As the atmosphere warms up, so do most freshwater lakes. But this isn’t always the case, and little is known about why. 

Now, an international team led by the Nanjing Institute of Geography and Limnology of the Chinese Academy of Sciences, sampled 345 lakes distributed across twelve countries, primarily in the United States and Europe, for the controls of thermal response of temperate lakes to atmospheric warming study. 

This study was published in the leading journal Nature Communications on October, 16. 

The team found that the rate of lake heating slows as air warms. The differences in local climate, land cover, geomorphology, and water transparency can help explain why the rate of lake heating doesn’t necessarily match the rate of air warming. 

Especially, lakes with more nutrient pollution – lakes that have layers of green on top of them – are less sensitive to global warming than lakes that are clear, and less polluted. The green lakes are already damaged by human activities in the surrounding landscape. Too many nutrients from land results in green surface waters that act as a shade, keeping the deep waters cool. But greener lakes also lose more oxygen from deep water which results in more fish dying. 

There is some good news. As lakes warm up, they start to lose water by evaporation and this acts to cool them off. “Just like we sweat to cool off, lakes ‘sweat’ by evaporating water to get rid of excess heat,” says Dr. ZHOU Jian, the first author on the study. 

“While the good news is that lakes can cool themselves for a period of time by sweating – which protects biodiversity in lakes, recreational fishing, and some aspects of water quality – it’s a short-term measure because those same lakes are losing water. Unfortunately, just like we can become dehydrated if we don’t drink, lakes can’t cool off by evaporation forever, because they will eventually dry out and disappear,” says Dr. Peter Leavitt, the co-author from University of Regina. 

The researchers also discovered that despite what we may think, remote, deep lakes, especially those at high elevation and far from human activity, are actually more sensitive to atmospheric warming. 

“Clear lakes aren’t already damaged by human activities, so they more readily respond to human-caused atmospheric warming,” says Prof. SHI Kun, the co-author on the study. 

Therefore, one-size-fits-all responses to global warming and land-use change won’t work. “Instead, our lake management practices need to consider where lakes are, what they are surrounded by, and how sensitive they might be to unique and interactive effects of climate change and human activities,” says Prof. QIN Boqiang, the co-author on the study.

Link: https://www.nature.com/articles/s41467-023-42262-x

 TAN Lei 

 Nanjing Institute of Geography and Limnology 

 E-mail: ltan@niglas.ac.cn