Climate Change Could More Than Double the Greenhouse Gas Emissions Freshwater Lakes Give Off, Scientists Warn

Climate change could double the amount of greenhouse gas emissions given off by freshwater lakes, scientists have warned.

If current global warming trends continue, greenhouse gas concentrations in lakes could rise by 1.5 to 2.7 times, on average, according to a study published in the journal PNAS.

Lead researcher Dr. Andrew Tanentzap of the University of Cambridge's department of Plant Sciences explained to Newsweek: "Climate change is increasing both forest cover and changing the types of tree species occurring around most of the world's lakes.

"These changes are important for lakes because they receive large amounts of dead plant material from the lands that surround them."

Sources of organic matter, like carbon compounds that come from the remains of plants, animals, and their waste products "is particularly large in nutrient-poor lakes that are the most common on Earth," Tanentzap said.

"Therefore, as vegetation changes around lakes because of climate change, we hypothesized that so too would the role that lakes play in emitting greenhouse gases," he explained.

To carry out the research, scientists filled containers with different amounts of rocks and organic material, like leaves from deciduous and coniferous plants, and plunged them into the shallow water of Lake Laurentian and Swan Lake in Ontario, Canada. Two months later, they used special equipment to examine the organic molecules in the containers.

Tanentzap said the team found that "chemical diversity is a stronger predictor of greenhouse gas concentrations in water than just microbial diversity.

"This is significant because most greenhouse gases come from biological
activity, namely the break down of carbon-based compounds by microbes. We think that chemical diversity can be more important because it can elevate microbial activity without necessarily changing diversity—which people have fixated on in the past—basically by offering more 'meal choices' for microbes. And because greater chemical diversity can also provide more opportunities for the chemical action of light to break down carbon-based compounds and release carbon dioxide."

Tanentzap described the experiments as "very hands-on."

"We had to collect hundreds of kilograms of tree leaves for making up the experimental treatments," he said. "Although there are lots of leaves on the forest floor, you'd be surprised at how many large garbage bags you need to collect to get anything weighing any mass. We then had to carry the experimental containers—each weighing up to 10 kilograms—through kilometers of forests to get them into the lakes."

Jens Holtvoeth, a lecturer and expert in organic chemistry at the University of Bristol who was not involved in the study, told Newsweek that the numbers may seem small compared to, for instance, the carbon exchange between the atmosphere and the oceans or carbon dioxide release from thawing permafrost.

"However, it may well be the small things that, altogether, make a big difference on a global scale," he said. "When we hear that some processes associated with climate have been found to progress faster than expected it almost certainly results from some supposedly minor mechanisms having been underestimated."

He praised the authors for "using a state-of-the-art analytical approach." The research "brings into the spotlight the delicate relations between microbial and molecular diversity, ecosystem functioning and greenhouse gas emissions from northern lakes."

"The study is a vital step towards a more detailed understanding of natural processes producing greenhouse gases in terrestrial settings. While accurate assessments of global fluxes may still be off for some time, if we want to get a better grip on nature's complex feedback mechanisms under a rapidly changing climate we certainly need more studies like this," concluded Holtvoeth.

Lake Moraine, Rocky Mountains, Alberta, Canada
A stock image of a canoe on Lake Moraine with glaciers in the Rocky Mountains, Alberta, Canada. The researchers carried out their research on Lake Laurentian and Swan Lake in Ontario, Canada. Getty