Talk like a limnologist

Logger — an instrument that continuously measures water properties

Peatland — a type of wetland in which waterlogged soils prevent the full decomposition of organic matter

Permafrost — ground that remains frozen for two or more consecutive years

Sediment core — a tube of mud collected from the bottom of a lake

Sporadic discontinuous permafrost — land in which 10-50% of the ground is permafrost

Two-Eyed Seeing — combining Indigenous knowledge with western science

Watershed — the land that drains into a river or lake

As the world warms up, the permafrost underlying Canada’s northern forests is thawing, resulting in dramatic changes to the landscape and significant impacts for communities in the region. Dr Jennifer Korosi, a limnologist at York University, is studying northern peatland lakes to understand the impacts of permafrost thaw on water quality.

How is permafrost thaw impacting peatlands?

“The sporadic discontinuous permafrost zone is very sensitive to increases in air temperatures, so climate warming is causing widespread permafrost degradation,” says Jennifer. “As the permafrost thaws, peatlands collapse causing trees to lean over (what we call ‘drunken trees’). And as the ground converts into wetland, the trees die due to the wetter soil conditions.”

Jennifer and her team are examining the impacts of permafrost thaw on inland waters by studying the lakes around the Scotty Creek Research Station, an Indigenous-led field research station in the Dehcho region of the Northwest Territories of Canada. Run by the Łı́ı́dlı̨ı̨ Kų́ę́ First Nation in partnership with Sambaa K’e and Tthets’éhk’edélî First Nations, the research station allows environmental scientists to study sporadic discontinuous permafrost peatlands in collaboration with Indigenous knowledge keepers. “The station provides a space for community members and academic researchers to learn from each other to understand how the lands and waters of the region are being transformed by climate change, and how communities can respond,” says Jennifer.

How is Jennifer studying peatland lakes?

“Our work combines lake sediment coring with intensive lake field studies to better understand the structure and function of the lakes, and how they are connected to their watersheds,” says Jennifer. She uses gravity coring to collect sediment cores, which involves lowering a tube from a boat to the bottom of a lake and allowing it to slowly sink into the mud. The top of the tube is then sealed, allowing the team to pull the tube back up through the water while keeping the sediment inside. “It’s much like if you put a straw in liquid, seal the top with your finger, then lift the straw up,” Jennifer explains. “Before we pull the tube fully out of the water, someone reaches under it and seals the bottom end to stop the mud from falling out.”

But extracting the mud is only the beginning of the process. “Lake sediment coring is a quick process – we can core several lakes in a day,” says Jennifer. “It then takes a year or more to analyse the cores back in the lab!” Mud builds up on the bottom of a lake over time, so the sediment at the top of the core is younger than the sediment at the bottom. This means sediment cores provide a history of the lake, and by analysing changes in the sediment throughout the core, Jennifer can uncover changes in the lake’s conditions through time.

For example, changes in sediment chemistry and the types of tiny fossils (e.g., algae, zooplankton and invertebrates) preserved in the sediment tell Jennifer how nutrient, temperature and light levels in the lake have changed throughout the past, how food web structures have evolved, whether there were past fires in the surrounding landscape, and if potential contaminants like mercury have increased in lakes. “All this information can be found in the lake mud!” she says.

To study how the watershed characteristics and weather conditions affect present-day lake conditions, Jennifer and the team put loggers in the lakes each year in early June. These continuously record measurements such as temperature, dissolved oxygen and light levels over the summer, before Jennifer returns in late August to collect them and retrieve the data. “We also collect water samples at the beginning and end of the summer to look at water chemistry and algal communities,” she says. “We’ve been doing this for several years now, building up a long-term dataset of lake conditions and how they are changing from year to year”.

What has Jennifer discovered?

“Lake responses to permafrost thaw are unique,” says Jennifer. “All lakes in the region are being impacted by accelerating permafrost thaw, but we aren’t seeing any consistent regional trends in how the lakes are responding.” Her team’s research indicates that fire is likely an important trigger for long-term lake change, which Jennifer suspects is because wildfires increase permafrost thaw.

As the peatland thaws, more nutrients and organic matter are being delivered to lakes via rivers, which is having various impacts on the lakes. Some, but not all, are turning darker in colour due to this organic matter.

“Overall, we’ve learnt that each lake has a unique relationship to its surrounding landscape,” concludes Jennifer. She is continuing to investigate how lakes reflect changes in their watersheds so she can better predict how they will respond to permafrost thaw. “By working together with community members, we can use a Two-Eyed Seeing approach to gain deeper insights into how and why lakes are changing,” says Jennifer. “I hope our research responds to concerns identified by communities about how their lands and waters are changing, and that they can use our findings in a meaningful way.”

Dr Jennifer Korosi

Limnology and Paleoenvironmental Research Group, Faculty of Environmental and Urban Change, York University, Canada

Field of research: Limnology

Research project: Studying past and present changes in northern peatland lakes to understand the impacts of permafrost thaw

Funders: Natural Sciences and Engineering Research Council of Canada (NSERC); ArcticNet

Website: lprg.ca

About limnology

Limnology is the study of inland waters. This includes lakes, ponds, rivers and streams, as well as wetlands like the permafrost peatlands Jennifer studies. Limnology is vital for conserving freshwater supplies and protecting aquatic ecosystems.

Jennifer’s research falls in the subdiscipline of paleolimnology – the study of lake sediment cores to reconstruct environmental change over time. “Paleolimnology lets us look back in time (decades, centuries or millennia – depending on how deep the sediment core is) to track environmental changes and better understand how human impacts like pollution and climate change have altered lake ecosystems,” she explains.