Biogeochemical Cycles
States of Matter > Our Environment
Biogeochemical cycle Biogeochemical cycle In ecology and Earth science, a biogeochemical cycle or nutrient cycle is a pathway by which a chemical element or molecule moves through both biotic (biosphere) and abiotic (lithosphere, atmosphere, and hydrosphere) compartments of Earth.

A cycle is a series of change which comes back to the starting point and which can be repeated. The term “biogeochemical” tells us that biological, geological and chemical factors are all involved. natural cycles are

  • The hydrological cycle (water cycle)
  • The oxygen cycle
  • The carbon cycle
  • The nitrogen cycle.
Water cycle Water cycle The water cycle (also known as the hydrological cycle) is the journey, water takes as it circulates from the land to the sky and back again. Water vapor condenses into millions of tiny droplets that form clouds. Clouds lose their water as rain or snow, which is called precipitation. Precipitation is either absorbed into the ground or runs off into rivers. Water that was absorbed into the ground is taken up by plants. Plants lose water from their surfaces as vapor back into the atmosphere. Water that runs off into rivers flows into ponds, lakes, or oceans where it evaporates back into the atmosphere and the cycle continues.

Water cycle:
The water cycle, also known as the hydrological cycle or H2O cycle, describes the continuous movement of water on, above and below the surface of the Earth. Water can change states among liquid, vapor and solid at various places in the water cycle.

Water never really goes away, it just changes form. The Sun drives the entire water cycle and is responsible for its two major components: condensation and evaporation. When the Sun heats the surface of water, it evaporates and ends up in the atmosphere as water vapor. It cools and rises, becoming clouds, which eventually condense into water droplets. Depending on the temperature of the atmosphere and other conditions, the water precipitates as rain, sleet, hail or snow.
Some of this precipitation is captured by tree canopies and evaporates again into the atmosphere. The precipitation that hits the ground becomes runoff, which can accumulate and freeze into snow caps or glaciers. It can also infiltrate the ground and accumulate, eventually storing in aquifers. An aquifer is a large deposit of groundwater that can be extracted and used. This runoff also comes from snowmelt, which occurs when the Sun and climate changes melt snow and ice. Finally, some of this runoff makes it a way back into lakes and oceans, where it is again evaporated by the Sun.

Water that falls to the ground and stays in the soil ends up evaporating and retiring to the atmosphere. But groundwater, which is the major source of our drinking water, can accumulate in aquifers over thousands of years. Unconfined aquifers have the water table or the surface where water pressure equals atmospheric pressure, as their upper boundaries. Confined aquifers often lie below unconfined aquifers and have a layer of rock or other materials as their upper boundaries.

Oxygen cycle Oxygen cycle Oxygen cycle is the process by which oxygen is released into the atmosphere by photosynthetic organisms which is taken up by the aerobic organisms while the carbon dioxide released as a by–product of respiration is taken up for photosynthesis.

Oxygen cycle:
The oxygen cycle is the biogeochemical cycle that describes the movement of oxygen within its three main reservoirs: the atmosphere (air), the total content of biological matter within the biosphere (the global sum of all ecosystems) and the lithosphere (Earth's crust).
The main driving factor of the oxygen cycle is photosynthesis, which is responsible for the modern Earth's atmosphere and life. The main source of atmospheric oxygen is photosynthesis, which produces sugars and oxygen from carbon dioxide and water

Photosynthesizing organism Photosynthesizing organism Cyanobacterium prochlorococcus is the photosynthesizing microorganisms that use light (radiant energy) as the energy for its life processes.

Photosynthesizing organisms include the plant life of the land areas as well as the phytoplankton of the oceans. The tiny marine cyanobacterium prochlorococcus was discovered in 1986 and accounts for more than half of the photosynthesis of the open ocean. An additional source of atmospheric oxygen comes from, whereby high energy ultraviolet radiation breaks down atmospheric water and nitrous oxide into component atoms. The free ‘H’ and ‘N’ atoms escape into space leaving O2 in the atmosphere:

The main way oxygen is lost from the atmosphere is via respiration and decay, mechanisms in which animal life and bacteria consume oxygen and release carbon dioxide, because the lithosphere consumes oxygen. An example of surface weathering chemistry is formation of iron–oxides (rust):

