Biogeochemical Cycles

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.

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 _________.

The Hydrologic (Water) Cycle

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.

The Hydrologic Cycle

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

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!!!

Carbon Cycle-All life is based on elemental carbon!

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)

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

Carbon Sinks/Reservoirs

Carbon Sinks/ReservoirsSink Amount Billions of Metric TonsAtmosphere 578 (as of 1700)

766 (as of 1999)Soil Organic Matter 1500 to 1600Ocean 38,000 to 40,000Marine Sediments/Sed Rocks

66,000,000 to 100,000,000Terrestrial Plants 540 to 610Fossil Fuel Deposits 4000

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

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

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

Nitrogen Cycle-All life requires nitrogen compounds!

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

Nitrogen ReservoirsExists 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

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)

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.

Nitrification/Denitrification

Nitrification/Denitrification

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

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

Phosphorus Cycle