sedimentary cycle; some cycle as both a gas and sediment.

In a gas cycle elements move through the atmosphere. Main reservoirs are the atmosphere and the ocean.

In a sedimentary cycle elements move from land to water to sediment. Main reservoirs are the soil and sedimentary rocks.  

    CARBON CYCLE                               

                                

                      Image above obtained from  http://www.cotf.edu/ete/modules/carbon/earthfire.html  

            Facts:

                - 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

               Amount of CO2 during the year:               - Every year there is a measurable difference in the                 concentration of atmospheric CO2 in phase with the seasons.                 For example, in winter there is almost no photosynthesis                 therefore there is a high concentration of CO2.                 - During the growing season there is a measurable differnece in the                 concentration of atmospheric CO2  over parts of each day. For                 example, at sunrise photosynthesis begins with the uptake of CO2,                 by afternoon plant respiration increases, at sunset photosynthesis                 stops so the concentration of CO2 in the atmosphere increases.

              Human induced changes in the global carbon cycle:                - The Earth is getting warmer.                 - The 20th century has been the warmest in the last 600 years.                 - This century is about 1 degree Fahrenheit warmer than last                 century.                 - The balance of evidence suggests that burning of fossil fuel                 (eg. coal, oil, natural gas), which emits CO2 as a waste, is the                  cause.                 - CO2 is a "Green House" gas - it traps heat at the Earth's surface.                 (H2O vapor and methane are also examples of green house gases)

            Signs that the climate is warming:                 - Plants start blooming 8 days earlier in spring than 11 years ago.                 - Birds from the United Kingom lay eggs earlier.                 - Buds on trees appear earlier and leaves fall later in the Northern                   Hemisphere.                 - Alaska, North West Canada, and Siberia have warmed up as                   much as 5 degrees Fahrenheit in the last 30 years.  

NITROGEN CYCLE                              

                            

                         Image obtained from http://muextension.missouri.edu/xplor/waterq/wq0252.htm  

                     Facts:

                - Nitrogen (N) is an essential constituent of protein, DNA,                 RNA, and chlorophyll.                      - N is the most abundant gas in the atmosphere, but it must                 be fixed or converted into a usable form.

             Nitrogen Fixation Methods:

                   1) High energy fixation- a small amount of atmospheric                 nitrogen is fixed by lightening. The high energy combines N and                 H2O resulting in ammonia (NH3) and nitrates (NO3). These forms                 are carried to Earth in precipitation.                          2) Biological fixation: achieves 90% of the nitrogen                 fixation. Atmospheric nitrogen (N2) is split and combined with                 hydrogen (H) atoms to form ammonia (NH3).

            Who performs nitrogen fixation?

               - symbiotic bacteria (eg. Rhizobium spp.) living in association                 with leguminous ( plants in the pea family), and root-noduled non-                 leguminous plants (eg. Alnus spp.).                    - free-living anaerobic bacteria                    - blue-green algae (cyanobacteria)

               Once NH3 is in the soil it combines with H+ ions to form                 ammonium ion (NH4), or without it to form NO3. NH4+ and                 NO3 are readily absorbed by plants.

   OXYGEN CYCLE                                           

                                         Image obtained from http://www.accessexcellence.com/AB/GG/photo_Resp.html    

                  Facts:

           Sources of Oxygen:

                     1) photodisassociation of H2O vapor                             2) photosynthesis

                   Since oxygen is so reactive its cycling is complex:

                     1) As a constituent of CO2 it circulates freely                     throughout the biosphere.                             2) Some CO2 combines with Ca to form carbonates.                             3) O2 combines with nitrogen compounds to form                     nitrates.                             4) O2 combines with iron compounds to form ferric                     oxides.                             5) Photosynthesis and respiration                             6) O2 in the troposphere is reduced to O3 (ozone).                     Ground level O3 is a pollutant which damages lungs.  

