Most will recall the 2018 heatwave in Europe with the warmest May-October average air temperatures since recordings began in the early 19th century. Extreme heat, as in this case, can influence the lake surface water temperature and negatively affect lake ecosystem services. The EU-funded IntEL project examined how lakes are responding to the increased occurrence of extreme events, offering the first systematic detailed study of lake responses to extreme weather. This research was undertaken with the support of the Marie Skłodowska-Curie Actions programme. Climatic changes have substantial implications for lake species as they have adapted to the local conditions and generally cannot migrate away from their lake habitat. Climate extremes can also affect the use of lakes by humans as they may lead to declines in fish species used for food or tourism or increases in toxic algal blooms that can affect the quality of drinking water. “Quantifying and understanding these changes is crucial if we are to try to mitigate these impacts. In addition, the ability to describe and quantify these effects can contribute to the weight of evidence indicating that the global population must reduce their output of greenhouse gases,” notes Eleanor Jennings, IntEL project coordinator.
Lake heatwave – monitoring atypical lake surface temperatures
IntEL research fellow Iestyn Woolway explains: “Lake heatwaves are defined as periods of anomalous lake surface temperatures (i.e. when temperatures exceed historical average conditions for that time of year). The metric developed can be applied to any lake on Earth but, in this study, we focused solely on lakes with satellite observations.” The satellite data used played a vital role in ensuring the models successfully captured observed historic changes and were fit for this purpose. This new metric that quantifies lake heatwaves, presented in the recent ‘Nature’ article published by Woolway and colleagues, modelled lake heatwaves for multiple sites across the globe. The most dramatic finding was that some lakes may reach a permanent heatwave state.
Looking at the future of lake ecosystems
There are important implications for the future of lake ecosystems and the services they provide. Project work provides a new metric for describing lake heatwaves and also future projections for how these will develop as global warming proceeds and impacts all lake organisms and people using them. IntEL findings show that lake temperatures are set to rise faster than the ability of some species to disperse to cooler areas. The consequences will be more serious for species that disperse less readily (e.g. freshwater molluscs), but even the more motile species that could migrate more rapidly (e.g. some fish species) are likely to be restricted by physical barriers. These developments could cause catastrophic damage to certain lake ecosystems, having irreversible impacts on ecological communities and a dramatic influence on local communities depending on lakes for survival. “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,” concludes Jennings.
IntEL, lakes, heatwave, lake ecosystem, extreme event, global warming, ecosystem services, extreme heat, climate change