Biogeochemical Cycles

In each Biogeochemical Cycle, a pathway forms when a substance enters living organisms such as trees from the atmosphere, water, or soil and stays for a time in the living organism.

Substances cycle between a living reservoir (an organism that lives in an ecosystem) and a nonliving reservoir. Examples of substances that cycle: –Water –Carbon –Nitrogen –Phosphorus

The Hydrologic (Water) Cycle is Driven by the Sun Hydrologic Cycle is divided into two general parts: –Living –Nonliving

Nonliving Portion Water vapor from atmosphere condenses and falls to earth’s surface as rain or snow. Some water seeps into ground (Groundwater) Some returns to the atmosphere (Evaporation)

Living portion In Plants: –Water is absorbed through the roots –Water then moves up through the plant and evaporates into the atmosphere (Transpiration)

More than 75% of the moisture in thickly vegetated ecosystems (ex. Rainforest) pass through plants and transpire.

The Hydrologic Cycle – one last look Click here to go to an online animation of the carbon cyclehere

Check-in Questions Why is the hydrologic cycle important? How can/do humans impact the hydrologic cycle? Why would farmers care about the hydrologic cycle?

The Carbon Cycle – first look

The Carbon Cycle Carbon is used by living organisms to produce organic molecules. Carbon returns to air and water in three ways: –Respiration –Combustion –Erosion

Respiration Oxygen used to oxidize organic molecules during cellular respiration. CO 2 is the end product.

Combustion Also known as burning. Carbon can become trapped in wood or other formerly living organisms. Heat and pressure underground transform remains of organisms into fossil fuels. The carbon is released when the fossil fuels are burned. Carbon is also released when living organisms are burned (i.e. forest fires)

Erosion Marine organisms use CO 2 in water to make calcium carbonate shells. Over long periods of time, these shells become limestone (CaCO 3 ) As limestone erodes, carbon is released.

Carbon Cycle – one last look Click here to view an animated version of the carbon cycle.here

Check-in & discussion questions What are some of the contributors to atmospheric CO 2 ? How is some of the CO 2 removed from the atmosphere? What are some of the carbon sinks in the environment? How can/do humans impact the carbon cycle?

The Nitrogen Cycle Nitrogen gas makes up 78% of Earth’s atmosphere. Most living things cannot use the gaseous form. Thus nitrogen is often a limiting factor for plant growth.

4 Major Parts of Nitrogen Cycle (1)Fixation (2)Assimilation (3)Ammonification (4)Nitrification (5)Denitrification

Nitrogen Fixation Makes inert N 2 gas usable by living things. Combining nitrogen with oxygen, hydrogen or carbon to form other molecules, like ammonia. Example: N H e − → 2 NH 3 + H 2 Fixation can occur: –By free-living and symbiotic bacteria (legumes host these in their root nodules) –Through lightning strikes

Ammonification Bacteria can turn N 2 gas into NH 4 + When a plant or animal dies, or an animal expels waste, bacteria or fungi convert the nitrogen back into ammonium (NH 4 + ). ammonium

Nitrification The conversion of ammonium ions [NH 4 + ] into nitrites [NO 2 - ] and then nitrates[NO 3 - ] by bacteria in the soil. Nitrites are very soluble in water and at this stage may get into the groundwater and contribute to eutrophication.

Assimilation Animals “assimilate” nitrogen by eating plants. Plants absorb nitrate or ammonium ions from the soil via their root hairs. Ammonium ions [NH 4 + ] are used to manufacture proteins and other molecules.

Denitrificaiton The conversion of nitrates back to gaseous nitrogen [N 2 ] by free-living bacteria in soil This conversion occurs in conditions with low levels of oxygen.

The Nitrogen Cycle – last look Click here to get to the online link of the animated nitrogen cyclehere

Check-in Questions What is nitrogen fixation? Why is nitrogen fixation important for living things? What is the role of bacteria in the nitrogen cycle? Why is nitrogen important to farmers? Why don't legumes need nitrogen-containing fertilizers? How can/do humans impact the nitrogen cycle?

The Phosphorus Cycle

Unique Features of the Phosphorus Cycle One of the slowest of all biogeochemical cycles. Does not include the atmosphere as a reservoir Often the limiting nutrient in aquatic environments. Largest reservoir of phosphorus is sedimentary rock.

The Phosphorus Cycle – one last look

Check-in Questions What is the largest reservoirs of phosphorus in the cycle? How does phosphorus get from rocks into the food chain? How does phosphorus get from the food chain back into sediments/rocks? How can/do humans impact the phosphorus cycle? Why should farmers care about phosphorus?

Atmospheric Cycle Source of sulfur is Earth’s crust. Sulfur (H 2 S) enters the atmosphere by: –Volcanic eruptions –Fossil fuel combustion –Released from bacteria as by-product of metabolism –From the ocean as sea spray (Dimethyl Sulfide – DMS)

Combines with O 2 to form SO 2 Sulfur returns to land as dry particles or in rain Sulfur dioxide gas (SO 2 ) can combine with water to form sulfuric acid (H 2 SO 4 ) – acid rain Acid Rain

Sulfur in the Food Chain Sulfur in soluble form is taken up by plant roots and incorporated into amino acids. It then travels through the food chain and is eventually released through decomposition.

Sulfur Cycle – one last look Click here for an animated version of the sulfur cycle.here

Check-in Questions What are the main transformations of S in the sulfur cycle? How does sulfur get from the Earth’s crust (rocks) into the atmosphere? How can/do humans impact the sulfur cycle?