Heatwaves can decrease the biomass of phytoplankton in lakes

Heatwaves can decrease the biomass of phytoplankton in lakes

A recently published study showed that heatwaves reduced the biomass of phytoplankton in a boreal lake. Summertime heatwaves will become more frequent and stronger with climate change and can reduce the biomass of phytoplankton in stratified lakes.

Researchers at the Department of Biological and Environmental Science at the University of Jyväskylä followed the daily biomass of phytoplankton and environmental conditions in a humic lake Jyväsjärvi in central Finland during a summer stratification period.

During that period, warmer and less dense surface water forms a mixed layer above colder and denser water at deeper depths. Phytoplankton occur mostly in the mixed layer, the depth of which is regulated by weather. The depth of the mixed layer controls light and nutrient availability of phytoplankton. Phytoplankton receive less light but more nutrients with an increasing depth of the mixed layer. Phytoplankton needs both light and nutrients for photosynthesis.

“We found that the depth of mixed layer controlled the biomass of phytoplankton. The biomass increased with deepening of the mixed layer and decreased with shallowing of the mixed layer. Phytoplankton is responsible for the primary production in lakes and thus its biomass is the source of energy to other aquatic organisms including fish”, says the lead author of the study Salla Ahonen, a doctoral researcher at the Department of Biological and Environmental Science.

Climatic drives such as wind speed and temperature difference between air and water regulate the depth of the mixed layer. During heatwaves, warm and calm weather reduces the depth of the mixed layer, whereas colder and windy weather deepens the mixed layer. Warming climate will increase heatwaves and thus the conditions that can reduce phytoplankton biomass in lakes.
Increasing air temperature relative to water temperature makes the mixed layer shallower, reducing phytoplankton biomass in a stratified lake, Salla A. Ahonen, Jukka Seppälä, Juha S. Karjalainen, Jonna Kuha, Anssi V. Vähätalo, Freshwater Biology, https://doi.org/10.1111/fwb.14048, published on 13 January 2023.
Attached files
  • Phytoplankton occur mostly in the mixed layer, the depth of which is regulated by weather. (Image: Salla Ahonen / JYU.)
Regions: Europe, Finland
Keywords: Science, Climate change, Environment - science, Life Sciences


For well over a decade, in my capacity as a researcher, broadcaster, and producer, I have relied heavily on Alphagalileo.
All of my work trips have been planned around stories that I've found on this site.
The under embargo section allows us to plan ahead and the news releases enable us to find key experts.
Going through the tailored daily updates is the best way to start the day. It's such a critical service for me and many of my colleagues.
Koula Bouloukos, Senior manager, Editorial & Production Underknown
We have used AlphaGalileo since its foundation but frankly we need it more than ever now to ensure our research news is heard across Europe, Asia and North America. As one of the UK’s leading research universities we want to continue to work with other outstanding researchers in Europe. AlphaGalileo helps us to continue to bring our research story to them and the rest of the world.
Peter Dunn, Director of Press and Media Relations at the University of Warwick
AlphaGalileo has helped us more than double our reach at SciDev.Net. The service has enabled our journalists around the world to reach the mainstream media with articles about the impact of science on people in low- and middle-income countries, leading to big increases in the number of SciDev.Net articles that have been republished.
Ben Deighton, SciDevNet

We Work Closely With...

  • BBC
  • The Times
  • National Geographic
  • The University of Edinburgh
  • University of Cambridge
Copyright 2023 by AlphaGalileo Terms Of Use Privacy Statement