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New Swedish research shows that lake-rich Arctic stream networks significantly reshape the global carbon cycle by releasing more carbon to the atmosphere instead of transporting it downstream.
By prolonging water residence time—from minutes to decades—lakes give microbes more opportunity to mineralise dissolved organic carbon into CO2, especially during warm, low-flow summers, underscoring the need to treat lakes and streams as a single, connected system.
Lakes have a significant say in what happens to carbon as it moves through a landscape. New research from Sweden showed that the more lake-rich a network of streams is, the more carbon is released into the atmosphere rather than carried downstream.
The findings published in Geophysical Research Letters on August 25, 2026, come from researchers led by Fredrik Alriksson of Umeå University, Sweden, who sampled 362 stream segments and 42 lakes across 32 nested Arctic stream-lake networks, repeated across four seasons with contrasting environmental conditions.
The study found that networks with more lakes retained water for longer periods and lost a greater portion of carbon to the atmosphere relative to downstream export, especially during warm low-flow conditions.
Results indicate that process-based effects imposed by lakes play a key role in regulating carbon emission export. These effects include a prolonged timeframe for dissolved organic carbon (DOC) mineralisation or differing dissolved inorganic carbon/DIC:DOC supply ratios in deeper (lake-rich) systems with higher groundwater connectivity.
Researchers refer to the duration water remains within a stream-and-lake network as its “network residence time.”
In the Swedish networks studied, the duration varied significantly, ranging from 42 minutes to 29 years, with lakes accounting for almost all of the total residence time. Longer water residence time gives microbes more opportunity to break down dissolved organic carbon, producing CO2 that can escape into the atmosphere.
Results further showed that components of the fluvial network that appear minor for individual fates, such as carbon emission from lakes, can alter the balance between carbon emission and export.
Rather than treating lakes and streams as separate landscape features, the researchers argued that they must be considered together as connected networks.
The findings stress the importance of accounting for lakes within stream networks and simultaneously “quantifying multiple carbon fates when assessing the role of inland waters in the carbon cycle.”
Lakes, in particular, slow the movement of carbon through the landscape, and increase the time available for carbon processing. Lake-rich networks thus have longer network residence times and are more efficient in mineralising dissolved organic carbon to CO2.
“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 study said.
The balance between carbon emissions and downstream export varied significantly with the seasons. Carbon emissions relative to downstream export were lowest in spring and autumn and highest in summer.
This pattern is especially important because summer measurements aligned with warmer, drier conditions and reduced stream flow. With less water moving through the system, carbon remains longer within it, while warmer temperatures accelerate the transformation of dissolved organic carbon.
As the Arctic warms and hydrological conditions shift, understanding these interconnected systems is becoming increasingly vital.
