Biogeochemical cycles Water, Carbon, Nitrogen

THE WATER CYCLE (hydrologic) Water moves between the ocean atmosphere, and land. Water molecules enter the atmosphere as water vapor, a gas that forms from bodies of water.

The process of water changing from liquid to atmospheric gas is called evaporation. Evaporation is the stage where water travels from the Earth’s surface to the atmosphere. Water molecules are heated up by the sun, and water is changed from a liquid form to a gas form. Evaporation can be seen in your life every day. Have you ever watched a kettle boil? The steam you see going in to the air is an example of evaporation!

It can also enter the atmosphere from the leaves of plants in a process called transpiration.

As warm moist air rises, it starts to cool As warm moist air rises, it starts to cool. Eventually, the water vapor forms tiny droplets that form clouds. This is known as condensation.

DROP SIZE AND CLOUD APPEARANCE The smaller the drops in a cloud the brighter the tops appear (and the darker the bases). Smaller droplets scatter more sunlight, while large drops allow more sunlight to pass through. This explains why the heavily raining part of a shower cloud or thunderstorm is usually brighter than just the cloudy part. The cloud droplets have combined into large raindrops, which allow more sunlight to pass through them.

When the droplets become large enough, the water returns to the Earth’s surface in the form of precipitation–rain, snow, sleet, or hail.

On land, much of the precipitation runs along the surface of the ground until it enters a river or stream that carries the runoff back to an ocean or lake.

Rain seeps into the soil, some of it deeply enough to become ground water. Water in the soil enters plants through roots, and the water cycle begins again.

THE WATER CYCLE:

What about the Carbon Cycle? Carbon is continually recycled between inorganic and organic forms.

THE CARBON CYCLE: Inorganic carbon exists as a gas in the atmosphere, and is dissolved in the ocean water.

Fixing Carbon, nitrogen and phosphorus is fixed when these elements are joined to atoms of other elements. This makes them useful for living organisms, which can use the fixed elements in organic compounds.

During the carbon cycle, inorganic carbon in the form of carbon dioxide (CO2) is converted to an organic form through photosynthesis. This is called fixing carbon. Plants and algae can fix carbon through photosynthesis.

Organic carbon is changed to inorganic carbon once again through metabolism (cellular respiration).

Fossil fuels are a form of stored organic carbon Fossil fuels are a form of stored organic carbon. When fossil fuels are burned through combustion (through human activities), CO2 is produced, which may then reenter the atmosphere.

CO2 is a greenhouse gas. An increase in greenhouse gases is causing global warming.

The Carbon Cycle

The Nitrogen Cycle Nitrogen is continually recycled between inorganic and organic forms.

All organisms require nitrogen to make proteins. Nitrogen exists in the atmosphere as inorganic N2. Inorganic nitrogen can be converted to an organic form that can be used by plants & algae.

N2 can be fixed by lightning. and soil bacteria (such as those in root nodules of plants). This is called fixing nitrogen, as atmospheric nitrogen is chemically joined or fixed to other atoms.

[Inorganic nitrogen is converted to organic forms such as: ammonia (NH3), nitrate ions (NO3-),and nitrite ions (NO2-) through the action of bacteria.

Farming adds organic nitrogen in the soil in the form of fertilizer.

Decomposers return nitrogen to the soil (in the form of ammonia), bacteria while other bacteria convert it to back to nitrogen gas (N2) in a process called Denitrification.

Nitrogen is continually recycled between inorganic and organic forms.