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At least 350 elephants died under mysterious circumstances in Botswana in 2020, sparking global concerns while leaving scientists puzzled about the reason for the mortalities. Four years later, a study conducted at King's College London may have finally unearthed the answer. As per the research, a "toxic brew" of open water tainted by a species of cyanobacteria that releases cyanotoxins, which contaminated the watering holes in the region, led to mass elephant deaths.
Combining satellite data and spatial analysis the study revealed that as many as 20 watering holes in the Okavango Delta had been contaminated across roughly 6,000 sq km. After drinking, elephants were estimated to have walked an average of 16.5 km from the toxic waterholes and died within about 88 hours of exposure.
"Our results highlight that seasonal, predominantly rain-fed pans, rather than the permanent waterbodies (i.e., lakes, rivers, and lagoons) within the Panhandle, were the likely source of cyanotoxin exposure," said Davide Lomeo, the lead scientist of the study.
Notably, the dead elephants were of varying ages, with tusks intact which led to scientists ruling out death by poaching. Additionally, no carcasses of other wildlife or livestock species were observed at the time of one of the aerial surveys.
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What promoted algae growth?
Not all cyanobacteria or blue-green algae is toxic but some cyanobacteria produce a type of deadly algal blooms (HABs) in standing water. As per the study, the shift from a dry 2019 (the driest year in decades in the region) to an extremely wet 2020, may have prompted the unprecedented algal growth due to the resuspension of significant amounts of sediments and nutrients from the ground.
"Scientists believe that the production of cyanotoxins is related to certain environmental triggers, for example, sudden rise in water temperature, nutrient loading, salinity," said Mr Lomeo.
Scientists have warned that such incidents may become frequent in the future owing to climate change.
"Southern Africa is projected to become drier and hotter under climate changes, and as a result, waterholes across this region will likely be drier for more months of the year. Our findings point to the potential negative effects on water quantity and quality, and the catastrophic repercussions on animals, this could have.
The study underscores the severe ecological consequences of toxic algal accumulation while emphasising the critical need for water quality surveillance across water bodies, including the smallest ones.