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Litter Bags

Time: 3 Class periods Setting: Schoolyard Type of Organism: invertebrates microorganisms plants Habitat: forest grassland urban
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Guiding Questions

Does decomposition vary in different places?
Do large soil organisms (e.g., worms) speed up decomposition?
Do environmental factors (e.g., moisture, temperature, nutrients) affect decomposition?
Do different materials (e.g., oak vs. maple leaves) decompose at different rates?

    Decomposition is the result of the use of dead material (detritus or litter) as food by many different organisms. A common approach used by scientists interested in the factors that speed or slow the process is to use Alitter bags". These usually are made from screening and hold a standard amount of detritus. They can be placed in the environmentCsoil, stream, pond, etc. and then retrieved after a set amount of time and the fate of the detritus determined. Bags can be buried in different places, treated in different ways and/or filled with different materials. They also can be crafted from screening with different sizes of holes to allow different kinds of organisms to get to the detritus inside.

    The instructions here are rather generic. They are intended to guide K-6 teachers to develop one or several investigations for or with their students to explore questions of their own interest.

    • Fiberglass window screening, nylon hose, or cheese cloth.
    • Stapler(s) and staples for sealing bags.
    • Scissors or paper cutter for cutting screening.
    • Shovel or trowel for burying bags.
    • Markers (stakes, flagging, etc.) for marking location of bags.
    • Material to be decomposed (e.g., leaves, paper towel, etc.).
    • Piece of cardboard to use as a template when cutting material to size.
    • Materials for different treatments if desired (e.g., chemicals, etc.).

    Reflect on decomposition and then plan a decomposition study

    1. Start with an exploration of your students' current understanding of the ideas they want to exploreCin this case, decomposition.  
    2. Next, give them some first-hand contact with decomposition materials that are rotting, decomposer organisms, etc.  
    3. Decide what factor (one is best) you want to explore by generating and then refining questions about decomposition.  
    4. Design a study using buried bags to test the factor you have identified.  

    Prepare the bags

    1. Cut the screening to the desired size (for 4" squares, cutting 4" x 8" pieces saves having to seal one edge).  
    2. Cut the material to be decomposed into a uniform size (e.g., 1" x 2") using the template and scissors, unless studying whole things like seeds, etc.  
    3. Make holes in the screening using a heavy duty hole puncher.  
    4. Fold over the screening and staple two of the remaining edges shut. Make sure there are no spaces between staples.  
    5. Place the desired number of pieces of the material to be decomposed into each bag. Make sure the pieces are arranged the same way in all bags. Include a marker inside the bag to identify it (use plastic or metal that won't decompose!) if desired.  
    6. Staple the remaining edge shut.

    Bury the bags

    1. Locate the sites where you will bury the bag and record the locations in your notebooks.  
    2. Randomly assign which treatments (e.g., sugar- versus water-treated paper towel pieces) will go where.  
    3. If burying in soil, dig under the top 1"-3" of soil and pull it up and back disturbing it as little as possible.  
    4. Place 1 bag in each hole, trying the get it as level as possible.  
    5. Replace the surface layer over the bag and make sure it is completely covered. Press firmly.  
    6. Mark the location of each bag. Use your creativity...this can be a real challenge!  
    7. Apply any treatments are included in your study, e.g., added water.

    Retrieve the bags and collect data

    1. Find the bags at the pre-determined time and carefully dig them up.  
    2. Make careful observations of organisms in and around the bags as you do thisCsome will scurry away and others, like plant roots growing through the bags, will be broken off.  
    3. Measure the amount of decomposition that has taken place. Decide with your class what the best way to do this is. Placing a grid (e.g., graph paper photocopied onto overhead acetate) over the detritus and determining the percentage of squares with evidence of decomposition is one method to consider.