Story at a glance
- A study outlines the hazards of warming temperatures on lake waters and environments.
- Rising temperatures associated with climate change reduce a lake’s ability to effectively dissolve oxygen and support its ecosystem.
- The lack of oxygen then rattles the balance of the lake’s environment, prompting an overabundance of harmful algae.
Declines in oxygen among ocean ecosystems have been well-documented as another consequence of climate change — a serious problem for all the species that call the ocean home.
A new study adds to this scientific literature by examining the effect of dwindling oxygen levels on lakes all over the world, analyzing more than 45,000 dissolved oxygen samples and temperature trends across 393 temperate lakes in North America and Europe based on data from 1941 to 2017.
Researchers observed temperatures across both surface water and deep waters levels, as well as the concentration of dissolved oxygen — the most important gas in aquatic ecosystems. An imbalance in oxygen can have negative effects on the biodiversity of water flora and fauna.
Published in the journal Nature, this study notes that the prevalence of harmful algal blooms prompted by deoxygenation can harm both animal and human health.
Prior to this study, this phenomenon was only studied in oceans, but the findings reveal that anthropomorphic climate change can affect lake ecosystems in a similarly destructive way.
“We find deep-water lake habitats are especially threatened, and deep-water DO [deoxygenation] trends may portend future losses of cold-water and oxygen-sensitive species, increased internal nutrient loading which exacerbates eutrophication and the formation of harmful algal blooms, and potentially increased storage and subsequent outgassing of methane,” said the study.
The decline in oxygen levels across both surface and deep lake waters was associated with an inability for oxygen to effectively dissolve as surface water temperatures increased. Researchers attribute this to increases in phytoplankton, which lead to increases in the production of harmful algae blooms that prompt the release of nutrients from sediments thanks to a loss of deep-water oxygen levels. An imbalance in these nutrients jumpstarts the development of bacterias that produce methane, causing further water heating.
Deeper in the lakes, deep water deoxygenation was notably harmful.
Scientists attribute the lack of oxygen past the surface to greater thermal stratification, or the process where lake water separates into three layers based on water temperature, with the upper surface layer being the warmest.
Eventually, as seasons change, surface temperatures cool and the lake waters become the same temperature, which leads to lake turnover. Lake turnover is a critical process that helps distribute the dissolved oxygen absorbed at the water’s surface to the deeper water environments, keeping aquatic organisms healthy. As thermal stratification becomes stronger and leads to a reduction in water circulation, deeper waters receive less oxygen, endangering the flora and fauna of lake environments.
Researchers add that warming trends indicate this is likely to worsen.
“We anticipate further DO losses in deep waters of lakes where water clarity continues to decline or thermal stratification intensifies, whether owing to atmospheric warming, stilling, or both,” the report said.
“The new study provides a much-needed global overview of what happens in the limited freshwater stores of the planet – their health is a prime concern,” Hans-Otto Poertner, a professor at the Alfred Wegener Institute in Germany, told The Guardian.
“Climate change, together with [agricultural pollution], threatens vulnerable freshwater systems, adding to the urgency to strongly cut emissions.”