C.R.K.

Topic: Nutrient Cycling In Nature

Definition

Nutrient Cycle is the movement and exchange of organic and inorganic matter back into the production of living matter. Nutrient cycles look at how important molecules in an ecosystem are transferred. Like energy, these nutrients are never lost from the cycle, merely stored in a different form - be it fossil fuels, living organisms or CO₂. A very important role played by microorganisms is that they feed on dead material by saprotrophic nutrition, and convert complex organic molecules to simple ones.

The Carbon Cycle

All life is based on carbon, it is contained in proteins, carbohydrates; indeed all organic molecules contain carbon. So it is the most important nutrient in an ecosystem. The carbon cycle involves several stages of carbon being fixed (incorporated as part of) by plants from the atmosphere. This carbon is transferred to consumers by eating, or it becomes fossil fuel in fossilisation

Below is an example of a carbon cycle. They cycles can be represented a number of ways, and this is just one example.

Although much is said about rising carbon dioxide in the atmosphere, only 0.04% of air is CO2, indeed most is in the ocean as hydrogen carbonate (HCO3-), and this is where most photosynthesis occurs. That isn't to say carbon dioxide rising in the atmosphere isn't a very important global problem, just that it only comprises a small aspect of our atmosphere.

The Process of Carbon Cycle

The atmospheric carbon dioxide is virtually the only source of carbon which is the basic constituent of all the organic compounds.

This gas is used by all plants in photosynthesis and the end products (organic substances) of this complex process are used in two ways.

One fraction is used in the construction of more living matter. The carbon and oxygen so supplied by SO₂

Decay subsequently returns CO₂ to the atmosphere, and this completes one possible carbon cycle. Another fraction of the organic substances is used as fuel in respiration by both plants and animals.

This process releases CO2 as a by-product. Such CO₂ may now be used in photosynthesis again, or it may return to the environment, completing the second possible carbon cycle (Fig. 5.6). Thus, photosynthesis and respiration are the two major processes that drive the global Carbon Cycle, with CO₂ as the main vehicle of flux between atmosphere, hydrosphere and biota.

The CO₂ content of the atmosphere is replenished not only through biological oxidation (respiration), but also through non living combustion i.e., forest fires and burning of industrial fuels release CO₂ intr Occasionally volcanic eruptions also add CO₂ remain in living matter until death

Occasionally volcanic eruptions also add CO₂ to the atmosphere.

It is clear that terrestrial plants utilize atmospheric CO₂ as their carbon source for photosynthesis, whereas aquatic plants use hydrosphere carbon i.e., dissolved carbonates.

Oxygen Cycle

The oxygen cycle elaborates how oxygen circulates in various forms through nature. Oxygen occurs freely in the air, trapped in the earth crust as chemical compounds, or dissolved in water. Oxygen in the atmosphere is about 21%, and it is the second most abundant gas after nitrogen. It is mostly utilized by living organisms, especially man and animals in respiration. Oxygen is also the most common element of human body.

Oxygen is also used during combustion, decomposition, and oxidation. The circulation of oxygen is through three main flow systems including the (air) atmosphere, the biosphere, and the earth's crust. In the oxygen cycle, the main driving factor is photosynthesis which is the process whereby green plants and algae make their own food by use of solar energy, water, and carbon dioxide to gives off oxygen as a by-product.

Hence, for oxygen to remain in the atmosphere, it has to circulate through various forms of nature which is essentially termed as the oxygen cycle. The circulation depends on the various activities on Earth.

Process of Oxygen Cycle

The Atmosphere (air)

The atmosphere carries a small quantity of all oxygen, only about 0.35% of the entire earth's oxygen. In the atmosphere, oxygen is released by the process known as photolysis. Photolysis happens when the ultraviolet radiation of sunlight breaks apart oxygen containing molecules such as nitrous oxide and atmospheric water to release free oxygen. The surplus oxygen recombines with other oxygen molecules to form ozone while the rest is freed into the atmosphere. Ozone is the layer that helps to shield the Earth from the dangerous ultra violet rays.

