By Nneka Nwogwugwu
The 117 million world lakes are gradually turning into hot water as a result of a new phenomenon called, Lake heatwaves.
Lake heatwave is when surface water temperatures rise above their average for longer than five days, the Conversation stated.
But by the end of this century, heatwaves could last between three and 12 times longer and become 0.3°C to 1.7°C 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 new study, researchers examined 393 lakes worldwide between 1981 and 2017 and found their temperatures rose by 0.39°C 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.
Implications of lake heatwaves
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.
Things won’t be easy for species which live above the water for most of their lives either. Dragonflies are a common sight flitting among the reeds on the lake side. They lay their eggs in the shallows, but as lakes are lowered or dry out during more frequent and severe heatwaves, this protection is lost. Those larvae which survive are likely to emerge early, when food and habitat may be lacking.
The Conversation says cliimate change will shift the types of organisms we find in lakes. Cold water 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 20°C compared to 15°C.
Heatwaves could accelerate the spread and size of pathogens in fish, with huge consequences for the aquaculture industry and wild populations. Human diseases, transmitted by freshwater organisms, may also increase.
Naegleria fowleri is a lake parasite that flourishes in warmer temperatures. Known as the brain-eating amoeba, this microbe can cause fatal meningoencephalitis if it enters the body through the nose. Prolonged periods when lake waters remain warmer than average could see this parasite expand into more temperate waters.
The Earth’s surface is splotched with 117 million lakes. 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 and it’s home to 2,500 species, including the Baikal seal – Earth’s only species of freshwater seal.
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 to the peculiarities of that habitat, giving rise to unique forms.
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.