Bioenergetics is the study of flow of energy into biosphere, absorption by producers and transformation in living beings. Fusion of about 4 million tonnes of hydrogen/sec in sun is the source of energy on this planet.
Only 47% solar radiations reach the surface of earth (53% are reflected or absorbed by clouds, dust particles etc.) This energy controls atmospheric temperature, soil temperature, seasons (angle of radiations), climatic zones, air currents, formation of water vapors, etc. Energy is ultimately dissipated.
Cycles of Matter/Biogeochemical Cycles/Recycling of Materials :
They are exchanges/circulation of biogenetic nutrients between living and non-living components of biosphere.
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Biogenetic Nutrients/ Biogeochemical:
They are essential elements required by organisms for their body building and metabolism which are provided by earth and return to the earth after their death and decay.
It is the reservoir of biogenetic nutrients from which the latter are slowly transferred to cycling pool, e.g. phosphates.
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Pool of biologenetic nutrients which is being emptied and filled repeatedly by exchange between biotic and abiotic components of biosphere.
Here the materials involved in circulation between biotic and abiotic components of biosphere are gases or vapor and the reservoir pool is atmosphere or hydrosphere, e.g. Carbon, Hydrogen, Oxygen, Nitrogen, and Water.
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Sedimentary Cycles of Matter :
Materials involved in circulation between biotic and abiotic components of biosphere are nongaseous and the reservoir pool is lithosphere, e.g. Phosphorus, Calcium, Magnesium, Sculpture has both sedimentary and gaseous phases. Gaseous cycles are rapid and more perfect as compared to sedimentary cycles.
Carbon occurs as CO2 in atmosphere (6 x 1014 kg); bicarbonate, carbonic acid in hydrosphere (1.3 – 5.0 x 1015 kg) and in lithosphere (1.8 x 1021 kg) as carbonate, graphite, shells, skeletatis, fossil fuels (coal, petroleum and natural gas). Carbon dioxide is being constantly added to the atmosphere through two types of processes:
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Respiration and decomposition release CO2. Methane is also produced during decomposition in rice fields, marshes and by ruminants. In atmosphere, methane is oxidized to CO2.
Burning of biomass and fossil fuel release a lot of C02. Burning of fossil fuels adds 6 x 1012 kg of carbon (as carbon dioxide) into atmosphere. 73% of it is produced by industrializations. Other sources are weathering of carbonate rocks, hot springs and volcanic eruptions. Photosynthesis fixes some 7 x 1013 kg of carbon. It releases oxygen (about 9 x 1013 kg). One hectare of good forests picks up 30,000 kg of CO2/8000 kg of carbon and releases 10,000 kg of oxygen annually. Small quantity of CO2 is taken out of cycling pool through fossilization, formation and sedimentation of carbonates, precipitation by plants and carbonaceous shells, skeletons etc.
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(B) Oxygen Cycle:
Oxygen occurs as free gas (20.99%) in atmosphere, dissolved in water, as component of CO2, nitrogen oxides, water, sulphate, phosphate and a number of other chemicals in the lithosphere:
(i) Consumption of Oxygen:
Oxygen is consumed in respiration, combustion and chemical oxidations.
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(ii) Liberation of Oxygen:
Major sources of oxygen liberation are photosynthesis. Photo dissociation liberates oxygen from water at higher altitudes. Decomposition and many chemical reactions also liberate oxygen.
(C) Nitrogen Cycle:
78.03% of the atmosphere consists of nitrogen. Some is being added to it through volcanic eruptions, erosion of sedimentary rocks and gentrification. Plants obtain nitrogen as nitrate (occasionally ammonia) which is available only in certain rocks. Atmospheric nitrogen (N2) is not utilized. At one time only al small amount of utilizable nitrogen is present in the soil and water bodies.
Therefore, nitrogen is a critical element. Besides very small amount of dissolution from weathering rocks, nitrogen compounds are formed through nitrogen fixation of three types:
(i) Atmospheric Nitrogen Fixation:
With the help of lightning (electro-chemical) and high energy radiations (photochemical reactions), a small quantity of nitrogen combines with oxygen to form nitrogen oxides that are washed down with rain water. Annual fixation is 35 mg/m2/yr.
(ii) Biological Nitrogen Fixation:
Free living bacteria (e.g. Azotobacter, Clostridium) symbiotic bacteria (e.g. Rhizobium, Frankia), free living cyanobacteria (e.g. Aulosira, Tolypothrise, Nostoc, Anabaena) and symbiotic cyanobacteria (e.g. Anabaena species) convert N2 into ammonia which combines with organic acids to produce amino-acids. Annual fixation is 140-700 mg/m2/yr, 175 million tonnes, 70% of the total supply.
