The international team of scientists buried 19,000 bags of green tea and rooibos in 180 wetlands across 28 countries to measure the ability for wetlands to hold carbon in their soil, known as wetland carbon sequestration.

While tea bags may seem an unusual instrument to measure this phenomenon, it is a proven proxy method to measure carbon release from soil into the atmosphere. However, this is the first time teabags have been used for a large-scale, long-term study and the tea leaves have revealed which types of wetlands are leaking the most 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.

The global study involved 110 co-authors on the paper, along with many others who helped such as undergraduate students and citizen scientists. Core team members included Dr Martino Malerba and Professor Peter Macreadie from Deakin University and RMIT, Dr Sebastian Kepfer-Rojas from the University of Copenhagen in Denmark 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 maximise carbon storage in wetlands and help lower emissions globally,” said Trevathan-Tackett, who is now in RMIT’s School of Science.

“Changes in carbon sinks can significantly influence global warming — the less carbon decomposed means more carbon stored and less carbon in the atmosphere.”

Reading the tea leaves

Tea bags provide a simple and standardised way to identify how climate, habitat type and soil type influence carbon breakdown rates in wetlands.

At each site, scientists buried between 40 and 80 tea bags about 15 cm underground and collected these at various time intervals over three years, tagging their GPS location. They then measured their remaining organic mass to assess how much carbon had been preserved in the wetlands.

The project used the two types of tea bags (green and rooibos) as measures for different kinds of organic matter found in soils. Green tea consists of organic matter that decomposes easily, whereas rooibos decomposes more slowly. Using both types of tea bags in this project enabled the researchers to gain a more comprehensive picture of the wetlands’ capacity for carbon storage.

“This data shows us how we can maximise carbon storage in wetlands globally,” Trevathan-Tackett said.

The findings

The team studied the effect of temperature in two ways: using local weather station data for each site and comparing differences in climate regions.

“Generally, warmer temperatures led to increased decay of organic matter, which translates to reduced carbon preservation in soil,” Trevathan-Tackett said.

The two tea types acted differently with increasing temperature.

“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,” Trevathan-Tackett said.

“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.”

Freshwater wetlands and tidal marshes had the highest tea mass remaining, indicating a greater potential for carbon storage in these ecosystems.

The study’s findings are helping piece together the puzzle of wetland carbon sequestration on a global scale. Within the terrestrial TeaComposition initiative led by Djukic, information on litter decomposition has been collected at about 500 sites worldwide resulting in several peer-review 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,” Djukic said.

“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.”

Next steps

The researchers will combine the data from this project with data from similar studies of land-based carbon sinks, including forests, to inform designs of predictive global models.

Two studies by Flinders University expand on existing evidence that a diet rich in fruits, vegetables, whole grains, fish, legumes and dairy may protect against the risk of gastrointestinal (GI) cancers — including bowel — and improve the outcomes of these diseases.

“We’ve identified many direct links between poor diet choices and digestive cancers,” says senior author Dr Yohannes Melaku from Flinders Health and Medical Research Institute (FHMRI).

“Importantly, we found that a diet high in healthy fats and vegetables whilst limiting the consumption of sugars and alcohol could potentially reduce the risk of bowel and other cancers.

“Unhealthy dietary patterns, marked by high consumption of red and processed meats, fast foods, refined grains, alcohol and sugary beverages, present a worrying relationship with an increased risk of GI cancers.

“Notably, we found that high-fibre foods such as fruits and vegetables promote healthy gut bacteria that can reduce inflammation. The emphasis on fibre and healthy fats should be an integral part of everyone’s diet.”

Whilst there is growing evidence that dietary interventions can be effective at preventing or delaying some diseases, the authors say that further trials are needed to investigate the impact that diet has on cancers and that diet is just one aspect of someone’s overall health and wellbeing.

Gastrointestinal cancers (GI) including cancer of the esophagus, stomach, pancreas, small bowel, colon, rectum and anus, are responsible for 1 in 4 cancer cases, and 1 in 3 cancer deaths worldwide.

“As awareness around bowel cancer grows, our research serves as a timely reminder of the power of nutrition in disease prevention. By adhering to healthy eating practices, we can take proactive steps in safeguarding our long-term health,” says Dr Melaku.

“With the growing number of digestive cancers, such as bowel cancer, being diagnosed worldwide, and increasingly in people under 50 years old, it’s time for action to protect people’s digestive health.”

Whilst there is growing evidence that dietary interventions can be effective at preventing or delaying some diseases, the authors say that further trials are needed to investigate the impact that diet has on cancers and that diet is just one aspect of someone’s overall health and wellbeing.

The findings support the World Cancer Research Fund (WCRF) and American Institute for Cancer Research (AICR) guidelines that advocate for diets rich in whole grains, vegetables, fruits, and legumes, while limiting red and processed meat, sugary drinks and processed foods.

“Our findings not only reinforce established guidelines but also highlight dietary choices that can proactively protect against this disease such as upping your fibre intake,” says Dr Melaku.

“Having a healthy diet is one of the simplest ways to improve our overall health and reduce the risk of diseases including cancers.

“Our studies demonstrate that nutrition education and promoting healthy eating patterns could be pivotal in reducing GI cancer risks and improving patient outcomes,” Dr Melaku adds.

“Whilst our results are promising, more work needs to be done with a greater focus on nutrition in clinical settings using nutritional biomarkers to better understand the relationship between diet and GI cancer,” says Associate Professor Amy Reynolds, an author on the paper.

“We need to understand how different dietary patterns may influence the risk of developing digestive cancers.

“We also want to see an increase in education around healthy eating which could lead to better health outcomes for those at risk for GI cancers,” she adds.