PHOSPHORUS CYCLE                         

                  

                    Image obtained from http://www.bsi.vt.edu/chagedor/biol_4684/Cycles/Pcycle.html  

     Facts:

      - Component of DNA, RNA, ATP, proteins and enzymes         - Cycles in a sedimentary cylce         - A good example of how a mineral element becomes part of an            organism.         - The source of Phosphorus (P) is rock.         - It is released into the cylce through erosion or mining.         - It is soluble in H2O as phosphate (PO4)         - It is taken up by plant roots, then travels through food chains.         - It is returned to sediment

SULFUR CYCLE                                         

                         

          Image obtained from http://www.agnr.umd.edu/users/agron/nutrient/Factshee/sulfur/Sulfur.html

   

                Facts:

              - Component of protein                 - Cycles in both a gas and sedimentary 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                    eruprtions, gas exchange at ocean surfaces, and                    decomposition.                 - H2S is immediately oxidized to sulfur dioxide (SO2)                 - SO2 and water vapor makes H2SO4 ( a weak sulfuric acid),                   which is then carried to Earth in rainfall.                 - 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.

Biogeochemical Cycles

There are a few types of atoms that can be a part of a plant one day, an animal the next day, and then travel downstream as a part of a river’s water the following day. These atoms can be a part of both living things like plants and animals, as well as non-living things like water, air, and even rocks. The same atoms are recycled over and over in different parts of the Earth. This type of cycle of atoms between living and non-living things is known as a biogeochemical cycle.

All of the atoms that are building blocks of living things are a part of biogeochemical cycles. The

most common of these are carbon and nitrogen.

The carbon cycle The nitrogen cycle

Tiny atoms of carbon and nitrogen have no legs to walk, no bicycles, cars, or airplanes. Yet they can travel around the world as a part of biogeochemical cycles. So, how do these little things move around the planet? Here’s an example: An atom of carbon is absorbed from the air into the ocean water where it is used by little floating plankton doing photosynthesis to get the nutrition they need. There is the possibility that this little carbon atom becomes part of the plankton’s skeleton, or a part of the skeleton of the larger animal that eats it, and then part of a sedimentary rock when the living things die and only bones are left behind. Carbon that is a part of rocks and fossil fuels like oil, coal, and natural gas may be held away from the rest of the carbon cycle for a long time. These long-term storage places are called “sinks”. When fossil fuels are burned, carbon that had been underground is sent into the air as carbon dioxide, a greenhouse gas.

Recently, people have been causing these biogeochemical cycles to change (see links below). When we cut down forests, make more factories, and drive more cars that burn fossil fuels, the way that carbon and nitrogen move around the Earth changes. These changes add more greenhouse gases in our atmosphere and this causes more global warming.

The carbon cycle, one of Earth's biogeochemical cycles NCAR

The Carbon Cycle

Carbon is an element. It is part of oceans, air, rocks, soil and all living things. Carbon doesn’t stay in one place. It is always on the move!

Carbon moves from the atmosphere to plants.In the atmosphere, carbon is attached to oxygen in a gas called carbon dioxide (CO2). With the help of the Sun, through the process of photosynthesis, carbon dioxide is pulled from the

air to make plant food from carbon. Carbon moves from plants to animals.

Through food chains, the carbon that is in plants moves to the animals that eat them. Animals that eat other animals get the carbon from their food too.

Carbon moves from plants and animals to the ground.When plants and animals die, their bodies, wood and leaves decay bringing the carbon into the ground. Some becomes buried miles underground and will become fossil fuels in millions and millions of years.

Carbon moves from living things to the atmosphere.Each time you exhale, you are releasing carbon dioxide gas (CO2) into the atmosphere. Animals and plants get rid of carbon dioxide gas through a process called respiration.

This drawing shows the carbon cycle.Click on image for full size version (191K JPG)

Carbon moves from fossil fuels to the atmosphere when fuels are burned.When humans burn fossil fuels to power factories, power plants, cars and trucks, most of the carbon quickly enters the atmosphere as carbon dioxide gas. Each year, five and a half billion tons of carbon is released .

Play the Carbon Cycle Game!

Changing the Nitrogen Cycle, Changing the Planet

The Nitrogen Cycle

Nitrogen is an element. It is found in living things like plants and animals. It is also an important part of non-living things like the air above and the dirt below. Atoms of nitrogen don't just stay in one place. They move slowly between living things, dead things, the air, soil and water. These movements are called the nitrogen cycle.

