A team of Chinese researchers has found lakes on the Tibetan Plateau have been decreasing in salinity over the past two decades because of expanding water volume – a trend that scientists say is encouraging for the region’s aquatic biodiversity.
These lakes account for half of China’s total lake surface area, and the change in salinity could also affect the region’s freshwater resources, according to researchers from the Chinese Academy of Sciences (CAS).
In a study published in the peer-reviewed journal International Journal of Digital Earth last month, the researchers tried to assess the impact of climate change on the salinity of Tibetan Plateau lakes.
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Zhu Liping, corresponding author of the study and researcher at the CAS Institute of Tibetan Plateau Research, said the water volume of lakes on the Tibetan Plateau expanded 17 per cent over the past three decades, increasing from 800 billion cubic metres (28.3 trillion cubic feet) in 1990 to 960 billion cubic metres now.
Zhu said the lakes’ expansion was caused by increased precipitation and glacial meltwater, both results of climate change. The expanding water volume has led to lakes that are less salty.
“Lake salinity directly affects aquatic ecosystems and the available freshwater resources,” he said.
“The declining trend in lake salinity on the Tibetan Plateau is certainly favourable to aquatic biodiversity. It will increase biodiversity and help it develop in a good direction,” Zhu said.
Zhu said lower salinity would also decrease the risk of eutrophication – a process in which a body of water becomes enriched with minerals or nutrients that can result in harmful algae blooms and the death of aquatic plants and animals.
He added the trend of declining salinity could supply more drinking water to the region.
“The lower salinity in lakes means a decrease in salinity levels in the whole region. And in some places, the groundwater may be drinkable when pumped,” Zhu said.
“The lake water can be used to irrigate farmland in high-altitude regions near Yamzho Yumco,” Zhu said, referring to one of the three largest lakes in Tibet autonomous region.
There are more than 1,400 lakes with an area greater than 1 sq km on the Tibetan Plateau. Most of them are located at an altitude of more than 4,000 metres (13,123 feet), where there is minimal human activity.
“Tibetan Plateau lakes are diverse in terms of area, depth, salinity, structural types and water supply conditions,” according to the study.
Zhu and his colleagues measured the salinity of 87 lakes on the Tibetan Plateau. The lakes sampled account for about 60 per cent of the plateau’s total lake area.
They came up with a formula to show the relationship between a lake’s salinity and its maximum clarity, or how transparent the water is at its clearest.
Then using satellite images, the team calculated the maximum clarity of 152 lakes in the region and figured out their salinity for the period from 2000 to 2019.
In general, they found a significant decrease in lake salinity during the time period. The average salinity in 2000 was 27.5 practical salinity units (psu), but it fell to 19.3 psu in 2019, according to the study.
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Although there was a slight increase in some years, they found that “the overall trend was a significant step-like decrease”, with salinity declining by a rate of 0.31 psu each year.
They also investigated the relationship between lake salinity and precipitation. They found that the decrease in lake salinity on the plateau was not directly affected by precipitation in the lake basin but rather the lake’s water volume, which can be affected by factors other than precipitation, such as glacial melt.
The study found that lakes with significant changes in salinity were mainly concentrated in the central and northern parts of the plateau. The changes in salinity in western, southern and eastern areas of the plateau were not significant.
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