Stormy waters: the effects of extreme weather on lake ecosystems
Climate change is increasing the frequency and intensity of extreme weather across the world. High winds and heavy rain during storm events can significantly affect freshwater systems. However, what is not yet fully understood is how extreme weather affects the health of lake ecosystems.
Freshwater scientists know that storms can alter physical processes in lakes such as water flows from tributaries, mixing in the water column, sediment disturbance and water temperature. At the moment though, scientists only have a limited understanding of how ecological processes – particularly those involving algae at the base of food webs – are affected by storms.
A new study from a global team of scientists warns that lakes around the world may undergo significant ecological shifts in response to extreme storms as a result of ongoing climate change. They state that there is a pressing need for research to inform adaptive conservation strategies.
“Though it is clear that storm events can affect water quality and wildlife in lake ecosystems, we need to develop a clearer understanding of where and when the impacts of these events might be most and least severe,” said co-author Dr. Stephen Thackeray from the Centre for Ecology and Hydrology, UK.
“If extreme weather events significantly change carbon, nutrient, or energy cycling in lakes, we better figure it out quickly,” said lead author Dr. Jason Stockwell, from the University of Vermont, USA, “because lakes can flip, like a lightbulb, from one healthy state to an unhealthy one – and it can be hard or impossible to flip them back again.”
Extreme weather and algae communities in lakes
The new open-access study, written by Dr. Stockwell and 38 co-authors, is published in the Global Change Biology journal. It focuses on algae – or phytoplankton – the microscopic organisms which support virtually every freshwater food web. Phytoplankton are vital in lake ecosystems as they take up carbon dioxide, make carbohydrates, and release oxygen using sunlight through photosynthesis. Phytoplankton are also a valuable food source for many aquatic animals.
So how might we better understand how phytoplankton – and by extension, wider lake ecosystems – respond to extreme storms?
The study authors reviewed and collated evidence from thousands of existing scientific studies. They found that only 31 studies have ever investigated the effects of storms on phytoplankton communities, and that their results provide no clear picture of the relationship. Similarly, there appeared to be no clear trends in how phytoplankton responses differ by storm types, in different lake ecosystem types, or at different times of year.
A framework for understanding the effects of storms on lake ecosystems
In response, the authors develop a framework for understanding the effects of storms on lake ecosystems, in an effort to encourage and guide future research. The framework shows that the impact of storm events on lakes is not simply the result of storm strength at one point in time and space. Instead, a watershed-scale approach is required to map the different relationships between storm, lake and watershed attributes.
As the paper’s conceptual framework (above) shows, the extent to which a lake ecosystem is affected by storm events depends on the characteristics of the storm, lake and watershed. These in turn influence lake conditions such as nutrient pollution and sediment movement during the storm event.
These altered lake conditions can then influence the dynamics of phytoplankton and zooplankton at the base of the food web, which can then cascade through higher trophic levels of the ecosystem, potentially altering its health and functioning.
“This paper provides a compelling framework on understanding both direct and indirect effects of storms on lake ecosystems,” said co-author Dr. Lisette de Senerpont Domis from the Netherlands Institute of Ecology. “In a wind exposed delta area such as the Netherlands with a lot of shallow lakes impacted by agriculture we will likely experience some of the negative impacts of storms, such as algal blooms.”
New research collaborations and lake monitoring
The authors call for major new interdisciplinary collaborations to research storm impacts on lake ecosystems through networks such as the Global Lake Ecological Observatory Network. They outline the value of integrating watershed and lake physical models with biological models to better predict lake ecosystem responses to storms. They also highlight the importance of expanding long-term lake monitoring schemes, and using sensors that provide detailed data on ecological parameters during storm events.
“The framework we outline provides exciting opportunities for researchers from different disciplines to work as teams to identify the conditions and mechanisms by which storms are likely to have negative impacts on lake ecosystems,” said Dr. Stockwell. “We must quickly learn more—so we can better respond to the very real and pressing threat of climate change on lakes around the world. Without healthy lakes, we are sunk,” he said.
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