In an international investigation, researchers from the University of Algarve's (UAlg) Centre for Marine Sciences (CCMAR) used tea bags as a tool to measure the rates at which organic matter decomposes. To assess the wetlands' capacity to sequester carbon in the soil, a global team of researchers buried 19 thousand tea bags of green and rooibos tea in 180 wetlands across 28 countries.

The tea bag technique was used in Ria Formosa, a coastal lagoon known for its high biodiversity and ecological significance in the district of Faro by researchers from CCMAR and UAlg. Intertidal seagrass (strips of coastal land situated between the mean levels of high and low tide), low-lying salt marches, and meadows of ‘caulerpa prolifera’, a species of green algae, are the three types of habitats in the Ria Formosa where the researchers buried 120 sachets.

Even though they may seem like an odd tool to quantify this occurrence the bags are “a proven method for measuring the release of carbon from the soil to the atmosphere”, as mentioned in a statement. According to Carmen Santos, a researcher at CCMAR, “Ria Formosa offers an excellent natural laboratory for understanding how temperature and ecosystem characteristics influence carbon storage”. This is the first-time tea bags have been utilised in long-term and large-scale studies.

As mentioned in the study, higher temperatures caused organic matter to decompose quicker, which resulted in less carbon being preserved in the soil, with the two distinct teas acting in different ways. “For the harder-to-degrade rooibos tea, it didn’t matter where it was – higher temperatures always led to greater decomposition, indicating that the type of carbon we would normally expect to last longer in the soil was vulnerable to higher temperatures”, explained the researcher and lead author of the study Stacey Trevathan-Tackett, from the Royal Melbourne Institute of Technology in Australia. As she added, “As temperatures rose, the green tea bags decomposed at different rates depending on the type of wetland: it was faster in freshwater wetlands, but slower in mangrove and seagrass wetlands”.