Biosphere

The biosphere carries the smallest quantity of all earth's oxygen, about 0.01%. In biosphere, the major oxygen cycles photosynthesis and respiration. In these two

Process of Oxygen Cycle

The Atmosphere (air)

Biosphere

The biosphere carries the smallest quantity of all earth's oxygen, about 0.01%. In the biosphere, the major oxygen cycles are photosynthesis and respiration. In these two processes of the oxygen cycle, it is interconnected with the carbon cycle and the water cycle. During photosynthesis, plants and planktons use sunlight energy, water, and carbon dioxide to make food (carbohydrates) and release oxygen as a -product. As such, plants and planktons are the main producers of oxygen in the ecosystem. They take in carbon dioxide and give out oxygen. Plants are estimated to replace about 99% of all the oxygen used.

On the other hand, respiration happens when humans and animals breathe in oxygen which is used during metabolism to break down carbohydrates and exhale carbon dioxide as a by-product. Such free carbon dioxide is then released into the environment and is used by plants and planktons during photosynthesis to give out molecular atmospheric oxygen, thus completing the oxygen cycle. Therefore, suffice is to say that oxygen enters organisms in the biosphere through respiration and is expelled through photosynthesis in a process that is interconnected with the carbon cycle plus the water cycle.

However, the continued release of carbon dioxide into the atmosphere by burning fossil fuels and automobile pollution affects the oxygen cycle.

The Lithosphere (Earth's Crust)

The lithosphere carries the largest quantity of all earth's oxygen, about 99,5%, because it is a constituent of the earth's lands, soils, organic matter, biomass, water, and rocks. Mostly, these constituents of the earth fix oxygen in mineral chemicals compounds such as oxides and silicates. The process is natural and happens automatically as the pure mineral elements absorb or react with the free oxygen. It happens similar to the manner in which iron picks up oxygen from the air, resulting in the formation of rust (iron oxides).

As such, during chemical reactions and some weathering processes, a portion of the trapped oxygen in the minerals is released into the atmosphere. Also, as animals and plants draw nutrient minerals from rocks, organic matter, or biomass, some of the trapped is freed in the process. Dissolved oxque is also present in water system which is essential for some oiner gases.

3. Decomposition: Decomposition occurs when plants and animals die. When this happens, they decompose and such process uses oxygen and releases carbon dioxide.

J4. Rusting: When things rust, they use oxygen. This is also called as oxidation.

Processes that Produce Oxygen

1.. Plants: Plants produce oxygen during the process of photosynthesis. During the process of photosynthesis, plants use carbon dioxide, sunlight, and water to create energy.

2 Sunlight: Some oxygen also gets produced when sunlight reacts with water vapor in the atmosphere Water Cycle aThe water cycle explains the continuous movement of water on, above, and below the surface of the earth. It is also referred to as the Hydrological Cycle. The cycle describes the properties of water that make it undergo the various movements on the planet. The water cycle has nine main physical processes that create a continuous water movement on the planet. Intricate sequences include the transition of water from the gaseous composition of the atmosphere; through the water bodies such as oceans, lakes, rivers; passage through the soil, rocks and underground waters, and later returns into the atmosphere. Simply put, the hydrological cycle has neither a beginning nor an end, it's an incessant process

Process Of Water Cycle

The water cycle processes involve evaporation, condensation, precipitation, interception, infiltration, percolation, transpiration, runoff, and storage.

1. Evaporation

Evaporation takes place when water changes from its liquid state to vapor or gaseous state. A substantial heat amount is exchanged during the process, roughly 600 calories of energy per gram of water. In most cases, the solar radiation and additional causes such as the wind, vapor pressure, atmospheric pressure, and air temperature influence the amount of natural evaporation in different geographical regions.

