Tea bag research brewing

Dr Barbara Anderson, of Landcare Research, Dunedin, is using tea bags to help track climate...
Dr Barbara Anderson, of Landcare Research, Dunedin, is using tea bags to help track climate change. Photo by Gerard O'Brien.
An Otago scientist has buried more than 800 Lipton tea bags on a mountainside near Wanaka to help her study climate change.

Landcare Research scientist Dr Barbara Anderson is studying, in minute detail, a ridge on Mt Cardrona stretching from the peak at 1936m to the valley floor at 500m.

The study will provide a benchmark of information against which future climate change can be measured.

As part of her study, Dr Anderson has included the ''Tea Bag Index'' (TBI).

The TBI was developed by scientists in the Netherlands and Iceland and is designed to measure the speed at which organic material decomposes.

The carbon in the decaying material is either retained in the soil or released into the atmosphere as carbon dioxide.

Dr Anderson said she wanted to see how decomposition rates were influenced by temperature and the specific plants and microbes at a location.

The traditional way to measure decomposition, Dr Anderson said, was to use hand-made bags of dried organic material, referred to as litter bags.

''The litter bags are not only time-consuming to make but there's a huge amount of variance in the plant material in the bags, unlike the tea bags which are standardised,'' she said.

All TBI studies use Lipton tetrahedron-shaped tea bags - the green tea and rooibos varieties - made of synthetic mesh, which ensures decomposition rates are dependent only on the environment they are placed in and not the tea bags themselves.

However, the tea sold in New Zealand comes in mesh bags designed to decompose, and that required Dr Anderson to ask colleagues, friends and family in the United States, Germany and the Netherlands to source the right tea bags.

PhD student Xiaoqing Li then spent nine days drying the 810 tea bags and individually labelling and weighing them.

After being buried for 90 days, the tea bags will be dug up and reweighed.

The leafy green tea was expected to decompose more quickly than the woody, waxy rooibos, Dr Anderson said.

''The decomposition rate is based on the difference between the weight change in the green tea and the rooibos.''

The data collected will be made available to the scientists who developed the TBI, and will be used in global soil maps and climate models.

Dr Anderson, who is on a five-year Rutherford Discovery Fellowship, said the rate organic matter degraded was ''one small piece in the puzzle'' of climate change.

A colleague was also using the TBI, and had buried 240 tea bags in the Takahe Valley, in Fiordland.


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