The Carbon Cycle: What Goes Around, Comes Around
Part A: A Forest Carbon Cycle
Plants and Food Webs: Passing the carbon on!
The global carbon cycle cannot exist without plants and the food webs they support. Plants are autotrophs and thus make their own food in the form of glucose sugar. Heterotrophs, like ourselves, do not photosynthesize and must instead find and eat food. This food is made of proteins, carbohydrates, fats and oils, and nucleic acids. Heterotrophs break these complex organic carbon compounds down into smaller molecules and biosynthesize new organic carbon compounds.
Soil microbes, the smallest organisms in the food web, have one of the most critical roles in transforming and moving carbon compounds through food webs and ecosystems. Their role is threefold:
- When soil microbes decompose dead material, they break down larger carbon compounds into smaller compounds. This process releases CO2 to the surrounding soil and to the atmosphere (soil respiration).
- Soil microbes move carbon down into the soil where it can be stored for hundreds of years.
- Soil microbes change nitrogen compounds into forms that can be used by plants.
Examine the terrestrial food web image below, taking take time to follow the carbon. Then, check your understanding of how carbon moves through food webs by answering the questions below.
Check your understanding of how carbon moves through food webs by answering the questions below. Select all the answers that are correct and then click the Check Answers button at the bottom of the list.
Stop and Think
1. Examine the Terrestrial Carbon Cycle food web diagram again. Describe how the carbon from carbon dioxide molecules in the atmosphere can end up in a coyote. Use a diagram to help you explain your answer if you need to.
The Forest Carbon Cycle Game
You can't see the carbon flowing through the image of the forest carbon cycle above, but taking on the role of a carbon atom moving through a forest carbon cycle will help you understand how carbon atoms move around the Earth' system. Before beginning the forest carbon cycle game, there are two carbon cycle terms you need to know before starting the game:
Carbon Reservoir:A carbon reservoir is a place in the Earth System where carbon is stored. These include bodies of water - oceans, lakes, streams- soil, rock, atmosphere, fossil fuels, living things such as animals and plants. A carbon reservoir is a place in the Earth System where carbon is stored. Carbon reservoirs can be large or small and somewhere in-between.
Carbon Process: A carbon cycle process (also called a flux) causes carbon to move from one reservoir to another. Examples of carbon processes are photosynthesis, respiration and combustion. A carbon cycle process (flux) causes carbon to move from one reservoir to another. Processes in the forest carbon cycle game include photosynthesis, respiration, decomposition, ingestion, excretion, combustion, exudation and diffusion
Your teacher will set up the stations and tickets for the Lodgepole Forest Carbon Cycle game in your classroom. As you play the Forest Carbon Cycle game developed by the University Corporation for Atmospheric Research, you will take on the role of carbon atoms traveling through the various carbon reservoirs of a forest. The stations that you see posted around the classroom represent reservoirs of carbon typically found in a forest ecosystem. For example, if you are at the "ATMOSPHERE" station, then you are a carbon compound currently stored in the atmosphere reservoir. Carbon can stay in these reservoirs sometimes for short time scales (minutes to years) and in some cases, for much longer time scales (thousands to millions of years).
Step 1: You will be given a Lodgepole Forest Carbon Cycle Passport Chart and assigned a carbon reservoir station to start at. This chart will be the record of your journey through the carbon reservoirs. Fill-in the name of reservoir and the Earth's sphere(s) in your Forest Carbon Cycle Passport Chart. Two examples have been provided for you on the chart.
Step 2: Draw a ticket. The ticket will tell you where you will be going next and how you will get there. The ticket may also have special instructions such as "count to 100 and then choose a different ticket."
Step 3: For each round, record the required information in the Lodgepole Pine Forest Carbon Cycle Chart.
Step 4: When your class has finished, compare your carbon cycle journeys. How were they the same? How were they different?
DiscussAs a class, discuss:
- Why weren't all the carbon journeys through the forest the same?
- Carbon does not spend the same amount of time in each of the carbon reservoirs. Why do you think that is?
Next watch a short animation Carbon Dioxide and The Carbon Cycle. Click on the carbon cycle button and spend some time following the carbon dioxide molecules as they cycle through the various carbon reservoirs. Note that the combustion of fossil fuels and wildfires also adds carbon to the forest carbon cycle. Finally, answer the Checking In questions below.
How much carbon moves? Gigatons, Carbon Sinks and Carbon Sources
Key ideas to remember about carbon sinks and sources are:.
- Carbon reservoirs can naturally fluctuate between being a source or a sink. For example, a forest made of deciduous trees Trees and other plants that seasonally lose their leaves- usually in Autumn. will be a carbon sink in the summer but change to a carbon source in the winter when photosynthesis stops.
- Human activity can change a carbon sink into a carbon source. For example, fossil fuels still in the ground are a carbon sink. When they are taken out of the ground and burned for fuel, they become a carbon source.
- Carbon sinks may have limitations on the amount of carbon they can absorb. For example, scientists are currently studying the ability of forests and oceans to absorb the increasing gigatons of carbon being emitted to the atmosphere from the burning of fossil fuels.
Examine the gigatons of carbon moving into and out of the atmosphere and then answer the Checking In questions below.
A carbon cycle out of balance?Scientists consider the carbon cycle to be in balance when the total amount of carbon moving into vegetation and oceans is equal to or greater than the amount of carbon going into the atmosphere. Examine the "Gigatons and The Carbon Cycle" diagram again and then answer the Stop and Think questions below.
Stop and Think:
2. Does the carbon cycle in this diagram appear to be in balance or out of balance? Use specific evidence from the diagram to support your answer.
3. Imagine that we could go back to pre-industrial times before fossil fuels were being burned for energy. Would a pre-industrial carbon cycle be in balance or out of balance? What makes you think so?
Research the latest research! New research on the carbon cycle, climate and the environment is on-going. You can use ScienceDaily and Phys.org to research recent research on ecosystem carbon cycles by using combinations of the following tags: ecosystem, carbon cycle, forests, soil nutrients, soil microbes, gigatons. Here are two examples:
Watch The Carbon Cycle