Water and Carbon as Natural Systems

Water and Carbon Cycles

Water and carbon as natural systems are two intricate systems that make life on earth possible. 

Carbon is the foundation of all life on earth. All organisms, their organic processes, and the organic products that they produce are all linked to this valuable element. The carbon cycle ensures that carbon can be used and reused over and over again by its benefactors. 

Water, on the other hand, plays a similar role in the facilitation of life on Earth. There is an abundance of water on earth, and this water plays a critical role in keeping our planet habitable and hospitable. Water that cycles between the land, air, and sea, maintains the various biotic and abiotic processes that rely on it. A great majority of organisms need water to survive. 

Both of these cycles can be understood as natural systems. This simply means that they are processes with inputs, outputs, and stores. In each system, input material is subjected to various interacting forces to produce a new output material, and some material is stored.

 The main inputs and outputs of the carbon cycle are photosynthesis, decomposition, respiration, and combustion. Its major stores include the atmosphere, oceans and other bodies of water, the cryosphere, soil, vegetation, and groundwater.

The water cycle’s main inputs and outputs are precipitation, snowmelt, evapotranspiration, and run-off. Similar to the carbon cycle, its major stores are the atmosphere, oceans and other bodies of water, the cryosphere, soil, vegetation, and groundwater. 

Water Cycle

Water and carbon as natural systems
The water cycle is an example of water and carbon as natural systems

On Earth, Water exists in three different phases: solid, liquid, and gas. Solid water comes in the form of ice, liquid water as the water in the oceans, lakes, rivers, and other bodies of water, and water in its gaseous state is called water vapour. 98% of the water on our planet is in its liquid state. 

Water passes through various key processes in the water cycle. The average time that water remains in a store varies according to the size of the store and the rate at which these processes move water between stores. For example, water remains in larger stores much longer than in smaller stores, and surface runoff transports water faster than groundwater flow. 

Read more about the hydrological cycle

Important Processes in the Water Cycle

Evapotranspiration

Illustration showing evapotranspiration

Evaporation is when water changes from its liquid state to its gaseous state. Evaporation occurs when water is exposed to open air. This usually happens in open water or wet surfaces. Evaporation rates can vary due to various factors such as heat, humidity, sunlight, and wind speed. Evaporation rates are much higher in the ocean than on land. 

Transpiration is the process in which plants lose water through evaporation. This often takes place in a plant’s leaves, stem, and flowers. Plant transpiration rates are determined by a plant’s species and growth condition. 

Evapotranspiration is the combination of these two processes. Furthermore, there are two kinds of evapotranspiration. Potential evapotranspiration is when water supply is not limited, therefore evapotranspiration is at its maximum level. Actual evapotranspiration is what happens in actual conditions. Actual evapotranspiration may fall below potential evapotranspiration due to a lack of soil moisture.

Precipitation

Photograph of precipitation in the form of rainfall

When water vapour in the atmosphere condenses, it falls back to the ground in the form of precipitation. In the atmosphere, condensation happens as a result of the movement of air masses, solar radiation, and the local topography. When combined, all these factors lead to precipitation. Precipitation can come in various forms such as rainfall, snowfall, and hail. 

Run-off Generation

The water that falls to the ground as precipitation is returned to the oceans by either surface run-off or groundwater flow. Water that flows over land or through rivers makes its way back to the ocean in a relatively quick fashion. However, the flow of water underground is very slow and sometimes takes a thousand years before returning to the ocean. 

Infiltration is the process which determines whether water will flow above ground as run-off or below ground as groundwater. Normally, water that falls to the ground percolates, and then infiltrates the soil and is stored as groundwater flow. When the amount of rainfall exceeds the ground’s infiltration capacity, water can no longer be stored in the soil and instead runs off the ground above. The observation and study of run-off is essential to land water management. 

Cryospheric Processes

Illustration showing cryospheric processes

Cryospheric water stores are second to oceanic stores in terms of size. 95% of this amount is stored as ice sheets covering Greenland and Antarctica. In cold environments such as these, precipitation falls in the form of snow. Snow that falls on top of ice caps eventually compresses into ice for long term storage. In the summer months, the increase in temperature causes ice caps to lose water through melting and run-off. During the winter, the low temperatures allow water to once again collect and accumulate in its solid state. On a larger scale, these two alternating processes of melting and accumulation are largely controlled by changes in temperature and the frequency of polar snowfall. 

