Lake heatwaves to become ‘hotter and longer’ by the end of the century
Lake ecosystems across the world are increasingly vulnerable to water temperature increases caused by ongoing climatic change. Species of plants, fish and animals that live in lakes are particularly susceptible to the effects of climate change, because they have often adapted to local conditions and lack the ability to migrate away from a changing habitat.
As recent research has shown, warming water temperatures can interact with other environmental stressors such as nutrient pollution to cause significant ecological issues like eutrophic algal blooms. However, until recently, little was known about lake heatwaves, particularly how and where they will occur in the future.
IntEL, a newly-completed EU-funded research project, has recently provided the first detailed study of lake ecosystem responses to warming temperatures under predicted future climate change. “Quantifying and understanding these changes is crucial if we are to try to mitigate these impacts,” says Prof. Eleanor Jennings, IntEL project coordinator. “In addition, the ability to describe and quantify these effects can contribute to the weight of evidence that the global population must reduce their output of greenhouse gases”
Writing in the Nature journal, IntEL researchers provide a new metric to quantify lake heatwaves, produced through computer modelling work across hundreds of sites globally. The research team show that lake heatwaves are likely to become “longer and hotter” by the end of the 21st Century. Significantly, they suggest that some lakes will reach a permanent heatwave state extended over multiple years.
“Lake heatwaves are defined as periods of anomalous lake surface temperatures, when temperatures exceed historical average conditions for that time of year,” says IntEL research fellow Dr. Iestyn Woolway. “The metric developed can be applied to any lake on Earth but, in this study, we focused solely on lakes using satellite observations.”
The researchers suggest that by the end of the 21st Century, many global lakes will have increased water temperatures as a result of more regular heatwave events. Heatwaves, in many lakes, will thus cease to be extreme events, and instead become part of ‘normal’ ecosystem conditions.
The project findings have significant implications for freshwater life in lakes. The researchers highlight the potential for ecosystem shifts as a result of decreased ice cover, decreased water oxygen levels, and increased cyanobacteria blooms in different lakes.
Similarly, they note the potential for warming water temperatures to alter the mixing and cycling of thermal layers and nutrients in some lakes. The likely result is the alteration, or loss, of habitat for biodiversity in many lakes, potentially causing the breakdown of food webs. Species already at the upper limit of their temperature tolerance, and those unable to migrate to more favourable habitats, may become locally extinct.
The researchers write, “These complex inter-actions are hard to forecast, but the extreme heatwave in the summer of 2003 in central Europe illustrated the range of effects that might be expected, including increased thermal stability and hypolimnetic oxygen depletion, production of cyanobacterial blooms and a regime shift from pelagic to benthic productivity.”
In other words, whilst we can expect lake heatwaves to increase in intensity and duration across the world in the coming decades, it is difficult to accurately forecast the resulting ecological impacts. This uncertainty provides a convincing argument both for transitioning to low-carbon economies to minimise future climatic change, and in building climate resilience into freshwater systems through habitat conservation and restoration work.
The IntEL researchers are not finished with their work, however. “Future work will investigate the influence of climate change on a host of other essential lake properties, including the phenology of lake stratification – the vertical layering that exists in many lakes in summer – and the influence of warming on greenhouse gas production in lakes,” says Prof. Jennings.
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