Carbon cycle Carbon cycle

Carbon cycle:
The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere and atmosphere of the Earth. It is one of the most important cycles of the Earth and allows for carbon to be recycled and reused throughout the biosphere and all of its organisms. The carbon cycle was initially discovered by Joseph Priestley and Antoine Lavoisier and popularized by Humphrey Davy. It is now usually thought of as including the following major reservoirs of carbon interconnected by pathways of exchange:

  • The atmosphere
  • The terrestrial biosphere, which is usually defined to include fresh water systems and non–living organic material, such as soil carbon.
  • The oceans, including dissolved inorganic carbon and living and non–living marine biota.
  • The sediments including fossil fuels.
  • The Earth's interior, carbon from the Earth's mantle and crust is released to the atmosphere and hydrosphere by volcanoes and geothermal systems.

The annual movements of carbon, the carbon exchanges between reservoirs, occur because of various chemical, physical, geological and biological processes. The ocean contains the largest active pool of carbon near the surface of the Earth, but the deep ocean part of this pool does not rapidly exchange with the atmosphere in the absence of an external influence, such as a black smoker or an uncontrolled deep–water oil well leak.

Nitrogen cycle Nitrogen cycle Nitrogen cycling is an extremely important natural process, in which nitrogen–containing species such as ammonia, nitrate and nitrite are absorbed into the soil, atmosphere or the ocean and are used by many living organisms to produce amino acids and proteins or other volatile gases. This movement of nitrogen between living organisms, soil, water and atmosphere is a crucial part of crop production on Earth.

Nitrogen cycle:
Nitrogen cycle, the series of natural processes by which certain nitrogen–containing substances from air and soil are made useful to living things, are used by them and are returned to the air and soil. All living things must have nitrogen to build proteins. Because of the chemical nature of nitrogen gas, however, they cannot obtain that element directly from the air. Instead, food–making organisms such as plants obtain it from the soil by absorbing nitrates (various nitrogen compounds containing oxygen) and ammonium compounds (various nitrogen compounds containing hydrogen). The nitrogen cycle is essential to plants in unfertilized soils because in such soils the nitrogen compounds are not available to the plants in any other way.
Animals and other living things that do not make their food, depend on the nitrogen cycle indirectly. Most animals, for example, eat plants or eat plant–eating animals. The nitrogen cycle consists of four natural processes: nitrogen fixation, nitrification, denitrification, and decay.

Nitrogen fixation:
Nitrogen fixation is the process in which nitrogen gas from the air is continuously made into nitrogen compounds. These compounds (primarily nitrates and ammonium compounds) are made by nitrogen–fixing microorganisms in the soil and by lightning.

Nitrification:
Nitrification is the process in which ammonia in the soil is converted to nitrates. Nitrification is performed by nitrifying bacteria. Plants absorb the nitrates and use them to make proteins.

Denitrification:
Denitrification is the reverse of the combined processes of nitrogen fixation and nitrification. It is the process by which nitrogen compounds, through the action of certain bacteria, give up nitrogen gas that then becomes part of the atmosphere. The amount of gas released by this process is relatively small.

The Ogallala Aquifer occupies the High Plains of the United States, extending northward from western Texas to South Dakota. The Ogallala is an unconfined aquifer and virtually all recharge comes from rainwater and snowmelt. As the High Plains has a semi–arid climate, recharge is minimal. Recharge varies by amount of precipitation, soil type, and vegetation cover and averages less than 25 millimeters (1 inch) annually for the region as a whole.

Decay processes:
Decay processes are those by which the organic nitrogen compounds of dead organisms and waste material are returned to the soil. These compounds are chiefly proteins and urea. The many bacteria and fungi causing decay convert them to ammonia and ammonium compounds in the soil. Thus, through the nitrogen cycle, food–making organisms obtain the necessary nitrogen through nitrogen fixation and (to a greater extent) through nitrification. At the same time, nitrogen compounds are returned to the soil through decay and nitrogen is returned to the air through denitrification. In soils, in which many plants are raised and few are left to decay (as in farm soils), the nitrogen cycle does not supply enough nitrogen to support plant growth. In these soils natural or artificial fertilizers, containing nitrates or ammonium compounds, are needed.

MORE INFO