Ecosystem Cycles

Ecosystem Cycles or Biogeochemical cycles circulate key elements and compounds between the biotic and abiotic components of ecosystems. Major cycles include water, carbon, nitrogen, oxygen, phosphorus, and Sulphur.

Water Cycle

The water cycle, also known as the hydrologic cycle, refers to the continuous movement of water within the earth and atmosphere. It consists of the following main processes:

• Evaporation – This is when liquid water from oceans, lakes, rivers, and soils turns into water vapor and enters the air. Factors like heat from the sun and wind influence the rate of evaporation.
• Condensation – As water vapor in the air rises and the air cools, it condenses back into tiny droplets that form clouds. The droplets accumulate onto particles floating in the air.
• Precipitation – When the water droplets in clouds combine and grow heavy enough, they fall back to the earth as precipitation. This includes rain, snow, sleet, and hail. Precipitation releases the water collected in clouds.
• Collection – Some precipitation collects into freshwater bodies like lakes, rivers, and oceans, while some seeps into the ground. This groundwater can later resurface through natural springs. Plants also take up large amounts of water from the soil to support their growth.

Carbon Cycle

The carbon cycle describes exchanges of carbon within various ‘sinks’ or carbon reservoirs on earth. It includes:

• Photosynthesis – Plants absorb carbon dioxide from the atmosphere. Using energy from sunlight, plants convert the carbon dioxide into energy-rich carbohydrates and release oxygen as a byproduct.
• Respiration – Both plants and animals later ‘burn’ these carbohydrates through respiration. This releases carbon dioxide and water as byproducts and gives them usable cellular energy.
• Fossilization – Over long periods of time, dead organisms accumulate and are compressed into fossil fuels like oil and coal. This locks away carbon in the geosphere.
• Combustion – The burning of fossil fuels releases large amounts of carbon dioxide back into the atmosphere at a faster rate than dead organisms can lock it away, elevating atmospheric carbon dioxide.

Nitrogen Cycle

The nitrogen cycle involves the transformations of nitrogen and nitrogen-containing compounds in nature. Key steps include:

• Nitrogen Fixation – Specialized bacteria in soil and the roots of some plants convert inert nitrogen gas from the atmosphere into more reactive nitrogen compounds like ammonia and nitrate. Lightning also naturally fixes nitrogen.
• Assimilation – Plants use these nitrogen compounds produced by nitrogen fixation to synthesize proteins and other organic compounds necessary for life. Animals get these nitrogen compounds by consuming protein-rich plants.
• Ammonification – When plants and animals die, decomposers convert the organic nitrogen back into ammonia in a process called ammonification. The ammonia is further converted by bacteria into either nitrites or nitrates through nitrification.
• Denitrification – In the oxygen-deprived sediments of surface water ecosystems, denitrifying bacteria turn nitrates back into nitrogen gas, closing the nitrogen cycle. This prepares nitrogen to start the cycle again.

Sulphur Cycle

The Sulphur cycle captures the transformations of Sulphur through geological and biological processes, including:

• Mineralization – Bacteria help convert soil organic Sulphur from decaying matter into hydrogen sulfide gas. Oxidation of hydrogen sulfide produces elemental Sulphur particles.
• Assimilation – Plants take up and assimilate sulfate ions dissolved in water and soil through their roots. The sulfate is used to synthesize certain amino acids and proteins vital to life.
• DeSulphurization – When plants and animals die and decompose, the Sulphur in their tissues is returned back to inorganic forms by deSulphurizing bacteria, closing the Sulphur loop.
• Volcanic Activity – Sulphur dioxide gas is emitted from volcanic eruptions. In the atmosphere, it mixes with water and oxygen to form Sulphuric acid which falls as acid rain, depositing the Sulphur back on the earth’s surface where the cycle continues.

Phosphorus Cycle

Unlike other nutrient cycles, phosphorus has no significant gaseous phases in nature. The soil phase is the most rapid phase of the phosphorus cycle. Key phases in the cycle include:

• Weathering – Phosphorus is released through the gradual breakdown and weathering of rocks and sediments on land. It ends up dissolved in soil-water.
• Assimilation – Plants take up phosphorus dissolved in water and soil. It is an essential nutrient used in cell membranes, genetic material, and energy processes. Animals acquire phosphorus eating plants.
• Decay – When plants and animals die, decomposers recycle the organic phosphorus back into dissolved inorganic phosphates usable by plants again.
• Sedimentation – In water, phosphates dissolve. But excess phosphate runoffs into water bodies where it can build up. Over time, it settles into ocean sediments made partly of animal bones and shells rich in phosphate mineral deposits.

Each of the above Ecosystem cycle is critical for sustaining life by circulating essential compounds and nutrients. These cycles recycle resources efficiently within the biotic and abiotic components across ecosystems, enabling the continued growth and nourishment of organisms. They also store nutrients for future use and regulate the amounts available at any given time. Stabilizing key elements via these cycles promotes habitat stability and mitigates resource scarcity. Disrupting cycles can negatively impact connected ecosystems and species.