SCI10‐CD4 Investigate the role of feedback mechanisms in biogeochemical cycles and in maintaining stability in ecosystems. [CP, DM, SI]

Water Cycle All of Earth’s water, both fresh and salt, forms what is called the hydrosphere.

The great majority of Earth’s water – about 97.6% - is salt water. The remaining 2.4% is fresh water. Most of the fresh water is locked up in glaciers and ice caps!

Because so much of Earth’s surface (71%) is covered by water, our weather systems depend greatly on water in its three states: solid, liquid and gas (vapour).

Carbon Cycle Because photosynthesis and cellular respiration are complementary processes, and because the carbon that they use is repeatedly cycled through both, its called a cycle!

Reservoirs of Inorganic Carbon: Delays in the Cycle Inorganic Carbon can be found in three main reservoirs (storage areas): Atmosphere (the smallest)

Oceans (largest) Dissolved carbon dioxide Carbonate ion (CO32-) Bicarbonate ion (HCO3-) Calcium carbonate (CaCO3)

Earth’s Crust The carbon in carbonates can be recycled, but in the ocean much of it ends up as sediment As layers of sediment form, the carbonates are crushed and heated and eventually become rock! Limestone is made from the discarded shells and bones of living things.

Reservoirs of Organic Carbon What would act as storage for organic carbon?? The bodies of living things! Which are eventually recycled because of decomposition.

One Exception: BOGS! Store huge quantities of carbon in organic form. There is very little oxygen, therefore decomposition is very slow. Carbon atoms may remain locked away in dead plant matter (peat) for many years.

And over the course of millions of years, forms the fossil fuel: coal! Occasionally these deposits of peat get buried and trapped. And over the course of millions of years, forms the fossil fuel: coal!

Oil is formed by decaying aquatic animals and plants are trapped under sediment in a low-oxygen environment.

Nitrogen Cycle Nitrogen is essential for: Making proteins Making DNA

Nitrogen can be “fixed” by: Lightning Bacteria

Denitrification: the break down of nitrates to nitrites, and then nitrites to nitrogen gas

How do farmers replace nutrients in soils? Nitrates and phosphates (nutrients) will deplete from soils if farmers do not replace them. How do farmers replace nutrients in soils?

Fertilizers need to be used with caution. Fertilizers are materials used to restore nutrients and increase production from land Fertilizers need to be used with caution. Fertilizers can cause: Acidity in soils (effecting plant growth) Eutrophication in water bodies