Most of the nitrogen on Earth is in the atmosphere. Approximately 80% of the molecules in Earth's atmosphere are made of two nitrogen atoms bonded together (N2). All plants and animals need nitrogen to make amino acids, proteins and DNA, but the nitrogen in the atmosphere is not in a

form that they can use. The molecules of nitrogen in the atmosphere can become usable for living things when they are broken apart during lightning strikes or fires, by certain types of bacteria, or by bacteria associated with bean plants.

The illustration above shows how nitrogen travels through the living and non-living parts of the Earth system. Click on image for full size (190 Kb)NCAR

Most plants get the nitrogen they need to grow from the soils or water in which they live. Animals get the nitrogen they need by eating plants or other animals that contain nitrogen. When organisms die, their bodies decompose bringing the nitrogen into soil on land or into ocean water. Bacteria alter the nitrogen into a form that plants are able to use. Other types of bacteria are able to change nitrogen dissolved in waterways into a form that allows it to return to the atmosphere.

Certain actions of humans are causing changes to the nitrogen cycle and the amount of nitrogen that is stored in the land, water, air, and organisms. The use of nitrogen-rich fertilizers can add too much nitrogen in nearby waterways as the fertilizer washes into streams and ponds. The waste associated with livestock farming also adds large amounts of nitrogen into soil and water. The increased nitrate levels cause plants to grow rapidly until they use up the supply and die. The number of plant-eating animals will increase when the plant supply increases and then the animals are left without any food when the plants die.

Biogeochemical Cycles

The Earth is a closed system for matter, except for small amounts of cosmic debris that enter the Earth's atmosphere. 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.

Many elements cycle through ecosystems, organisms, air, water, and soil. Many of these are trace elements. Other elements, including carbon, nitrogen, oxygen, hydrogen, sulfur, and phosphorus are critical components of all biological life. 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 storage places, where elements may reside for short or long periods of time. Each of the chemical, biological, and geological processes varies in their rates of cycling. Some molecules may cycle very quickly depending on the pathway. Carbon atoms in deep ocean sediments may take hundreds to millions of years to cycle completely through the system. An average water molecule resides in the atmosphere for about ten days, although it may be transported many miles before it falls back to the Earth as rain.

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.

Phosphorous has no gaseous phase and is relatively unreactive, so it moves very slowly through its cycle. Phosphorus is stored in large amounts in sediment in the oceans or in the Earth's crust and is recycled back to the surface only over very long periods of time through upwelling of ocean waters or weathering of rocks.

Biogeochemical cycles are subject to disturbance by human activities. Humans accelerate natural biogeochemical cycles when elements are extracted from their reservoirs, or sources, and deposited back into the environment (sinks). For example, humans have significantly altered the carbon cycle by extracting and combusting billions of tons of hydrocarbons in fossil that were buried deep in the Earth's crust, in addition to clearing vegetation that stores carbon. Global release of carbon through human activities has increased from 1 billion tons per year in 1940 to 6.5 billion tons per year in 2000. About half of this extra carbon is taken up by plants and the oceans, while the other half remains in the atmosphere.

In addition to carbon cycle, humans have altered the nitrogen and phosphorus cycles by adding these elements to croplands as fertilizers, which has contributed to over-fertilization of aquatic ecosystems when excess amounts are carried by runoff into local waterways.

Researchers are trying to understand all of the various pathways and flows of each of the biogeochemical cycles in order to understand how human activities affect these cycles. While many important processes have been understood for more than century, there are many phenomena that scientists are just beginning to investigate. Satellite technology, among other tools, has revealed new information about interactions between the oceans and atmosphere that contribute to knowledge about the carbon cycle, but there remain many unanswered questions.

Global Biogeochemical Cycles and the Physical Climate System This module, written by Fred T. Mackenzie of the University of Hawaii, is a part of the Global Change Instruction Program. Presented by the University Corporation for Atmospheric Research, this module describes biogeochemical cycles and their role in climate.

Life and Biogeochemical Cycles This article, part of the California State University Monteray Bay's Ecosystem Service's website, offers an overview of biogeochemical cycles and highlights their relationship to climate, agricultural productivity, and acid precipitation.

Utah Education Network: Cycles The UT Education Network Themepark website includes a section on biogeochemical cycles. The cycles page includes links to information on various cycles, including water, energy, seasonal, planetary cycles and animal and plant lifecycles. Each cycle page

provides a list of online resources for additional information as well as links to teacher resources.