Lake rich Arctic networks retain carbon longer, giving microbes more time to convert dissolved organic carbon into atmospheric CO₂, particularly during warm, low flow summers.
Lakes and streams could play a more significant role in the global carbon cycle than previously understood, with a new Swedish study finding that lake rich Arctic stream networks release a greater share of carbon into the atmosphere instead of transporting it downstream.
The study published in Geophysical Research Letters on August 25, 2026, found that lakes significantly extend the time water and carbon remain within interconnected stream networks. This longer residence time provides microbes with more opportunity to break down dissolved organic carbon (DOC) into carbon dioxide (CO₂), which can subsequently escape into the atmosphere.
Researchers led by Fredrik Alriksson of Umeå University analysed 362 stream segments and 42 lakes across 32 interconnected Arctic stream-lake networks in Sweden. Sampling was conducted across four seasons with different environmental conditions.
The researchers found that networks containing more lakes retained water for longer periods and consequently released a larger proportion of their carbon to the atmosphere compared with the amount exported downstream.
Lakes extend carbon processing time
The study introduced the concept of “network residence time” to describe how long water remains within an interconnected stream and lake system.
Across the Swedish networks examined, residence times varied dramatically, from about 42 minutes to 29 years. Lakes accounted for almost all of the longest residence times.
This extended period allows microorganisms to mineralise dissolved organic carbon more extensively, producing CO₂. As a result, carbon that might otherwise have travelled downstream can instead be released into the atmosphere.
The researchers also identified differences in the supply of dissolved inorganic carbon and dissolved organic carbon, as well as stronger groundwater connectivity, as factors that can influence carbon processing in deeper, lake rich systems.
Lakes and streams need to be viewed as one system
The researchers argue that lakes and streams should not be treated as isolated components of the landscape when assessing the role of inland waters in the carbon cycle.
Even processes that may appear relatively small when considered individually, such as carbon emissions from lakes, can substantially influence the overall balance between carbon released into the atmosphere and carbon exported downstream.
The study therefore calls for approaches that consider the entire fluvial network and account for multiple carbon pathways at the same time.
“Comprehensive approaches that account for multiple carbon fates and components of inland waters are essential for understanding their current and future roles in the global carbon cycle,” the researchers said.
Summer conditions increase carbon release
The balance between carbon emissions and downstream carbon export also changed markedly with the seasons.
Carbon emissions relative to downstream export were lowest during spring and autumn but reached their highest levels in summer.
Researchers linked the summer increase to warmer, drier conditions and reduced streamflow. Lower water flow can increase the amount of time carbon remains within the network, while warmer temperatures can accelerate microbial processing of dissolved organic carbon.
The findings could become increasingly important as the Arctic experiences rising temperatures and changes in precipitation and hydrological patterns.
As climate change alters the amount and movement of water through Arctic landscapes, changes in lake and stream connectivity could influence how much carbon is retained within inland water systems, transported downstream or released into the atmosphere.
The study suggests that understanding these interconnected pathways will be essential for accurately assessing the role of Arctic inland waters in the global carbon cycle and how that role may change in a warming climate.