1. Biogeochemical Cycles

2. Introduction Most elements can exist in different states and chemical forms as they move within and between the 4 spheres. Examples of elements:______________ Elements exist in different compounds as they move from one reservoir to another. Examples of compounds:_____________ Elements and compounds have significant impacts on the spheres, as well as on the well-being of living things.

3. The Cycles The water cycle, the carbon cycle, nitrogen cycle, phosphorus cycle, etc. all involve _____________ among the four spheres of Earth. A cycle is a __________ of events that _________.

4. The Hydrologic (Water) Cycle

5. Hydrosphere-Atmosphere Interactions Heat from Sun causes water to evaporate becoming water vapor, the gaseous state of water. Water vapor rises/cools becoming clouds and forming precipitation. Precipitation falls down to Earth and fills the rivers, streams etc.

6. The Hydrologic Cycle Water cycles through the Earth system in solid, liquid and gas forms, but the total amount of water remains relatively CONSTANT.

7. Hydrosphere-Atmosphere Interactions Evapotranspiration- the rapid cycling of water vapor into the atmosphere by evaporation from the Earth’s surface and transpiration from plants. When water returns to the oceans, one turn of the water cycle is complete. Water is never created or destroyed only changed!!!

8. Carbon Cycle-All life is based on elemental carbon!

9. Carbon Cycle Not much in Earth’s crust (mostly oxygen and silicon) Carbon extracted from atmosphere through photosynthesis Combines w/other elements to form many organic molecules Transferred to organisms who consume plants Returns to atmosphere when organism decomposes Becomes trapped in sediment; forms fossil fuels---back to atmosphere (when we burn)

10. Carbon Sinks/Reservoirs Stored in sinks (reservoirs) in spheres: Biosphere- molecules in dead and living things; organic matter in soils Atmosphere- CO2 gas Geosphere- fossil fuels in sedimentary rock Hydrosphere- in oceans as dissolved atmospheric CO2; calcium carbonate in shells

11. Carbon Sinks/Reservoirs

12. SinkAmount Billions of Metric Tons Atmosphere578 (as of 1700) 766 (as of 1999) Soil Organic Matter1500 to 1600 Ocean38,000 to 40,000 Marine Sediments/Sed Rocks 66,000,000 to 100,000,000 Terrestrial Plants540 to 610 Fossil Fuel Deposits4000

13. Lake Nyos Crater lake w/in Oku volcanic field; extinct stratovolcano Pocket of magma leaks CO2 into water One of only 3 lakes w/CO2 saturation Named “most dangerous lake” by Guinness Book of World Records

14. Lake Nyos Disaster Sudden outgassing of 1.6 million tons of CO2 Cloud rose 100 km Displaced air; suffocated 1700 people w/in 25km Rising water generated wave

15. Lake Nyos Disaster CO2 1.5 times more dense than air Caused cloud to “hug” the ground as it travelled Natural dam could fail, causing floods Scientists using “degassing” method

16. Nitrogen Cycle-All life requires nitrogen compounds!

17. Nitrogen Cycle The nitrogen in the air is absorbed by bacteria in the soil or water The bacteria chemically change nitrogen from the air into nitrogen compounds, which are vital to the growth of plants. Animals eat the plants, absorbing the nitrogen As animals decay nitrogen reenters the soil and chemical processes release nitrogen back into the atmosphere

18. Nitrogen Reservoirs Exists in many forms-organic, ammonium, nitrate, nitrogen gas Atmosphere- ~78 % as N2 gas ***MAJOR RESERVIOR! Biosphere- used by living organisms to build amino acids, DNA, & proteins; organic matter in oceans and soils Hydrosphere-deposited from atmosphere via precipitation Geosphere- small amounts

19. Nitrogen Fixation/Nitrification N2 not usable by living things “Fixed” to organic form in soil and water by bacteria Both N atoms separate and combine with hydrogen to form NH4 (ammonia) Ammonia toxic to most organisms--- plants convert to nitrate (NO3)

20. Lightening and Nitrogen Fixation *Lightning plays a minor part in the fixation of atmospheric nitrogen. The extreme heat of a lightning flash causes nitrogen to combine with oxygen of the air to form nitrogen oxides. The oxides combine with moisture in the air. The fixed nitrogen is carried by rain to the earth, where, in the form of nitrates, it is used by plants.

21. Nitrification/Denitrification

23. Denitrification When plants and animals die, or excrete waste, nitrogen re-enters soil where decomposers break down and produce ammonia, then nitrate Gets back to atmosphere by bacteria that convert nitrate (NO3) into N2 gas

24. Human Impacts Nitrogen fertilizers-increase denitrification; leach into groundwater… Fossil fuel and forest burning-release solid N into atmosphere Livestock ranching- releases large amounts of ammonia into soil/water from wastes Sewage waste/leaking septic tanks

25. Phosphorus Cycle