In a unique approach to studying the environment, a team of scientists from RMIT has used teabags to uncover how rising temperatures might affect the ability of wetlands to store carbon.
RMIT University’s Dr Stacey Trevathan-Tackett led the study published in Environmental Science and Technology as part of an Australian Research Council DECRA Fellowship while at Deakin University. Image Credit: Paul Carnell
An international team of scientists used an unconventional yet effective method to study wetlands' ability to store carbon, known as wetland carbon sequestration. They buried 19,000 green tea and rooibos tea bags across 180 wetlands in 28 countries to measure carbon retention in the soil.
Although using tea bags might seem unusual, they serve as a reliable proxy for tracking how carbon is released from soil into the atmosphere. This study marks the first large-scale, long-term application of this method, revealing which wetland types are losing the most carbon.
The research was led by RMIT University’s Dr. Stacey Trevathan-Tackett under an Australian Research Council DECRA Fellowship during her time at Deakin University and was published in Environmental Science and Technology.
The global study brought together a team of 110 co-authors, supported by numerous contributors, including undergraduate students and citizen scientists. Key team members included Dr. Martino Malerba and Professor Peter Macreadie from Deakin University and RMIT, Dr. Sebastian Kepfer-Rojas from the University of Copenhagen, and Dr. Ika Djukic from the Swiss Federal Institute for Forest, Snow, and Landscape Research (WSL).
This is the first long-term study of its kind, using this tea bags method, which will help guide how we can maximize carbon storage in wetlands and help lower emissions globally. Changes in carbon sinks can significantly influence global warming – the less carbon decomposed means more carbon stored and less carbon in the atmosphere.
Dr. Stacey Trevathan-Tackett, Senior Lecturer, RMIT University
Reading the Tea Leaves
Tea bags offer a simple and standardized method to explore how climate, habitat, and soil type impact carbon breakdown rates in wetlands.
At each wetland site, scientists buried 40 to 80 tea bags about 15 cm below the surface, marking their locations with GPS. Over a period of three years, they periodically retrieved the tea bags and measured the remaining organic mass to determine how much carbon the wetlands had preserved.
The study used two types of tea bags: green tea, which decomposes quickly, and rooibos, which breaks down more slowly. This dual approach allowed researchers to examine different types of organic matter and gain a detailed understanding of the wetlands' ability to store carbon.
“This data shows us how we can maximize carbon storage in wetlands globally,” Trevathan-Tackett added.
The Findings
The team explored the impact of temperature on carbon preservation in wetlands by analyzing local weather station data and comparing different climate regions.
“Generally, warmer temperatures led to increased decay of organic matter, which translates to reduced carbon preservation in soil,” explained Dr. Trevathan-Tackett.
The two types of tea used in the study reacted differently to temperature changes.
“For the harder to degrade rooibos tea, it didn’t matter where it was – higher temperature always led to more decay, which indicates that types of carbon we’d typically expect to see last longer in the soil were vulnerable to higher temperatures. With increasing temperatures, the green tea bags decayed at different rates depending on the type of wetland – it was faster in freshwater wetlands but slower in mangrove and seagrass wetlands. Increasing temperatures may also help boost carbon production and storage in plants, which could help offset carbon losses in wetlands due to warmer weather, but this warrants further investigation with future studies,” Trevathan-Tackett stated.
Freshwater wetlands and tidal marshes retained the most tea mass, highlighting their greater capacity for carbon storage compared to other wetland ecosystems.
The study’s findings are helping to build a greater understanding of wetland carbon sequestration. As part of the terrestrial TeaComposition initiative, led by Dr. Ika Djukic, data on litter decomposition has been collected from around 500 sites worldwide, leading to several peer-reviewed publications.
Applying the common metric across aquatic, wetland, marine and terrestrial ecosystems allows for a conceptual comparison and understanding of key drivers involved in the control of global litter carbon turnover. Now that we are starting to get a better understanding of which environments are storing more carbon than others, we can use this information to ensure we protect these areas from environmental or land-use change.
Dr. Ika Djukic, Researcher, The Swiss Federal Institute for Forest, Snow and Landscape Research WSL
Next Steps
The researchers will combine the data from this project with data from similar studies of land-based carbon sinks, such as forests, to guide the development of predictive global models.
Journal Reference
Trevathan-Tackett, S. M., et. al. (2024) Climate Effects on Belowground Tea Litter Decomposition Depend on Ecosystem and Organic Matter Types in Global Wetlands. Environmental Science and Technology. doi.org/10.1021/acs.est.4c02116