Tea bag decomposition

Decomposition is a critical ecosystem process that mediates nutrient recycling and the carbon cycle in ecosystems. In freshwater systems, decomposition is often mediated by the microbial and invertebrate communities. Decomposition releases CO2 into the atmosphere. Faster decomposition of organic material can release more CO2 than what is being stored by the system, and could potentially contribute to global warming. Tea bags are an easy and cheap way of measuring decomposition rates, which can change rapidly when under treatments such as warming. A similar alternative, cotton strips, can also be used.

Materials

Tea bags (Lipton Green Tea or Lipton Rooibos)
Mesh bags (coarse or fine) to hold the tea bags
Bricks (or other heavy material)
Drying oven
Dessicator
Scale

Procedures

Setup

Put tea bags in mesh bags and close them firmly (e.g. with staples). Determine the number of tea bags you want to experiment with depending on the number of replicates or sampling events you want to carry out.
Attach mesh bags to bricks using zip ties so that they will sit above the sediment when in the water (see illustration)

For deployment and collection use arm-length work gloves to prevent DNA contamination and protect against chemicals in the water. Bleach and rinse the gloves between each pond.

Deployment

Lay the bricks in the same location in each pond, ensuring that no bags are trapped under the bricks (see illustration)
Mesh bag collection periods will vary depending on the experiment carried out.

Collection

Slowly remove the bricks from the mesocosm floor to minimise disturbances to the system. Lift brick with both hands.
Remove the mesh bags from the bricks using scissors. Make sure to keep the different types of tea bags separate and labelled.

Analysis

The tea bags first need to be carefully cleaned to remove any algae or other dirt from them. Gently wash them in a shallow tray of deionised water if they do not look too delicate. If there are rips or tears in the bag, do not wash them. If any tea escapes the bag, make sure it is collected and added to the weighing boat.
Check the tag of the tea bag to determine which kind of tea it is and make note of it. Different types of tea may decompose at different rates.
Dry the tea bags overnight at 40 °C, then store them in a dessicator for at least 2 hours to remove all water weight.
Weigh the tea bags and compare it to the original standardised weight of that tea bag flavour and brand.

Weight (before) - Weight (after) / Days in pond = Decomposition Rate

Potential responses

Decomposition rates are known to respond positively to increases in temperature. These increases could be exponential, linear, or eventually plateau after reaching a certain "maximum" temperature. The graph below illustrates these potential response curves.

Tea bag setup

ILlustrations

Place the bricks on the mesocosm floor, ensuring that no bags are trapped under the bricks. The zip ties used to tie the mesh bags to the bricks ensure they float above the sediment.

The diagram to the left also includes leaf bags, which are an alternative method of measuring decomposition.

A tea bag being weighed after they have been in the mesocosms for 5 weeks. The tea bags are very delicate at this stage and must be handled carefully.

Organised and labelled tea bags after weighing. You can clearly see the varying stages of decomposition in these bags.