The Natural Cycles

1. The Water Cycle

The water cycle is the continuous movement of water on, above,

and below the Earth's surface. It is a major biogeochemical cycle

that sustains life on Earth.

The water cycle has four main stages:

● Evaporation: Water evaporates from the Earth's surface,

such as from oceans, lakes, rivers, and soil.

● Transpiration: Plants release water vapor into the atmosphere

through their leaves.

● Condensation: Water vapor in the atmosphere condenses to

form clouds.

● Precipitation: Water falls back to Earth as rain, snow, sleet,

or hail.

The water cycle is driven by solar energy. The sun heats the

Earth's surface, causing water to evaporate. The water vapor rises

into the atmosphere, where it cools and condenses to form clouds.

The clouds release the water back to Earth as precipitation.

The water cycle is important for many reasons. It provides water

for drinking, irrigation, and industrial use. It also helps to regulate

the Earth's temperature and climate.

Groundwater:

Aquifers are underground reservoirs or storage areas that hold

groundwater.

Groundwater can take hundreds or even thousands of years to

recharge fully after being depleted, if it ever recharges, so it is

an extremely precious resource.

Human Impacts:

1. Clearing plants increases runoff, erosion, evaporation and

reduces transpiration.

2. Spreading water on farm fields can deplete surface water and

groundwater and increase evaporation.

3. Releasing pollutants into the atmosphere causes precipitation

to become acidic.

4. Unstrained use of groundwater by irrigation and industry

causes depletion of groundwater. (This is our biggest threat)

2. The Carbon Cycle

The carbon cycle is the biogeochemical cycle that describes the

movement of carbon through the Earth's ecosystems. Carbon is an

essential element for all living things. It is found in the molecules

of all organic compounds, including carbohydrates, proteins, and

fats.

The carbon cycle has four main stages:

● Photosynthesis: Plants use carbon dioxide from the

atmosphere to make carbohydrates and release oxygen.

● Respiration: Animals and other organisms use carbohydrates

to produce energy. This process releases carbon dioxide back

into the atmosphere.

● Decomposition: When plants and animals die, their bodies

decompose, releasing carbon dioxide back into the

atmosphere.

● Fossilization: Over millions of years, some of the carbon

dioxide from decomposition is buried underground and forms

fossil fuels.

The carbon cycle is a relatively slow cycle, and it can take

millions of years for carbon to move from one reservoir to

another.

Human Impacts:

1. Extracting fossil fuels removes carbon from the

lithosphere.

2. Burning fossil fuels moves carbon dioxide into the

atmosphere.

3. Cutting down trees to plant farm fields increases carbon

in the atmosphere.

3. Phosphorus Cycle

The phosphorus cycle is the biogeochemical cycle that describes

the movement of phosphorus through the Earth's ecosystems.

Phosphorus is an essential nutrient for all living things. It is found

in the bones and teeth of animals, the DNA and the RNA of all

organisms, and the cell membranes of plants.

The phosphorus cycle is the only cycle that is all underground, not

in the atmosphere.

The phosphorus cycle has four main stages:

● Weathering: Rocks and minerals on the Earth's surface are

weathered, releasing phosphorus into the soil.

● Uptake: Plants take up phosphorus from the soil.

(Then animals eat those plants)

● Decomposition: When plants and animals die, their bodies

decompose, releasing phosphorus back into the soil.

● Erosion: Phosphorus can be eroded from the soil and carried

away by water or wind.

The phosphorus cycle is a relatively slow cycle, and it can

take many years for phosphorus to move from one reservoir to

another.

Human Impacts:

1. Mining Phosphorus to use as fertilizer.

2. Releasing phosphorus-rich wastewater from houses and

businesses. Phosphorus runs off or leaches into

waterways adding phosphorus to them. This may lead to

eutrophication.

4. The Nitrogen Cycle

The nitrogen cycle is the biogeochemical cycle that describes the

movement of nitrogen through the Earth's ecosystems. Nitrogen is

an essential nutrient for all living things. It is found in proteins,

DNA, and RNA.

The nitrogen cycle has four main stages:

● Fixation: Nitrogen gas in the atmosphere is converted into

ammonia; a form that can be used by plants. This process is

carried out by bacteria and lightning.

● Nitrification: Plants take up nitrogen from the soil (after

fixation) in the form of ammonia. Bacteria in the soil convert

ammonia into nitrites and then nitrates; a form that can be

used by plants.

● Denitrification: When plants and animals die, their bodies

decompose, releasing nitrogen back into the atmosphere

through the action of denitrifying bacteria.

● Assimilation: Plants use nitrates to make proteins and other

nitrogen-containing compounds. Then animals eat those plants.

The nitrogen cycle is a relatively fast cycle, and it can take only a

few days for nitrogen to move from one reservoir to another.

Human Impacts:

The Haber-Bosch process allowed for the production of ammonia on

a large scale. This enabled people to overcome the limits on plant

productivity imposed by the scarcity of natural nitrogen.

● Eutrophication: An overabundance of nutrients—primarily

nitrogen and phosphorus—in water. Algae feed on the

nutrients, growing, spreading, and turning the water green.

Algae blooms can smell bad, block sunlight, and may even

release toxins. Extreme cases of eutrophication lead to

hypoxia.

5. The Sulfur Cycle:

The sulfur cycle is a biogeochemical cycle that describes the

movement of sulfur in the Earth's atmosphere, land, oceans, and

living organisms. Sulfur is an essential element for life, but it can

also be a pollutant in certain forms.

Stages of the Sulfur Cycle:

1. Weathering: Sulfur-containing minerals in rocks are

weathered by wind, rain, and other natural processes,

releasing sulfur into the environment.

2. Volcanic Activity: Volcanic eruptions release sulfur dioxide

(SO 2 ) and other sulfur-containing gases into the

atmosphere.

3. Atmospheric Oxidation: Sulfur dioxide reacts with oxygen

and other atmospheric gases to form sulfate aerosols

(SO 4 ²⁻).

4. Wet Deposition: Sulfate aerosols can return to the Earth's

surface as rain or snow, containing sulfuric acid.

5. Dry Deposition: Sulfate aerosols can also settle onto land

or water bodies as particulate matter.

6. Assimilation: Plants and microorganisms absorb sulfate from

the soil or water and incorporate it into their organic

compounds.

7. Decomposition: When organisms die or decompose, their

organic sulfur compounds are released back into the

environment.

8. Sedimentation: Some sulfur-containing compounds may be

deposited in sediments and buried over time.

Human Impact on the Sulfur Cycle and Effects:

Human activities have significantly altered the sulfur cycle,

primarily through the burning of fossil fuels (coal, oil, natural gas)

and industrial processes. This has led to increased emissions of

sulfur dioxide, contributing to:

● Acid rain: The formation of sulfuric acid from sulfur dioxide

can cause acid rain, which damages forests, lakes, and

buildings.

● Air pollution: Sulfur dioxide and particulate matter from

sulfur emissions can cause respiratory problems and other

health issues.

● Climate change: Sulfur emissions can contribute to climate

change by influencing cloud formation and reflecting sunlight.