Evaporation occurs over the surfaces of the water bodies such as oceans, streams, and lakes. It can also occur on raindrops, rocks, snow, soil or vegetation. When evaporation happens, anything present in the water such as salts and minerals is left behind. Thus, evaporation purifies the water. The evaporated moisture then rises into the atmosphere from the evaporation sources as water vapor or in a gaseous state. At any particular moment, some water vapor is present in the atmosphere..

2 Condensation

Condensation is the process whereby the water vapor changes from its gaseous physical state to liquid or crystal solid. The water vapor condenses on minute air particles due to the cooling of the air, freezing temperatures, or increased vapor amounts to the point of saturation in the upper stratospheres.The condensed vapor then forms fog, dew or clouds. When the condensed clouds, dew, and fogs become too large and heavy to remain suspended in the atmosphere, they fall back on earth as precipitation due to gravity. The 600 calories of energy per gram of water needed during evaporations are released into the environment.

3. Precipitation

Precipitation takes place whenever any or all forms of water particles fall from the atmosphere and reach the earth surface. Precipitation occurs when the liquid or solid particles in the clouds, dew, and fog drops to the ground because of frictional drag and gravity. One falling particle leaves behind a turbulent wake, causing faster and continued drops. The crystallized ice may reach the ground as ice pellets or snow or may melt and change into raindrops before reaching the surface of the earth depending on the atmospheric temperatures. Precipitation falls on water bodies or on ground surface where it disperses in various ways. For sometime, precipitation can remain on the surface as runoff or overland flow. It may be carried into waterways, intercepted by plants, or infiltrate into the soil. A good percentage of precipitation goes back to the atmosphere as evaporation.

4. Interception

Interception is whereby the water movement is interrupted in the various paths during transportation events over the land surface. Interception takes place when the water is absorbed by vegetation cover and trees, absorbed into the ground, or stored in puddles and land formations such as furrows and streamlets. These waters can either infiltrate into the soil or return to the atmosphere through evapotranspiration or evation.

5. Infiltration

Infiltration is the physical process involving the slow passage of water through the soil. This phenomenon is influenced by the soll surface conditions such as permeability and porosity of the soil profile. Other factors include soil texture, soil moisture content, and soil structure. The infiltrated water is stored in the soil and can later return to the atmosphere via evapotranspiration.

6. Percolation

Percolation is the flow of water through the soil and rocks by the influence of capillary and gravity forces. All water on the earth's surface move by the forces of gravity and capillarity to rest beneath the earth as groundwater. Once beneath the earth, below the water table, the water mostly moves horizontally rather than downwards based on the geologi dary formations.

This area normally acts as reservoirs for storing water. Some geologic formations may conduct this water back to the surface such as springs.

7. Transpiration

Transpiration is a process in all plants that normally takes place during the day, giving off water vapor from the leaves openings. Plants transpire to move nutrients to the upper sections of the plant and to cool the plants. Most of the water absorbed by the plants are transpired into the atmosphere until a water deficit point is reached whereby the plant resorts to releasing water vapor at a much slower rate. Transpiration is important in the water cycle because plants absorb the moisture from the soil and releases it into the atmosphere as water vapor.

8. Runoff

Runoff is the occurrence of excess water from watershed or drainage basin that flows on the surface. The flow is as a result of precipitation above waterways, groundwater runoff from deep percolations, subsurface runoff that infiltrates the surface soils, and surface runoff that flows on the land surface. As the water flows, it can be used for agricultural and domestic purposes, it may seep into the ground, stored in reservoirs or water bodies, or evaporate into the atmosphere.

9. Storage

Storage refers to the various water reservoir in the planetary water or hydrological cycle.The water is primarily stored in the atmosphere, the surface of the earth, and in the ground. Storage in the atmosphere is in the form of water vapor. Storage on the surface of the earth includes lakes, oceans, rivers, glaciers, and reservoirs. Storage in the ground pertains to the soils, rock formations, and aquifers.