Northern-most lakes are considered the bellwethers of environmental change, but research shows consequences of climate change can affect any of the more than 100 million lakes in the world.
To get a cohesive picture of how climate change is threatening lakes, Reader R. Iestyn Woolway of Bangor University, Associate Professor Sapna Sharma of York University (Canada), and Distinguished University Professor John Smol of Queen’s University (Canada), reviewed and synthesized available studies on freshwater lakes from across the globe.
The research team found that the effects of climate change on lakes are often cumulative. Warmer water temperatures lead to changes in stratification regimes, declines in dissolved oxygen, a higher risk of cyanobacterial algal blooms, as well as a loss of habitat for native cold-water fish. It can affect not only water quality and quantity, but also cultural and recreational activities, and local economies.
The ecological consequences of climate change coupled with the impacts of extreme climate events are already occurring in lakes globally and will continue to do so in the future, often without warning or time to adapt,
The results of these kinds of changes have been felt in lakes from Algonquin Park in Ontario to Lake Chad in Africa, the English Lake District in the U.K. to Lake Mead in the United States.
Far-reaching social and ecological repercussions
Commenting on how the changes can affect not only water quality and quantity, but also cultural and recreational activities, and local economies, Sapna Sharma of Canada’s York University said:
“Climate change has far-reaching social and ecological repercussions, but the impacts of climate change, combined with other environmental pressures, are often little understood and the significance of them has not been appreciated at a global level. There is still much work to be done.”
Warmer air temperatures can impact winter ice cover in the case of northern lakes. Ice loss is one of the most blatant consequences of climate warming on lakes, which can increase winter evaporation rates and water temperatures, and lead to a multitude of physical and chemical effects, including greater salinity. The global mean annual evaporation of lakes is expected to increase by 16 per cent by century’s end. In addition, lower levels of precipitation can also have a significant effect on lake levels.
Declines in water levels can be severe in some regions. Historically ranked as one of the largest lakes in Africa, Lake Chad, which borders Chad, Cameroon, Niger and Nigeria, has shrunk considerably because of decreases in local precipitation and discharge from its catchment, as well as increased evaporation.
“Events like an earlier summer season can also cause mismatches in fish spawning and foraging, often with widespread ramifications across the food web. Although a ‘longer summer’ may be welcome to many cottagers and campers, such weather conditions increase the risk of algal blooms, and especially cyanobacterial blooms, which can have far-reaching ecological consequences and even make drinking water toxic,” says Sapna Smol.
Some of the effects of climate change are creating conditions where lakes are losing oxygen needed for fish and other aquatic species. This deoxygenation can be made worse by cyanobacterial blooms. A decline in the availability of safe drinking water caused by harmful algal blooms is considerably worse when combined with a reduction in water quantity. In 2014, a Cyanobacteria bloom in Lake Erie shut down the water supply in Toledo, Ohio, while a massive toxic cyanobacterial bloom in Lake Taihu, China, shut down the water supply for two million people for a week in Wuxi city.
“Algal blooms can block sunlight from reaching the deeper waters and bacterial decomposition of sedimented algae can lead to a decrease in oxygen for deep-water fish and other aquatic life,” says Iestyn Woolway. “In addition, episodic storms can cause nutrients to suddenly wash into lakes and foster the development of cyanobacterial blooms.”
“Warmer summers are creating the perfect conditions for earlier, more frequent, and intense algal blooms, such as those frequently seen in Llyn Tegid, (or Bala Lake, north Wales). Harmful blue-green algae that frequently form floating surface blooms can pose a serious health threat for cattle, pets, wildlife and humans” says Iestyn Woolway.
“These blooms could also affect tourism and lakeside property values.”
He continues: “As lake water quality deteriorates, the ecosystem services provided by lakes can be expected follow suit. For instance, the United Kingdom’s biggest wild swimming event, the Great North Swim, was cancelled in 2010 as a result of algal blooms, and the availability of fresh drinking water may soon be threatened.”
Warmer water temperatures, algal blooms, earlier onset, and longer periods of thermal stratification, combined with lower dissolved oxygen concentrations can have important cumulative and potentially negative effects on aquatic organisms, such as fish.
“The effects of climate change also interact synergistically with multiple environmental stressors exacerbating problems with water quantity and quality, including salinization, contamination, and the spread of invasive species,” says Sapna Smol. “As humans can’t survive without water, a better understanding of how climate change affects lake function is needed along with recognition of early warning signals.”
The researchers hope that recent advances in technology, such as remote sensing and environmental DNA, combined with a move to work beyond traditional silos, will allow for a better understanding of lake responses in the future.
For the United Nations’ Sustainable Development Goal of equitable access to clean water to be realized by 2030, the inclusion of diverse voices from researchers worldwide, including the Global South, and the cross-pollination of ideas across disciplines, will be essential.
The paper, Lakes in Hot Water: The Impacts of a Changing Climate on Aquatic Ecosystems, was published today in the journal BioScience.