View Of Lake

Climate Change is Choking the World’s Lakes

Global climate change is seriously impacting the fragile ecosystems of the world’s lakes.

There are some 117 million lakes scattered over the surface of the Earth. Some are scarcely more than ponds, while others are so big they can be seen from space. At 395 miles long, 49 miles wide, and just over 1 mile deep, Lake Baikal in Siberia is one of the world’s largest, It is home to 2,500 species, including the Baikal seal – Earth’s only species of freshwater seal. It, and indeed all of the world’s lakes, are threatened by global climate change.

Lakes and rivers occupy just 1% of the Earth’s surface but are incredible hotspots for biodiversity, sheltering 10% of all species globally. Particularly in older and deeper lakes, life has had millions of years to evolve and adapt. But since 1970, numbers of freshwater vertebrates, including birds, fish, amphibians, reptiles, and mammals, have declined by a staggering 83% through the extraction of lake water, pollution, invasive species, and disease. Now, climate change threatens to drive even deeper losses among lake-dwelling flora and fauna.

Lake heatwaves – when surface water temperatures rise above their average for longer than five days – are a relatively new phenomenon but have been occurring far more often. By the end of this century, lake heatwaves are projected to last between three and 12 times longer and become much hotter. In some places, particularly near the equator, lakes may enter a permanent heatwave state. Smaller lakes may shrink or disappear entirely, along with the wildlife they contain, while deeper lakes will face less intense but longer heatwaves.

In a recent study, researchers examined 393 lakes worldwide between 1981 and 2017 and found their temperatures rose by 32°F every decade, while dissolved oxygen fell by 5% at the surface and 19% in the depths. It’s in these cooler, deeper parts of lakes where trout, burbot, and salmon usually thrive thanks to sufficient oxygen, especially in the summer. Largely due to warming air temperatures, 68% of the lakes in the study had lost this important niche to rising temperatures and falling oxygen levels.

All of these changes are having a devastating impact on the billions of creatures that call the world’s lakes their home.

How Lake Warming Affects Lake Dwelling Species

Most organisms that live in lakes can only thrive in water with just the right temperature and concentration of nutrients and oxygen. Warmer lakes hold less oxygen and lose more water through evaporation, forcing species to live in saltier and less oxygenated habitats. The experts say that climate change will shift the types of organisms we find in lakes. Coldwater fish, such as trout and salmon, need cooler temperatures and higher oxygen concentrations than warm water species such as largemouth bass and white perch. One cold-loving species, Arctic char, could vanish from 73% of its Swedish range by 2100 just as a result of warming. Meanwhile, rising temperatures could mean parasites that infect fish grow faster and larger. In one study, parasitic worms infecting stickleback fish grew four times faster in water at 68°F compared to 58°F.

Heatwaves also accelerate the growth of pathogens and bacteria that affect fish, leading to large-scale fish kills. This can even impact humans, as parasites that can harm people also thrive in warmer lakes, where people recreate, such as Naegleria fowleri, the so-called “brain-eating amoeba.”

Lake heatwaves are increasing the frequency of harmful algal blooms and causing mass mortality events where thousands of animals die in a few days. Algal blooms block out the light and suffocate fish, either by crashing oxygen levels or clogging up their gills. An enormous algal bloom in Loch Leven in Scotland in 1992 killed 1,000 brown trout over 24 hours.

Unlike those living elsewhere, most lake animals cannot simply move to another habitat once their lake becomes uninhabitable. As lake heatwaves proliferate and oxygen levels decline, mass fish die-offs are predicted to double from the 2040s in lakes in the northern hemisphere and increase fourfold in the southern hemisphere from the 2080s onwards. Without immediate action to curb emissions and slow climate change, many of the world’s lakes are on course for a sweltering, breathless and lifeless future.

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