A new study published in PNAS has found that oxygen levels in small lakes remain critically low despite shorter ice cover caused by climate change. Researchers discovered that while larger northern lakes, such as Lake Päijänne, benefit from improved oxygen levels due to extended autumn mixing and reduced ice cover, smaller lakes face worsening conditions.
The international research team, led by Joachim Jansen from the University of Helsinki, analyzed lake data from 1960 to 2022. They found that in small lakes, oxygen depletion during summer persists into winter, expanding under-ice anoxic zones. This “ecological memory” effect is especially severe in nutrient-rich lakes where oxygen consumption is high.
Conversely, nutrient-poor lakes and larger lakes over 10 km² showed positive trends, with reduced risk of winter fish kills. Mid-sized lakes displayed no clear trend, as oxygen gains and losses balanced out.
“These results show that climate change impacts on lakes are complex and size-dependent,” said Jansen. The findings provide vital insights for lake conservation and fishery management in a warming climate.
Source: University of Helsinki
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