The equilibrium line altitude (ELA) is the elevation at which a glacier’s annual accumulation is equal to its annual melting. Global warming has led to an increase in the melting of polar ice caps, which in turn leads to a rise in sea levels. This rise in sea levels can cause glaciers and ice streams to destabilise, exacerbating iceberg calving. The total melting of all the world’s polar ice sheets would result in a 60m increase in sea levels worldwide. Today, polar ice regions and cryospheric processes are under the careful surveillance and monitoring of scientists. 

Carbon Cycle

The carbon cycle and its many processes are essential to the existence of life on earth. All living organisms depend on carbon and many carbon-based molecules. In the atmosphere, there are gases such as carbon dioxide and methane. In the lithosphere, carbon exists as carbonate rocks. In the soil, it takes the form of organic molecules that came from decomposed material. 

Carbon is stored in the soil, bedrock, vegetation and flora, the ocean, ocean sediments, and the atmosphere. In the recent century, atmospheric carbon has been the focus of many studies and changes in policy, as carbon dioxide and methane are greenhouse gases. The properties of these two carbon-based gases allow them to effectively trap heat within the atmosphere and worsen the so-called greenhouse effect.

Modern human activity and advances in industry has led to the rise of an excess of carbon in our atmosphere. The combustion of fossil fuels accounts for 90% of anthropogenic carbon release, while the remaining 10% comes from changes in how we use land. Of all the carbon that human activity releases into the atmosphere, 24% is incorporated into the ocean and 26% is absorbed by plants. To this day, human consumption still contributes to the great excess of carbon in our atmosphere. 

Important Processes in the Carbon Cycle

Photosynthesis and Respiration

Photosynthesis and respiration are two critical processes in the terrestrial carbon cycle.

Photosynthesis is the process in which an organism produces carbohydrates from water, carbon dioxide, and by use of solar energy. Plants, algae, and some bacteria use this process to extract carbon dioxide from the air and incorporate it into its tissues in its solid state. 

Respiration is the process in which various living organisms produce energy by taking in oxygen from the air around them and combining it with sugars in their body. Living organisms release carbon dioxide into the atmosphere as a byproduct of this process.

Decomposition

Decomposition is a natural process in which dead organic material is consumed by fungi and bacteria. This process returns carbon dioxide into the atmosphere, but it can also produce organic compounds that are returned to the soil below. 

Methanogenesis

In anaerobic environments, a type of bacteria called methanogenic bacteria produces methane as a byproduct of respiration. Methanogenesis often occurs in wetland environments such as rice paddies and peatlands. 

Carbon use and storage in oceans

In the process, sometimes referred to as the physical pump, carbon dioxide from the atmosphere that reaches the ocean through diffusion is dissolved in the ocean’s surface. The carbon dioxide would then be transported to the deep ocean in areas where surface waters sink due to their low temperature and higher density. 

Carbon dioxide is also stored in phytoplankton by means of photosynthesis. Furthermore, carbon also makes its way into the deep ocean when dead organic material sinks down or is pulled by downwelling waters. Shell-building organisms also take carbonate from the water around them. This is another process important to the transport of carbon to deep ocean sediments. 

Fossil Fuels

Fossil fuel reserves buried deep in the earth are important stores of fossilised carbon. For example, coal is peaty deposits that, over time have lithified and turned into rock. Combustion achieved through the burning of fossil fuels releases carbon dioxide into the atmosphere. This primarily artificially induced process releases carbon from sources that were originally in long-term storage deep in the earth. Excessive human consumption of fossil fuels puts a significant strain on the carbon cycle’s natural load, causing an acceleration in the cycling of this carbon.  

Terrestrial Carbon Cycle

Much of the terrestrial carbon cycle is dependent on plants’ photosynthesis. This critical natural process takes up great amounts of carbon dioxide from the atmosphere. On the opposite side, animals and plants release carbon dioxide back into the atmosphere through the process of respiration. The decomposition of dead organic matter also leads to the release of carbon dioxide and methane. The cycling of carbon in between these living processes happens simultaneously and in a relatively quick fashion. It is sometimes referred to as the fast carbon cycle. 

Human consumption and activity have grown to be significantly impactful on our environment. The terrestrial carbon cycle is not exempt from its harmful effects as these can upset the balance of carbon intake and release in terrestrial carbon systems. 

Oceanic Carbon Cycle

The oceans are one of our planet’s largest and most significant carbon stores. In these environments, carbon can be found dissolved in the water and in the bodies of marine organisms. Carbon is mainly introduced to the oceanic carbon cycle through gas exchange in the atmosphere. However, a significant amount of carbon is also inputted into the system through continental runoff and the organic carbon and carbonate ions it contains. Only a small part of the carbon stored in the ocean is buried in ocean sediment, however, these ocean sediments are also important for the long term storage of carbon. The oceanic carbon cycle fluxes under the influence of physical, chemical, and biological processes. Due to the great size of the oceanic carbon store, minute variations in the cycling of carbon can have sizable global effects. 

