Warming lakes cause problems for ecosystems

As intense heat waves hit the UK, Spain, France and Portugal, sometimes exceeding 40°C, as well as parts of North America and Asia, the lakes of people around the world are feeling the heat of climate change, which is creating a cascade of ecological changes and environmental problems.

The northernmost lakes are considered indicators of environmental change, but research shows that the consequences of climate change can affect any of the more than 100 million lakes worldwide.

To get a cohesive picture of how climate change threatens the lakes, Reader R. Iestyn Woolway of Bangor University, Wales, Associate Professor Sapna Sharma of York University and Emeritus Professor John Smol of Queen’s University reviewed and synthesized available studies on freshwater lakes. of the whole world.

The research team found that the effects of climate change on lakes are often cumulative. Warmer water temperatures lead to changes in stratification regimes, decreased dissolved oxygen, increased risk of cyanobacterial algal blooms, as well as loss of habitat for native water fish. cold. It can affect not only water quality and quantity, but also cultural and recreational activities and local economies.

“Climate change has far-reaching social and ecological implications, but the impacts of climate change, combined with other environmental pressures, are often poorly understood and their significance has not been appreciated on a global scale,” says Sharma of York’s Faculty of Science. “There is still a lot of work to do.”

Warmer air temperatures may impact winter ice cover for the northern lakes. Ice loss is one of the most glaring consequences of global warming on lakes, which can increase evaporation rates and winter water temperatures, and lead to a host of physical and chemical effects, including higher salinity. Global average annual evaporation from lakes is expected to increase by 16% by the end of the century. Additionally, lower levels of precipitation can also have a significant effect on lake levels.

“The ecological consequences of climate change associated with the impacts of extreme weather events are already happening in lakes around the world and will continue to do so in the future, often without warning or time to adapt,” says Woolway. “The results of these kinds of changes have been felt in lakes from Algonquin Park in Ontario to Lake Chad in Africa, from the English Lakes District in the UK to Lake Mead in the US.”

The drop in water levels can be severe in some areas. Historically ranked as one of Africa’s largest lakes, Lake Chad, which borders Chad, Cameroon, Niger and Nigeria, has shrunk significantly due to reduced local rainfall and discharges from its catchment area. , as well as increased evaporation.

“Events like an earlier summer season can also cause mismatches in fish spawning and foraging, often with widespread ramifications through the food web. Although a “longer summer” may be welcome for many cabin owners and campers, such weather conditions increase the risk of algal blooms, and in particular cyanobacteria, which can have far-reaching ecological consequences and even make drinking water toxic,” says Smol.

Some of the effects of climate change create conditions in which lakes lose oxygen needed by fish and other aquatic life. This deoxygenation can be aggravated by cyanobacterial blooms.

“Algal blooms can block sunlight from reaching deep waters and bacterial breakdown of sedimented algae can lead to decreased oxygen for deep-sea fish and other aquatic life,” says Woolway. “Additionally, episodic storms can cause lakes to suddenly wash nutrients and promote the development of cyanobacterial blooms.”

A decline in drinking water availability due to harmful algal blooms is significantly worse when combined with a reduction in water quantity. In 2014, a cyanobacterial bloom in Lake Erie cut off water supplies in Toledo, Ohio, while a massive toxic cyanobacterial bloom in Lake Taihu, China cut off water supplies of two million people for a week in the city of Wuxi.

“In Ontario, reports of algal blooms have not only increased, but have been reported through November, which was not generally the case in previous years,” says Sharma. “These blooms could also affect tourism and lakeside property values.”

Seven years ago, Algonquin Park banned overnight camping on remote, nutrient-poor Dickson Lake because cyanobacterial blooms were causing health concerns. A sediment-based study determined that these blooms were new to the lake and that no comparable event had occurred in the past century, but that is changing.

Warmer water temperatures, algal blooms, earlier onset and longer periods of thermal stratification, combined with lower dissolved oxygen concentrations, can have significant and potentially negative cumulative effects on aquatic organisms, like fish.

“The effects of climate change also interact synergistically with multiple environmental stressors that exacerbate water quantity and quality issues, including salinization, contamination, and the spread of invasive species,” says Smol. “As humans cannot survive without water, a better understanding of how climate change is affecting lake functioning is needed as well as recognition of early warning signals.”

Researchers hope that recent advances in technology, such as remote sensing and environmental DNA, combined with a movement to work beyond traditional silos, will lead to a better understanding of lake responses in the future.

To ensure that the United Nations Sustainable Development Goal of equitable access to safe drinking water is achieved by 2030, the inclusion of diverse voices from researchers around the world, including the South, and the cross-pollination of ideas between disciplines will be essential.

Reference: Woolway RI, Sharma S, Smol JP. Warm Water Lakes: The Impacts of Climate Change on Aquatic Ecosystems. Bioscience. 2022:biac052. doi:10.1093/biosci/biac052

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