Large amounts of methane emissions from baffle researchers in Swedish lakes

A new study from the Chalmers Institute of Technology found that unexpectedly strong methane emissions were detected in several locations in Lake Siljan, Sweden. Based on new measurement techniques developed by the researchers, the researchers are revealing sustained, concentrated methane leaks that have never been observed in the lake environment before. Scientists will investigate whether these emissions are endemic to Siljan or part of the broader phenomenon that can occur in lakes around the world.

Lake Siljan is the largest of several lakes in the Siljanling area and is a 370 million-year-old impact crater in central Sweden, formed by a meterite strike. The infiltration of natural methane from the lakes in the area has long been known, and locals have reported permanent winter ice holes – “ice awakening” – grows at the same spot every year. Chalmers’s study focused precisely on these sites as methane leaks could be the underlying cause of recurrence openings in the ice.

The study, led by Professor Johann Mercvist and Professor Vladimir Condes of Chalmers, measured methane emissions from the lakes of Siljanling during two field campaigns in 2023 and 2024. The results surprised scientists in several ways.

The large-scale emissions were surprising

Researchers identified several “hot spots,” localized sites with severe methane leaks, forming visible gas plumes in the air. When researchers returned six months later to repeat the measurements, they had a strong emissions estimated to be around 3.5 tons of methane per year, corresponding to 85 tons of Co2 equivalent.

“Natural methane emissions from Lake Siljanling appear to be much more extensive than previously known. In certain locations, we recorded emission rates up to 300 times higher than those commonly found in lakes.”

He points out that methane is a powerful greenhouse gas with much higher global warming potential than carbon dioxide.

“The crucial importance of methane emissions in Siljan provides important insights into the budgets and sources of natural greenhouse gases in Swedish. The individual sources we identified may still be minor in the national context, but if future research reveals even larger emissions, it can reveal efforts to reduce them.

High concentration emissions

Methane emissions from a lake are usually generated as “bubbles ejection.” There are sporadic, scattered leaks that appear everywhere on the surface of the water. These arise from organic matter that rot at the lake bottom and form foaming methane. However, researchers were surprised that Shirjan’s emissions were much more concentrated than typical bubble emissions.

“It’s rare and very strange that emissions were very localized. To our knowledge, this type of strictly concentrated methane leak has never been measured in the lake before, and we’ve only looked at the tip of the iceberg to date. We’ve only seen the tip of the iceberg,” says Mercubist.

To perform the measurements, the researchers partially used a new method developed at Chalmers. It releases tracer gas to understand the dispersion of methane in the air and quantify how much it is leaking.

“This method allows us to measure concentrated emissions much more effectively than traditional approaches, such as floating chambers designed for widespread, uniform surface discharges. One important question now is whether similar local emissions exist in other lakes, but were not detected because the previous method is not suitable for finding them,” he says.

The origin of the emissions is still unknown

The key issue is the origin of methane. One possibility is that it is what is called “deep gas” from underground. It is caused by the impact of met stones at Siljan. Another possibility is that emissions come from methane pockets. Gas trapped in sediments beneath the lakebed is slowly leaking.

“If it turns out to be a deep gas, this may be inherent to the Siljunling and impact craters. However, if it comes from a shallower sediment pocket, this type of emission can be present in more places,” explains Mellqvist.

Researchers will now map Siljan and most of the nearby lakes, including deeper depths than previously studied.

“We need to understand the number of hotspots in this region and identify the origin of emissions, and we would also like to explore possible strategies to limit them. Our findings have meaning far beyond the Siljan region and may help us reassess the way we see natural gas penetration in geological layers around the world,” he concludes.