64 Ecology and Applied Environmental Science
ecosystems, as well as energy flow, are phenomena that may be associated
with pollution, e.g. toxic substance concentration in food chains.
4.3.1 Water Cycle
Water is the inorganic compound present in the greatest proportion within
the living matter. Water percentage fluctuates from around 10% in plant
seeds to 98% in some aquatic animals, whereas it is about 63% in the
human body. The significance of water for life is evident by the fact that the
biomass of each terrestrial ecosystem is almost proportional to the volume
of rainfall in that area.
Water is present in the biosphere (atmosphere, hydrosphere, lithosphere) in
three phases (solid, liquid, gaseous). Its distribution, however, is very unequal.
If the water present in oceans could be uniformly spread upon the Earth’s
surface, a layer with a thickness of 2.7 kilometres would be created. If the
same happened for the water of the glaciers, the layer would have a thickness
of about 100 meters, whereas with underground fresh water the thickness
would be 15 meters, for surface fresh water it would be 40 centimetres, and
with the water-vapour present in the atmosphere only 3 centimetres.
The greatest part of the water cycle is realised between the sea and the
atmosphere. Vapours liquefy in the clouds and descend on the Earth’s surface in the form of rain, snow, hail, dew or frost. Water reaching land surface can follow three paths: penetration in the ground, evapotranspiration
or surface flow. In the first case the containment and storage of water is
ensured; vegetation and the soil’s organic matter play a significant role in
this process. In the second case, the water returns swiftly to the atmosphere,
either through direct evaporation or through plant transpiration; plants
accelerate to a great degree the return of the water to the atmosphere, since
they absorb important water quantities through their roots and discard
them into the atmosphere through their leaves. The third case is favoured
by vegetation deficiency and constitutes the main factor of ground erosion.
Ultimately, a large part of terrestrial waters end up in the oceans through
surface or underground flow. Evaporation from the ocean’s surface is the
most important path water follows in order to return to the atmosphere.
4.3.2 Carbon Cycle
4.3.2.1 Main Features of the Cycle
Carbon, life’s primary element, forms the most perfect of all biogeochemical cycles and circulates with a relatively rapid velocity in biocoenosis
through food chains. The most essential inorganic forms of carbon presence in nature are carbon dioxide (CO 2 ) and calcium carbonate (CaCO 3 ).
The part of carbon that is naturally circulating in the biosphere goes
ecosystems, as well as energy flow, are phenomena that may be associated
with pollution, e.g. toxic substance concentration in food chains.
4.3.1 Water Cycle
Water is the inorganic compound present in the greatest proportion within
the living matter. Water percentage fluctuates from around 10% in plant
seeds to 98% in some aquatic animals, whereas it is about 63% in the
human body. The significance of water for life is evident by the fact that the
biomass of each terrestrial ecosystem is almost proportional to the volume
of rainfall in that area.
Water is present in the biosphere (atmosphere, hydrosphere, lithosphere) in
three phases (solid, liquid, gaseous). Its distribution, however, is very unequal.
If the water present in oceans could be uniformly spread upon the Earth’s
surface, a layer with a thickness of 2.7 kilometres would be created. If the
same happened for the water of the glaciers, the layer would have a thickness
of about 100 meters, whereas with underground fresh water the thickness
would be 15 meters, for surface fresh water it would be 40 centimetres, and
with the water-vapour present in the atmosphere only 3 centimetres.
The greatest part of the water cycle is realised between the sea and the
atmosphere. Vapours liquefy in the clouds and descend on the Earth’s surface in the form of rain, snow, hail, dew or frost. Water reaching land surface can follow three paths: penetration in the ground, evapotranspiration
or surface flow. In the first case the containment and storage of water is
ensured; vegetation and the soil’s organic matter play a significant role in
this process. In the second case, the water returns swiftly to the atmosphere,
either through direct evaporation or through plant transpiration; plants
accelerate to a great degree the return of the water to the atmosphere, since
they absorb important water quantities through their roots and discard
them into the atmosphere through their leaves. The third case is favoured
by vegetation deficiency and constitutes the main factor of ground erosion.
Ultimately, a large part of terrestrial waters end up in the oceans through
surface or underground flow. Evaporation from the ocean’s surface is the
most important path water follows in order to return to the atmosphere.
4.3.2 Carbon Cycle
4.3.2.1 Main Features of the Cycle
Carbon, life’s primary element, forms the most perfect of all biogeochemical cycles and circulates with a relatively rapid velocity in biocoenosis
through food chains. The most essential inorganic forms of carbon presence in nature are carbon dioxide (CO 2 ) and calcium carbonate (CaCO 3 ).
The part of carbon that is naturally circulating in the biosphere goes