(iii) Industrial Nitrogen Fixation:
Ammonia is produced industrially (N2 + 3H2 -» 2NH3). It is also converted to urea. Nitrate/ammonia is absorbed by plants, changed to ammonia, amino acids, proteins, nucleotides etc. Animals obtain their requirement of organic nitrogen from plants Animal excretions, dead bodies of plants and animals are acted upon by decomposers or ‘ammonifying bacteria’ (e.g. Bacillus vulgarism, B. ramous) to liberate ammonia. Ammonia is 1 changed to nitrite by nitrite bacteria (e.g. Nitrosamines, Micrococcus) which are then oxidized to nitrate by nitrate bacteria. There are some bacteria which reduce nitrates and change them into free nitrogen. They are called ‘denitrifying bacteria’ (e.g. Thiobacillus denitrificans, Pseudomonas denitrificans).
Phosphorus is a critical element. It occurs in nucleic acid, nucleotides including ATP, bones, teeth, phospholipids etc. It is obtained form soil as phosphate. Organic phosphorus circulates in nature from plants to animals. Phosphate is released by decomposers back to soil. Some phosphate is lost through leaching or precipitation. Phosphate is extracted from mines having rock phosphate or metal phosphates. Guano (excreta of Sea Birds) and bone meal are used to enrich soil. Phosphorus circulates through hydrosphere and lithosphere. Atmosphere component is absent.
Sculpture is a constituent of many proteins, vitamins, enzymes and coenzymes. It is obtained by plants as sulphate. From plants, the organic sculpture circulates in food chain and is released to abiotic environment by decomposers. Decomposers produce H2S and diethyl supplied (anaerobic breakdown from water logged soils, ponds, lakes, continental shelf), S and SO2. Both H2S and SO2 pass into atmosphere where H2S is oxidized to SO2. Sculpture dioxide comes back to soil as sulphite/thiosulphate with rain to soil as sulphite/ thiosulphate with rain water. Combustion of fossil fuels and smelting also releases SO2 into atmosphere. Some sulphur is extracted from mines (as S, metal supplied and sulphate).
97% of water occurs in oceans. Only 3% is fresh water. (2.1% of total) is found as ice/snow, 22.4% (0.67%) as ground water while the remaining is present in lakes, rivers, etc. water evaporates from oceans, ponds, lakes, ground, plants (as transpiration) and animals (as sweat and in breath), water vapors condense and form clouds which precipitate to produce rain and snow. 90% of ocean evaporation returns to it as rain while 10% extra falls on land surface.
This forms lakes, rivers, and ground water. Rivers are constantly pouring water into oceans. Ground water is pumped and withdrawn by plants. At any time atmosphere contains 0.13 x 1020G (1G = 1020g) water vapors. Annual precipitation is around 4.46 x 1020 G. This requires constant addition of water vapors and their condensation. Hydrologic cycle has two components, global and local.
Local component is called short cycle. It involves evaporation of water from an area, its condensation high up in the atmosphere and precipitation over the same area. Local rain also occurs in some forests. Global component is long cycle that involves circulation of water vapors in the atmosphere, movement of clouds; precipitation, movement of water from one area to another. Hydrological or water cycle is energized by solar energy.
Evaporation is conversion of liquid water into gaseous state on absorption of energy. It occurs from both oceans and land mass. Transpiration is release of water vapors from vegetation. Some 83% of total evaporation occurs from oceans. Only 17% evaporation occurs over land. It includes both evaporation and transpiration.
Water vapours passing into atmosphere condense over minute particles suspended in it. The particles over the sea are those of dimethyl sulphate which are formed by reaction of dimethyl sulphide (released by algae) with oxygen. The particles function as nuclei. The condensed water vapours turn into liquid state of very small size (less than 40 (im). This forms mass of warm moist air.
Moist warm air masses may ascend to cold region of the atmosphere, move to region of cold air or over high mountains. Condensed water vapors coalesce and undergo precipitation. 76% of total precipitation occurs over oceans while 24% falls over land (some 43% more than evaporation).
(d) Infiltration and Run-off :
Part of precipitation falling on land sinks into soil. It is called infiltration. The latter forms ground water well as moistens the soil. The remaining water flows over the surface. It is sealed run-off. The latter forms lakes and streams. Precipitation in cold areas occurs as snow. It melts and undergoes infiltration and run-off.
It is water that lies inside the earth over impervious strata. Ground water may come out as spring or surface seepage. Some water is drawn up by humans for agriculture, industry and domestic consumption. Ground water also passes into lakes, streams and oceans.