Phosphorus Cycle

• How and in what form(s) does phosphorus enter and leave the cycle?

• What are the human impacts on the cycle?

• Abundant phosphorus stimulates plant and algal productivity.– Major component of water

pollution.

Reduced levels of dissolved oxygen.

Phosphorus Cycle

Phosphorus Cycle

Phosphorus Cycle

Sulfur Cycle

Sulfur Cycle• Sulfur is an essential component of proteins for living organisms.• Sulfur compounds determine the acidity of rainfall, surface water and soil.• Sulfur is tied up in soil as mineral rocks.• Weathering or emission from deep seafloor vent or volcanic eruption releases

sulfur.• Sulfur compounds are important determinants of the acidity of water.

– Particulates may also act as critical regulators of global climate.• Sulfur cycle is complicated by a large number of possible oxidation states. There

are many micororganisms oxidizing or reducing various sulfur species.• Sulfur is oxidised to sulfur dioxide (SO2), sulfate (SO4

2-)or hydrogen sulfide (H2S).• Human activities also releases a large quantity of sulfur, primarily through burning

fossil fuels.• Sulfur dioxide and sulfate causes human health problems.• When ocean water warms up, tiny organisms produces dimethylsulphide(DMS)

which oxidises sulfur dioxide and then sulfate to the atmosphere.

The Human System

• Excessive use of fossil fuels• Feeding largely on the third trophic level• Use of coal or nuclear power• Use of agricultural land to produce meats

In 1965, J.E.Lovelock suggested the Gaia Hypothesis.

The Gaia hypothesis states that the temperature and composition of the Earth's surface are actively controlled by life on the planet. If changes happen, life responds to these changes by modifying the abiotic environment through growth and metabolism.

In simpler terms, biological responses tend to regulate the state of the Earth's environment in their favor.

Gaia Hypothesis

Gaia Hypothesis

• Life has greatly affected the planetary environment.

• This alteration has allowed life to persist.

• The Earth is a “super-organism”: Life controls the environment in a fashion that is equivalent to the way an organism controls its various systems.