Biogeochemical Cycles

Energy flows directionally through ecosystems, entering as sunlight and leaving as heat during energy transformation between trophic levels but the flow of nutrient is cyclic. The nutrients are vital for the growth of organisms and sustenance of life in the biosphere is derived by the interaction of matter and energy. The organic and inorganic matters move reversibly in the atmosphere, hydrosphere, biosphere and Lithosphere through various cycles known as a Biogeochemical cycle. This recycling of the nutrients is called biogeochemical or nutrient cycling. (Bio - living; geo - rock; chemical - element)

TYPES OF BIOGEOCHEMICAL CYCLES

Gaseous Cycle

In this type of cycle, the reservoir is either atmosphere or hydrosphere and it includes Water, Carbon, Nitrogen Cycle etc.

Sedimentary Cycle

 In this type of cycle, the reservoir is the earth crust and it includes Potassium, Calcium, Magnesium, Phosphorus, Sulphur Cycle etc.

CARBON CYCLE

Atmospheric carbon in the form of carbon dioxide is the critical source of carbon in an ecosystem. The Ecosystems gain most of the carbon from the atmosphere by the process of photosynthesis. In the process of photosynthesis carbon dioxide from the atmosphere, together with solar energy and water is converted into food and carbon gets trapped in the biomolecules. Carbon moves from one reservoir to another by these processes:

Combustion: Burning of wood and fossil fuels by factory and auto emissions transfers carbon to the atmosphere as carbon dioxide.

Photosynthesis: Carbon dioxide is taken up by plants during photosynthesis and is converted into energy rich organic molecules, such as glucose, which contains carbon.

Metabolism: Autotrophs convert carbon into organic molecules like fats, carbohydrates and proteins, which animals can eat.

Cellular respiration: Animals eat plants for food, taking up the organic carbon (carbohydrates). Plants and animals break down these organic molecules during the process of cellular respiration and release energy, water and carbon dioxide. Carbon dioxide is returned to the atmosphere during gaseous exchange.

Precipitate: Carbon dioxide in the atmosphere can also precipitate as carbonate in ocean sediments.

Decay: Carbon dioxide gas is also released into the atmosphere during the decay of all organisms.

WATER CYCLE 

Over two thirds of the Earth's surface is covered by water. It forms an important component of most life forms, with up to 70% of plants and animals being composed of water. Vast quantities of water cycle through Earth's atmosphere, oceans, land and biosphere. This cycling of water is called the water or hydrological cycle. The cycling of water is important in determining our weather and climate, supports plant growth and makes life possible.

Evaporation: Most water evaporates from the oceans, where water is found in highest abundance. However some evaporation also occurs from lakes, rivers, streams and following rain.

Transpiration: Is the water loss from the surface area (particularly the stomata) of plants.

Evapotranspiration: The processes of evaporation and transpiration are often collectively referred to as evapotranspiration.

Condensation: The process by which water vapour is converted back into liquid is called condensation. You may have observed a similar process occurring when dew drops form on a blade of grass or on cold glass. Water in the atmosphere condenses to form clouds.

Precipitation: Water returns to Earth through precipitation in the form of rain, sleet, snow or ice (hail). When rain occurs due to precipitation, most of it runs

off into lakes and rivers while a significant portion of it sinks into the ground.

Infiltration: The process through which water sinks into the ground is known as infiltration and is determined by the soil or rock type through which water

moves. During the process of sinking into the Earth's surface, water is filtered and purified.

Melting  and freezing: Some water freezes and is 'locked up' in ice, such as in glaciers and ice sheets. Similarly, water sometimes melts and is returned to oceans and seas.

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.  The nitrogen cycle is essential to plants in unfertilised 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 five natural processes: nitrogen fixation, nitrification, assimilation, denitrification, and decay(ammonification).

