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




Source of CO2

Way to Reduce

burning fossil fuels

Use solar energy, wind energy


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 CaO + CO2


Nitrogen Cycle


1. production of industrial fertilizer

Human waste


2. fixation by bacteria


Animal waste


3. runoff

Plant growth



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.