Biogeochemical cycles (biological, geological and chemical interactions) are nothing but the movement and circulation of soluble inorganic substances (nutrients) derived from soil and atmospheric phases of inorganic substances through organic phase of various biotic components.
Similarly, a return circulation and movement of organic substances takes place in favour of inorganic objects such as soil and atmosphere.
Thus these two systems are supplementary to each other and complete the cycle.
The study of biogeochemical cycles can be approached on two scales e.g.,
(I) cycling of all elements together or
(II) cycling of individual elements e.g., hydrological cycle, carbon cycle, nitrogen cycle, phosphorous cycle, oxygen cycle, sulphur cycle etc.
Besides these cycles, sediment cycles and mineral cycles are also included in the broader biogeochemical cycles.
These natural or biogeochemical cycles functions in a balanced manner which stabilizes biosphere and sustains the life processes on the earth.
The Hydrological Cycle —
This cycle helps in exchange of water between air, land, sea, living plants and animals.
Solar energy is used to drive the hydrological cycle.
Massive evaporation of water from the oceans, cloud formation and rainfall gives us our supply and reserves of fresh water.
At sub-zero temperature, rainwater freezes into snow and in presence of strong wind forms hail.
Water as rain, snow and hail is precipitated on land and water surfaces.
On land surface water seeps into the soil and is stored as ground water.
The natural water level or water table exists below the ground.
The water table is supported by the underlying clay and rock strata.
Ground water does not remain static but moves in various directions.
It moves up through capillary action and reaches soil surfaces where it is drawn by plant roots.
The Nitrogen Cycle —
Nitrogen and its compounds are essential for life processes in the biosphere.
There is continuous exchange of nitrogen within the ecosystem operating the nitrogen cycle.
Proteins produced by plants and animals in their metabolic processes are organic compounds of nitrogen.
The major load of nitrogenous organic residue in soil originates from death and decay of plants and excreta of animals.
These organic residues in soil are taken up by various soil micro-organisms who break down soil nitrate into nitrogen by denitrification process while others transform nitrogen into soluble nitrogen compounds.
The Carbon Cycle —
The carbon cycle is a very important chemical cycle.
The atmosphere is the minor reservoir of carbon.
Hydrosphere is the major reservoir which contains approximately 50 times more as that of atmosphere.
It is stored as bicarbonate mineral deposit on the ocean floor.
The later regulates the carbon dioxide level in the atmosphere.
The cycle operates in the form of carbon dioxide exchanging among the atmosphere, biosphere and the oceans.