NITROGEN FIXATION

a)  Nitrogen is an essential constituent of protein and is a basic block of al living tissue. It constitutes nearly 16% by weight of al proteins but the elemental Nitrogen is useless for living organism.

b)  Only a few single-cell organisms, like bacteria can use nitrogen from the atmosphere directly. The elemental nitrogen is needed to be converted into

organic compounds(nitrates or ammonia) which can be absorbed by the living organisms. This process is known as nitrogen fixation. It is carried out by

nitrogen-fixing bacteria.

c) Nitrogen fixation on earth is accomplished in three different ways:

1.  By microorganisms- bacteria and blue-green algae.

2. By man using industrial processes- e.g., fertilizer factories.

3. To a limited extent by atmospheric phenomena such as thunder and lighting.

NITRIFICATION

Nitrifying bacteria change the ammonium ions into nitrites and nitrates. Nitrosomonas and Nitrobacter are examples. Some of the nitrates are used by plants. The process of converting ammonium ions to nitrites or nitrates is called nitrification.

 ASSIMILATION

In this process nitrogen fixed by plants (nitrate) is converted into organic molecules such as proteins, DNA, RNA etc. These molecules make the plant and animal tissue. Plants assimilate ammonium and nitrates into proteins which are transferred through the food chain.

AMMONIFICATION

a)  Assimilation produces large quantities of organic nitrogen, including proteins, amino acids, and nucleic acids. Ammonification is the conversion of organic nitrogen into ammonia.

b) The ammonia produced by this process is excreted into the environment and is then available for either nitrification or assimilation.

 DENITRIFICATION

 Denitrification is the reduction of NO3- to gaseous N2 by anaerobic bacteria. This process only occurs where there is little to no oxygen, such as deep in the soil near the water table.  Hence, areas such as wetlands provide a valuable place for reducing excess nitrogen levels via denitrification processes.

SULPHUR CYCLE

The SO2 emissions by the volcanoes, which occur naturally. They either go up in the air, or be decomposed to become H2S .In the air, the sulphates promote condensation, then when it  precipitates it goes to either land or water.

When it  precipitates to land, the plants receive them through the soil. When the plant dies and decomposes it becomes sulfate again. Then the microorganisms

in the soil reduce the sulfate to hydrogen sulfide.

The decaying of organisms may lead to the sedimentation of sulfates and sulfides and the organic sedimentation. In the organic sedimentations, it takes millions of years to turn them into fossil fuel. Fossil Fuels are then dug up by energy companies, which produces smoke in the process.

PHOSPHORUS CYCLE

Phosphorus is an important element for all forms of life. As phosphate (PO4), it  makes up an important part of the structural framework that holds DNA and RNA together. Like calcium, phosphorus is important to vertebrates; in the human body, 80% of phosphorus is found in teeth and bones.

The phosphorus cycle differs from the other major biogeochemical cycles in that it  does not include a gas phase; although small  amounts of phosphoric acid (H3P04) may make their way into the atmosphere, contributing—in some cases - to acid rain.

The water, carbon, nitrogen and sulfur cycles all include at least one phase in  which the element is in  its gaseous state. Very little phosphorus circulates in the atmosphere because at Earth's normal temperatures and pressures, phosphorus and its various compounds are not gases. The largest reservoir of phosphorus is in sedimentary rock.

When it rains, phosphates are removed from the rocks (via weathering) and are distributed throughout both soils and water. Plants take up the phosphate ions from the soil. Plants take up inorganic phosphate from the soil. The plants may then be consumed by animals. Once in the plant or animal, the phosphate is incorporated into organic molecules such as DNA.

When the plant or animal dies, it decays, and the organic phosphate is returned to the soil. Within the soil, organic forms of phosphate can be made available to plants by bacteria that break down organic matter to inorganic forms of phosphorus. This process is known as mineralisation.

 Since most of our phosphorus is locked up in sediments and rocks, it's not available for plants to use. A lot of the phosphorus in soils is also not available to plants.

These cycles are interconnected, as elements such as carbon, nitrogen, and phosphorus are essential for the growth and survival of organisms, and they influence each other's availability and cycling in ecosystems. Human activities, such as burning fossil fuels, deforestation, and industrial agriculture, can disrupt these cycles, leading to environmental problems such as climate change, eutrophication, and habitat degradation. Therefore, understanding and managing biogeochemical cycles are crucial for maintaining the health and sustainability of ecosystems.