Measuring decomposition with litterbags

Principle

A known mass of litter (e.g. leaves) is put inside a permeable bag and left out in the field. The bag is later collected and re-weighed; assuming minimal litter material enters or leaves the bag, the lost mass is a function of the decomposition rate.

Notes

The size and mesh size of litterbags can be chosen to match your project interests and site characteristics. However, you should make all of the litterbags in your study the same. If you don't have a pressing reason to do otherwise, make the litterbags 20 cm by 20 cm. Typical mesh sizes are less than 2 mm but be aware that this excludes macroinvertebrates from the bags, underestimating decomposition rate.

Equipment:

  • Leaf litter collected from the site
  • Trays
  • For the bags:
    • Fiberglass screen mesh
    • Hardware shears
    • Ruler
    • Safety pins
    • Metal tags
  • Balance
  • Drying oven
  • Flagging tape for putting litterbags in the field
  • Ziplock bags, sharpie, and cooler for collecting bags from the field
  • Beakers
  • Waxed paper

Procedure:

Air-dry the leaf litter on clean trays in the laboratory for up to seven days, depending on how dry the litter was when you collected it.

  1. For each litterbag:
    1. Using the shears, cut out a piece of mesh for each bag, measuring about 30 by 45 cm.
    2. Fold the mesh 20 cm from one of the short edges (leaving 5 cm sticking out at the top).
    3. Fold 5 cm in from each side, and secure each side with safety pins. You should now have a 20 cm x 20 cm pouch with an open flap.
    4. Fill out a metal label with an identification number unique to each litterbag. Put the label into the bag. Weigh the bag plus label and record the ID number and tare weight.
    5. Load the bag with litter. Less than 5 g of dry deciduous leaf litter per bag is about right. You don't want to overfill the bags or break the leaves.
    6. Weigh the filled bag and record its weight.
    7. Close the flap on the litterbag and secure it with safety pin(s).
      1. When all of the litterbags are complete, place them at your field site(s). Be sure that you will be able to find them again. If you bury them, use flagging tape to mark the bag's location above ground.
      2. At each sampling time:
        1. Collect the bags from the field site (at least four). Put each bag into a ziplock bag and place in a cooler for transport back to the lab as soon as possible.
        2. One at a time, process each sample:
          1. Brush off litter and soil from the outside of the bag Take off the metal label and make a new label with the sample number (from the metal label), the pickup date, the treatment (e.g. the soil type or litter type), and your initials. Put the label on a clean beaker.
          2. Weigh the empty labeled beaker and record the tare weight.
          3. Above a sheet of waxed paper, carefully open the litterbag. If there is any soil inside the bag, take it out as best you can.
          4. Carefully put the litter into the beaker, including material that fell on the waxed paper.
        3. Oven-dry the sample beakers at 60 degrees C for 48 hours (or a little more if necessary).
        4. Record the dry weight of each beaker. Transfer the litter to a labeled paper bag.

Analysis:

Your results are the percent of dry mass lost from each litter bag:



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