Phosphorus Cycle

5. Raising phosphate increases runoff and it will lead to eutrophication. This overgrowth of algae depletes oxygen once they die and while some species thrive they relase toxins. Repeated cycles of life and death of algae can make small lakes shallow as mats of dead algae accumulate on lake beds.

Carbon Cycle

1.

Source of CO2	Way to Reduce
burning fossil fuels	Use solar energy, wind energy
Respiration	Limit population growth
Producing cement	Look for alternative building materials; build smaller ones

2. forest fires, animal respiration, volcanoes, decomposition

3. Life removes CO₂ from the atmosphere through photosynthesis but replaces it through respiration.

4. Replanting of trees.

5. We burn too many fossil fuels.

6. Methane, coal and petroleum contain carbon which combines with oxygen to produce carbon dioxide.

7. CaCO₃ àCaO + CO₂

Nitrogen Cycle

1. production of industrial fertilizer

Human waste

2. fixation by bacteria

Lightning

Animal waste

3. runoff

Plant growth

Denitrification

4. Plants need nitrates and ammonium to produce protein

5. Animals get their nitrogen from meat or plant protein.

6. Fertilizer production requires energy, which is often obtained fro burning fossil fuels.