Biogeochemical Cycles

WATER CYCLE • Also called the Hydrologic Cycle • Water is circulated through the global ecosystem.

• Fresh water evaporates and condenses back to earth.

OVERVIEW Water evaporates into the atmosphere, condenses, and falls to earth as rain, snow, or sleet. The water then flows to the oceans to begin the cycle again. Energy to keep the cycle moving comes from the sun.

KEY PROCESSES OF THE WATER CYCLE



Evaporation



Transpiration



Condensation



Precipitation

EVAPORATION *Occurs when solar energy causes water from oceans, fresh water bodies, land, and plants to move from the earth to the atmosphere * All impurities dissolved in water are left behind; water vapor is water pure

Transpiration •The evaporation of water from leaves

CONDENSATION * The process by which a gas becomes a liquid * Clouds form from the condensation of water vapor

PRECIPITATION * The process by which water falls from clouds as rain, snow, sleet, and hail.

OTHER STUFF ABOUT WATER *

Water flows over the land as runoff or soaks deep into the soil and rock underground becoming groundwater .

* An aquifer is an underground reservoir of fresh water trapped by rocks.

Planet earth’s water system is a closed system. Water molecules are used over and over again. No new water molecules leave or enter the water system.

BIG IDEA: The water we drink connects us with living organisms from our distant past.

This same water will be used by organisms in the future.

Critical Thinking

“Water, water everywhere, but not a drop to drink!” Water covers 75% of planet earth. The water cycle is a closed system that returns water repeatedly to our planet. So, water is a renewable resource. If this is true, why is it important to conserve water?

The Carbon Cycle

• Basic constituent of all organic compounds (Life !) • 760 billion tons in the atmosphere.

• 0.035% of the atmospheric elements.

Forms of Carbon • Atmosphere = CO 2 • Living and decaying matter = proteins and carbohydrates • Oceans • Rocks = salts = carbonate solids • Fossil fuels = Petroleum, hydrocarbons, and coal

Atmospheric Carbon Sources Carbon enters the atmosphere in many ways: • Cellular Respiration • The decay of plant and animal matter • The evaporation of the ocean waters • Volcanic activity • The burning of fossil fuels

Terrestrial Carbon • Assimilation through photosynthesis by autotrophs • Ocean reservoirs (“sink”) • The weathering of rocks • Organic matter which becomes fossil fuels.

CARBON CYCLE

Carbon Cycle

The Carbon Balance

• The net result of all of these interactions in that the amount of carbon in the atmosphere remains constant even though carbon atoms constantly leave and enter the atmosphere as they cycle.

Upsetting the Balance • Burning of fossil fuels (6 billion tons per year) • Deforestation (1 billion tons per year) The concentration of carbon in our atmosphere has increased 25% in the last century alone!

Critical Thinking The increase in carbon dioxide in the atmosphere has precipitated what scientists now call “The Greenhouse Effect”. The CO 2 molecules trap the suns energy and heat as it is reflected from the planet back towards the atmosphere. As global temperatures continue to rise, the concern is not with the fact that we have a greenhouse effect, but whether human activities are leading to an enhancement of the greenhouse effect by the emission of greenhouse gases through fossil fuel combustion and deforestation. Create a graph to show how human activities could make the temperature on our planet rise regardless of natural temperature cycles over long periods of time on the planet. (Hint: Think slope of the temperature line.)

NITROGEN CYCLE • Overview – Needed by organisms to make proteins – Makes up 80% of our atmosphere – Nitrogen (N must be 2 ) can not be used by organisms and “fixed”

NITROGEN CYCLE

STEPS OF THE NITROGEN CYCLE •Nitrogen Fixation •Nitrogen Reservoirs •Nitrogen Release

NITROGEN FIXATION Nitrogen-fixing bacteria are found in soil, water, and the roots of some plants.

Nitrogen fixation: process by which bacteria converts gaseous nitrogen (N 2 ) into ammonia (NH 3 ).

NITRIFICATION



bacteria take ammonia (NH

3

) and convert it into nitrites (NO

2 -

) and nitrates (NO

3 -

)

NITROGEN RESERVOIRS Plants nitrates from the soil.

take in Animals can obtain nitrogen by eating plants.

NITROGEN RELEASE Returned to the soil by:

•

Animal waste

•

Decomposition of organisms

•

Ammonification = the decomposition of organic nitrogen to ammonia

NITROGEN RELEASE Returned to the atmosphere by:



Denitrification: process by which bacteria convert nitrate (NO 3 ) back to gaseous nitrogen (N 2 ).

Critical Thinking Farmers add fertilizer to their crops to increase their yield. Extra fertilizer often is carried in irrigation waters to rivers, streams, ponds, and lakes nearby. What are some of the possible outcomes for a lake ecosystem that receives the fertilizer runoff?