Atmospheric Carbon Cycle

Carbon in the atmosphere mainly comes in two forms: carbon dioxide (CO2) and methane (CH4). Both are greenhouse gases, but they differ in how they interact with the atmosphere. Carbon dioxide stays in the atmosphere for an extended period of time–roughly 50 years. It is relatively unreactive and can be removed from the atmosphere through the processes in terrestrial and oceanic carbon cycles. On the other hand, methane is short-lived yet 23 times more powerful than carbon dioxide as a greenhouse gas. Methane stays in the atmosphere for around 12 years. 

Slow Carbon Cycle

The cycling of carbon between the atmosphere and bedrock stores is called the slow carbon cycle. The weathering of terrestrial material over millions of years leads to a net sink of carbon in oceanic environments. Carbonate in run-off water is also produced by the chemical weathering of rocks through carbonic acid. Run-off flow would then transport this carbonate into the ocean. Certain marine organisms make use of this carbonate to make their shells. Later on, these organisms will die, decompose, and their shells fall to the ocean floor to be incorporated as sediment rich in carbonate. This carbonate is lithified and is used to create limestone, keeping carbon in long term storage. Submarine volcanic activity can melt these rocks, returning carbon to the atmosphere above. 

Interaction of Water and Carbon Systems

Both the water cycle and carbon cycle are inextricably linked and interdependent one one another. These two systems are almost always present where the other is present. A few examples of such intersections include the atmosphere, the oceans, the earth, and vegetation. Human activities also have significant impacts on both systems, and a change in one system can have implications in the other. Furthermore, both systems are inadvertently affected by long-term changes in the Earth’s climate. 

In recent years, people have grown more knowledgeable of the effects of human activity on these important natural systems. Multiple efforts are now directed towards the sustainable management of both water and carbon resources. In attempts to preserve the carbon cycle’s balance, some efforts include reforestation, wetland restoration, the improvement of agricultural practices, and reducing carbon emissions. On the other hand, some examples of efforts to keep the water cycle in balance include water use management, the improvement of forestry techniques, and water allocations for domestic, industrial, and agricultural sectors. 

Frequently Asked Questions

How does the water cycle regulate Earth’s climate?

The water cycle transports heat and moisture, moderating temperatures and distributing water vapour, which influences weather patterns and global climate.

What is the role of oceans in the carbon cycle?

Oceans absorb and release carbon dioxide, acting as a crucial carbon sink that helps regulate atmospheric carbon levels and mitigate climate change.

How do plants contribute to the carbon cycle?

Plants absorb carbon dioxide during photosynthesis, converting it into organic matter, which is eventually returned to the atmosphere through respiration and decay.

How does deforestation impact the water and carbon cycles?

Deforestation disrupts the water cycle by reducing transpiration and increasing runoff, while releasing stored carbon into the atmosphere, contributing to greenhouse gas emissions.

How can disruptions in water and carbon cycles impact ecosystems?

Imbalances can lead to droughts, flooding, and disruptions in food chains, affecting biodiversity and ecosystem health.

References

Carbon & water cycles – Life on Earth (n.d.). Retrieved from CoolGeography: https://www.coolgeography.co.uk/advanced/Carbon_water_cycles_Life_Earth.php

Changes to the carbon cycle over time. (n.d.). Retrieved from Tutor 2U: https://www.tutor2u.net/geography/reference/changes-to-the-carbon-cycle-over-time

Water and carbon cycling. (n.d.). Retrieved from Royal Geographical Society: https://www.rgs.org/CMSPages/GetFile.aspx?nodeguid=6dc9f1c1-f92d-4c04-9f85-9985844a6a79&lang=en-GB

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Cite/Link to This Article

  • "Water and Carbon as Natural Systems". Geography Revision. Accessed on March 28, 2024. https://geography-revision.co.uk/a-level/physical/water-and-carbon-as-natural-systems/.

  • "Water and Carbon as Natural Systems". Geography Revision, https://geography-revision.co.uk/a-level/physical/water-and-carbon-as-natural-systems/. Accessed 28 March, 2024.

  • Water and Carbon as Natural Systems. Geography Revision. Retrieved from https://geography-revision.co.uk/a-level/physical/water-and-carbon-as-natural-systems/.